Hamilton West Apartments Ecoroof 

1212 SW Clay Street, Portland, OR 

Project Summary 

Project Type: Multi-family residential – demonstration project

Technologies: Ecoroof 

Major Benefits: • Increased roof longevity – The ecoroof should double the life of the roof. 

• Stormwater management – There is a substantial reduction in runoff from more than 

8,400 sq. ft. of roof. 

• Over the course of a typical year, the stormwater facilities manage about 768,000 gallons of 

potential stormwater assuming an average retention rate of 53.5% and an average annual

rainfall of 37 inches. 

• 5,140 sq. ft. of landscaping was added, improving the urban environment and the aesthetic 

appeal of the property. 

Cost: $127,500 (unit cost of $15 per sq. ft. of impervious area managed). Environmental Services

granted $90,000 for the project. 

Constructed: September 1999

Background 

In fall 1999, an ecoroof was installed on the newly 

constructed Hamilton West Apartments building. This was a 

joint project between the Housing Authority of Portland 

(HAP), the City of Portland Bureau of Environmental 

Services (BES), and the Portland Development Commission 

(PDC). It was the City’s first ecoroof demonstration and 

testing facility. At Hamilton, the City measures stormwater 

capture and water quality and compares the success of 

planting methods, soil type and depth, and vegetation 

selection. 

Hamilton and other ecoroofs represent an important 

sustainable stormwater (low impact development) strategy. 

They manage stormwater at the source, using natural systems 

that have positive impacts for stormwater runoff volume and 

quality. Associated benefits such as energy cost reduction, air 

pollution and heat reduction, bird and insect habitat, e

roof lifespan, and urban beautification, make ecoroofs a

valuable urban asset. 

xtended

The 8,700 square foot roof is divided into an elevator vestibule (not vegetated), a 1,000 square 

foot concrete paver terrace with seating and tables, and a 5,140 square foot ecoroof containing 

succulents, grasses and flowers. The Hamilton Apartments ecoroof showcases opportunities for 

partnerships by public and private organizations and has served as a catalyst for other groups to 

pursue this method of stormwater runoff reduction. The building and roof terrace are an example 

Report Completed: January 5, 2005 Page 1
of how to maximize density on an urban infill site while providing outdoor amenities for tenants. 

Based on monitoring results, the ecoroof provides excellent stormwater management. 

Overview of the Stormwater System 

In order to test the stormwater capacity of different types and depths of soil, the ecoroof was 

divided into east and west sections. Each side was planted using identical methods and types of 

vegetation. The east side consists of 2,620 square feet of vegetated cover with initial substrate 

depth of 3 inches. Saturated weight is 10 pounds per square foot. The west side consists of 2,520 

square feet of vegetated cover with initial soil substrate depth of 5 inches. Saturated weight is 25 

pounds per square foot. There are two roof drains one in the west section and one in the east 

section. Each section slopes toward its roof drain. 

The vegetated portion of the roof receives precipitation directly. Runoff from the stone terrace 

infiltrates through the pavers to the sand bed below and into the ecoroof substrate. Air 

conditioning condensate and runoff from the elevator vestibule is piped directly to the roof drain 

so that it does not skew stormwater measurement data. 

Stormwater Capacity and System Components 

Stormwater Management Goals

The ecoroof is a demonstration project in stormwater management. It was designed to meet 

multiple goals and objectives that benefit tenants, partners, and the larger community. Goals 

include reducing peak flows and volume of stormwater, which helps alleviate Portland’s 

combined sewer overflow (CSO) problem; and providing opportunities for research and 

education in development of ecoroof technology specific to the Pacific Northwest. 

Report Completed: January 5, 2005 Page 2
System Components

Ecoroof 

Catchment area: 7,800 square feet 

Facility footprint: 5,140 square feet

Overflow: Drains to storm sewers 

Additional information: 

• The roof is built in layers. From the bottom up, they are: 

o A waterproofing membrane over the roof structure 

o Root-resistant barrier made from 6 mm polyethylene 

o A drainage layer made from a geotextile drainage fabric 

o 1 cm thick Poly-scrim root reinforcement material 

o Soil substrate (organic and coarse aggregate) 

o Irrigation system

o Plants and walkway stones 

Each side of the roof drains into a gravel filtering area then into a drainpipe inside the building 

that then connects to the City storm drain system. A small, 60 degree, V-trapezoidal flume is 

installed immediately upstream of each primary roof drain. A bubbler-type flow meter measures 

the water level at each flume. The primary roof drain is sealed and isolated to direct all flow 

through the flume prior to entering the drain. The possibility exists that during very large storms, 

some water may flow out the secondary drain and not flow through the flume. 

Report Completed: January 5, 2005 Page 3
Emergency Overflow

The primary roof drains are plumbed directly to the City storm sewer system. The secondary 

drains function as emergency overflow drains if the primary drains become plugged. Since the 

secondary drains are fitted with a two-inch extension collar, water enters the secondary drains 

only if the pooled water level around the drains exceeds the collar. The secondary drains 

discharge directly off the side of the building. 

Landscaping 

Each side of the roof was divided into three sections and planted identically using the following 

three methods. Plants include a mix of natives and hardy ornamentals. 

• NE and NW sections planted with 11 x 22-inch (1.8 square foot) mats of pre-germinated 

seedlings and root cuttings 

• West and east sections planted with plugs and containers of sedums, succulents, and 

perennials 

• SE and SW sections planted with hand-broadcast mix of sedum sprigs, and hydro-seed 

matrix of perennial flowers and grasses. A small area of the south section was planted 

with native grasses and wildflowers such as lupine and yarrow. 

Soil or substrate 

The roof uses two types of substrate, one for the east side, and one for the west. 

• The east side was installed with three inches of very lightweight mixture with a 

maximum saturated weight of 10 pounds per square foot. 

• The west side was installed with five inches of lightweight mixture with a maximum 

saturated weight of 25 pounds per square foot. 

• Lightweight soils erode easily. Because of soil loss due to wind, red pumice stone was 

added to the NE section. This treatment is now being measured to test its ability to 

control erosion, provide mineral content and pore space for plant roots, and suppress 

weeds. 

Irrigation 

The roof uses an automatic irrigation system with spray heads on 12-inch risers. Irrigation is 

applied each summer. In summer 2001, about 6 inches was applied to the east side and 4 inches 

to the west. After the initial plant establishment period, irrigation amounts were reduced. During 

the very dry summer of 2002, 3 inches of irrigation was applied to the east side and 2 inches to 

the west side. 

Typically, irrigation is only used on the roof in limited amounts and when plants show effects 

from prolonged periods of dry, hot weather. 

 

Report Completed: January 5, 2005 Page 4
Budget 

The final project budget submitted by the HAP was $127,485 including management, design, 

materials and construction. The budget breaks down as shown below. 

Budget Elements

Activity Cost % of Total Cost 

Design $17,900 14.0 %

Permitting $2,292 1.8 %

Roof Construction $43,620 34.2 %

Plantings $9,740 7.6 %

Soil and waterproof membrane $41,483 32.5 %

Irrigation $2,500 2.0 %

Miscellaneous $7,950 6.2 %

Total $127, 485 100 %

Cost Comparisons 

Because roofscaping covers and protects the waterproofing and structural components of a roof, 

ecoroofs typically last twice as long as conventional roofs. This means that in the long-term, 

higher construction costs are offset by lower repair and replacement costs. 

The Hamilton West Apartments roof is designed as a building amenity and includes extra 

features not required for stormwater management. These include a terrace with tables, planters 

and seating, a fence separating this from the vegetated portion of the roof, and elevator access to 

the terrace. Additionally, the project was the first of its kind in Portland and required special 

attention. 

This roof tested the effectiveness of different types of plant establishment. Techniques that were 

tested included installing grass sod and non-grassy sod, hydroseeding annuals and installing 

small plants by hand. A typical ecoroof would not include this research component and could 

choose the most cost-effective way of establishing the plants, rather than testing methods with a 

higher initial cost. 

Maintenance and Monitoring 

The City is required to monitor the effectiveness of stormwater best management practices 

(BMP) per the City’s National Pollutant Discharge Elimination System (NPDES) Stormwater 

Discharge permit. Flow monitoring and water quality sampling at the Hamilton ecoroof 

evaluates the stormwater management characteristics of this type of BMP and compares the 

relative effectiveness of the two different ecoroof soil types and depths. Monitoring for flow 

control, water quantity and water quality has been ongoing since 2000. 

Report Completed: January 5, 2005 Page 5
Hamilton W est Ecoroof Stormwater Retention by Month

0

1

2

3

4

5

6

7

8

9

10

Jan-02

Feb-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02

Sep-02

Oct-02

Nov-02*

Dec-02**

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Jun-03

Jul-03

Aug-03

Sep-03

Oct-03

Nov-03

Dec-03

Jan-04

Feb-04

Mar-04***

Rainfall (in.)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% Retention

Monthly Rainfall (in.) Monthly % Stormwater Retention

* Rain/Flow data m is s ing from Novem ber 27 - 30, 2002

** Rain/Flow data m is s ing from Decm ber 1-15, 2002

*** Includes data from March 1 - 19, 2004

The chart above shows the seasonal variation in the percentage and amounts of stormwater that 

the ecoroof is able to manage. The columns show the amount of rainfall received during each 

month. The connecting line shows the percent of that rainfall that the ecoroof retains. As you can 

see from the rainfall columns, Portland has pronounced wet and dry seasons, which affects 

stormwater performance. 

During dry months, the ecoroof retains and manages nearly all of the stormwater. This is 

important because runoff from a conventional roof during summer storms tends to contain more 

pollutants and will enter waterways at a higher temperature. During the rainy months, the 

ecoroof manages much higher volumes of water than the conventional roof. It eventually 

becomes saturated but even when it does not retain all of the water, it slows and filters the flow. 

BES data show that the performance of the ecoroof is improving as the plants mature. During the 

first 16 months of monitoring, the ecoroof retained an average of 52.5% of all the rainfall it 

received. In the following 12 months, the roof retained 55.6% of the total rainfall, an 

improvement of 3%. 

The next graph shows the performance of the ecoroof during a typical winter storm. You can see 

that the rainfall occurs in jagged spikes of differing intensity. Traditional roofs with drainpipe 

systems would discharge almost all of that water directly. 

Report Completed: January 5, 2005 Page 6
The smoother line on the chart represents the runoff from the ecoroof, as measured by the flow 

meters at the roof drains. As you can see, the sharp surges in rainfall are moderated. More than a 

third of the rain never flows out. The soil and the plants retain it. The rest of the runoff is delayed 

and slowly leaves the ecoroof even several hours later. 

The City also evaluated the performance of the construction, soil, and plants installed on the 

roof. As of 2004, approximately one inch of soil had been lost on both sides of the roof due to 

wind erosion and soil decomposition. In late spring 2004, lightweight red pumice of less than 3⁄4 

inch size was applied to sparsely vegetated areas. This should prevent further wind erosion and 

allow an opportunity to observe any benefits to plant health from added mineral content and pore 

space for root growth. 

Regular maintenance activities include the following components: 

• About 1 inch of irrigation has been applied each summer during prolonged dry 

periods (typically ten or more days of no rain). 

• The roof uses no fertilizers or herbicides. Hand weeding of the ecoroof occurs at least 

once a year in late spring. 

• The owner of the property manages the terrace and accepts responsibility for all 

maintenance activities for the seating areas, planters, pavers, trash and the fence 

around the ecoroof. Periodic damage, primarily to the irrigation system, occurs from

various human activities. 

Report Completed: January 5, 2005 Page 7
Successes and Lessons Learned

The Hamilton West Apartments ecoroof was one of the earliest ecoroof projects in the City of

Portland. It has provided data on stormwater retention, plant cover establishment, cost factors, 

and substrate performance. Ongoing monitoring at the site continues to refine our knowledge of 

the performance and capabilities of the ecoroof. 

After five years, the roof is beautiful and plant coverage has increased substantially from

planting. Some species originally planted have died away, while others have spread rapidly. 

Certain plants that thrive on one side of the roof do less well on the other, highlighting the 

importance of selecting plants adapted to the conditions and depth of the soil. This data is 

helping the City develop a list of recommended ecoroof plant species and their growth 

requirements. The plants highlighted at the end of this section have proved particularly 

successful, and continue to spread and thrive on the roof habitat. 

Before full plant coverage was established, wind erosion of 

soil occurred to a much greater degree than expected. About 

an inch of soil was lost from both sides of the roof. Care 

must be taken to protect the lightweight ecoroof soil from

wind erosion or exposure. Early in 2004, lightweight 

pumice gravel was used to cover areas where soil was 

exposed in order to reduce further soil erosion. This 

technique seems to be successful. Plants are spreading 

through the gravel and birds do not expose underlying soil 

when they dig for insects. Plants growing through red pumice 

Water quality control tests reveal that elevated levels of certain metals are leaching from one of 

the two types of soils. This is one of the earliest studies of ecoroof water quality considerations, 

and these unexpected results show the value of experimentation and monitoring. Depending on 

water quality concerns in the area and the type of soil substrate used, it may prove useful to test 

the soil levels of materials of concern before installation. 

The volume of water that the roof controls has increased as the plants on the roof have matured. 

Summer stormwater retention now reaches 100% and wet-season retention rates continue to 

increase. In a typical winter rain event, storm surges are eliminated and runoff release is delayed 

by about 4 hours. Delaying runoff that the roof cannot hold helps moderate flooding and 

combined sewer overflow events. 

Other known benefits from the roof that have not been specifically quantified are reductions in 

ambient air temperature and building energy costs, increased urban habitat values for birds and 

other wildlife, and an open-space venue for the building tenants. 

Residents frequent the roof terrace, particularly in sunny summer weather. It is an attractive and 

pleasant place and a considerable amenity to the building in a dense urban environment. This 

demonstration project has also shown the feasibility of this type of stormwater management 

practice, and many other projects in Portland have followed its example. 

Report Completed: January 5, 2005 Page 8
Soil monitoring shows that both very shallow and slightly deeper roof soils can support thriving 

plant communities. Very shallow soils are most favorable to sedum species and showed more 

bare areas than the deeper soil on the west side. Care must be taken in preventing wind erosion in 

very shallow soils, as erosion can easily expose the underlying drainage layers in areas without 

plant coverage. 

The slightly deeper soil on the West side of the roof shows greater plant coverage, but also has 

greater problems with weeds. Weedy plants such as vetch and red clover each cover up to 30% 

of the roof’s west side. Most of the roof plants are low growing and these plants can grow right 

over them. Areas where taller grasses are established seem more able to resist weeds.

More than 40 types of plants grow on the Hamilton ecoroof. Some plants clearly prefer the 

deeper soil on the west side of the roof, and some do better on the thinner soil on the east side. 

These lists show currently predominant plants on each side of the roof, in order of their 

prevalence. Many other plants are also present in trace amounts. You can find a more complete 

discussion of ecoroof vegetation in the document Plant Survival Findings in the Pacific 

Northwest, published by the City of Portland Bureau of Environmental Services in summer 2005. 

West side dominants (deeper soil) East side dominants (shallow soil) 

Blue Fescue (Festuca glauca) Spanish stonecrop (Sedum hispanicum) 

Cascade stonecrop (Sedum divergens) Kirin-so (Sedum kamtschaticum) 

Iceplant (Delosperma cooperii) Iceplant (Delosperma cooperii) 

Spanish stonecrop (Sedum hispanicum) Redstem filaree (Erodium cicutarium) 

Common thyme (Thymus vulgaris) Dragon’s blood (Sedum spurium) 

Dragon’s blood (Sedum spurium) Oregon stonecrop (Sedum oreganum) 

The following sampling of species have spread and thrived particularly well. They represent a 

mix of native and ornamental plants. These plants are very hardy and should do well in most roof 

garden settings. Monitor plants closely immediately after planting, as the initial establishment 

period is the most difficult time for the plant. 

Kirin-so: Sedum kamtschaticum This type of stonecrop was included in the 

vegetated mats placed on the North sections of the roof during initial 

planting. This is a perennial plant. Bright green leaves turn red in October 

before going dormant. New growth begins in March. Growing habit is 

compact, upright and spreading. Kirin-so has yellow flowers from June 

through early November and reaches less than 6 inches in height. 

Report Completed: January 5, 2005 Page 9
Iceplant: Delosperma cooperii Both red and purple varieties of this 

ornamental plant grow on the Hamilton ecoroof. Most of the red variety 

died back during a prolonged cold spell in January 2004. These plants 

are noted for thriving particularly well near air exhaust vents, which c

ordinarily be a very stressful environment for plants. They form low,

creeping mats around six inches in height, with bright green veget

and conspicuous flowers. Flowers begin in summer and persist throu

mid-winter. 

an

ation

gh

is

ved in late April.

Spanish stonecrop: Sedum hispanicum var. minus This stonecrop 

species is most prevalent on the south portions of the ecoroof, where it 

was covered with the hydro-seed mix of the initial planting. Spanish 

stonecrop has a spreading habit, and forms a dense, creeping mat of 

gray-green leaves. Pale pink flowers bloom from July through August. 

Spanish stonecrop reaches between 4 and 6 inches in height. 

Blue fescue: Festuca glauca Blue fescue is a perennial grass that was 

included in the vegetated mats from the original planting. Blue fescue

a persistent spreader and grows about 14 inches high. It is located 

primarily in the north sections, especially on the west side where the 

soil is deeper (5 inches deep rather than 3). The grass grows in bunches

of fine, bluish-green leaves. Some outer leaves brown out in the fall. 

Blooms obser

Common thyme: Thymus vulgaris Common thyme has an upright, 

bushy growing habit and reaches about 8 to 10 inches in height. This 

plant showed stress immediately after the initial planting and

experienced some dieback, but those plants that survived the first year 

are now vigorous and spreading slowly. 

Environmental Services 

Sustainable Stormwater Management 

www.portlandonline.com/bes

Report Completed: January 5, 2005 Page 10