12/9/2004;Multnomah County Green Roof 1 

# Multnomah Building Green Roof

501 SE Hawthorne Blvd.

Project Summary

Introduction Multnomah County considered a number of options in 2000 when it became clear the leaky roof on the Multnomah Building was in need of replacement. With the encouragement of Portland’s Bureau of Environment Services (BES), the Count y evaluated the potential for an ecor oof and ultimately decided to cover most of the west-facing roof with a vegetated system.

The County Commissioners endorsed the pr oject because of the longevity of the green roof, the predicted costeffectiveness over the long term, and th e environmental benefits. They also supported the pr oject because it offered a unique opportunity to promote the technology. The 12,000 sq. ft. ecoroof is accessible and open to the public and is visible fr om many nearby offices.

The project’s demonstration value led to strong financial support from outside parties: th e Department of EnvironmentalQuality (DEQ) contributed $75,000 of Federal funds for nonpoint source pollution contro l, and BES contributed $50,000 from the Willamette Stormwater Control Program 1 . Tremco Roofing provided certain components at no cost, and BES and Portland State University committed resources for monitoring the performance of the roof.

The project goal was to crea te a landmark demonstration
ecoroof with amenities such as a stone terrace and educational signage. The focus of this repor t is limited to the design, construction, and cost of the vegetated ecoroof.

1 Portland’s Bureau of Environmental Services implemented th e Willamette Stormwater Control Program in 2001. The Program offered financial grants and technical support for a series of projects to retrofit existing commercial properties with stormwa ter controls incorporating green technologies. The Program recruited these demonstration projects in order to research the feasibi lity, cost and performance of commercial stormwater retrof its in the area served by the combined sewer. Project Type: Commercial / Industrial retrofit - demonstration project
Technologies: Green roof (ecoroof); 12,000 sq. ft. (area); 6-in. deep growth medium (soil)

Major Benefits: • Roof longevity - the ecoroof should double the life of the roof.

• Stormwater management - there will be a substa ntial reduction in runoff from the roof, with improvements in the quality of the runoff (reduced pollutant loads; lower temperature).

• Improvements to the urban environment - the new landscape adds green space to the urban
environment and enhances the aesth etic appeal of the property.

Cost: • Total project cost: $343,000 (include s design, terrace construction, etc.)

• Ecoroof construction cost: $179,801 ($15 per sq. ft.)

• BES provided a $50,000 grant for the project.

Constructed: April - July 2003

Looking north across the newly planted roo f (taken from the upper roof); 200312/9/2004;Multnomah County Green Roof 2 Figure 1. Diagram of the ecoroof system components Overview of the Stormwater System The roof absorbs rainfall that falls directly on it. Th e roof also receives runoff from a flagstone terrace (1,660 sq. ft.) and pavers along the peri meter of the roof (1,780 sq. ft.). The average depth of the growing medium (soil) is 6 in. Although the performance of the roof will vary dependi ng on a number of factors - storm size, soil moisture content, a nd temperature - researchers hope to c onfirm that the roof retains more than 50% of the total annual runoff.



### Stormwater Capacity and System Components

Stormwater Management Goal

The overall stormwater management goal was to redu ce the peak runoff and volume that would otherwise contribute to combined sewer overflow (CSO) events in the adjacent Willamette River. Although the project did not trigger the requirements of the City’s Stormw ater Management Manual (S WMM), it meets the general
standards for ecoroofs.

System Components

Planted Roof portion (See Planting Plan for more details, pg. 10)

• The footprint of the vegetated portion of the eco roof is approximately 11,900 sq. ft. The catchment is 15,420 sq. ft., including the planted area, stone te rrace, and the pavers along the roof’s perimeter.

• Overflow drains to internal downspouts that are connected to the combined sewer system.12/9/2004;Multnomah County Green Roof 3 Refer to Figure 1 for the following description: a. Structural roof support (previously existed) b. 5-ply roofing system (previously existed): A built-up roof (3-ply polyester and 2-ply fiberglass membrane) set in hot asphalt atop three inches of polyisocyanurate and
fiberboard insulation. c. 1⁄4 in. protection board over existing roof: laid on top of the existing roof, provides roof protection during
construction as well as additio nal root barrier protection. d. 1⁄2 in. drainage mat with root barrier: A hollow core layer of TremCo GR with a top layer of fabric that allows water to pass th rough while restricting the movement of soil. The fabric is treated with copper hydroxide to restrict root penetration. e. Stainless steel edging: Retains the soil around the perimeter of the roof and prevents it from entering the
drains. f. 6 in. growth medium (soil) : see “Landscaping” section g. Green roof vegetation: see “Landscaping” section h. Drip irrigation system: see “Irrigation” section
i. Gravel ballast: Surrounds the roof drains. Secures the draina ge mat and allows free movement of runoff
around the roof drains. j. Roof drain: Provides overflow drai nage for runoff that is not absorb ed, evaporated, or evapotranspired. k. Monitoring equipment: Measures the rate and volume of runoff. l. Concrete pavers: Provides access for maintenance personnel.

Additional Information :

• The saturated soil weight is approximately 28 pounds per sq. ft.

• The planted area is gently mounded in the center due to th e roofing structure. The slightly western aspect adds visual interest.

Landscaping

• The growth medium (soil) is a proprietary aggreg ate from a local company. The 6-in. deep soil is comprised of pumice, perlite, digested fiber, a nd paper pulp (reclaimed); it has a higher proportion of mineral content than organic content. The co mposition meets the structural requirements of the roof, and is free draining to promote plant growth

• A seed mix was broadcast by hand. The mix includes va rious wildflower specie s and fescue grass.

• The vegetated portion directly adjacent to the building was densely planted with plugs and containers of sedum species, perennial s, bulbs, and ornamental grasses.

• The project designers selected th e plants with advice from a green roof consultant from Toronto,
Canada. The selection criteria in cluded adaptability to roof c onditions, ecological function, local availability, drought tolerance, s easonal interest, aesth etics, and maintenan ce requirements.

Irrigation Portland’s extensive summer dry periods made an ir rigation system a requirement. The system includes:

• A permanent drip irrigation system, approximately 3 in. below the soil surface, that delivers water directly to the plant roots.

• Soil moisture sensors to control the drip irriga tion system, delivering water only when needed. View of the terrace with the green roof in the background.; note educational signage and fence preventing public access to the roof;

summer 2004.12/9/2004;Multnomah County Green Roof 4 • A temporary above-ground, spray irrigation system , to ensure that the new seeds received sufficient water for germination. The system also helped the new plantings survive the establishment period while their roots were still fairly shallow. The temporary system was removed in late spring 2004.

Stone Terrace Planter

• The footprint of the terrace planter is approximately 200 sq. ft. It is filled to a depth of 6 in. with the same proprietary soil mi x used on the roof.

• The raised planter, featuring a built-in bench seat , is incorporated into the patio hardscape.

• The planter receives precipitati on and some supplemental water fr om a drip irrigation system.

• It is planted with perennial flower species and varieties of sedum.



### Budget

The final budget for construction of the Multnomah County building ecoroof was $179,807. This cost covers all of the construction activities for the vege tated ecoroof; it does not in clude any design activities
or costs associated with c onstruction of the terrace.

Over $125,000 in grant funds and in-kind donations of ma terials and services were provided by interested professionals, businesses, and agen cies. BES contributed $50,000. The in-k ind costs are included in the
costs summarized below.

Item Item Cost

or Value Total Cost
Construction: 131,462.00 $ Protection board (material & labor) 8,644.00 $ Ecoroof components (drain mat, root barrier, filter fabric, soil) 48,517.00 $ Ecoroof installation (labor) 38,121.00 $ *Mobilization/demolition/cleaning 4,800.00 $ *Crane 12,480.00 $ *Miscellaneous supplies 2,400.00 $ Rock removal (labor) 16,500.00 $
Landscaping (11,900 s.f.) 44,418.00 $ Plant /seed material 10,475.00 $ Installation (labor) 15,712.00 $ Irrigation: Permanent drip 16,362.00 $ Temporary overhead spray 1,869.00 $ Irrigation booster pump Permitting Construction bonds/permits 3,927.00 $ 3,927.00 $ TOTAL 179,807.00 $ Multnomah County Budget Summary for Ecoroof Construction

* Mobilization costs for the ecoroof were estimated by pro-rating themobilization costs for the entire roof project (including the terrace). Eightypercent of the costs were attributed to the vegetated portion of the ecoroof because it occupies 80% of the roof area.12/9/2004;Multnomah County Green Roof 5 I. Budget Elements

Non-Construction Activities The cost for management, design, and permitting was not fully
documented and therefore is not included in the budget.

Construction Activities The total construction cost wa s $179,807. The activities include general construction, landscaping, the value of in-kind materials and labor, and the cost of the permits.

Construction The core construction activities incl ude removal of the existing rock ballast, mobilization and demobilization of a crane to transfer the rock and import soil, and installati on of the ecoroof components.
The cost of these activities wa s $131,462, which is approximately 73% of the overall construction budget

.

Mobilization costs for the ecoroof were estimated by pro-rating the mobilization costs for the entire roof project (including the terrace). Eighty-percent of the costs were attr ibuted to the green roof because it occupies 80% of the roof area. Permit costs for mobilization, including contract bonds, total $3,927.

Landscaping The cost of the landscaping, exclud ing the soil matrix but including irrigation, was $44,418. The associated unit cost was approximately $3.73 per sq. ft. Landscaping costs comprised approximately 25% of the total construction budget (excluding soil matrix). The costs for the soil matrix are included in “ecoroof components” under construction activities.

The irrigation system was va lued at $18,231, including both the permanent drip system and the temporary overhead spray system.

II. Cost Components

Construction – Mobilization and installa tion of the structural components comprised approximately 75% of the total construction budget; landscaping costs were about 25% of the total budget (excluding soil matrix).

Labor vs. Materials – Labor accounted for approx imately half the total construction budget. Installing the drainage mat

Installing drip irrigation system

Bringing the soil up from the street

Installing the soil

Plants ready for installation12/9/2004;Multnomah County Green Roof 6 Irrigation – The County simply expanded the existing irrigation systems, which included valves , a backflow preventer, and a
controller. Construction of a new system would have been substantially more expensive.

Pavers – The County saved money by re -using the pavers from the previous roof. The pavers were placed around the perimeter to provide access for maintenance staff.

III. Cost Comparisons

Construction costs for the eco-roof project may be low, relative to other similar projects, for retrofitt ing existing roofs with ecoroofs. Although mobilization costs to raise materials to the 5 th floor were substantial, the project saved on other activities that sometimes account for higher costs on similar re trofit projects. For example, the roof was sound and required no st ructural alterations - its load bearing capacity had been previously certified; the existing 5-ply roof was in good condition and di d not necessitate removal or replacement.



### Maintenance and Monitoring

Multnomah County owns the facility and is responsible for all
maintenance activities.

BES, the County, and PSU, are jointly funding hydraulic monitoring. Led by PSU, the team will intensively monitor the performance of the ecor oof facility for at least five years, and perhaps longer. BES will also regularly evaluate the level of effort required to maintain the facilit y, the success and viability of the planting regime (which may cha nge over time), and any comments
received.

A detailed Operations and Mainte nance Manual includes site plans, operation and performance requirement s for vegetative care, natural pest/weed reduction, safety precautions to protect workers and visitors, erosion & litter control measures, and a detailed schedule and timeline for maintenance of the irrigation system. SE corner, planted with a variety of sedum species, bulbs and purple coneflower; early summer, 2004.

Looking east across the ecoroof, toward the terrace, early summer,

2004.

View of the ecoroof with wildflowers in full bloom; spring 2004.12/9/2004;Multnomah County Green Roof 7 

### Successes and Lessons Learned

Multiple Benefits - The project is a great exam ple of how an ecoroof can be a central feature in the urban environment, with multiple benefits:

• Many nearby offices enjoy views of the green roof and it provides an appealing picnic spot. It
should continue to attract visito rs interested in ecoroofs.

• The roof will provide ongoing benefits for the County and th e City in terms of stormwater management and moderating temperatures on the r oof (including reductions in heating and cooling costs for the building).

• The roof provides habitat for urban life – birds, butterflies, etc.

Roof Longevity and Cost Effectiveness – In 2000 the County conducted a life cycle cost analysis comparing a conventional roof with an ecoroof. Th e study concluded the ecoroofwould be more costeffective than a standard roof ove r a 60-year period. The analysis a ssumed that the ecoroof would double the life of the impermeable seal on the roof (a common assumption in the industry). More information about the study is available from Multnomah Co unty or Allen Lee at allenl@quantecllc.com.

Construction Schedule - The project confirmed the crucial infl uence of seasonal weat her on installation schedules: in Portland planting should occur in early spring or early fall when the temperatures are cool and precipitation is most likely to assist with plant establishment. Seeds are especially vulnerable to prolonged dry periods.12/9/2004;Multnomah County Green Roof 8 Multnomah County Ecoroof Planting Plan