why consider a green roof?

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??