A REVIEW OF GREEN ROOFS. BY ERICA SCHUTT MSRE Class of 2012 University of San Diego

Transcription

1 BY ERICA SCHUTT MSRE Class of 2012 University of San Diego 1

2 WHAT ARE? A vegetative layer grown on a rooftop Can be installed on a wide range of buildings including commercial and residential property Roofs can represent up to 32% of the horizontal surface of builtup areas* Images Source: Google images * Orbendorfer, Erica, et al. Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services. BioScience Nov

3 HOW THEY WORK Shading Block sunlight from reaching the underlying roof membrane Reduce surface temperatures below the plants = reduce heat transmitted into buildings or re-emitted into the atmosphere Evapotranspiration = evaporation + transpiration Cools a green roof surface and the surrounding air by using heat to evaporate water from the growing medium and plant surfaces Results The surface temp. of a green roof can be cooler than air temp., while a conventional rooftop surface can be up to 90 F warmer* Chicago study: Green roof surface temp. up to 70 F cooler than the conventional roof of an adjacent building** Florida study: Average max. surface temp. of a green roof was 48 F cooler than the adjacent light-colored roof* * EPA. **EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct

4 BENEFITS PRIVATE Increased roof life Conventional roof = yrs* Life span of waterproofing can increase by as much as double** Thermal insulation (R-value) Reduction of HVAC equip req. Reduction in energy consumption Heat shield Reduces indoor temps. though transpiration Free plot of land Increases space for tenant use and recreation Increases fire resistance Determined by level of hydration Reduced noise levels* Up to 3 db of sound reflection Up to 8 db of sound insulation PUBLIC Storm water management: Retains 50%-90% of a typical rainfall on the roof, reducing peak flow rates*** Filters pollutants from rainwater Negates Urban Heat Island problems*** Reduction of dust & smog levels Processes airborne toxins and re-oxygenates the air Enhances building s aesthetic appearance Creates therapeutic and peaceful environments * IGRA. ** IGRA Green Roof Pocket Guide ***EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct ****EPA. Green Roofs for Stormwater Runoff Control. Feb

5 TYPES OF EXTENSIVE ROOF SEMI - INTENSIVE ROOF INTENSIVE ROOF PURPOSE Strictly functional Functional + aesthetic Functional + aesthetic; living and recreation space STRUCTURAL REQUIREMENTS Typ. within standard roof weight bearing parameters Some structural improvements may be necessary WEIGHT lb/sf lb/sf lb/sf MAINTENANCE (Annual costs may vary from $ $1.50+ psf) Low some weeding or mowing as necessary Periodically IRRIGATION Seldom or never Periodically Regularly PLANT COMMUNITIES SUBSTRATE TYPE SYSTEM BUILD-UP HEIGHT COSTS (above waterproofing membrane) ACCESSIBILITY Low-growing plants and mosses selected for stress tolerance qualities; Moss, sedum, herbs, and grasses Lightweight; high porosity, low organic matter (10%) Restricted mainly by substrate depth; Grass, herbs, and shrubs Lightweight; high porosity, low organic matter (10%) Planning req. in design phase or structural improvements necessary High Restricted only by substrate depth, climate, building height and exposure, and irrigation facilities; Lawn or Perennials, shrubs, and trees Lightweight to heavy; high porosity, low organic matter (10%) ( up to 36 + on underground garages) Low; $10 to $30 psf Middle High; $20 or more psf Generally functional rather than accessible; will need basic access maintenance. Limited to full access; bylaw considerations Typically accessible; bylaw considerations Sources: Orbendorfer, Erica, et al. Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services. BioScience Nov EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct IGRA Green Roof Pocket Guide

6 ROOF CONSTRUCTION Typical Layers & Types of Extensive Green Roofing Technology* * Orbendorfer, Erica, et al. Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services. BioScience Nov. 2007

7 ROOF CONSTRUCTION* Waterproofing Must be protected to avoid root damage. There is a procedure for determining root resistance. 70+ products meet these requirements. Drain Layer Stores water for plant use and regulates water runoff Selection of material should be based on: structural load capacity of the roof desired vegetation per design water permeability storage capability Filter Layer A thin mat filter layer is necessary to prevent the growing medium from leaching into the drain layer. The mat filter also needs to allow roots to grow through the filter layer and into the drain layer below. Growing Medium Must be appropriate for planting selection Includes a mixture or mineral and organic soil components and mineral bulk material. Weighs aprox. 65 lb/cf, while regular soil weighs aprox. 110 lb/cf. Topped by a ¼ biodegradable mesh (prevents water loss in initial growing season) *

8 COST + FEASIBILITY Up-front costs: $10-$20+ psf *, plus any additional structural improvements and building modifications Savings vary by location, due to differences in climate, sun exposure, and energy costs, among other factors. Sustainability is local. Life-cycle costing & typical economic life: still researching In case study of 21,000 sf roof: $129,000 higher upfront costs, but lifetime savings were estimated to be about $200,000. 2/3 would come from reduced energy needs.** Maintenance: estimated $0.75 to $1.50 psf on an annual basis** Applicable in both new construction and retrofit buildings. In retrofit buildings it is more common to see extensive green roofs (little to no structural improvements necessary). * Orbendorfer, Erica, et al. Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services. BioScience Nov ** EPA. Heat Island Mitigation: Green Roofs.

9 COST + FEASIBILITY If considering an accessible green roof, consider the costs of making the roof occupant accessible (formal access, increased parapet height, additional live loads, etc.). Alternatives: Cool roofs Option with minimal incremental cost Roof surface that stays relatively cool compared to the ambient or surrounding temp. Between F cooler than traditional materials at peak summer hours.* These are highly reflective, typically light colored surfaces (include membrane, coatings, painted metal, or granule surface asphalt sheets).** More benefits in warmer climates. Lack the insulation, stormwater management, smog cleansing, and aesthetic advantages of green roofs. * EPA. Reducing Urban Heat Islands: Compendium of Strategies Cool Roofs. Oct ** Cool Roofing Rating Council (CRRC). Everything you need to Know about Cool Roofs.

10 ROOF POLICIES Local governments may offer forms of sponsorship: Financial subsidies Stipulations for green roofs in building codes Recognition of an ecological compensatory measure In Downtown San Diego: FAR bonuses offered* Roofs accessible to occupants up to 1.0 FAR Bonus Non- accessible roofs up to 0.5 FAR Bonus LEED Certification points (up to 14)** Reduced Site Disturbance 1 Stormwater Design 1 2 Heat Island Effect 1 Water Efficient Landscaping 1 2 Optimize Energy Performance 1-8 Incentives are similar to that of any green initiative: now they have become market driven - need to be green to stay competitive. Many green roof projects are motivated not by government policies but by a desire to show a commitment to sustainable design and the environment. *** *Centre City Planned District Ordinance, San Diego Municipal Code. ** LEED For New Construction & Major Renovations. USGBC. ***EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct

11 EXAMPLES IN THE NEWS Chicago City Hall* 20,300 sf of green roof Combination of extensive/intensive green roof. First planted in 2000 as part of the City's Urban Heat Island Initiative Can retain up to 75% of a 1 rainfall Ballard Public Library in Seattle** 20,500 sf of green roof $20 psf cost 4-6 of growing medium, plating is indigenous grasses and sedum. Used to demonstrate the benefits of green roofs and the feasibility of the technology. Wal-mart in Portland 40,600 sf roof; one of the largest in the city Parts of the roof will be cool roof Portland has stated a goal of having 43 acres of new ecoroofs installed by 2013.*** * ** *** Williams, Christina. New Portland Walmart to Sport Ecoroof. Sustainable Business Oregon 27 Dec Web. 02 Mar Image Source: EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct

12 EXAMPLES IN THE NEWS Ford Deerborn Truck Plant, Michigan* Clean Water Act regulations required storm water mitigation that would cost up to $48 million. Installed an extensive green roof capable of holding 2 of rainwater, and porous parking lots that can also absorb and store water. Storm water management was treated as a visible, enjoyable asset, instead of a huge invisible liability. The eco-effective approach saved the company up to $35 million, by one estimate. Shows company s commitment to ecology and the economic bottom line. *Braugart, Michael, and William McDonough. Cradle to Cradle: Re-Making the Way We Make Things. London: Vintage, Print. Image Source: EPA. Reducing Urban Heat Islands: Compendium of Strategies Green Roofs. Oct

13 VENDORS + PRODUCTS American Hydrotech, Inc. < Intensive & extensive green roofs, sloped & special conditions TectaGreen from Tecta America < Eco-Roofs: Green Roof Systems < Green Roof Trays Green Living Technologies < Green roofs, walls, and urban farms GreenGrid Roofs < Modular tray system

14 LINKS + RESOURCES Environmental Protection Agency (EPA) < Green Roofs for Healthy Cities < Greenroofs.com: the green roof industry resource portal < International Green Roof Association (IGRA) < U.S. Department of Energy Federal Technology Alert: Green Roofs < National Roofing Contractors Association Green Roof Systems Manual <

15 Integrating green roofs into design: Design a building like a machine but this time, instead of a machine for living in, a machine that s alive. -Cradle to Cradle* *Braugart, Michael, and William McDonough. Cradle to Cradle: Re-Making the Way We Make Things. London: Vintage, Print.