Internet: www.eere.energy.gov/femp/

No portion of this publication may be altered in any form without 

prior written consent from the U.S. Department of Energy, Energy 

Efficiency and Renewable Energy, and the authoring national laboratory.

Leading by example,

saving energy and 

taxpayer dollars in 

federal facilities

Technology Focus

A New Technology Demonstration Publication

Green Roofs 

Green roofs can improve the energy performance of federal buildings, 

help manage stormwater, reduce airborne emissions, and mitigate the 

effects of urban heat islands

Executive Summary

Because of their many energy-saving and environmental benefits, green roofs are a promising technology for energy-efficient buildings. In a green roof, a layer of vegetation covers the 

surface of a roof to provide shade, cool indoor and outdoor temperatures, stormwater 

management, and more. The main components are waterproofing, soil, and plants. 

Federal facility managers in particular might want to consider 

green roofs in responding to Executive Order 13123, Greening 

the Government through Efficient Energy Management. That 

order, signed in 1999, directs agencies to improve the energy 

performance of their buildings, reduce their use of potable 

water, and assist in curbing the greenhouse gas emissions 

associated with energy use in the United States. 

Today, there are two distinct types of green roofs: extensive 

and intensive. An extensive green roof contains shallow soil 

and low-growing, horizontally spreading plants. These plants 

are primarily succulents that can thrive in the somewhat 

alpine conditions of many rooftops. In other words, there 

is not much water or soil, but the roof does experience a 

significant amount of exposure to the sun and wind. 

Intensive green roofs are more complex, and they require 

more maintenance. They feature deeper soil (usually more 

than 12 inches in depth) and more diverse plants, such as 

shrubs and trees. They are usually not as cost-effective as extensive green roofs, and they 

require more structural support. They are also considered to be less environmentally effective 

than extensive green roofs. Therefore, this Federal Technology Alert focuses on the design and 

implementation of extensive green roofs. 

This technology is especially effective in urban areas, because roofs make up such a large percentage of a city’s impervious surfaces. Impervious surfaces contribute to two key problems—

the urban heat island effect and urban stormwater runoff—and both affect the consumption 

of energy and water as well as the demand on energy and water systems. 

Green roofs contribute to energy- and water-saving goals both directly and indirectly. By shading the surfaces of a roof, they reduce heat gain through it by nearly 100 percent. In addition, 

a green roof’s soil and vegetation layer absorbs and filters rain, preventing it from quickly 

becoming runoff from the roof’s surface. Studies have also shown that the photosynthesis 

process of the plants reduces the amount of greenhouse gas emissions in the surrounding air.

The roof of the 12-

story Chicago City 

Hall building has 

been retrofitted with 

a 22,000-square-foot 

rooftop garden. The 

primary goal of this 

installation, which was 

completed in 2001, 

was to demonstrate 

that green roofs help 

to reduce urban air 

temperatures.

DOE/EE-0298

Katrin Scholz-Barth/PIX13397
Federal Technology Alert

ii — FEDERAL ENERGY MANAGEMENT PROGRAM

Energy- and WaterSaving Mechanisms

Conventional roof surfaces absorb 

solar radiation, and this has an impact 

on both outdoor and indoor air quality. Outdoors, the absorbed radiation 

raises the temperature not only of the 

roof (and other impervious surfaces) 

but also of the surrounding air in 

densely populated urban areas; this 

is known as the “urban heat island 

effect.” The result is ground-level 

ozone, in many cities—a temperaturedependent reaction. The higher ambient air temperature acts like a catalyst 

and adds to smog, making air quality 

problems worse.

Indoors, the higher air temperatures 

caused by solar gain through the roof 

result in greater use of air conditioning. This in turn raises electricity 

demand and causes additional waste 

heat to be emitted into the urban 

environment. 

A green roof forms a buffer zone 

between the roof and the sun’s radiation and shades the roof, preventing its surface from heating up and 

increasing outdoor and indoor air 

temperatures. Thus, this technology 

directly benefits both air temperatures and air quality and reduces the 

amount of energy needed for air conditioning. In addition, green roofs use 

rainwater for irrigation needs, reducing the demand for potable water for 

irrigation.

Scientists at the U.S. Department of 

Energy’s Lawrence Berkeley National 

Laboratory (LBNL) have been studying 

the urban heat island effect. They estimate that using alternative surfaces to 

reduce the temperature of ambient air 

in cities by just 5.4 degrees Fahrenheit 

(3 degrees Celsius) would save up to 

$6 billion per year in energy costs, 

nationwide. Green roofs could help 

cities achieve these temperature 

reductions.

No specific studies have been done 

in the United States on the amount 

of energy saved by a green roof. 

However, a “cool roof” study by 

LNBL concluded that another alternative surface, a reflective roofing 

membrane, should save $65,000 over 

the lifetime of the roof on a 100,000-

square-foot retail store.1 And studies 

by the National Research Council of 

Canada have shown that green roofs 

are very effective in reducing heat 

transfer through a roof; one green 

roof reduced average daily energy 

demand by 75 percent in a test 

facility with a 400-square-foot roof.2

The extensive research conducted 

by national laboratories and others 

to understand the urban heat island 

effect and develop strategies to reduce 

it could be tremendously helpful in 

introducing green roofs into the mainstream building industry. However, 

the two technologies—cool roofs and 

green roofs—have different objectives. 

A highly reflective cool roof is primarily intended to reflect solar energy 

away from a building, whereas a living 

green roof absorbs solar energy but 

reduces heat transfer through the roof 

by means of biochemical processes 

and added mass. 

These two technologies might not 

be suitable for every type of building, however, although they are both 

very effective in reducing surface 

temperatures. But sometimes they can 

be applied in tandem to maximize 

benefits. Because urban heat islands 

clearly contribute to increases in temperature, energy use, and pollution, 

the U.S. Environmental Protection 

Agency (EPA) and the Cool Roof 

Rating Council are preparing a guidebook on strategies for reducing the 

effects of these heat islands. 

Green roofs are not just effective in 

reducing urban heat islands, however; 

they also provide several cumulative 

benefits. Stormwater management 

is probably the most tangible direct 

benefit. In urban areas, precipitation 

becomes runoff because impervious 

surfaces—such as buildings, sidewalks, 

parking lots, and streets—cannot 

absorb it. 

Runoff from a rainstorm can quickly 

overburden an urban sewer system, 

especially a combined one that 

captures sanitary waste as well as 

storm water. Curbs, gutters, pipes, and 

gullies all direct the runoff to the same 

sewer system and outlets. Therefore, 

the first half-inch of runoff is the 

most challenging because of its large 

volume at peak flow rates. Runoff can 

overload sewers, cause floods, and prevent the replenishing of local aquifers. 

Untreated runoff also carries nonpoint-source pollutants—such as sediment, nutrients, oil, and grease—into 

sewer and water treatment systems.

Another environmental problem 

can occur when urban roofs heat up 

stormwater runoff before it reaches 

the receiving streams. The subsequent 

thermal shock to the streams can 

have adverse effects on the aquatic 

ecology. Any runoff that occurs from 

a green roof, however, will have a 

lower temperature than runoff from a 

conventional roof, so thermal shock is 

usually not a problem.

On a green roof, rain passes slowly 

through a layer of soil. This reduces 

the peak flow rate of the runoff and 

aids in regulating flow into sewer and 

water treatment facilities during periods of heavy rain. On an impervious 

roof, rainwater is usually conveyed 

quickly to gutters and downspouts as 

runoff and then pumped through sewers and treatment plants; a green roof, 

however, can absorb and use much of 

this rainwater. Thus, green roofs help 

to reduce the energy costs associated 

with pumping and treating stormwater runoff as well as the cost of 

heating and cooling buildings.

Potential Applications

Considering the vast number of federal buildings, there is great potential 

for green roof applications in this 

sector. There are good candidates in 

all government building categories, 
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — iii

including office buildings, housing, 

and hospitals. The energy benefits 

of green roofs are probably greater 

for single-story or low-rise buildings, 

however. 

Green roofs could also provide costeffective stormwater management for 

nearly all federal facilities or housing 

complexes. Therefore, facility managers in areas with strict stormwater 

regulations should seriously consider 

using green roofs in lieu of conventional methods to control the quality 

and quantity of stormwater on site. 

Nutrients stemming from urban 

runoff are the number one violation of National Pollutant Discharge 

Elimination System permits, which 

are issued under a federal monitoring 

program to protect U.S. waterways. 

The EPA is in the process of publishing 

regional criteria for total maximum 

daily loads of nutrients for the entire 

country; these criteria will be more 

stringent then ever before. To help 

cities meet the criteria, green roofs can 

be designed to have a specific waterretention capacity. They can then be 

incorporated into stormwater management plans without the need for 

additional land for retention basins. 

Federal buildings that are concentrated in a particular area, as is often 

the case, could realize even greater 

energy and environmental benefits by 

combining or clustering their green 

roofs.

Field Experiences

Green roofs technology has been a 

subject of great interest in business 

and academic communities over the 

past two years. However, only a few 

U.S. green roof applications have been 

monitored to provide data for future 

projects. Although extensive research 

has been conducted in Europe for 

many years, resources are still needed 

on the design, construction, and 

installation of green roofs in the 

United States, so that performance 

data can be collected and energy cost 

savings can be estimated. 

Therefore, this publication is based 

in part on experiences in Europe and 

in part on anecdotal evidence from 

observations of green roofs in the 

United States. As a result, we are not 

yet able to calculate with precision the 

cost savings resulting from the energyand water-saving features of a green 

roof on a federal facility. Rather, we 

can lay out a road map for interested 

facility managers who wish to become 

familiar with the technology and 

better understand its broad potential 

impact on buildings, regions, and 

resources. 

Implementation Barriers

Despite the growing interest in green 

roofs technology, there is some 

resistance to applying it widely. One 

reason for this is that there are no 

consistent guidelines or standards 

for determining structural and load 

requirements and then designing and 

installing a green roof. However, these 

standards are now being developed.

Implementation barriers can be 

attributed in part to decision makers’ experiences with poorly installed 

waterproofing systems and persistent 

leaks from conventional roofs. As a 

result, building and facility managers 

have some reservations about retaining water on their rooftops. They 

know that a waterproofing failure 

underneath a green roof’s vegetation 

layer would mandate very expensive 

repairs, including the cost of removing and reinstalling vegetation. Also, 

decision makers sometimes fear that 

installing a green roof retrofit could 

void the waterproofing warranty of 

their existing roof system.

The fear of leaks thus appears to be 

the single greatest barrier to implementation. It can even outweigh the 

realization that a green roof provides 

numerous cumulative benefits, both 

direct and indirect, to facilities, 

occupants, and outdoor and indoor 

environments. The lack of data on 

these benefits is another hurdle that 

appears to be difficult to overcome. 

Other barriers include a lack of, and 

need for, the following:

• Information and familiarity with 

green roof technology, design, 

and function

• Knowledge about maintenance 

requirements

• Industry standards and design 

guidelines and specifications 

• Qualified designers and contractors

• Incentives to make green roof 

applications more attractive

• Available funding to absorb higher 

first costs

These implementation barriers 

are reflected in the low number of 

installed green roofs in the United 

States. They also reflect the complexity of green roof designs and 

functions. Many industry members, 

researchers, and practitioners are 

conducting research, development, 

and demonstrations to address and 

overcome these barriers. 

Conclusion

Green roof technology is emerging as 

an effective, practical way to increase 

the energy performance of buildings 

and limit stormwater runoff. Adapting 

green roofs for federal buildings can 

provide significant benefits, especially 

to low-rise office buildings and facilities in districts with strict stormwater 

regulations. Integrating green roofs 

into stormwater permitting requirements may become a realistic solution 

to making them financially viable. 

For those who would like more 

information, a list of manufacturers, 

contractors, consultants, and additional publications is provided at the 

end of this publication. 
Federal Technology Alert

iv — FEDERAL ENERGY MANAGEMENT PROGRAM

Disclaimer

This report was sponsored by the United States Department of Energy, Office of Energy Efficiency and Renewable Energy, 

Federal Energy Management Program. Neither the United States Government nor any agency or contractor thereof, nor any 

of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would 

not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring 

by the United States Government or any agency or contractor thereof. The views and opinions of authors expressed herein 

do not necessarily state or reflect those of the United States Government or any agency or contractor thereof.
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 1

Contents

Abstract ................................................................................................. 2

About the Technology ......................................................................... 3

 Application Domain

 Energy-Saving Mechanism

 Benefits

 Variations

 Architectural Criteria

Federal-Sector Potential ...................................................................... 12

 Estimated Savings and Market Potential

 Laboratory Perspective

 Implementation Barriers

Application.......................................................................................... 14

 Where To Apply

 What To Avoid

 Installation, Integration, and Maintenance

 Warranties, Standards, and Codes 

 Costs

 Utility Incentives and Support

Technology Performance.................................................................... 21

Case Study—Chicago City Hall Rooftop Garden Retrofit ...................22

The Technology in Perspective........................................................... 23

 Technology Development

 Technology Outlook

Conclusion.......................................................................................... 24

For More Information......................................................................... 24

 Consultants and Designers

 Waterproofing and Green Roof Systems Manufacturers

 Modular Green Roof Systems

 Selected Nurseries

 Other Resources

 Publications

References ........................................................................................... 25
Federal Technology Alert

2 — FEDERAL ENERGY MANAGEMENT PROGRAM

Abstract

In North America, green roofs are 

gradually being accepted as a sustainable design practice for the environmental benefits they provide. The U.S. 

Green Building Council (USGBC) has 

adopted green roofs as an effective 

technology for reducing stormwater 

runoff and mitigating urban heat 

islands. The council has incorporated 

green roofs into the Green Building 

Rating System of the Leadership in 

Energy & Environmental Design 

(LEEDTM) program (LEED is a trademark of the USGBC).

In addition, the General Services 

Administration (GSA) has issued a 

directive that requires all new federal 

buildings or renovations completed 

after 2002 in the National Capital 

Region to achieve a LEED silver rating. 

Installing a green roof contributes 

to obtaining a silver rating by earning two credits in the sustainable 

sites section for on-site stormwater 

management (Credit 6: Stormwater 

Management) and for shading the 

impervious roof surface (Credit 7: 

Landscape and Exterior Design to 

Reduce Heat Islands). 

A cost-benefit analysis will not favor 

such an installation for LEED credits, 

however, unless the green roof is 

integrated into the building design 

and stormwater plan. Green roofs can 

also be helpful in meeting Executive 

Order 13123, Greening the Government 

Through Efficient Energy Management, 

established to improve the energy 

performance of government buildings 

and reduce the use of potable water.

This Federal Technology Alert discusses 

the benefits that green roofs provide 

as well as the design, function, maintenance and technical issues related 

to green roof design and installation. 

It is intended to help federal facility 

managers determine whether or not a 

green roof is appropriate for their facilities and if so, what types of green roof 

systems are available. Energy-saving 

mechanisms and benefits are reviewed 

for inclusion in the design process in 

order to maximize returns on investments. Also included are architectural 

criteria such as additional loads, roof 

slopes, and equipment integration. 

Finally, this publication addresses 

material selection, waterproofing 

and related warranties, codes and 

standards, incentive programs, and 

technology performance. A case study 

includes a cost-benefit analysis comparing initial capital costs and anticipated payback periods. There are also 

lists of sources of further information.
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 3

About the Technology

A green roof is a continuous layer of 

vegetation and soil that covers a roof’s 

surface. The main components are 

waterproofing, soil, and the plants 

themselves. Green roofs are an important conservation technology because 

they increase the energy performance 

of buildings, improve indoor as well 

as outdoor air quality, and enhance 

the health of urban watersheds. There 

are two distinct types of contemporary 

green roofs: extensive and intensive. 

An extensive green roof consists of a 

shallow soil profile with low-growing, 

horizontally spreading plants. These 

plants are primarily succulents that 

are adapted to the alpine (highelevation) conditions that predominate on a rooftop, where there is often 

little water and soil but significant 

exposure to sunlight and wind. 

Intensive green roofs are more complex systems that require greater maintenance. They are constructed with 

deep soil profiles (more than 12 inches 

of soil depth) and feature greater plant 

diversity, including shrubs and trees. 

Intensive green roofs are considerably 

less cost-effective than extensive green 

roofs are, however. 

Extensive green roofs usually require 

less structural support than intensive 

ones, and they are considered to 

be more environmentally effective. 

Therefore, this publication focuses 

on the design and installation of 

extensive green roofs.

All green roofs are natural systems 

that effectively cool the temperature 

of ambient air at roof level. The 

vegetation layer shades the roofing 

membrane, thus significantly reducing heat gain through the roof. The 

vegetation cover itself adds green 

space to areas that otherwise would 

remain impervious and uninhabitable 

to birds, butterflies, and other small 

wildlife. 

Green roofs are important to consider 

in designing a sustainable facility, 

especially in urban areas, because 

roofs make up such a large percentage 

of the impervious surfaces in cities. 

Thus, they contribute to two key 

problems: the “urban heat island” 

effect and urban stormwater runoff. 

Both problems affect the consumption 

of energy and water and the demand 

on energy and water systems. 

Pavement (roadways, sidewalks, 

parking lots), and buildings are the 

predominant surface covers in urban 

areas. These hard surfaces absorb solar 

radiation and transmit heat back into 

the atmosphere, and they prevent 

rainwater from filtering down through 

subsoil. Green roofs technology makes 

use of the natural processes and functions of vegetation to minimize the 

adverse effects of these impervious 

surfaces, especially where green space 

is limited and there are few trees to 

absorb water.

Green roofs contribute to energy 

management and water conservation 

in both direct and indirect ways. They 

provide shade, which reduces solar 

heat gain through the roof by almost 

100 percent and mitigates the urban 

heat island effect. Also, a green roof’s 

soil and vegetation layer absorbs and 

filters rain, preventing it from becoming polluted runoff from the roof’s 

surface. And the photosynthesis process in vegetation has been shown to 

help reduce greenhouse gas emissions.

Green roofs absorb, filter, and temporarily store precipitation. This water 

storage and filtration feature helps to 

mitigate the impacts of urban stormwater runoff. Volume, peak runoff 

rates, and associated non-point-source 

pollution—primarily sediments and 

nutrients such as nitrogen and phosphorus—are of great concern to the 

The drawings show the general buildup of a gravel-ballasted roof and that of a green 

roof, in cross section. The buildup is very similar in both, but the performance of a green 

roof is superior to that of gravel-ballasted roofs on many levels. (Source: A. Dürr, Roof 

Greening; An Ecological Balance, 1995; reprinted with permission) 

Gravel

Protection layer

Waterproofing

Moisture barrier

Insulation

Separation layer

Substrate

Filter fabric

Drainage

Protection layer

Waterproofing

Moisture barrier

Insulation

Separation layer

Conventional gravel-ballasted roof

Green roof
Federal Technology Alert

4 — FEDERAL ENERGY MANAGEMENT PROGRAM

health of watersheds, aquatic life, and 

air quality, especially in urban centers.

During low-intensity periods of 

rainfall (about one-half inch or less), 

green roofs have the potential to 

completely eliminate runoff as the soil 

layer absorbs the rain. During longer 

periods of rainfall, or rainstorms of 

greater intensity (1 to 2 inches or 

more), green roofs reduce peak flow 

rates and delay any runoff that might 

occur later, thus reducing the total 

volume of water that reaches sewer 

systems. Watersheds are also protected 

from non-point-source pollution, such 

as sediments and nutrient overload. 

Green roofs are considered to be a 

form of low-impact development, and 

they are becoming more accepted as 

sustainable planning and design practices. Today, green roofs technology is 

anchored in the U.S. Green Building 

Council’s Leadership in Energy & 

Environmental Design (LEED) building rating system because of the ways 

that green roofs help to minimize the 

environmental footprint of buildings 

and mitigate the impacts of urban 

runoff and urban heat islands.

The following sections provide more 

detailed information and criteria for 

federal facility managers to use in considering, evaluating, and implementing green roofs at their facilities. Note, 

however, that green roof technology 

is a general technique rather than a 

specific system that can be universally 

applied. It is thus important to understand the concept before selecting 

appropriate design criteria and designing a site-specific green roof. A case 

study is included to show how these 

concepts are implemented. 

Energy and cost savings are difficult 

to predict because monitoring data are 

not yet available in North America. 

However, many research projects are 

under way, and several have produced 

data that verify the cooling effectiveness of green roofs. 

Application Domain

The design intent and goals of a green 

roof need to be defined before the 

design begins. Installation techniques 

and material and plant selections 

can vary and depend on the climate 

zone in which the roof is installed. 

In general, green roof applications 

are appropriate for a variety of government buildings and roof types, 

including office buildings, housing, 

and hospitals in warm or cool climates 

throughout North America. Green 

roofs are particularly effective when 

used to increase the energy efficiency 

of single-story or low-rise buildings, 

because of the high roof-to-wall ratio. 

They are also very effective when used 

for stormwater management on largefootprint buildings. 

Facilities in areas with strict stormwater regulations, and those that must 

meet National Pollutant Discharge 

Elimination System (NPDES) permit 

requirements and criteria for total 

maximum daily loads (TMDLs), 

should consider using green roofs 

in lieu of conventional systems to 

control the quality and quantity of 

stormwater. Since federal buildings 

are often concentrated in one area, 

they can combine and maximize the 

environmental benefits of individual 

green roofs.

Green roofs are appropriate for both 

new and existing federal buildings. 

They can be incorporated into new 

building designs without much difficulty. Structural load requirements 

will usually need to be adjusted to 

accommodate the additional weight, 

beyond wind and snow loads, as 

required by building codes. 

It is also possible to retrofit existing 

buildings with green roofs. But this 

requires a feasibility study to evaluate 

the structural integrity of the existing 

building and roof. Gravel-ballasted 

roofs are often suitable for a green roof 

retrofit because the gravel layer can 

be replaced with a green roof layer 

An extensive green roof by Charlie Miller, Roofscapes, Inc., for the Chiropractic Life 

Expression Wellness Center in Sugar Loaf, Pennsylvania.

Charlie Miller/PIX
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 5

without adding much weight. It is 

important to protect existing waterproofing systems from root penetration, however. Tile and metal roofs 

are not usually suitable for green roof 

applications. 

Energy-Saving Mechanism

Green roofs represent a unique, 

unconventional approach to increasing the energy performance of buildings through shading, insulation, 

evapotranspiration, and thermal mass. 

Measurable direct benefits are lower 

roof surface temperatures and reduced 

heat transfer through the roof, which 

reduce peak air-conditioning and 

energy demand. These energy-saving 

properties are different in summer 

and winter. 

Summer energy savings. In summer, 

a green roof forms a protective layer 

over the waterproofing membrane, 

thereby shading the roofing system 

from direct ultraviolet (UV) radiation. 

From March to November, a chemical 

process occurs in plants known 

as photosynthesis, in which plants 

use the energy in sunlight to form 

carbohydrates from the carbon dioxide in the air and the water in the soil. 

Plants on a green roof thus prevent 

the surface of the roof from absorbing 

Heat flow through a gravel-ballasted roof (left) and through a green roof. The added 

thermal mass of the green roof prevents a large amount of air from escaping through 

the roof system. (Source: A. Dürr, Roof Greening; An Ecological Balance, 1995; 

reprinted with permission)

Measurements of heat flow show that average daily energy demand for the green roof was significantly less than that 

of the reference roof in spring and summer. (Source: National Research Council of Canada) 

8

7

6

5

4

3

2

1

0

2000 2001 2002

Average Daily Heat Flow Through Roof Systems

(Nov. 22, 2000 — Sep. 30, 2002)

Reference

Green

Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Heat Flow (kWh/day)
Federal Technology Alert

6 — FEDERAL ENERGY MANAGEMENT PROGRAM

the sun’s heat energy. This has a direct 

impact on the temperature of the 

indoor air immediately beneath the 

roof. The plenum heat gain is reduced, 

and energy demand for space conditioning is correspondingly reduced. 

As plants take up water from soil and 

transport it through their leaves to the 

atmosphere (transpiration), water also 

evaporates from the soil’s surface and 

leaves. The total water loss—evapotranspiration—helps to effectively cool 

ambient air temperatures at roof level. 

This has a significant impact on mitigating the urban heat island effect. 

Winter energy savings. In winter, 

plants are dormant, and neither photosynthesis nor evapotranspiration 

take place. During this season, the 

thin vegetation layer of an extensive 

green roof adds thermal mass and 

provides a barrier that prevents some 

of the warm air from escaping through 

the roof. Small air pockets in the soil 

and around the roots add insulation. The insulation value depends 

on the soil’s moisture content, and it 

decreases with greater moisture.

The plants, with their various heights 

and surface textures, help to reduce 

the velocity of cold winter winds over 

the roof, preventing additional heat 

loss through the surface.

The National Research Council of 

Canada conducted a field study over 

a two-year period (2000 to 2002) to 

evaluate the thermal performance of 

green roofs. The test facility in Ottawa 

has a total roof surface of 800 square 

feet (72 square meters). The test roof 

was evenly divided into an extensive 

green roof (green roof) and a modified 

bituminous roof covered with light 

gray gravel (reference roof).3

The study found that the daily maximum membrane temperature underneath the green roof was significantly 

lower than the daily maximum membrane temperature of the reference 

roof. During a 660-day monitoring 

period, the temperature of the green 

roof exceeded 86 degrees Fahrenheit 

(°F) (30 degrees Celsius [°C]) on only 

18 days, or 3 percent of the time. 

In contrast, the ambient air temperature exceeded 86°F (30°C) on 

63 days, or 10 percent of the time. 

The temperature of the reference roof 

was significantly higher throughout 

the monitoring period. Temperatures 

climbed above 122°F (50°C) on more 

than 219 days, or 33 percent of the 

time, as shown in Table 1.4

The data show that green roofs 

effectively cooled the roofing membrane underlying the green roof to 

below ambient air temperatures in 

this field study. 

Reference Roof Green Roof Reduction

Heat Gain 5900 Btu/ft2

(19.3 kWh/m2)

270 Btu/ft2

(0.9 kWh/m2) 95%

Heat Loss 13500 Btu/ft2

(44.1 kWh/m2)

10100 Btu/ft2

(32.8 kWh/m2) 26%

Total Heat Flow 19400 Btu/ft2

(63.4 kWh/m2)

271 Btu/ft2

(33.7 kWh/m2) 47%

Temperature 

Greater Than

Reference Roof Green Roof Ambient

No. of 

Days % of Days No. of Days % of Days No. of Days % of Days

86°F (30°C) 342 52 18 3 63 10

104°F (40°C) 291 44 0 0 0 0

122°F (50°C) 219 33 0 0 0 0

140°F (60°C) 89 13 0 0 0 0

158°F (70°C) 2 0.3 0 0 0 0

Source: National Research Council of Canada

Table 1. Daily Maximum Temperatures of Roof Membranes on Test Green Roof and Reference Roof during 

a 660-Day Observation Period

Table 2. Normalized (per unit area) Heat Flow through the Roof Surfaces of the Test Roof during the 

Observation Period (November 22, 2000–September 30, 2002)

Source: National Research Council of Canada
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 7

The study also found that the test 

green roof significantly reduced heat 

flow through the roof. It also reduced 

the average daily energy demand for 

space conditioning by 75 percent in 

summer. Table 2 shows heat gain and 

heat loss in total Btu per square foot; 

the graph on page 5 shows average 

daily heat flow through the reference 

roof in comparison to that of the 

green roof. 

The green roof appeared highly effective in reducing heat gain in summer. 

It was less effective in winter, reducing 

heat loss an average of 26 percent, as 

compared with a reduction in heat 

transfer of 75 percent in summer.

Benefits

Green roofs provide a wide array of 

benefits:

• Shading the roof and cooling ambient air temperatures in summer

• Shielding the roof from wind and 

preventing heat transfer in winter

• Absorbing, retaining, filtering, and 

storing precipitation 

• Reducing the temperature of runoff

• Minimizing the impacts of impervious surfaces on watersheds

• Extending the lifetime of roofing 

membranes 

• Increasing the area’s green space 

and wildlife habitat

• Enhancing the aesthetic of 

cityscapes

• Improving air quality

• Sequestering carbon dioxide

• Reducing traffic noise through 

absorption by the soil layer

• Ballasting the roofing membrane

• Mitigating floods in certain regions

• Reducing runoff and the need 

to expand the urban stormwater 

infrastructure’s capacity 

Several of these benefits are addressed 

in greater detail below.

In regard to energy savings, the U.S. 

Environmental Protection Agency 

(EPA) estimates that annual U.S. 

energy demand for air conditioning 

accounts for almost one-sixth of the 

energy generated per year. That also 

represents an expenditure of approximately $40 billion to fight heat gain 

in buildings. Careful selection of 

building materials and their surface 

albedo (or reflectivity) values can have 

a significant effect on the heat gain of 

surfaces as well as on ambient air temperatures, which in turn can reduce 

the demand for air conditioning. 

New studies indicate that reflective surfaces, especially those used 

on roofs, can help reduce cooling 

demand by 10 to 15 percent. This can 

result in direct energy savings of up to 

50 percent.5

Several kinds of reflective roofing 

membranes have been tested. Within 

EPA’s ENERGY STAR® Program, reflective roofs are encouraged to improve 

energy efficiency. Reflective roofing 

membranes are usually light in color; 

therefore, they absorb less heat from 

sunlight than dark, conventional roofs 

do. This means lower heat gain, which 

impacts the energy performance of a 

building directly.

Hashem Akbari of Lawrence Berkeley 

National Laboratory (LBNL) has 

tested and evaluated the performance 

of reflective roofing membranes. A 

100,000-square-foot, single-story retail 

store in Austin, Texas, served as the 

test site. Energy used for air conditioning was measured before and after 

the installation of a reflective roofing 

membrane. In the test, the reflective membrane lowered the average 

summertime roof surface temperature 

from 168°F (76°C) to 126°F (52°C), a 

difference of 42°F. 

The final report on this test states, 

“The total air-conditioning energy 

use was reduced by 11 percent and 

peak air-conditioning demand fell by 

14 percent. The 100,000 square feet 

building is predicted to save $65,000 

over the life of the roof.”6

The typical albedo value for green 

roofs is not as high as that of the 

reflective roofing materials featured 

in the study above, which means 

that green roofs are not as reflective 

Table 3. Typical Surface Albedo Values 

Material Surface Albedo 

Value

Highly reflective roof 0.60-0.70

White paint 0.50-0.90

Grass 0.25-0.30

Brick/stone 0.20-0.40

Colored paint 0.15-0.35

Trees 0.15-0.18

Red/brown tile 0.10-0.35

Concrete 0.10-0.35

Corrugated roof 0.10-0.16

Tar and gravel 0.08-0.18

Asphalt 0.05-0.20

Source: U.S. EPA, Cooling Our Communities. A Guide to Tree Planting and Light 

Colored Surfacing.
Federal Technology Alert

8 — FEDERAL ENERGY MANAGEMENT PROGRAM

(see also Table 3). However, comparing only the reflectivity of a green 

roof with that of a light-colored 

roof surface can be misleading when 

determining the more energy-efficient 

surface. Almost all traditional building materials, regardless of color, will 

transmit some heat; a green roof, 

however, is a live ecosystem that 

performs natural processes. Green 

roofs, though darker in color and correspondingly lower in reflectivity than 

light roof surfaces, do not reflect solar 

radiation; instead, this solar energy is 

used by the green roof’s vegetation. 

Almost none of the sun’s heat passes 

into the building. The vegetation uses 

the solar energy to provide effective 

cooling through the evapotranspiration process described above.

Also, because green roofs do not 

reflect solar radiation, occupants of 

neighboring buildings do not have 

to restrict reflections from them 

by installing additional shading. 

Therefore, albedo value is not an effective or accurate measure for predicting 

the energy efficiency of green roofs. 

Nevertheless, cool roofs can be very 

effective on some buildings. Because 

steeply sloped roofs can be unsuitable 

for cost-effective green roof technologies, a reflective roofing membrane 

should be considered because of its 

energy benefits and ability to alleviate the urban heat island problem. A 

cool roof should be considered when 

an existing roof cannot withstand 

the additional load of a green roof. In 

summary, these are some advantages 

and disadvantages to be aware of in 

choosing between the two kinds of 

roofs:

Some advantages of green roofs 

in comparison to reflective roofs:

• Besides reducing heat transfer 

through the roof, they are also 

beneficial in controlling stormwater quality and quantity and in 

mitigating the effects of impervious 

surfaces.

• They do not reflect sunlight into 

adjacent buildings; rather, they use 

radiant energy to cool ambient air.

• They are not vulnerable to UV 

radiation.

• They can protect the roofing membrane and increase its longevity.

• They provide green space and have 

aesthetic value.

• They reduce noise by absorbing 

sound in the soil medium.

Some disadvantages of green roofs 

in comparison to reflective roofs:

• They have higher first costs because 

of the additional material needed 

and high installation costs.

• They require higher maintenance 

for plant care and upkeep until 

plants are fully established and the 

roof is fully covered (about two 

years); some ongoing maintenance 

80

70

60

50

40

30

20

10

0

10

20

30

+

–

0 3 6 9 12 15 18 21 24

80

70

60

50

40

30

20

10

0

10

20

30

+

–

0 3 6 9 12 15 18 21 24

80° 25°

Maximum Temperature Fluctuations for a Conventional Roof and a Green Roof

Hour Hour

Temperature

Max. temp.

fluctuation in 

a year: 100°C

Avg. course of temperatures

on summer day (simplified)

Avg. course of temperatures

on summer day (simplified)

Avg. course of temperatures

on winter day (simplified)

Avg. course of temperatures

on winter day (simplified)

Max. temp.

fluctuation in 

a year: 35°C

In the graph on the left, the arrow shows the maximum temperature fluctuation of a typical flat conventional roof, up to 60°C (140°F) in a 

single day, and up to 100°C (212°F) during the year. The graph on the right shows a significantly lower temperature fluctuation on a green 

roof. The protective green-roof layer moderates temperature extremes and protects the roofing membrane from accelerated aging caused 

by UV radiation. 7 (Source: A. Dürr, 1995; adapted with permission)
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 9

is also required, such as fertilizing 

vegetation annually and checking 

on plants.

• They are vulnerable to high winds 

because they are not mechanically 

fastened to the roof.

• It is more difficult to locate any 

leaks in waterproofing material. 

• Waterproofing must be protected 

from root penetration.

• They do not work well (if at all) on 

roofs with very steep slopes.

Note that cool roofs also tend to 

collect airborne dust and particulate 

matter. Some cool roofs, such as metal 

ones, are less susceptible to the elements. However, the dust that usually 

accumulates on light-colored roofs, 

and the acid rain that stains them, 

can darken the surface, reducing 

solar reflectance and infrared emittance properties by 8 to 11 percent. 

However, cool roofs can usually be 

power-washed to reinstall their reflective properties. 

In comparison, airborne dust and 

particulate matter are usually fixed on 

the leaves and foliage of a green roof 

and do not compromise its heat-flow 

reduction properties or any other 

performance parameter. Because of 

the benefits a green roof provides as 

an ecosystem, it can outperform a 

reflective roof with regard to energy 

efficiency and mitigating urban heat 

islands. 

The multifunctional, cumulative 

benefits of green roofs make them 

attractive and unmatched by other 

technologies. Therefore, designers and 

facility manager might select a green 

roof for reasons other than its energy 

efficiency. Besides technical performance, green roofs offer improved 

aesthetics and a multitude of other 

benefits, as listed below.

Cost: Green roofs offer direct cost 

benefits when the design is integrated 

into a stormwater management plan 

to offset permit fees and runoff treatment requirements. Another cost 

benefit is the extended lifetime of the 

waterproofing system. Conventional 

roofing systems are typically replaced 

every 20 to 30 years. A green roof, in 

contrast, protects the waterproofing 

membrane from UV exposure and 

temperature fluctuations that accelerate the breakdown of the membrane. 

In Europe, green roofs have extended 

the lifespan of a roofing membrane to 

two or three times that of a conventional roofing system. 

Stormwater management:

Converting conventional roof surfaces to green roofs is potentially the 

single greatest way to reduce or delay 

stormwater runoff on a large scale. 

The stormwater benefits of green 

roofs are greatest in densely populated 

urban centers. Cities that are serviced 

by combined sewer networks benefit 

from the resulting reductions in the 

volume and rate of runoff. Green roofs 

should be incorporated into a building design in the conceptual planning 

phase for new construction to reduce 

the need for a costly stormwater retention and treatment infrastructure. 

Depending on the intensity of rainfall, 

the growing season, and the soil moisture content at the site, an extensive 

green roof can eliminate runoff from a 

building and reduce the peak flow rate 

and volume of the sewer system. 

A layer of soil 3 to 4 inches deep in 

an extensive green roof can absorb 

about 1 inch of water. Green roofs are 

estimated to absorb, filter, retain, and 

store an average of about 75 percent of 

the annual precipitation that falls on 

them. This applies to most areas in the 

United States.

A green roof’s health, durability, and 

return on investment increase along 

with the depth of the soil. Plants grow 

and spread more vigorously in 3 to 

4 inches of soil than in more shallow 

soils. This depth also allows greater 

plant diversity and provides greater 

resistance to diseases. 

The water-retention capacity of a 

green roof depends on the type of 

growing media used. Water retention 

can be increased by either mixing 

lightweight, water-retaining aggregate 

into the soil, or using this kind of 

aggregate for the topsoil layer. See also 

the sections on architectural criteria 

and installation for load issues associated with different growing media. 

58%

67%

71%

Runoff vs. Water Retention at Different Soil Depths

1 in.

soil

2.5 in.

soil

4 in.

soil

Runoff

Water retention capacity

The graphs show runoff vs. water retention capacities of extensive green roofs at 1-inch, 

2.5-inch, and 4-inch depths. The first bar represents a 1-inch deep soil and vegetation 

mat over a 2-inch gravel bed. This green roof can retain an average of 58% of annual 

precipitation. The second bar represents a 2.5-inch-deep soil and vegetation mat, which 

can retain an average of 67% of annual precipitation. The third represents a 4-inch soil 

and vegetation mat, which can retain an average of 71% of annual precipitation.8 

(Source: A. Dürr, 1995; adapted with permission)
Federal Technology Alert

10 — FEDERAL ENERGY MANAGEMENT PROGRAM

Engineers who design stormwater 

infrastructure usually design for a 

worst-case scenario—urban runoff 

from a 100-year storm. Green roofs, 

however, absorb and use much of the 

rain that falls on them at intensities at 

or below 1/2 inch. The first 1/2-inch 

of runoff, referred to as the first flush, 

is of the greatest concern to municipalities because it carries the most 

concentrated pollutants. Extensive 

green roofs can absorb up to 1 inch 

of rain and effectively reduce storm 

runoff to sewer systems. Excess rainfall 

can them be conveyed away by a 

smaller-than-usual system.

Nitrogen and phosphorus stemming 

from atmospheric deposition become 

fixed in the soil and serve as plant 

fertilizer. Sediments are trapped as 

water slowly percolates through the 

soil medium. Green roofs reduce this 

non-point-source pollution, and any 

runoff is thus cooler and cleaner than 

it would be if it came from conventional roofs.

Green space and wildlife: Green 

roofs benefit urban areas by adding 

green space and offering resting places 

and food sources for wildlife. These 

elevated ecosystems are sheltered from 

human activities and traffic noise as 

well as from predators. Migratory birds 

and butterflies especially benefit from 

green roofs, because their habitat in 

urban areas is limited and fragmented. 

Studies show that butterflies will fly as 

high as 20 stories for access to green 

space.9 Green roofs might not be able 

to replace ecosystems, but multiple 

green roof applications in urban areas 

may play an important role in reconnecting fragmented habitats. 

Air quality: Densely built-up urban 

areas often lack enough green spaces 

and trees to enrich the urban environment and offset air pollution. Green 

roof plants sequester carbon dioxide 

like other plants do, and release oxygen back into the environment.

The annual cost of air pollution in 

the United States is estimated to be 

about $10 billion.10 This estimate is 

based on the cost of health care as 

well as the loss of productivity. Smog 

accounts for about 30 percent of air 

pollution, or $3 billion per year.11

Smog forms when nitrogen oxides 

(NOx) react with volatile organic 

compounds, and it accelerates at high 

ambient air temperatures. Acid rain, 

smog-related respiratory illnesses, and 

impaired visibility (because of “brown 

clouds” over cities). Air pollution can 

also reduce water quality by polluting 

runoff, as noted earlier. 

Green roofs have great potential 

to collectively improve air quality 

because they can reduce air temperatures. As evapotranspiration lowers 

the ambient air temperature at roof 

level, this slows the formation of 

lower atmospheric ozone, the prime 

component of smog. Green roofs can 

also improve air quality by fixing 

dust particles and particulate matter 

from the atmosphere on plant foliage. 

Particulate matter includes dust particles that are smaller than 10 microns 

and that pass right through air filters 

without being trapped; they can cause 

lung damage, respiratory illnesses, and 

even premature death.

Utilities burn fuels at high temperatures to generate energy, which 

emits 27 percent of all NOx into the 

air. Nitrogen oxide emissions from 

motor vehicles and from combined 

industrial, commercial, and residential 

sources also generate NOx emissions: 

49 percent and 19 percent, respectively.12 The foliage in trees and other 

vegetation, such as green roofs, can 

help to reduce these emissions in the 

air through pollutant fixation and 

uptake. Studies show that trees near 

streets reduce both particulate and 

gaseous pollution up to 90 percent. 

Some measurements show about 

10,000–12,000 dust particles per liter 

of air in streets without trees and 

about 1,000–3,000 dust particles per 

liter of air in streets with trees.13

0

20

40

60

80

100

120

(a) < 1/2 inch (b) 1/2 – 1 inch (c) > 1 inch

Rainfall Intensity (inches)

1-Hour Precipitation in Washington, D.C.

1998 1999 2000 2001 2002

Number of Events

This graph shows the total number of annual rainfall events for the District of Columbia 

over five years at (a) less than 1/2-inch, (b) from 1/2-inch to 1-inch, and (c) greater than 

1-inch intensities. (Source: National Oceanic and Atmospheric Adiministration, National 

Weather Service; see www.erh.noaa.gov/box/dailystns.shtml) 
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 11

It is difficult to predict specific emission reductions from green roofs on a 

per-building basis. However, the Rocky 

Mountain Institute estimates that 

electricity demand in buildings could 

be reduced by 45 percent through 

conservation alone. This reduction in 

energy use could result in a 10 percent 

reduction in total carbon emissions, 

which in turn would yield a net 

energy cost savings of $56 per ton of 

carbon emission reductions associated 

with reductions in energy use.14 Green 

roofs could help to increase this result 

by reducing the heating and cooling 

needs of spaces underneath the roofs. 

Aesthetic: Green roofs can enhance 

urban environments by adding green 

space and habitat that attract wildlife. 

They do not reflect sunlight, and they 

contribute to the urban aesthetic.

Traffic noise: Green roofs also provide noise-reduction benefits. The soil 

layer in a green roof can absorb traffic 

noise. The amount of the reduction 

depends on the thickness of the layer. 

An 8-inch deep cover has been found 

to reduce traffic noise by as much as 

46 decibels.15

Roof ballast: Green roofs can replace 

conventional gravel ballast while 

providing the same benefits. The sole 

purpose of gravel ballast on traditional 

roofs is to weigh down the waterproofing membrane and protect it from 

being uplifted by wind. The gravel 

ballast can easily be replaced with an 

extensive green roof to function as 

ballast.

Variations

Contractors can design and install 

green roofs as entire manufactured 

systems. Green roofs can also be 

designed specifically for a site by a 

consultant or installed as prefabricated 

roof modules. 

Entire systems: Several American 

roofing companies have partnered or 

arranged franchise agreements with 

European manufacturers to offer green 

roof systems in North America. The 

advantage of these systems is that, in 

most cases, only one contractor will 

be needed to install the waterproofing 

and the green roof system, minimizing the number of contractors at 

the site and potential damage to the 

waterproofing. Green roof systems are 

most cost-effective on large surfaces, 

because the larger size often results in 

material discounts per square foot. 

Because only one contractor is used, 

manufacturer’s warranty questions 

and maintenance calls can be directed 

to a single point of contact. A disadvantage is limited design flexibility. 

Because they are proprietary, these 

kinds of green roof systems come as 

fixed assemblies. This makes it harder 

to design for specific site conditions 

and to meet design goals. 

Design consultants: For small projects or those with restricted budgets, 

it might be more appropriate to work 

with a green roof consultant who will 

specify components individually. The 

advantages of a site-specific green roof 

design are greater design flexibility 

and better cost control. Materials and 

layers can be selected that perform 

multiple necessary functions, thus 

eliminating the labor and costs associated with optional layers that are 

unnecessary in some applications. 

Modular systems: Modular green 

roof systems are also available for rooftop applications, and they are effective for large roof applications with 

uninterrupted surfaces. Traditionally 

used for athletic fields, modules can be 

pregrown as green roofs. The advantage of modular systems is that they 

can be installed quickly. 

The modules are perforated, which 

permits drainage and eliminates the 

need for an additional drainage layer. 

Drainage channels on the bottom 

provide sufficient space for excess 

water to flow freely to reach gutters, 

drains, and other collection points. 

The channels can also be used for 

irrigation piping, if a permanent 

irrigation system is required. The modules interlock for greater stability. 

A disadvantage is that the height of 

the module dictates the soil depth, 

and this limits design flexibility. 

Also, modules might not suitable for 

a retrofit because of load restrictions. 

They are very heavy and thus must be 

lifted onto the roof by a crane and put 

in place by a forklift or manual labor. 

Some modules are made of plastic 

that is not UV-resistant and can 

degrade over time. The coordination 

of preplanting and scheduling, as well 

as high costs, still limit wider use of 

modular systems. 

Architectural Criteria

Loads and structural upgrades:

The weight added by an extensive 

green roof is comparable to that of the 

gravel ballast on a conventional roof—

about 15 to 30 pounds per square 

foot, depending on the soil media, the 

depth of the soil layer, and the weight 

and depth of any additional layers. 

The load of the green roof must be 

figured in addition to snow and wind 

loads, as required by all applicable 

building codes, to ensure that it does 

not exceed the structural capacity of 

the building. The maximum weight of 

a green roof occurs at full saturation 

or supersaturation. Supersaturation, 

a kind of worst-case scenario, could 

occur if malfunctioning roof drains 

cause the roof to flood to a certain 

depth. Therefore, the design load must 

always be calculated at full saturation. 

Structural upgrade requirements for 

green roofs on new buildings add a 

negligible increase in cost. For existing 

buildings, a structural analysis is necessary to determine whether structural 

upgrades are required. The cost benefit 

must be determined on a case-by-case 

basis.

Roof slope: Almost any roof surface 

can be vegetated. Typically, government buildings have flat or only 

slightly sloped roofs. These surfaces 
Federal Technology Alert

12 — FEDERAL ENERGY MANAGEMENT PROGRAM

are the most suitable for green roof 

applications and retrofits, depending 

on the roof’s structural integrity. Roofs 

with steep slopes can be used in some 

green roof applications, but they are 

more difficult to accommodate. The 

friction coefficient between two 

neighboring materials (for example, 

waterproofing and geotextile, waterproofing and root-resistant liner, or 

root-resistant liner and geotextile) 

defines the critical practical slope 

angle. Roofs pitched at up to a 

10-degree angle (17 percent, or up 

to 2:12) can be greened without using 

special stabilization techniques. 

Roofs pitched between 10 and 30 

degrees (17 percent to 58 percent, or 

2:12 to 7:12) require standard slope 

stabilization techniques, such as 

wooden lath grids, eave-supported 

frames, or ridge-supported mesh. 

These techniques help to form smaller 

fields that reduce friction forces and 

keep soil and vegetation in place until 

plants have formed a dense vegetation 

mat with interlocking roots. Greening 

or retrofitting steeper roof surfaces 

with an extensive green roof would 

be more material- and labor-intensive 

and thus more expensive.

Roofs with a pitch greater than 30 

degrees (58 percent, or 7:12) require a 

mechanically fastened, pregrown vegetation mat. However, in most cases 

this is cost-prohibitive and will not 

yield substantial stormwater retention 

benefits.

Root barrier: In sharp contrast to 

conventional gravel-ballasted roofs, 

green roofs need a root-resistant 

liner as well as waterproofing. 

Waterproofing based on organic 

materials (such as bitumen or asphalt) 

is susceptible to root penetration. 

If these materials are used, a barrier will be needed to prevent roots 

from puncturing the waterproofing. 

Synthetic waterproofing membranes, 

such as rubber (EPDM) and polyvinyl 

chloride (PVC) plastic, provide a root 

barrier within the membrane. Thus, 

no additional barrier is needed. 

Drainage: The performance and success of green roofs depend to a great 

extent on efficient drainage. Although 

green roofs are designed to retain 

water, they are not intended to hold 

water beyond the absorption capacity 

of the soil layer, and standing water 

is detrimental to the plants. Thus, flat 

roofs require drainage mats to allow 

excess water to drain away. Drainage 

on low-sloped roofs occurs via gravity, 

which eliminates the need for additional drainage mats. Along the perimeter of the roof, a gravel strip conveys 

water to a standard gutter system.

Federal Sector Potential

Estimated Savings and Market 

Potential

Improvements in energy efficiency 

resulting from the use of green roofs 

can be attributed to reductions in roof 

surface temperatures, in heat transfer 

through the roof, and in peak power 

demand. Reduced heat gain ultimately 

means lower indoor air temperatures 

and less need to use air conditioning 

for cooling. Energy savings result from 

these reductions in energy use.

Research and pilot studies on buildings have been conducted by SHADE 

Consulting, using a roofing system 

heat transfer analysis method. They 

indicate that green roofs consistently 

outperform cool roof systems (highly 

reflective roofs) in terms of energy 

cost savings and long-term overall 

savings—in some cases, by a significant amount.16 If these data could 

be verified and made available to the 

public, green roofs could soon become 

another viable alternative to highperforming roofs. 

Additional energy savings could be 

obtained by carefully locating air 

intake vents. Placing the air intake 

vent over or near a green rooftop takes 

advantage of the smaller temperature difference between outdoor and 

indoor air for a green roof than for a 

conventional roof. This means that 

less energy would be needed to cool 

indoor air to desired levels, and 

Katrin Scholz-Barth/PIX13398

The Montgomery Park Business Center in Baltimore, Maryland, features a 20,000-squarefoot extensive green roof that has a suitable slope for this technology.
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 13

it would also improve the efficiency 

of the mechanical system. 

It is important to note, however, 

that every green roof has a different 

thermal impact on a building. Small 

variations in the design, installation, 

components, material selection, and 

geographic location will affect the 

energy performance of the roof and 

the building. 

Building scale: Exact energy savings 

are difficult to predict at this time. 

However, field tests17 (see the section 

on energy-saving mechanisms) and 

research18 have already produced data 

that indicate the potential of green 

roofs to save energy by lowering roof 

surface temperatures as well as energy 

demands. 

The effects of UV radiation and heat 

exposure can accelerate the aging 

process of waterproofing systems; this 

can compromise the quality of the 

waterproofing and the durability of a 

roofing system. As noted earlier, green 

roofs shade the roofing system and 

protect the waterproofing membrane 

from exposure to UV radiation and 

extreme temperature fluctuations. 

Thus, they can be said to slow down 

the aging process. Long-term savings 

result from extending the lifetime of a 

waterproofing system, but they cannot 

be predicted because they depend on 

the quality of workmanship and the 

long-term performance of the waterproofing. In Berlin, Germany, 100-

year-old green roofs have not failed,19

and they have more than doubled 

the lifetime of their waterproofing 

systems.

The waterproofing of a roof on a 

GSA-managed building is typically 

replaced every 15 to 25 years. Even if a 

green roof only doubles the lifetime of 

the waterproofing system, the resulting savings could significantly offset 

the initial costs of the roof. Savings 

to the federal government could be 

considerable. For example, the federal 

government owns or manages more 

than 500,000 facilities nationwide 

and spends about $8 to $10 per square 

foot to replace a roof and dispose of 

old materials every 15 to 35 years.20

Assuming that the average roof surface 

of each building is 10,000 square feet, 

the savings from green roofs could 

amount to $80,000 to $100,000 per 

building in roof replacement costs 

alone. This is roughly equivalent to 

the initial capital investment in a 

green roof system (see the section on 

costs), excluding maintenance. If only 

half of all government facilities were 

retrofitted with green roofs, the savings could be in the millions of dollars 

over 15 to 25 years, despite additional 

maintenance expenses.

To minimize extra costs, green roofs 

could be installed on existing buildings to coincide with the next waterproofing replacement. The potential 

savings and environmental impact 

of such a phased-in approach are 

significant. If only 50 percent of all 

buildings are suitable for a green roof 

application, approximately 2.5 billion 

square feet, or nearly 60,000 acres, 

of green roof installations could be 

completed within the next 15 to 25 

years on government buildings alone. 

This example is based solely on the 

extended life cycle of the waterproofing system; it does not take energy-use 

reductions and savings into account. 

Regional scale: Air and water quality 

improvements will be measurable only 

when enough green roof installations 

are completed to make measurements 

meaningful. Meanwhile, the green 

roof initiative conducted by the 

National Research Council of Canada, 

along with field studies conducted by 

Environment Canada, has produced 

data that could lead to greater acceptance of green roofs. 

The Canadian study finds that if only 

6 percent of Toronto’s roofs, or 1,600 

acres (6.5 square kilometers), were 

green roofs, summer temperatures 

could potentially be reduced by 1.8° to 

3.6°F (1° to 2°C) in this urban center. 

These lower ambient air temperatures 

could help reduce energy demand by 

as much as 5 to 10 percent, for a direct 

savings of more than $1 million in 

annual energy costs. The study also 

shows that 1,600 acres (6.5 square 

kilometers) of green roofs could help 

reduce greenhouse gas emissions, 

particularly carbon dioxide, by an 

estimated 2.2 megatons and remove 

30 tons of pollutants from the air.21

Laboratory Perspective

Laboratory testing, field-testing, and 

theoretical analyses are currently 

under way at various research universities, such as Pennsylvania State. Data 

could be available in a few years that 

will provide additional statistical and 

empirical evidence as to the effectiveness of green roofs and their associated cost savings. 

Implementation Barriers

The fear that waterproofing will 

leak underneath a green roof is one 

implementation barrier that seems 

to outweigh all its benefits, for some 

people. They often assume that green 

roofs cause leaks. But actually, a watertight system is the single most important prerequisite for any effective 

roof, whether it is a gravel-ballasted 

inverted roof membrane assembly 

(IRMA) or a green roof. Waterproofing 

keeps precipitation out of the building 

and is the basis of a successful green 

roof. 

Additional barriers involve a lack of 

the following:

• Information and familiarity with 

green roof technology, design, and 

function

• Knowledge about maintenance 

requirements

• Industry standards and design 

guidelines and specifications 

• Qualified designers and contractors

• Incentives to make green roof 

applications more attractive
Federal Technology Alert

14 — FEDERAL ENERGY MANAGEMENT PROGRAM

Lack of information and familiarity with green roof technology, 

design, and function: This lack of 

information, as well as inadequate 

distribution of currently available 

information, has to be overcome 

before green roofs can be adopted 

more widely. But several groups are 

making progress. Green Roofs for 

Healthy Cities, a Toronto-based organization, is advocating the technology, organizing annual green roof 

conferences, and helping to develop a 

viable industry to support the emerging green roofs market.22 The City of 

Chicago hosted “Greening Rooftops 

for Sustainable Communities,” the 

First North American Green Roofs 

Infrastructure Conference, Awards, 

and Trade Show in May 2003. About 

500 attendees from a wide range of 

professions learned about green roof 

designs and opportunities for application. The City of Portland, Oregon, 

hosted the second annual conference 

in 2004; 512 professionals attended.

In addition, green roof consultants, 

roofing manufacturers, and other 

organizations have started offering 

green roof seminars nationwide to 

staff in government, industry, and 

design firms. Research is being conducted by universities, government, 

and the public as well as private entities,23 but English-language publications evaluating and discussing the 

data usually lag months or even years 

behind. A number of book projects are 

under way, however, and publications 

by Schiffer Books, Timber Press, and 

Wiley and Sons have been scheduled 

for 2004 and 2005. Basic monitoring 

devices such as temperature gauges 

could also be installed easily on green 

roofs to collect more data for widespread use.

Lack of knowledge about maintenance requirements: People often 

mistakenly assume that green roofs 

require a lot of maintenance throughout their life cycle. Rather, case 

studies show that, once green roofs are 

established, they require only annual 

maintenance surveys and occasional 

fertilizing if the soil becomes too 

acidic because of nitrogen deposits. 

However, they should always be 

inspected for damage to plants and 

soil following severe weather (e.g., 

high winds, drought, hurricanes, 

tornadoes, or heavy snow and ice 

storms). 

Lack of industry standards and 

design guidelines and specifications: The term “green roof” is not 

yet standard and has been criticized as 

misleading by some GSA consultants. 

For example, in terms of environmental qualities, “green” roofs could mean 

reflective roofs, roofs made of recycled 

materials, vegetated roofs, or any 

other sustainable type. 

To address this lack, a green roof task 

group under the American Society 

for Testing and Materials (ASTM) 

Subcommittee E06.71 on sustainability is developing a standard practice 

guide. It will establish a procedure 

for assessing green roofs and include 

technical requirements as well as 

considerations for sustainable development. The Canadian-based Green 

Roofs for Healthy Cities has developd 

a green roof training seminar that was 

first presented in June 2004, during 

the second annual green roof conference in Portland, Oregon. 

Lack of qualified designers and 

contractors: Designing a green roof 

requires knowledge of the complex 

interactions and performance of all 

its layers. Training seminars would 

help to offset the shortage of qualified 

designers. However, the practical skills 

and knowledge needed to install a 

green roof are not highly specialized. 

Most qualified contractors can install 

one successfully without special training. The industry guidelines described 

above should make it possible for both 

designers and contractors to specify 

green roofs with little difficulty. 

Lack of incentives to make green 

roof applications more attractive:

Green roofs have higher up-front costs 

than other kinds because of the additional materials and special installation required. Too often, this premium 

is used as an excuse to forego a green 

roof application without evaluating 

its potential for savings and amenities. Limited funding may be available for green roofs that are designed 

to manage stormwater and control 

non-point-source pollution. More 

readily available research data are 

needed to further demonstrate that an 

integrated green roof design pays for 

itself when we take into account the 

savings resulting from reduced energy 

demand, reduced stormwater management requirements (treatment and 

retention basin size), and extended 

roof life. 

Application

Many governmental buildings have 

flat or low-sloping roofs, and some 

have multiple roof elevations. These 

types are ideally suited for green roof 

applications. 

Where To Apply 

Green roof technology can be used on 

most building types that have concrete, wood, or composite (wood fibers 

and cement) roof decks. Metal roofs 

expand and contract and are thus not 

suitable for a green roof retrofit. To 

maximize their benefits, green roofs 

should be considered for office buildings in urban areas, military facilities, 

and buildings along coastal areas, in 

areas with combined sewer systems, 

and in areas where green space and 

habitat are limited or fragmented, 

once microclimate and plant selection 

criteria are fully understood. 

What To Avoid 

Except for the best practice guide 

being developed by ASTM, there 

are no recognized industrywide 
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 15

design specifications for green roofs. 

Therefore, it is essential to define a 

primary design goal before beginning 

the design. This will determine what 

materials and layers are required to 

achieve your goal. Here are some 

general guidelines on what to do 

and what to avoid.

DO: Prioritize desired green roof benefits and specify one primary goal. This 

allows you to stay focused during the 

design and specification process, while 

still receiving additional benefits.

DON’T: Try to make every benefit a 

priority.

DO: Ask an experienced professional 

to develop or review your green roof 

design specifications, to avoid costly 

mistakes and streamline the bidding 

process. 

DON’T: Combine the cost estimate 

for the waterproofing with that of the 

green roof. The basic waterproofing 

system is usually not part of the green 

roof bid, because waterproofing is part 

of the building, whether you are planning new construction or a replacement for an existing roof. Separating 

the cost of green roof components 

from that of the basic waterproofing 

system allows you to make a more 

realistic cost estimate. 

DO: Coordinate the selection of a 

waterproofing system with your green 

roof application, and choose one that 

is suitable, such as a root-resistant synthetic membrane. Avoid asphalt-based 

systems for waterproofing, because 

they are not root-resistant. 

DON’T: Choose single-ply roofing 

membranes with adhered seams, 

because there is a greater risk of leaks.

DO: Use a heat welding or vulcanizing 

process to adhere seams on waterproofing. 

DON’T: Use grasses or sod for green 

roof vegetation, as they are not 

suitable and can be a fire hazard.

DO: Choose suitable vegetation for 

your extensive green roof, that can 

withstand the extreme sun and wind 

exposure on roof tops.

Installation, Integration, and 

Maintenance

Green roofs can be used in place of 

conventional gravel-ballasted roofs. 

All the materials needed are readily 

available in the United States. Aside 

from specific layers for the green roof, 

construction and installation processes 

are very similar to those for conventional roofs and do not required 

specialized tools or equipment. 

Time: In general, installing a green 

roof requires more time and labor 

than a conventional roof needs. 

Additional material has to be applied 

according to specifications. The 

planting can be handled by a roofing 

contractor or by a contracted landscape company. 

Scheduling: To ensure a high plant 

survival rate, green roofs should be 

installed in cool seasons, such as 

spring or fall, when natural precipitation can be utilized most effectively 

to establish the plants. Hot and dry 

seasons should be avoided. If construction schedules dictate installation 

and planting during hot or dry periods, plants must be watered enough 

to avoid damage. 

The installation of the soil and the 

planting should coincide. This helps 

to stabilize the soil immediately, and 

it avoids exposing a barren soil layer 

to erosion by wind or precipitation. 

Contractors: Few U.S. contractors 

have special experience with green 

roof installations. However, any 

roofing contractor who is committed to high-quality work should be 

qualified to install a green roof under 

the supervision of an experienced and 

knowledgeable consultant. 

Soil media: The soil media add 

weight to the structure; the type and 

thickness of the media determine the 

system’s water-absorption capacity. 

The soil has also a significant impact 

on how well plants will establish and 

how much maintenance and weeding 

will be necessary. Lightweight aggregate is often preferred. Pumice, lava 

rock, perlite, compost, peat, or sand 

can be added to create suitable weedfree soil media. The added weight 

of water in the spaces between soil 

particles must also be calculated.

The weight of green roof soil media 

is always specified at maximum waterretention capacity per inch depth. See 

Table 4 for examples.

Aside from weight considerations, soil 

media must have some very important 

characteristics. These include grain 

size, soil density, porosity, water retention capacity, pH, organic substances, 

and nutrients.

Table 4. Loads for Various Green Roof Soil Media or Substrates

Substrate Load per 1-inch 

Depth (lb/ft2)

Topsoil with mineral and 

organic content 8-10

Mineral substrate with high 

organic content 5-7

Mineral substrate with low 

organic content 5-7

Expanded clay or slate 3.5-4

Recycled aggregates (broken 

bricks) 5-7

Expanded clay or slate 3.5-4
Federal Technology Alert

16 — FEDERAL ENERGY MANAGEMENT PROGRAM

It is important to select the right growing media for a green roof. Selection criteria depend on the intent and desired performance of 

the green roof. The photo shows, from left, plant establishment in 100 percent gravel, an 80/20 mix of gravel and topsoil, a 20/80 mix of 

topsoil and expanded clay, 100 percent topsoil, 100 percent expanded clay, and a mix of compost, clay, and sand.

Katrin Scholz-Barth/PIX13399

Not surprisingly, plants generally 

establish best in topsoil, because it 

provides the best environment for 

plants in terms of nutrients, porosity, 

and grain size. Plant establishment 

was poor in pure gravel and expanded 

clay aggregate and fair in the three 

other soil compositions shown in 

the photo. The disadvantage of using 

topsoil in a green roof is (a) its weight 

and (b) decomposition, because of 

its high organic content. In order to 

maintain a constant medium depth, 

the soil medium should have a high 

mineral content that does not decompose. Mixing in 15 percent compost 

maximizes plant establishment while 

maintaining the overall performance 

of the green roof.

Plants: Plants must withstand significant exposure to the sun and wind 

and thrive in both stormy and dry 

conditions. Alpine and rock garden 

types of plants are well suited to 

these conditions. They store water in 

their leaves, which makes them ideal 

for the often harsh environment of 

rooftops. 

Grasses and sod are not well suited to 

the green roof environment. Grasses 

dry up during hot, dry periods and 

are easily ignited by summer thunderstorms; thus, they can be fire hazards. 

Unless they are irrigated, grasses and 

sod should not be considered for 

extensive green roof plantings.

There are important distinctions 

among the plants to use in different 

regions of the United States. The plant 

hardiness zones defined by the USDA 

should be used as a guideline for 

selecting green roof plants for specific 

regions. Zone 1 has the coldest average temperature year-round, and Zone 

11 has the warmest winter temperatures. Please see Table 5 for a selected 

Plants growing on the Montgomery Park Business Center’s roof include Sempervivum 

tectorum, Sedum spurium ‘Roseum,’ Sedum sexangulare, and Sedum album.

Katrin Scholz-Barth/PIX13400
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 17

list of suitable plants for extensive 

green roofs in different zones.

Plants are a vital component of green 

roofs. Their hardiness, aesthetics, and 

survival define the success of a green 

roof. There are three principal ways to 

establish a vegetation layer: 

1. Use plant plugs with established 

root systems, 

2. Apply plant cuttings to the soil 

layer, or

3. Seed the soil layer.

Plant plugs have fully established root 

systems and thus an 80 to 90 percent 

survival rate. They spread their roots 

horizontally almost instantly after 

installation, helping to stabilize the 

soil layer. Within one to two vegetation seasons, plant plugs will grow 

into a dense vegetation mat and 

almost fully cover the designated roof 

surface. Because plugs are planted by 

hand, this is a labor-intensive option 

and the most expensive one of the 

three. 

In the second method, plant cuttings 

(mostly from sedum) are applied 

directly over the soil layer and held 

in place by a jute fabric. They have 

to develop roots before they can hold 

soil particles together and protect the 

soil from erosion, which takes time. 

Under ideal conditions, root development and growth can take from 3 to 

6 months during the growing season 

(e.g., between April and October). 

Root development usually does not 

occur in the dormant season (e.g., 

between November and March). 

Using plant cuttings as an installation 

method is cheaper than using plant 

plugs. But if the condition of the cuttings and the soil preparation are not 

optimum, the survival of the cuttings 

is greatly compromised. 

Cuttings may appear more attractive 

from a first-cost perspective. However, 

their survival rate is only about 50 

percent, compared with 80 percent for 

plant plugs. Initial savings on labor 

may disappear when the roof has to be 

replanted. The third method, seeding, 

is not recommended. 

Green roof plants vary in appearance, 

depending on the time of year. Many 

nondeciduous plants change color as 

they go dormant; others remain green 

throughout winter. 

In terms of integration, large, singlestory buildings benefit more from 

installations of green roofs than tall, 

multistory buildings do. The large 

roof-to-wall ratio of single-story 

buildings maximizes energy savings, 

because total energy use has a direct 

correlation to roof area. Because 

they help to improve energy efficiency, green roofs installed along 

with other energy-efficient measures 

often allow facility managers to 

downsize a building’s chiller capacity. 

An existing heating, ventilating, and 

air-conditioning (HVAC) system might 

also be able to operate less intensively 

and at higher efficiency. 

Mechanical systems, including air 

intake vents for the main HVAC systems, are usually on a large building’s 

rooftop. Green roofs can be installed 

to easily accommodate these systems 

and their maintenance requirements. 

To provide proper access to equipment 

and ensure proper airflow, the vegetation layer should be installed at least 

2 feet away from mechanical systems 

and air intakes. 

Pathways in the form of pavers or 

gravel can be installed along the 

perimeter and around equipment for 

access and routine maintenance. For 

window cleaning and repair tasks 

other than HVAC maintenance, 

facility managers might want to 

consider installing a walkway made 

of 5-foot-wide pavers or a sufficiently 

wide gravel path around the perimeter 

of the vegetation. 

Historic preservation may need to 

be addressed in regard to green roof 

installations in some areas. For example, Washington, D.C., has established Ed Snodgrass/PIX13401

Plants make up a large part of the cost of a green roof. The photo shows establishment 

using both plant plugs (background) and cuttings (foreground). The plant plugs are 

forming a dense vegetation cover, whereas the cuttings are developing slowly, leaving 

most of the soil exposed.
Federal Technology Alert

18 — FEDERAL ENERGY MANAGEMENT PROGRAM

Botanical Name Common Name Height 

(Inches) Flower Color USDA Zone Bloom Time

Antennaria diocia* Pink Pussy Toes 3” Pink

Armeria juniperifolia* Spanish Thrift 2” Pink 2 June

Armeria maritima ʻPride of Dusseldorfʼ* Common Thrift 5” Pink 2 April-June

Aubrieta ʻArgenteo-variegataʼ* Rock Cress 4” Purple 4 April-June

Campanula ʻBirch Hybridʼ Bellflower 4” Blue 4 June-Sept

Sedum acre ʻAureumʼ Golden Stonecrop 3” Yellow 3 June-August

Sedum aizoon 4” Yellow 5 July-August

Sedum album ʻMuraleʼ 1” White 4

Sedum cyaneum ʻRose Carpetʼ 2” Pink

Sedum dasyphyllum 3” White 5 June

Sedum dasyphyllum ʻBlue Cadetʼ 1.5” White 5

Sedum dasyphyllum ʻBlue Carpetʼ 1” White/Pink 5

Sedum divergens Old Man Bones 4-6” Yellow 5 July-August

Sedum ewersii Pink Stonecrop 6” Rose-Pink 3 Late Summer

Sedum ʻJelly Beanʼ Jellybean Sedum 4” 

Sedum kamtschaticum Russian Stonecrop 6” Yellow 3 June-July

Sedum linare ʻVariegatumʼ 5” Yellow

Sedum lineare ʻGolden Teardropʼ 3” Yellow 3 May-June

Sedum matrona 24” Pink 6 Sept

Sedum ʻMentha Requeinʼ False artillery fern 2” 4

Sedum pinifolium ʻBlue Spruceʼ 8” Yellow 4 June-July

Sedum reflexum 4” Yellow

Sedum sexangulare 4” Yellow 4

Sedum spurium ʻFuldaglutʼ Dragonʼs Blood Sedum 6” Red 3 Fall

Sedum spurium ʻRoseumʼ 6” Pink 3

Sedum spurium ʻTri-Colorʼ 6” Pink 3

Sedum spurium ʻWhite Formʼ 6” White 3

Sedum ternatum ʻLarinem Parkʼ Shale Barrens 2” White 3 May-June

Sedum tetractinum 4” 5

Sedum floriforum ʻWeihenstephaner Goldʼ Yellow

Sedum ʻArthur Branchʼ 18” Red 4 August-Sept

Sempervivum arachnoideum ʻSparkleʼ Spider-web Hen & Chicks

Thymus praecox ʻCoccineusʼ Red Creeping Thyme 1” Red/Purple 2 July-August

Thymus praecox ʻElfinʼ Miniature Thyme 1/2” Pink 2 July-August

Thymus praecox ʻPseudolanuginosusʼ Woolly Thyme 1” Pink 2 July-August

Note: Invasive sedum species—such as Sedum sarmentosum, a native of China—should be avoided on green roof applications. Delosperma, or ice plant, is also difficult to control on some roofs.

* These require about 4 inces of soil.

Table 5. Plants Suitable for Green Roofs in Various USDA Zones
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 19

some strict guidelines for historic 

preservation, and green roof retrofits 

might not be allowed on certain roofs 

of historic significance. 

Typically, historic preservation 

guidelines require that the appearance 

of a building from street level may 

not be altered. However, many 

government-style buildings have 

parapet walls around the edges of the 

roof. These walls can ensure the continuity of a building’s appearance from 

street level while allowing a green roof 

application, if desired and permitted. 

Specific design details would need to 

be addressed on a case-by-case basis. 

If a green roof is installed as part of an 

on-site stormwater management plan, 

the design should be integrated with 

the plan early in the design process, 

in collaboration with site engineers. 

Only if the green roof becomes an 

integral part of the whole project can 

its benefits be fully realized.

In terms of maintenance, an immediate commitment to weed control 

is imperative. Although plants on 

extensive green roofs do not typically 

produce the pollen that can cause 

allergic reactions in people working 

in or around the building, during 

the first two years weed control is 

needed to prevent ragweed and other 

pioneer exotics from taking root. 

Once the plant community forms a 

dense mat of vegetation, the opportunity for weeds to invade is greatly 

reduced because the soil, where weed 

seeds settle and sprout, is no longer 

exposed. Maintenance can thus be 

less frequent. 

In fact, extensive green roofs are 

designed to require very little maintenance. When they are first installed, 

green roofs require some care to 

ensure that plants take root in the 

new environment, remain healthy, 

and grow vigorously to form a dense 

vegetation mat. During the first two 

years, weed control can be done 

monthly or quarterly, depending on 

the site’s conditions; this can often 

be reduced to once a year after the 

second year. 

Irrigation: If natural precipitation 

at the site is insufficient to establish 

the plants at the time of installation, 

green roofs may need at least initial 

irrigation. The planting schedule and 

time of year can often be chosen to 

make use of natural irrigation. Note, 

however, that a permanent irrigation 

system that waters the plants regularly 

would keep the soil moist constantly 

and thus reduce the capacity of the 

green roof to retain and redirect 

precipitation. Therefore, permanent 

irrigation should be avoided unless it 

is required by climate conditions at 

the site. Selecting suitable, site-specific 

plants helps to eliminate this problem. 

Fertilizer: A thin layer of soil can 

become acidic over time. Therefore, 

it is advisable to apply a slow-release 

fertilizer during an annual maintenance walk, either in spring or in fall 

(whichever is the drier season).

Weeding: Initially, during one to 

two growing seasons, weeding may be 

required at least quarterly. After the 

soil layer is fully shaded by plants, 

weeding may be required only annually, in conjunction with regular roof 

drain cleaning and maintenance.

Leaks in waterproofing: Leaks in 

the waterproofing can result from 

problems with the waterproofing itself 

or with quality control and workmanship during installation. These leaks 

are difficult to detect and repair once 

vegetation covers the waterproofing. 

Here are a few simple measures that 

can reduce the potential for leaks: 

• Coordinate and time your waterproofing installation to prevent 

debris from falling onto it before 

the green roof is installed.

• Limit access to the roof once the 

waterproofing is installed to prevent 

workers from stepping on sharp 

objects like nails or glass and 

causing potential damage to the 

waterproofing.

• Flood-test the roof before the green 

roof installation to detect any 

construction-related damage while 

there is time to correct it fairly easily 

and while the membrane is accessible. Whether it is a prefabricated 

system or assembled with separate 

materials, a green roof requires care 

and quality control to prevent 

damage to the waterproofing.

Some roofing and green roof consultants offer leak detection services 

that will locate a leak underneath 

any protective roofing system, gravel 

ballast, IRMA, or vegetation layer. The 

electric field vector mapping (EFVM) 

technique is a method frequently used 

to test the water-tightness of existing 

roof surfaces before installing a green 

roof. It can also be used for annual 

surveys of green roofs to verify that 

the waterproofing system remains 

watertight below the vegetation. The 

EFVM method enables the source of 

any leak, even pin-hole-sized defects, 

to be located, but it requires that a 

fine grid of metal wire be installed 

initially within the green roof and 

waterproofing layers.

Occasional replanting: If large 

areas remain bare, replanting is recommended to stabilize soils and control 

erosion. If a green roof is designed 

for a specific performance goal (e.g., 

stormwater retention), the soil depth 

has to remain constant to ensure a 

certain water-retention capacity. If 

the growing medium compacts or 

decomposes to a lower depth, the 

green roof needs to be top-dressed 

with additional soil. 

Gutters: These require routine cleaning, just as those of conventional 

roofs do, to avoid standing water and 

hydrostatic pressure, which could lead 

to leaks. 

Monitoring is not a maintenance 

requirement. However, government 

agencies might want to monitor 

performance to quantify benefits in 

specific regions and to contribute to 
Federal Technology Alert

20 — FEDERAL ENERGY MANAGEMENT PROGRAM

data on the most suitable green roofs 

for various building types. 

Warranties, Standards, and Codes

Manufacturers typically guarantee 

waterproofing systems for 15 to 25 

years. These warranties can generally 

be extended to the same number of 

years for a green roof application if 

the same contractor installs the waterproofing and the green roof, or if the 

green roof system is supplied by the 

same manufacturer as the waterproofing membrane. The warranty may 

also be extended if a representative 

of the waterproofing company is on 

site during the subsequent green roof 

installation to ensure that no damage was done to the waterproofing. 

Warranties for maintenance and repair 

of the waterproofing are commonly 

based on the condition that the building owner bears the responsibility for 

removing the overburden (green roof) 

in case of a leak. 

Currently, there are no codes or 

standards for green roofs in the United 

States. The best practice guide being 

developed by the ASTM green roof 

task group will establish a procedure 

for assessment that includes both 

technical requirements and considerations for sustainable development. 

Costs

The cost of a green roof varies widely, 

depending on geographic area, materials used, and the contractor selected. 

Excluding structural upgrades, green 

roofs used to be widely quoted in 

the United States at $15 to $20 per 

square foot. But over the past few 

years, quotes have fallen to $8 to $15 

per square foot. These quotes might 

appear high in comparison to those 

common in Europe. This might be 

due in part to contractors’ unfamiliarity with the technology, to the use 

of imported materials from European 

manufacturers, and to the current lack 

of industry standards.

Waterproofing can cost from $3 to 

$6 for built-up or PVC roofs. The cost 

of the soil media varies, depending 

on its content, which can range from 

lightweight shale or clay aggregates 

mixed with topsoil to almost 100 

percent expanded clay or shale aggregates. The cost of the growing media 

varies widely, from $1 to $5 per square 

foot for a 4-inch-deep layer. Plant 

plugs should be budgeted at a minimum of $1 per square foot, or about 

$0.50 per plant plus shipping and 

handling, not including installation. 

In addition, the cost of drainage 

mats, optional irrigation and waterretention layers, root-resistant liners, 

and other layers must be included 

in the cost estimate. In line with the 

overall sustainability of a project, all 

green roof components should be 

obtained locally, if possible, to reduce 

costs.

Retrofit costs are harder to estimate. 

The cost of disposing of old material, 

structural upgrades, and new waterproofing might have to be added to 

the estimate, and these can make the 

total cost somewhat misleading.

The payback period for a green roof 

is also not easy to calculate, because 

it depends on many variables. These 

include new construction versus a 

retrofit; the scope and cost of the 

green roof design; whether the roof 

is installed on a single or multistory 

building; the total energy demand 

of the building versus the offset in 

energy demand; and stormwater 

permit requirements. At present, no 

procurement information is known 

to be available for green roofs on 

government buildings.

Utility Incentives and Support

Executive Order 13123, Greening the 

Government Through Efficient Energy 

Management, signed in 1999, directs 

all federal agencies to significantly 

improve the energy performance of 

government buildings and to reduce 

greenhouse gas emissions. In addition, 

agencies have to reduce their energy 

consumption per gross square foot by 

35 percent by the year 2010, relative 

to 198524 levels, and green roofs can 

contribute to all these directives. At 

Voltage Indicator

Energizer

Ground

Ground

Waterproofing

Membrane

Insulation

Roof of

Deck

Electric Field Vector

Defect

EFVM

Leak Survey

System

Electric field vector mapping (EFVM) technique for detecting leaks (Sources: International 

Leak Detection, Ltd.; Roofscapes, Inc.).
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 21

present, no direct rebates or incentive 

programs support the installation of 

new green roofs or retrofits. 

Stormwater quality and quantity 

requirements apply almost everywhere. However, several jurisdictions 

and regulatory agencies—including 

the Maryland Department of the 

Environment; the City of Portland, 

Oregon; the City of Seattle; and the 

District of Columbia—allow the runoff 

rates and volume of green roofs to 

be like those of forests or meadows. 

The resulting credits can help ease 

and speed the environmental permit 

process and save on construction costs 

for stormwater controls that would be 

required otherwise.

Some communities and cities in North 

America collect stormwater utility 

fees. Revisions are under way to assess 

how these fees can be adjusted to 

reflect the actual impact of impervious 

surfaces on sewer systems and urban 

watersheds, based on the actual footprint of a building rather than on a 

universal flat fee. This would allow the 

calculation of the actual amount of 

stormwater runoff generated by each 

property. Because green roofs filter, 

store, and absorb rainwater, buildings 

with a green roof do not generate the 

usual peak runoff rates, volume, or 

non-point-source pollution generally associated with urban runoff. To 

encourage low-impact development 

strategies, utilities might want to 

create incentive programs or provide 

exemptions to stormwater fees. 

Many local governments in the United 

States have based their green building 

initiatives on the U.S. Green Building 

Council’s LEED rating system, and 

they grant floor area ratio and height 

bonuses to those achieving a minimum LEED rating. However, a costbenefit analysis would probably not 

support installing a green roof as 

a way to obtain LEED credits. 

In terms of building codes, many cities 

and communities in North America 

are reviewing and revising their codes 

to remove barriers for green building 

practices and to address green roofs 

specifically. Landscaped roofs and 

roof gardens are generally allowed 

in building codes, as long as the roof 

structures are properly designed to 

carry the additional loads. 

The City of Chicago recently updated 

its energy code, requiring light-colored 

roofs as one way to reduce the urban 

heat island effect. Chicago might also 

allow the use of green roofs that have 

the same benefits to meet this code. 

In addition, landscape ordinances 

throughout North America now 

specify minimum shading requirements for large lots to reduce urban 

heat islands and to meet open space 

requirements. Those ordinances might 

also allow green roofs to be used to 

comply with those goals, in whole or 

in part.

Technology Performance

Green roofs technology is not new. 

However, it has only recently been 

introduced into North America. A 

limited number of projects have been 

completed, and little performance 

data are available to date. 

Project monitoring: The roof of the 

combined City Hall and Cook County 

building in Chicago was retrofitted 

with a 22,000-square-foot green roof 

on the City Hall side in 2001. The 

rooftop of the county’s portion of the 

building remains black. These two 

roof surfaces are undergoing intensive 

monitoring programs to evaluate the 

green roof’s performance in mitigating heat gain at the surface and thus 

in reducing the effects of urban heat 

islands. Data should be available in 

the near future. 

Academic research: The State 

University of Pennsylvania, under 

the supervision of Dr. David Beattie 

in the Horticulture Department, is 

undertaking an extensive research 

project to evaluate the performance 

of green roofs for energy efficiency, 

stormwater management, and the 

mitigation of heat gain. The study also 

aims to evaluate a green roof’s impacts 

on indoor environments and ability 

to neutralize acid rain, as well as to 

define physiological, biological, and 

ecological factors influencing plant 

survival.25

The research project makes use of 

six small structures; three of them 

are covered with an extensive green 

roof with a 4-inch thick soil layer. 

The other three structures have 

conventional black roof surfaces. 

All the buildings are equipped with 

multiple sensors and connected to an 

electronic data logger to continually 

collect and record data, including 

heat flux, stormwater runoff, and 

nutrient filtration. Each building is 

metered separately to evaluate its 

energy consumption for heating and 

cooling. These data will be published 

to aid in establishing protocols for 

the performance of green roofs. Note, 

however, that the roof-to-wall ratio 

in this study is not representative of 

a typical single-story building with a 

large footprint.

International performance and 

evaluation: In Europe, green roof 

technology has been applied for more 

than 20 years. Many projects have 

been monitored, and performance 

data are available, but not in English. 

Germany recently developed an evaluation matrix in an effort to quantify 

green roof performance. This matrix 

will allow comparisons of several different green roof systems, despite the 

broad spectrum of design parameters 

used, based on a point value rating 

system. 

Performance is rated on the basis of 

ecological functions, ability to mitigate the effects of impervious surfaces, 

and economic benefits. Design parameters include the type of green roof 

(single- or multiple-layer construction), the use of recycled and locally 

available materials, soil depth, plant 

diversity, maintenance requirements, 
Federal Technology Alert

22 — FEDERAL ENERGY MANAGEMENT PROGRAM

insulation properties, and cost-benefit 

ratio. However, it stops short of actually requiring monitoring the green 

roof’s performance. 

Case Study

Chicago City Hall Rooftop Garden 

Retrofit

Chicago, Illinois 

The City of Chicago is one of five U.S. 

cities selected by the EPA to participate in the Urban Heat Island Pilot 

Project. The goal of the pilot study is 

to measure elevated ambient air temperatures in a metropolitan area and 

study the benefits of cooling urban 

heat islands to improve air quality. 

Chicago’s current Mayor, Richard M. 

Daley, learned about green roofs when 

he visited Europe. Upon his return 

to the United States, he decided to 

support a demonstration of green roof 

technology on the City Hall building 

(see cover photo) for three reasons: 

(1) to showcase green roof technology 

in Chicago and lead by example, (2) to 

study its effectiveness in lowering 

ambient air temperatures, and (3) to 

promote public interest in this new 

technology.

City Hall shares a 12-story building 

in downtown Chicago with Cook 

County’s administrative offices. Each 

government agency is responsible 

for the maintenance and upkeep 

of its half of the building’s roof. All 

mechanical systems are located on 

the roof in the penthouse. The green 

roof retrofit of the City Hall half—

including permitting, structural, and 

maintenance issues—was quite 

a challenge for city engineers. 

During the design process, energy 

modeling was conducted to predict 

the environmental benefits of a green 

roof on the City Hall roof and on 

those of all the buildings in Chicago, 

which make up about 30 percent of 

the city’s surface area. The energy 

model estimated that City Hall 

might save $4,000 in annual energy 

costs from reduced heating and airconditioning demands. The model 

also estimated that the entire city 

could reduce its energy demand by 

as much as 720 megawatts and thus 

save as much as $100,000,000 if all 

the buildings in Chicago were covered 

with green roofs. The lower energy 

demand would also result in a 460-

ton reduction in NOx and a 570-ton 

reduction in sulfur dioxide (SO2) 

each year.26

The soil layer of the Chicago City 

Hall green roof was designed to have 

a variety of depths, ranging from 3- to 

4-inch layers to semi-intensive layers 

of about 8 to 10 inches. Two small 

intensive areas contain one tree each. 

The initial green roof design turned 

out to be cost-prohibitive at $2.9 million, or about $1.5 million over budget. As a result, it was redesigned and 

rebid by an experienced installer. This 

setback shows how an unfamiliarity 

with green roofs can cause unnecessary, time-consuming, and expensive 

delays in the design process. The 

experienced green roof consultant 

was brought in too late to maximize 

the functionality of the roof, beyond 

its ability to reduce ambient air 

temperatures. 

For construction to proceed, a building permit was required. Questions 

arose about how to permit a green 

roof and which building codes applied 

to the project. The design was found 

to not have to meet requirements 

for accessibility in the Americans 

with Disabilities Act, nor were long 

plumbing extensions needed. The 

building permit was granted in 6 

weeks. However, another major setback was prompted by the extensive 

deterioration in the parapet walls. The 

brick mortar, which was susceptible 

to the penetration of water, had to be 

repaired before the installation could 

continue. When the waterproofing 

installation was completed, a flood 

test was conducted. 

The City Hall roof measures about 

38,800 square feet. The green roof 

now occupies 22,000 square feet of the 

total and consists of 156 plant varieties. Planting occurred in two stages, 

from September to early November 

2000, and the installation was completed in spring 2001. 

The first interesting effect, the reduction in heat flow resulting from the 

green roof, was observed during 

the first winter. A snowfall in late 

2000 offered a protective cover for 

the tender plants that were feared 

lost because of the lateness of the 

Plantings for the green roof of Chicago’s City Hall were done in two stages in the fall of 

2000.

Credit: City of Chicago
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 23

installation. The snow lasted for an 

extended period of time, as observed 

by engineers in the city’s Environment 

Department, while the snow on the 

adjacent county building’s roof melted 

in just two weeks, indicating reduced 

heat flow on the green roof.

Data loggers were used to monitor 

ambient air temperatures over City 

Hall’s green roof and over the County 

Building’s black tar roof, collecting 

data every 30 minutes. In August 

2001, the temperature of ambient air 

over the County Building’s black tar 

roof measured 114°F (45.5°C), and 

the temperature over City Hall’s green 

roof measured 107°F (41.6°C). The air 

over the green roof was thus cooler by 

7°F (3.9°C) than that over the black 

tar roof, which is consistent with measurements taken in a Toronto project 

and with estimates by LBNL.

The roof temperatures shown below 

were taken with an infrared thermometer on August 9, 2001. Although this 

method is less accurate than using a 

data logger, surface temperatures can 

be instantly measured and recorded 

by using a hand-held infrared thermometer. The August 2001 data are 

as follows:

City Hall green roof paved surfaces 

 126°–130°F (52.2°–54.5°C)

City Hall green roof surface 

 91°–119°F (32.7°–48.3°C)

Cook County black tar roof 

 169°F (76°C)

The average temperature difference 

between the city’s and the county’s 

roof surfaces was thus found to be 

64°F (35.5°C). This indicates the 

potential of green roofs to efficiently 

lower ambient air temperatures. The 

graph on this page compares cumulative data for the City Hall green roof 

and the Cook County black tar roof 

taken during August 2002. 

The City Hall green roof cost $24.60 

per square foot (about $500,000). The 

cost was higher than average because 

it was constructed as a combined, 

semi-extensive/intensive green roof. It 

includes the cost of irrigation and two 

trees, which are usually not part of an 

extensive green roof design. The total 

cost—including removal and disposal 

of the old roof, new waterproofing, 

structural upgrades, and the green 

roof retrofit—was $1.5 million. Actual 

energy savings have not yet been 

determined and will be needed to 

calculate the payback period for this 

retrofit.27

The Technology in 

Perspective

Technology Development 

Some of the earliest known examples 

of green roofs—roof gardens dating 

back to 600 B.C. and earlier—might 

have been similar to the fabled 

Hanging Gardens of Babylon. These 

apparently were planted on terraced 

rooftops to cool the buildings underneath them. 

Green roofs and traditional sod bricks 

have been used for many centuries in 

Iceland, Scandinavia, Alaska, and parts 

of Africa to protect inhabitants from 

the effects of extreme climate conditions. Both the Vikings and the French 

apparently brought the practice with 

them to areas that are now part of 

Nova Scotia and Newfoundland in 

northeastern Canada. 

In modern times, the architects Le 

Corbusier and Frank Lloyd Wright 

were both notable advocates of green 

roof technology. In northern Europe, 

there has been a considerable resurgence of interest in green roofs since 

the 1960s for their ability to improve 

the environment of densely populated 

urban areas. Germany’s interest in 

the technology began to surge about 

20 years ago, when it became evident 

that stormwater runoff in densely 

populated areas was exceeding the 

capacity of the sewer systems to 

handle it. 

Chicago, IL, Rooftop Ambient Air Temperature

60

70

80

90

100

110

120

Date

Cook County — Black Tar Roof 

08/11/02

113.4 F

City Hall — Green Roof 

08/11/02

99.9 F

08/02/02 08/31/02

August 2002

Temperature (F)
Federal Technology Alert

24 — FEDERAL ENERGY MANAGEMENT PROGRAM

In Germany, people began to realize 

that the capacity of the sewer infrastructure could not be expanded in 

many areas, so alternatives had to be 

found. They discovered that using 

green roofs in lieu of conventional 

roof surfaces could be the single greatest way to reduce and delay stormwater runoff and to significantly 

reduce the load on a sewer system. 

Several private companies have 

brought some of Europe’s newest 

green roof designs across the Atlantic 

to North America. 

Technology Outlook

In recent years, several research, demonstration, and test projects have been 

conducted in both Canada and the 

United States—in cities like Ottawa, 

Winnipeg, Chicago, and Portland, 

among others. Early results indicate 

that green roofs hold great promise 

as an effective way to help solve a 

number of modern urban problems 

in North America.

Recent studies conducted by the 

National Research Council of Canada 

show that green roofs are highly effective in reducing heat transfer. And 

extensive research is being conducted 

in the United States on strategies for 

mitigating urban heat islands; it could 

prove to be very helpful in introducing green roofs into the mainstream of 

the building industry in this country. 

Because thousands of government 

buildings are good candidates for 

green roof retrofits, there is great 

potential for this technology in 

federal facilities. Green roofs could be 

gradually phased in as part of standard 

roof replacement and modernization efforts. This would also assist in 

extending the lifetimes of replacement 

roofs.

For new construction, federal agencies 

could make green roofs mandatory 

because of their energy and environmental benefits, such as stormwater 

management. If green roofs could be 

integrated into building design and 

stormwater permitting processes, they 

would be more cost-effective because 

the resulting cost savings would be 

significant.

Because they are such a beneficial, 

multifunctional technology, green 

roofs are likely to become more widely 

used in the United States in future 

years. This is particularly true in 

urban areas, where the need for such 

a benign technology is becoming 

more urgent all the time. 

Conclusion

Green roof technology is an effective, 

practical way to increase the energy 

performance of buildings and limit 

stormwater runoff. Adapting green 

roofs for federal buildings can provide important benefits, especially 

to low-rise buildings and facilities in 

districts with strict stormwater regulations. Integrating green roofs into 

stormwater permitting requirements 

may be the most realistic way to make 

them more financially viable. Green 

roofs are also effective in reducing the 

effects of urban heat islands.

The lack of information and education 

about green roofs must be addressed, 

however, if they are to be used more 

widely. This is especially important 

in areas with combined sewer systems 

and in coastal areas where reducing 

stormwater runoff can be critically 

important to public health and to the 

health of our watersheds. 

For More Information

The following lists include companies 

identified as being involved in designing, manufacturing, or installing green 

roofs. We made every effort to identify 

current manufacturers; however, this 

listing is not purported to be complete 

or to reflect future market conditions. Please see the Thomas Register

(www.thomasregister.com) for more 

information.

Consultants and Designers

Charlie Miller, P.E.

Roofscapes, Inc.

7114 McCallum Street

Philadelphia, PA 19119

Phone: 215-247-8784 

Fax: 215-247-4659

Katrin Scholz-Barth

Katrin Scholz-Barth Consulting

1246 Duncan Place, N.E.

Washington, D.C. 20002

Phone: 202-544-8453

Robert Hermann

Uncommon Plants

P.O. Box 493

New Hartford, CT 06057

Phone/fax: 860-379-0327

Waterproofing and Green Roof 

Systems Manufacturers

American Hydrotech, 

 in partnership with Zinco, Inc.

303 E. Ohio Street 

Chicago, IL 60611

Phone: 800-877-6125

Fax: 312-661-0731

Barrett Company

P.O. Box 421

Millington, NJ 07946

Phone: 800-647-0100

Fax: 908-647-0278
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 25

The Garland Company

3800 East 91st Street

Cleveland, OH 44105

Phone: 800-741-3157

Sarnafill, Inc.

100 Dan Road

Canton, MA 02021

Phone: 781-828-5400

Fax: 781-828-5365

Suprema, Inc.

310 Quadral Drive

Wadsworth, Ohio 4428

Phone: 800-356-3521 

 or 330-334-0066

W. P. Hickman Systems, Inc.,

 in partnership with the German 

 firm FAMOS 

30700 Solon Industrial Parkway 

Solon, Ohio 44139

Phone: 440-248-7760

Fax: 440-248-6524

Modular Green Roof Systems

GreenTech, Inc.

8401-F Mayland Drive

Richmond, VA 23294

Phone: 804-965-0026

Fax: 804-965-9630

GreenGrid 

20 North Wacker, Suite 1210 

Chicago, IL 60606

Phone: 312-424-3306

Fax: 312-424-3330

Selected Nurseries

Emory Knoll Farms

3410 Ady Road

Street, MD 21154

Phone: 410-452-5880

Fax: 410-452-5319

North Creek Nurseries, Inc. 

388 North Creek Road 

Landenberg, PA 19350 

Phone: 610-255-0100 

Fax: 610-255-4762 

ItSaul Natural

1115 West Nancy Creek Drive

Atlanta, GA 30319

Phone: 404-257-3339

Rice Creek Gardens, Inc.

11506 Highway 65

Blaine, MN 55434

Phone: 763-754-8090

Other Resources

Pennsylvania State University

Green Roof Research Center

University Park, PA 16802 http:

//hortweb.cas.psu.edu/research/

greenroofcenter/research.html 

Green Roof Innovations,

 a division of SHADE Consulting, LLC

P.O. Box 2775

Carmel, CA 93921

Phone: 831-625-5625

Fax: 831-625-0525

Publications

The Green Roof Infrastructure Monitor, 

an online newsletter published by 

the Cardinal Group, Inc.; available at www.greenroofs.ca/grhcc/

publications.htm.

Johnston, Jacklyn, and John Newton. 

Building Green: A Guide to Using 

Plants on Roofs, Walls, and Pavements. 

London: The London Ecology Unit, 

1992.

Osmundson, Theodore. Roof Gardens: 

History, Design and Construction. 

New York: W.W. Norton & Company, 

1999.

Peck, Steven, and Monica Kuhn. 

Design Guidelines for Green Roofs. 

Toronto, Ontario, Canada: Ontario 

Association of Architects, with the 

Canada Mortgage and Housing 

Corporation SCHL. Accessed in 

April 2004. www.greenroofs.com/

Greenroofs101/how-tos.htm.

Peck, Steven, Chris Callaghan, Monica 

E. Kuhn, and Brad Bass. Greenbacks 

from Green Roofs: Forging a New 

Industry in Canada. Toronto: Canada 

Mortgage and Housing Corporation, 

March 1999. www.greenroofs.ca/

grhcc/Greenbacks.pdf.

Scholz-Barth, Katrin. “Green Roofs: 

Storm-water Management from the 

Top Down.” Environmental Design and 

Construction, January/February 2001: 

pp. 63-69. www.edcmag.com/edc/

cda/articleinformation/features/bnp_

features_item/0,4120,18769,00.html.

References

1 Konopacki, S., and H. Akbari. 

Measured Energy Savings and Demand 

Reduction from a Reflective Roof 

Membrane on a Large Retail Store in 

Austin. Report LBNL-47149. Berkeley, 

CA: Lawrence Berkeley National 

Laboratory, June 28, 2001.

2 Liu, K.L., and B. Baskaran. “Thermal 

Performance of Green Roofs through 

Field Evaluation.” Presented at 

“Greening Rooftops for Sustainable 

Communities,” the First North 

American Green Roofs Infrastructure 

Conference, Awards, and Trade 

Show, Chicago, IL, May 29-30, 2003. 

National Research Council, Institute 

for Research in Construction, 1500 

Montreal Road, Ottawa, Ontario, 

Canada K1A O6R.

3 Ibid.

4 Ibid.

5 U.S. Department of Energy. “Recent 

Studies and New Financial Incentives 

Bolster Use of Cool Roofs.” Rebuild 

America Web site, www.rebuild.org/

news/newsdetail.asp?NewsID=1173.

Accessed April 2004. See also the U.S. 

Environmental Protection Agency 

Web site, Energy Star for Roof 

Products, Fact Sheet for Contractors, 

<www.energystar.gov/ia/partners/

manuf_res/rooffactsheetcontractor.

pdf>. Accessed May 2004.

6 Konopacki, S., and Akbari, H. 

Measured Energy Savings and Demand 

Reduction from a Reflective Roof 

Membrane on a Large Retail Store in 

Austin. Op. cit., 2001.
Federal Technology Alert

26 — FEDERAL ENERGY MANAGEMENT PROGRAM

7 Dürr, A. Dachbegrunung: Ein 

Okologischer Ausgleich (Translated: 

Roof Greening: An Ecological Balance). 

Gütersloh, Germany: Bauverlag BV 

GmbH. 1995.

8 Ibid.

9 Johnston, J., and J. Newton. Building 

Green: A Guide to Using Plants on Roofs, 

Walls, and Pavement. London: The 

Ecology Unit, 1992, p. 49.

10 Akbari, H. “Heat Island Reduction: 

An Overview—Effects of Trees and 

Implementation Issues.” Presentation 

by Lawrence Berkeley Laboratory at 

the University of Pennsylvania, LAPR 

760. November 13, 2002.

11 Ibid. 

12 U.S. Environmental Protection 

Agency, Office of Air Quality Planning 

& Standards. “NOx—How Nitrogen 

Oxides Affect the Way We Live and 

Breathe.” September 1998. U.S. EPA 

Web site, www.epa.gov/air/urbanair/

nox/index.html. Accessed May 2004.

13 Johnston, J., and J. Newton. Building 

Green: A Guide to Using Plants on Roofs, 

Walls, and Pavement. Op. cit., 1992.

14 McCann, R.J., and S.J. Moss. “NUTS 

AND BOLTS: The Implications of 

Choosing Greenhouse-Gas Emission 

Reduction Strategies. Reason Public 

Policy Institute, Policy Study No. 

171. November 1993. RPPI Web 

site, <www.rppi.org/environment/

ps171.html>. Accessed May 2004.

15 Dürr, A. Roof Greening; An Ecological 

Balance (transl.). Op. cit., 1995, p. 17.

16 Scholz-Barth, K. Personal conversation with Chris Warck, Shade 

Consulting. September 2003.

17 Liu, K.L., and B. Baskaran. “Thermal 

Performance of Green Roofs through 

Field Evaluation.” Op. cit., 2003. 

18 Pennsylvania State University. 

Green Roof Research Center Web site, 

<http://hortweb.cas.psu.edu/research/

greenroofcenter/about_ctr.html>. 

Accessed May 2004.

19 Dürr, A. Roof Greening: An Ecological 

Balance. Op. cit., 1995.

20 Interview with representative of 

Seal Engineering, Inc., Roofing and 

Waterproofing Consultant for the 

General Services Administration. 

February 2004.

21 Burton, B. “NRC Launches Green 

Roof Demonstration Project.” 

Landcaping and Groundskeeping Journal. 

Vancouver, British Columbia, Canada: 

Baum Publications Ltd., July/August 

2003.

22 Green Roofs for Healthy Cities. 

www.greenroofs.org. Accessed April 

2004.

23 For a list of selected research institutes conducting green roof research, 

see <www.greenroofs.com/research_

links.htm>.

24 Executive Order 13123, “Greening 

the Government Through Efficient 

Energy Management.” Signed June 3, 

1999. 64 FR 30851, June 8, 1999. 

<http://frwebgate.access.gpo.gov/

cgi-bin/getdoc.cgi?dbname=1999_

register&docid=fr08jn99-171.pdf>. 

Accessed March 2003.

25 See the Penn State Green Roof 

Research Center Web site, <http:

//hortweb.cas.psu.edu/research/

greenroofcenter/research.html>. 

Accessed May 2004.

26 Laberge, K.M., P.E., Chicago 

Department of Environment. 

“Urban Oasis: Chicago’s City 

Hall Green Roof.” Presented at 

“Greening Rooftops for Sustainable 

Communities,” the First North 

American Green Roofs Infrastructure 

Conference, Awards, and Trade Show. 

Chicago, IL May 29-30, 2003.

27 See the City of Chicago Rooftop 

garden Web site, <www.cityofchicago.

org/Env/rooftopgarden/index.html>. 

Accessed April 2004.
Federal Technology Alert

FEDERAL ENERGY MANAGEMENT PROGRAM — 27

Federal Energy Management Program

The federal government is the largest energy consumer in the nation. Annually, the total primary energy consumed 

by the federal government is 1.4 quadrillion British thermal units (quads), costing $9.6 billion. This represents 1.4% 

of the primary energy consumption in the United States. The Federal Energy Management Program was established 

in 1974 to provide direction, guidance, and assistance to federal agencies in planning and implementing energy 

management programs that will improve the energy efficiency and fuel flexibility of the federal infrastructure. 

Over the years, several federal laws and Executive Orders have shaped FEMP’s mission. These include the Energy 

Policy and Conservation Act of 1975; the National Energy Conservation and Policy Act of 1978; the Federal Energy 

Management Improvement Act of 1988; the National Energy Policy Act of 1992; Executive Order 13123, signed in 

1999; and, most recently, Executive Order 13221, signed in 2001, and the Presidential Directive of May 3, 2001.

FEMP is currently involved in a wide range of energy-assessment activities, including conducting new technology 

demonstrations, to hasten the penetration of energy-efficient technologies into the federal marketplace.

About FEMP’s New Technology Demonstrations

The Energy Policy Act of 1992 and 

subsequent Executive Orders mandate that energy consumption in 

federal buildings be reduced by 

35% from 1985 levels by the year 

2010. To achieve this goal, the U.S. 

Department of Energy’s Federal 

Energy Management Program (FEMP) 

sponsors a series of activities to 

reduce energy consumption at federal installations nationwide. One 

of these activities, new technology 

demonstrations, is tasked to accelerate 

the introduction of energy-efficient 

and renewable technologies into the 

federal sector and to improve the rate 

of technology transfer. 

As part of this effort, FEMP sponsors 

the following series of publications 

that are designed to disseminate 

information on new and emerging 

technologies:

Technology Focuses—brief information on new, energy-efficient, environmentally friendly technologies of 

potential interest to the federal sector.

Federal Technology Alerts—longer 

summary reports that provide details 

on energy-efficient, water-conserving, 

and renewable-energy technologies 

that have been selected for further 

study for possible implementation in 

the federal sector. Additional information on Federal Technology Alerts 

(FTAs) is provided below.

Technology Installation Reviews—

concise reports describing a new 

technology and providing case study 

results, typically from another demonstration or pilot project.

Other Publications—we also issue 

other publications on energy-saving 

technologies with potential use in the 

federal sector.

More on Federal Technology Alerts

Federal Technology Alerts, our signature reports, provide summary information on candidate energy-saving 

technologies developed and manufactured in the United States. The 

technologies featured in the FTAs have 

already entered the market and have 

some experience but are not in general 

use in the federal sector.

The goal of the FTAs is to improve 

the rate of technology transfer of new 

energy-saving technologies within 

the federal sector and to provide the 

right people in the field with accurate, 

up-to-date information on the new 

technologies so that they can make 

educated judgments on whether the 

technologies are suitable for their 

federal sites.

The information in the FTAs typically 

includes a description of the candidate 

technology; the results of its screening 

tests; a description of its performance, 

applications, and field experience 

to date; a list of manufacturers; and 

important contact information. 

Attached appendixes provide supplemental information and example 

worksheets on the technology.

FEMP sponsors publication of the 

FTAs to facilitate information-sharing 

between manufacturers and government staff. While the technology 

featured promises significant federalsector savings, the FTAs do not 

constitute FEMP’s endorsement of a 

particular product, as FEMP has not 

independently verified performance 

data provided by manufacturers. 

Nor do the FTAs attempt to chart 

market activity vis-a-vis the technology featured. Readers should note the 

publication date on the back cover, 

and consider the FTAs as an accurate 

picture of the technology and its performance at the time of publication. 

Product innovations and the entrance 

of new manufacturers or suppliers 

should be anticipated since the date 

of publication. FEMP encourages 

interested federal energy and facility 

managers to contact the manufacturers and other federal sites directly, and 

to use the worksheets in the FTAs to 

aid in their purchasing decisions.
Log on to FEMPʼs Web site for information about 

New Technology Demonstrations 

www.eere.energy.gov/femp/

You will find links to

• A New Technology Demonstration Overview

• Information on technology demonstrations

• Downloadable versions of publications in Adobe Portable 

Document Format (pdf)

• A list of new technology projects under way

• Electronic access to a regular mailing list for new products 

when they become available

• How federal agencies may submit requests to us to assess 

new and emerging technologies

Printed with a renewable-source ink on paper containing

at least 50% wastepaper, including 10% postconsumer waste

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy independence for America. 

Working with a wide array of state, community, industry, and university 

partners, the U.S. Department of Energy’s Office of Energy Efficiency and 

Renewable Energy invests in a diverse portfolio of energy technologies.

Produced for the U.S. Department 

of Energy, Energy Efficiency and 

Renewable Energy, by the National Renewable Energy Laboratory

DOE/EE-0298

August 2004

For More Information

EERE Information Center

1-877-EERE-INF or

1-877-337-3463

www.eere.energy/gov/femp

General Program Contacts

Ted Collins

Program Manager

New Technology Demonstrations

Federal Energy Management Program

U.S. Department of Energy

1000 Independence Ave., S.W.

Washington, D.C. 20585

Phone: (202) 586-8017

Fax: (202) 586-3000

theodore.collins@ee.doe.gov

Steven A. Parker

Pacific Northwest National Laboratory

P.O. Box 999, MSIN: K5-08

Richland, WA 99352

Phone: (509) 375-6366

Fax: (509) 375-3614

steven.parker@pnl.gov

Technical Contacts and Authors

Stephanie Tanner

National Renewable Energy Laboratory

901 D Street, S.W., Suite 930

Washington, DC 20024

Phone: (202) 646-5218

E-mail: stephanie_tanner@nrel.gov

Katrin Scholz-Barth 

1246 Duncan Place, N.E.

Washington, DC 20002

Phone: (202) 544-8453

E-mail: Katrin@scholz-barth.com