eco roofs portland oregon: questions and answers
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- 1. Portlands EcoroofQ&Program is a cooperativeAeffort of the Bureau ofEnvironmental Services and the Office of Sustainableuestions n s we r sDevelopment. Theprogram promotesecoroofs by researching ecoroof technologies and providinginformation and technical assistance to community members.
2. WHAT IS AN ECOROOF?An ecoroof is a lightweight, low-maintenance vegetated roofsystem used in place of a conventional roof. The City ofPortland is encouraging the use of ecoroofs as part of itsefforts to promote sustainable development. This means usingpractices that respect natural systems and limit impacts on theenvironment. Sustainable development practices promoteenvironmental, economic, and social health today, while alsoprotecting and sustaining the well-being of future generations.Ecoroof opportunities come in all sizes:Large commercial buildings, residential homes and garages, or as small as a toolshed or kiosk.C I T Y O F P O R T L A N D E C O R O O F P R O G R A M - Q U E S T I O N S & A N S W E R S2 3. Ecoroofs area proventechnologyq What are the benefits of Ecoroofs ? Provides an attractive alternative toand have a conventional roof.been usedBased on documented experience and studies, an Lasts twice as long as a conventional in Europeecoroof offers several important benefits not found roof, saving replacement costsin conventional roofing: and materials for over 40 Captures and evaporates from 10 to100 percent Creates a market for recycled materials, years. Theyof the precipitation that falls on it. This reducessuch as compost, mulch, soil and otherthe volume and speed of stormwater runoff are now ecoroof components.leaving the site, helping prevent sewer over-gainingflows and protect receiving rivers and streams. Creates jobs in multiple industries.recognition Lowers the temperature of stormwater runoff, Is an approved stormwater management technique under Portlands Stormwater in the USwhich helps maintain the cool stream tempera-tures needed by fish.Management Manual requirements forfor the new development and redevelopment. Improves outdoor air quality by decreasing airenvironmental,temperatures and reducing smog. Can earn floor area bonuses for pro- posed buildings in Portlands Central Cityeconomic, Increases vegetation and wildlife habitat on Plan District. Increasing the buildingand socialurban sites that typically have neither. space that would otherwise be allowed.benefits they Provides insulation and lowers cooling costs forthe building.provide.C I T Y O FP O R T L A N DE C O R O O F P R O G R A M- Q U E S T I O N S & A N S W E R S3 4. r Where can an Ecoroof be used ? s What does an Ecoroof cost ? Ecoroofs can be located on flat or pitched roofIt is important to note that there is a wide range ofstructures at a slope up to 40 percent (or 5 in 12 costs, depending on many factors. Installation of anpitch). They can be used on most types of com- ecoroof costs from $10 to $25 per square foot (sf).mercial, multifamily, and industrial structures, This includes materials, labor, and structuralas well as single-family homes and garages.upgrades. A conventional roof installation ranges Ecoroofs can be used for new construction or tofrom $3 to $20 per sf. As the ecoroof market devel-re-roof an existing building.ops, costs may decrease. EcoroofConventional Roof (cost per square foot) (cost per square foot) New construction (including $10 to $15 $3 to $9 structural support) Re-roofing$15 to $25 $5 to $20Source: Bureau of Environmental Services estimates based on City of Portlanddemonstration projects, and information obtained from roof contractors. Although ecoroofs initially cost more than conven- tional roofs, they are competitive on a life-cycle basis because of reduced maintenance and replacement costs (see question #5).C I T Y O F P O R T L A N DE C O R O O F P R O G R A M -Q U E S T I O N S & A N S W E R S4 5. t What Are the Components of an Ecoroof ?Ecoroof configurations vary, but typically include the elements shown in the diagram and described on pages 4-8.ECOROOF diagram (figure 1) section view - not to scale F - Vegetation (succulents, such as sedum; herbs; grasses G - Gravel Ballast (optional)Parapet Flashing(edge ofSeparation structure Mulch or materialsbuilding)(optional)to prevent windand rain erosionA - Structural roof supportB - Waterproof membraneC - Root barrier (if needed)D - Drainage H - DrainE - Growth medium (soil)2-6 inchesC I T Y O FP O R T L A N DE C O R O O F P R O G R A M - Q U E S T I O N S& A N S W E R S5 6. A - STRUCTURAL ROOF SUPPORT B - WATERPROOF MEMBRANE (IMPERMEABLE LINER) For Re-RoofingWaterproof membranes are made of various materi-The structural roof support must be sufficient to holdals, such as modified asphalts (bitumens), syntheticthe additional weight of the ecoroof. Check with anrubber (EPDM), hypolan (CPSE), and reinforced PVC.architect, structural engineer, or roof consultant toSome of the materials come in sheets or rolls anddetermine the condition of the existing buildingsome are in liquid form. They have differentstructure and what might be needed to support anstrengths and functional characteristics. Many ofecoroof. This might include additional decking, roofthese products require root inhibitors (refer to C) andtrusses, joists, columns, and/or foundations.other materials to protect the membrane. NumerousGenerally, the building structure must be adequate to companies manufacture waterproofing materialshold an additional 10 to 25 pounds per square footappropriate for ecoroofs.(psf) saturated weight, depending on the vegetationand growth medium that will be used. (This is inC - ROOT BARRIER (IF NEEDED)addition to snow load requirements.) An existing rock Root barriers are made of dense materials that inhibitballast roof may be structurally sufficient to hold a root penetration.10-12 psf ecoroof. (Ballast typically weighs 10-12 psf.)The need for a root barrier depends on the water- For New Construction proof membrane selected. Modified asphalts usuallyThe project architects and structural engineers can require a root barrier, while synthetic rubber (EPDM)address the structural requirements of an ecoroof dur-and reinforced PVC generally do not. Check with theing the design process. Greater flexibility and options manufacturer to determine if a root barrier isare available for new buildings than for re-roofing.required for a particular product.The procedures for the remaining components(B through I) are the same for both re-roofing andnew construction.C I T Y O F P O R T L A N DE C O R O O FP R O G R A M- Q U E S T I O N S &A N S W E R S6 7. D - DRAINAGE LAYER (IF NEEDED)There are numerous ways to provide drainage.Ecoroofs are an evolving industry, with new mate-Products range from manufactured perforated plas- rials and approaches continually being developed.tic sheets to a thin layer of gravel. Some ecoroofIn Europe, for example, recycled clay roof tile isdesigns do not require any drainage layer other being used as a growing medium and a modularthan the growth medium itself, depending on roofdesign has recently been developed by a US firm.slope and size (for example, pitched roofs and smallflat roofs).E - GROWTH MEDIUM (SOIL)The growth medium is generally 2 to 6 inches thickand well drained. It weighs from 10 to 25 poundsper square foot when saturated. A simple mix of1/3 topsoil, 1/3 compost, and 1/3 perlite may be suf-ficient for many applications. Some companieshave their own growth medium specifications.Other components could include: Digested fiber Expanded clay or shaleThese soils are Pumiceprone to wind Coir erosion whenexposed. Itspring blooms is important late summer color to ensuregood plantcoverageand/or mulch.C I T YO F P O R T L A N D E C O R O O FP R O G R A M- Q U E S T I O N S & A N S W E R S7 8. New modularunits with soiland vegetationF - VEGETATIONhave beenEcoroof vegetation should have theInstallationdeveloped andfollowing attributes: Four methods (or combinations of are now Drought-tolerant, requiring little or nothem) are generally used to install theirrigation after establishmentvegetation: vegetation mats, plugs/pot-available. A growth pattern that allows the plant to ted plants, sprigs, and seeds.thoroughly cover the soil 1 Vegetation mats are sod-like, Self-sustaining, without the need for fertilizers,pre-germinated mats that achieve immediate fullpesticides, or herbicides plant coverage. They provide immediate erosion Able to withstand heat, cold, and high windscontrol, do not need mulch, and minimize weedintrusion. They also need minimal maintenance Very low-maintenance, needing little or noduring the establishment period and little ongo-mowing or trimminging watering and weeding. Perennial or self-sowing2 Plugs or potted plants may provide more design Fire resistantflexibility than mats. However, they take longerA mix of sedum/succulent plant communities is to achieve full coverage, are more prone torecommended because they possess many of theseerosion, need more watering during establish-attributes. Herbs, forbs, grasses, and other lowment, require mulching and more weeding.groundcovers can also be used to provide addition-3 Sprigs are hand broadcast. They requireal benefits and aesthetics; however, these plants more weeding, erosion control, and wateringmay need more watering and maintenance to than mats.survive and keep their appearance.4 Seeds can be either hand broadcast orhydraseeded. Like sprigs, they requiremore weeding, erosion control, and wateringthan mats. For plugs, sprigs, and seeds, it is extremely important to protectthe growth medium from erosion (e.g., using mulch, netting, or gravel)until it is fully covered by vegetation.C I T Y O F P O R T L A N DE C O R O O F P R O G R A M-Q U E S T I O N S & A N S W E R S8 9. Spraying seed mix for new ecoroofG - GRAVEL BALLAST (IF NEEDED)Gravel ballast is sometimes placed along theperimeter of the roof a