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A A Green RoofGreen Roof Presentation:Presentation:Why Consider a Why Consider a Green RoofGreen Roof??
specially prepared by Karen L. Weber forspecially prepared by Karen L. Weber forNEXUS Green RoundtableNEXUS Green Roundtable
Spring 2009Spring 2009
Best Practices/AIA
• NEXUS Green Roundtable is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
• This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of the presentation.
Learning Objectives• To understand green roof ROI for
commercial buildings• To compare stormwater strategies
– green roofs v underground cisterns and porous pavers
• To compare green roofs to a solar roof or a white reflective roof
Chinatrust BankAccording to Chinese belief, the roof of a building belongs to the spirit world and
acts as a landing platform for spirits to descend and ascend.
Learning Objective #1
Green Roof Return On Investment
On a hot summer day, temperatures on a conventional roof can soar to 150ºF to 200ºF
while a green roof remains between 77ºF to 90ºF.
Roof Replacement• Conventional roofs are replaced every 15-20 years.
– 62% of roofs in the US have problems in the first year– 99% have problems in the first 10 years– (source: National Research Council of Canada, 1997)
• Well-installed green roofs are replaced every 50-100 years or more.– German and European experience prove this
• New Green Roof technology in Germany functioning > 50 yrs• Green Roofs in Berlin last over 90 yrs before needing
attention• Green Roof in Zurich planted in 1914 still thriving
– In the US, we’ve already seen excellent results for roofs that are 12 years old.
– (source: Roofscapes, Inc. Summer Assessment 2007)
Moos Water Filtration PlantZurich, Switzerland
This green roof was established as an earth roof in 1914 and was colonized by 175 plants along with 9 local orchids, several of which only exist here. Very little work has been done to maintain this 350,000 sf green roof. The substrate has 5 cm of sand and gravel and 15-20 cm of topsoil.
Weathering
• Green Roofs allow the roof to better weather the effects of climate & UV rays:– Protect against UV rays– Protect against wind, rain, sleet– Protect against expansion & contraction– Protect against sub-zero temperatures– Protects from temperature spikes & dips
5.00
15.00
25.00
35.00
45.00
55.00
65.00
75.00
7-Jun 11-Jun 15-Jun 19-Jun
Time
Tem
pera
ture
(Deg
. C)
Bare Roof
Below Vegetated Roof Cover
Daily Variation in TemperaturePerformance of a 3-inch Vegetated Cover
Fencing Academy of Philadelphia
-15
-10
-5
0
5
10
15
20
25
30
35
3-Feb 7-Feb 11-Feb 15-Feb 19-Feb 23-Feb 27-Feb 3-Mar
Time
Tem
pera
ture
(Deg
. C)
Bare Roof
Below Vegetated Roof Cover
SUMMER
WINTER
Energy Transfer
s
freezing
HVAC Longevity
• Green Roofs serve as biofilter:
– Trap large amounts of dusts and toxins.
– NOx – SOx – Absorb CO2 and Produce O2– (source: studies done by
Michigan State)• Reduce load on HVAC filters
and overall system.
Marketing, Aesthetics, RE Value
From Vancouver Convention Center to NYC Clinton Park
Green Roofs as Equivalent to Open Space: Jackson
Square• 10-year 24-hour rainfall event• 4 inch Type I
– C = .40– CN = 70
• 6 inch Type III (dual media)– C = .33– CN = 66
• Runoff/Rainfall = 35% (22% in summer)– 2 feet/year (15,000 gal for 1,000 sf roof area)
ROI Summary• Cooling/Reduce Use of ACand Reduce Peak Demand• Roof Longevity• HVAC Longevity• Building Longevity• Reduce heating bills• Increase RE Value• Increase usable space• Marketing• STORMWATER MANAGEMENT
Zurich Airport
Learning Objective #2
Green Roof Stormwater Management
Comparison
Stormwater Strategies
• Green roofs• Underground cisterns• Rainwater recovery• Porous pavers and rain gardens• What are the objectives?
Green Roofs Comprehensively Manage Stormwater
• Retention Function (Permanent Storage):
15% by volume (moisture content at 1/3 bar capillary pressure)
• Detention Function (Transient Storage):
15% - 35% by volume (Maximum Water Capacity)
A green roof demonstrates a first-order discharge rate – performing as well as a detention basin.
Stormwater Runoff v. Retained
Total Rain Fall and Roof Runoff in Summer 2002 (Ottawa)
0
5
10
15
20
Rain Fall Mod Bit. Green Roof
Rai
n/R
unof
f (in
ches
)
LEGEND
Total Vol. Rain
Rain Water Retained
Rain Water Runoff
Time
Run
off R
ate
With 4" extensiveGreen roof
Direct Runoff
PeakAttenuation
Green Roofs Decrease Stormwater Runoff Rates
• Reduce stormwater runoff by about 50% over the course of the year
• Control runoff from over 95% of storms
• Prohibit any immediate runoff from the smallest 25% of all storms
• Substantially reduce peak flow rates
An extensive green roof with 4” of soil (media) can:
Other Stormwater Strategies
• Subsurface rainwater detention:– $2-2.50/gallon installed
• Harvest pump– $10,000-100,000– Pump works– Filtration treatment– Cooling
• Porous pavers ($4-5/sf)– Drainage layer– Piping
Learning Objective #3
Green Roof Comparison with Solar Roof,
White Roof & Heliotstats
Solar Roofs
Energy Cooling properties of green roofs improve, while white roofs degrade over time and are affected by dust accumulation.
WhiteReflectiveRoofs
Skylights/Heliostats
Comparison of White & Green Roofs
• Green roofs cool primarily by latent heat loss and high natural albedo.
• Green roofs reduce heat flow into the building below to levels not achievable by white roofs.
• White roof albedo declines by .15/year but can occur in just 2 months. Brightness can be restored by regular washing at least twice per year.
• Every 2-3 years the white roof needs resurfacing.
• Main Source: Gaffin, et. al., Energy Balance Modeling Applied to a Comparison of White and Green Roof Cooling Efficiency.
Heliostats on Green Roof
Life Cycle Analysis• Higher initial cost, however:
– Membrane will last at least 50 years – non-green roofs only 15-20 yrs
– Energy savings in cooling and heating & HVAC
– Stormwater savings in piping & retention
• When taking these factors into account, the savings gained by a green roof come within about 15% of the cost of a conventional roof according to Damon Farber Associates and Miller Dunwiddie Architecture of Minneapolis.
• Short Term Owners:– Increased cost of roof
system– Will not see return on
investment long-term– Will increase marketability– Points for LEED
Accreditation
• Long Term Owners– Increased life of roof
membrane– Heating and cooling
savings– Will see return on
investment in 8-13 years– Points for LEED
Accreditation
Green Roof Types
• Extensive v Intensive– Extensive: 3-5” unirrigated– Semi-intensive: 6-8”– Intensive: 9”+
• Comparison of extensive green roof systems: containers v. integrated or contiguous systems– Modular/containers– Pre-vegetated mats– Cuttings– plugs
• Load, Maintenance– Index for extensive roofs: 6.75 lbs/planting inch/sf (fully
saturated)– 2-3 hrs/1000 sf/yr/split between spring and fall
World Trade Center, West Podium Park, Boston, MA
Boston World Trade Center, West Podium Park, 5” extensive podium green roof
Integrated Green Roof Technology
Modular Green Roof
Pre-Grown Mats
Sedum Cuttings
Sedum Plugs
Wal-Mart Store #5402
11 months
Wal-Mart Store #5402
Placing Pavers & Media
Installing Drainage Layer
Wal-Mart Store #5402
Distributing Sedum cuttings
Installing hydromulch
Wal-Mart Store #5402Freshly Planted
Largest Green Roof Monitoring Program in
World at Wal-Mart
Installing the Green Roof on WGBH
Green Roof/Solar Combination: Installing Green
Roof on WGBH
Newly Planted Solar/Green Roof WGBH Headquarters, Boston, MA
• E2397: Standard Practice for Determination of Dead Loads and Live Loads for Green Roof Systems
• E2399: Standard Test Method for Maximum Media Density for Dead Load Analysis of Green Roof Systems
• Density• Maximum water retention• Non-capillary porosity• Permeability
• E 2398: Standard Test Method for Water and Media Retention of Geocomposite Drain Layers for Green Roof Systems
• E 2396: Standard Test Method for Saturated Water Permeability of Granular Drainage Media for Green Roof Systems
ASTM Standards
LEED@ CERTIFICATION
• Site Development (p.69) Protect or restore habitat
• Green Roof can contribute towards 1 point
• Site Development (p.73) Maximize Open Space
• Green Roof can contribute to credit compliance towards 1 pt
• Stormwater Design– Quantity Control (p. 77) – 1
point• Stormwater Design
– Quality Control (p. 85) – 1 point• Heat Island Effect (p.91) – Non-
roof– Consider replacing constructed
surfaces with Green Roofs – 1 pt• Heat Island Effect (p. 97) – Roof
– Install a Green Roof at least 50% of roof area – 1 point
• Building Reuse (p. 247)– Potential role in maintaining
existing roof 1-2 points• Construction Waste Management (p.255)
– Potential role in construction waste management in diverting roofing materials from disposal 1-2 points
• Materials & Resources (p. 263) – Green Roof could help contribute
for materials reuse 1-2 points– Recycled content (p. 264) –
contribution to 1-2 points• Recycled Content (p. 269)
– Green Roof helps with 1 to 2 points• Regional Materials (p. 276)
– Green Roofs when extracted, processed and manufactured regionally can help towards 1 to 2 points
• Rapidly Renewable Materials (p. 283) – 1 point• Innovation in Design (p. 395) – Green Roof 1 to 4
points• POSSIBLE TOTAL = 23 POINTS
Green Roof Design GREEN ROOF SYSTEMS
Green Roof Design GREEN ROOF SYSTEMS
Vegetative Cover
Green Roof Design GREEN ROOF SYSTEMS
Vegetative Cover
Water Retention Drainage System
Green Roof Design GREEN ROOF SYSTEMS
Vegetative Cover
Water Retention Drainage System
High Performance Waterproofing
Waterproofing Membrane
One of the most critical design elements of any Green Roof System is the Waterproofing Membrane. No matter how good it looks on top, what is below must keep the water out!
Deck
Hot Applied Rubberized Waterproofing
Polymer Modified Primer
Hot Applied Rubberized Waterproofing
790-11 EV Membrane
Hot Applied Rubberized Waterproofing
Protection Course
Hot Applied Rubberized Waterproofing
Insulation
Hot Applied Rubberized Waterproofing
Root Barrier/Water Retention
Hot Applied Rubberized Waterproofing
Filter Fabric
Hot Applied Rubberized Waterproofing
Growing Medium, Plants and Wind Erosion Layer
Hot Applied Rubberized Waterproofing
Base coat applied at 90 mils
Waterproofing
Applying Hot Applied Rubberized Waterproofing
Seasonal High Water Table
Bedrock
Soil Horizon
Vegetation
Emulating Nature
Drain Sheets
Mats
Dual Media
Mineral Drainage LayersEmulating Nature
Reasons to Irrigate
• Support specific plant palate
• Optimize Evapotranspiration Losses
– Reduce Runoff
– Modify Micro-Climate
• Optimize Thermal Benefit
– Evaporative Cooling (Latent heat transfer)
Irrigation Methods
Surface Systems [Required for most systems with artificial drainage layers]
– Drip (Media depth of 6”, or greater, recommended)
– Overhead Spray
Base Systems [Single layer systems, or systems with granular drainage layer]
– Capillary– ‘Standing Water’ Method
Capillary Irrigation Method
Drip Line
Capillary Fabric
Capillary Irrigation Method
Base Flood Irrigation
• Water dispensed at the rate that plants require it
• Little direct evaporation• No fancy sensors or controllers
are required• Water levels are maintained by
float valve
One-inch of water sustained
by float valve
Roots drink from the drainage zone
Base Flood Irrigation Approach
Strategic Use of BasalIrrigation Techniques
float controller boxes
ponding riffles
ponding elementbonded to protection sheet
water surface
separationfabric
primarymembrane
Enhanced Water Retention Using Ponding Riffles
Ponding Riffles
Optigrün Trickle Irrigation Modules
Trickle Irrigation Modules
Augmenting System Drainage
Internal Drainage
Wind-Stabilized Designs
Artificial Terrain Elements
Free-Standing Railing System
• Does not penetrate waterproofing
• Satisfies code requirements
Unit Paver System
Life Expression Wellness Center – Pennsylvania
Intensive: Oaklyn Branch Library
Intensive: Oaklyn Branch Library
14” irrigated green roof assembly
Oaklyn Library, Evansville, IN
The Four Seasons Hotel, Boston, MARoofscapes, Inc.
Chicago City HallRoofscapes, Inc.
Chicago saves $4000-5000 per year on the City Hall energy bill since its roof was greened.
Notebaert Nature Museum (6.0” thick irrigated )
Veneer Wetlands
Mass General Healing Garden
Heinz Headquarters, PennsylvaniaRoofscapes, Inc.
In our every deliberation we must consider the impact of our decisions on the next seven generations.
-The Great Law of the Iroquois Confederacy
Green Roofs in Germany
Green Curves
Working toward the green skyline of the future.Earth Our Only Home, Inc.
This concludes The American Institute of Architects
Continuing Education Systems Program
Thank you for your time!ANY QUESTIONS??