Sustainable Building Envelope â€“ Green Roof Technology

School of Construction and the Environment

Centre for the Advancement of Green Roof Technology

Sustainable Building Envelope –Green Roof Technology

Dr. Karen Liu

School of Construction and the EnvironmentBritish Columbia Institute of Technology

BCBEC luncheon meeting, Feb 08, 2007



→ Presentation Outline

1. Introduction2. Green Roof Materials3. Green Roof FAQ4. Standards and Guidelines 5. Green Roof Research at BCIT



→

specialized roofing system that supportsvegetation growth on rooftops

A green roof in Europe

What is a Green Roof?



→

Vancouver Public Library (HydroTech)

FeaturesDeep soil (>200 mm)Heavy weight (> 300 kg/m2)Traditional garden plants and shrubsFavourable conditionsHigh maintenancePark-like setting

Intensive Systems



→

401 Richmond, Toronto(Xero Flor)

Extensive SystemsFeatures

Shallow medium(<200 mm)Light weight (< 300 kg/m2)Grasses, sedums and herbsHarsh conditionsLow maintenanceEcological setting



→

Roof assembly(Conventional or PMRA)

Root resistant layer

Drainage layerFilter layer

Growing medium

Vegetation

Green Roof - Principal Components



→ Green Roof on Conventional Roof

Cover Board

Insulation

Deck

Vapour Barrier

Membrane

Considerations:• Rooftop traffic• Load distribution



→ Green Roof on PMRA

Insulation

Deck

Membrane

Filter cloth

Considerations:• Rooftop traffic• Load distribution• Vapour diffusion







→ Root Barrier - Physical

Root barrier and installation (Source: HydroTech)



→ Root Barrier - Chemical

Root barrier chemical treated filter cloth



→ Drainage Layer

Extensive – 3D filament mesh Extensive – dimpled system



→ Drainage / Storage Layer

Extensive – dimple with cups

Intensive – drain channel with cups



→ Drainage / Storage Layer

Source: greenrooftops.com



→ Filter Membrane

Source: HydroTech



→ Growing Medium

Soil is blown onto roof (Source: HydroTech)



→ Examples – Sedums and Grasses







→

6 m (2

0 ft.)

15 m (30 ft.)

5 m

(16

ft.)

N

Green Roof Research Facility (GRRF)Parapet355 mm(14 in.)

REF GR-1GR-2



→

Structural supportVapour control layer

Thermal insulationSupport panel

Reference Roof Green Roof

Drainage layerFilter membraneGrowing medium

Vegetation

Roof membrane

ThermocoupleHeat Flux Transducer

VB

IN

INS

SB

Layer

SM

OUT

MEM

Cross-Section of GRRF Roof



→

GR-1

GR-2

REF

3 Test Roof Sections



→ Growing Medium and VegetationGreen Roof “GR-2”Green Roof “GR-1”

GM = 150 mm, GrassesGM = 75 mm, Sedums

Objectives: Compare performance of GR-1 & GR-2



→ FAQ #1: Extensive Green Roof

How much growing medium do we need?



→ Energy EfficiencyAverage Total Daily Heat Flow Through Roof Surfaces at GRRF

(Jan 1, 2005 - Dec 31, 2005)

0.00

0.05

0.10

0.15

Winter Spring Summer Fall

Hea

t Flo

w (k

Wh/

m2/

day)

REFGR-1GR-2

Average Daily Heat Flow Through Roof Surfaces

(Jan 1, 2005 – Dec 31, 2005)

=> Thermally, GR-1 performs similarly to GR-2 in Vancouver



→

Rainfall and Runoff in Dry Season(May 20-21, 2005)

0

0.5

1

1.5

2

2.5

1830

2030

2230 30 23

0

430

630

830

1030

1230

1430

1630

1830

2030

Rai

nfal

l / R

unof

f (m

m)

Dry Season: Apr – Sep, total rainfall = 231 mm

Dry Season Event - Vancouver

Delay

Peak Flow

Amount

May 20 May 21

RainGR-1

GR-2

Rain = 18mmGR-1 = 10mm (44%)GR-2 = 3 mm (86%)



→

Wet Season: Oct – Mar, total rainfall = 1277 mm

Wet Season Event - Vancouver

Rainfall and Runoff in Wet Season(Apr 5-6, 2005)

0

0.2

0.4

0.6

0.8

1

1015

1215

1415

1615

1815

2015

2215 15 21

5

415

615

815

1015

1215

Rai

nfal

l / R

unof

f (m

m)

Apr 5 Apr 6

RainGR-1GR-2

Rain = 17mmGR-1 = 13mm (22%)GR-2 = 14 mm (17%)



→

Rainfall and Roof Runoff at GRRF(Jan 1, 2005 - Dec 31, 2005)

0

50

100

150

200

250

300

350

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rai

n / R

unof

f (m

m)

WS

GR1

GR2

Wet Dry Wet

RAIN

Runoff Retention

Wet season: reduction=15%Dry season: reduction=90%

Overall Reduction = 28%

=> Rain pattern affects retention efficiency of green roofs



→ Other considerationsLocal Climate

Vancouver’s unique weather pattern

Summer – mild, dry; Winter – cool, wet

Effects of plant on growing mediumRoot system cause uneven flow???

Plant internal water storage, transpiration



→ FAQ #2: Membrane Durability

Does green roof make a roof membrane last longer?



→ What affects membrane durability?Aging

Heat, ultra-violet radiation

MechanicalThermal stresses, building movement

PhysicalWind, puncture (e.g. hail, foot traffic)



→ Membrane Temperature - VancouverRoof Membrane Temperature - REF

(Jan 1, 2005 - Dec 31, 2005)

-20

0

20

40

60

80

Jan-

05

Jan-

05

Jan-

05

Feb-

05

Feb-

05

Mar

-05

Mar

-05

Apr

-05

Apr

-05

May

-05

May

-05

Jun-

05

Jun-

05

Jul-0

5

Jul-0

5

Jul-0

5

Aug

-05

Aug

-05

Sep-

05

Sep-

05

Oct

-05

Oct

-05

Nov

-05

Nov

-05

Dec

-05

Dec

-05

Dec

-05

Tem

pera

ture

(°C

)

TmaxTmin


Reference Roof, GRRF 2005



→ Membrane TemperatureRoof Membrane Temperature - GR-1

(Jan 1, 2005 - Dec 31, 2005)

-20

0

20

40

60

80

Jan-

05

Jan-

05

Jan-

05

Feb-

05

Feb-

05

Mar

-05

Mar

-05

Apr

-05

Apr

-05

May

-05

May

-05

Jun-

05

Jun-

05

Jul-0

5

Jul-0

5

Jul-0

5

Aug

-05

Aug

-05

Sep-

05

Sep-

05

Oct

-05

Oct

-05

Nov

-05

Nov

-05

Dec

-05

Dec

-05

Dec

-05

Tem

pera

ture

(°C

)

TmaxTmin


Membrane Temperature - VancouverGreen Roof “GR-1”, GRRF 2005



→

Statistics on Daily Maximum Temperature Jan 1 – Dec 31 ,2005

Reference Roof

No. ofDays

% ofDays

TemperatureGreater Than:

20°C

40°C

50°C

60°C

257

158

100

41

70

43

27

11

Green Roof - 1

No. ofDays

% ofDays

121

0

0

0

33

0

0

0

Green Roof - 2

No. ofDays

% ofDays

68

0

0

0

19

0

0

0

=> GRS can slow down the aging process of the roof membrane

Membrane Temperature Statistics

30°C 206 56 5 1 0 0



→ Membrane Temperature FluctuationsMedian Daily Membrane Temperature Fluctuations

(Jan 1, 2005 - Dec 31, 2005)

19

43

48

16

24 5

21 1 1 10

10

20

30

40

50

Winter Spring Summer Fall

Tem

pera

ture

Flu

ctua

tion

(°C

)

REFGR-1GR-2

=> GRS can reduce thermal stress on the roof membrane



→ FAQ #3: Energy Efficiency

What is the "R" value of a green roof?



→ What is “R-value”?

R-value is a measure of thermal resistance of insulation materials

SI unit (RSI): K.m2/WImperial unit (R-value): ft2.F.h/BTU

Hot Cold

Th Tc

L

A

Q

Qt x A x ΔT

R =

Thermal Resistance (R)



→

Thermal mass

Evapotranspiration

Insulatingproperty

Shading

Indoor

How does green roof work?

Summer



→ Problem with “R-value”?Green roof cools a building with more than insulation

ShadingEvaporative coolingThermal mass

R-value of wet soil is low but evaporative cooling is high

What about “equivalent” R-value?



→ FAQ #4: Lightweight Systems

Can lightweight systems perform at holding water?



→ Extensive Green Roof Systems

Generic green roof system (75 mm)• Generic green roof growing medium (75mm)

• Vegetation carrier with growing medium (25mm)

• Water retention fleece (10 mm)

Proprietary green roof system (45 mm)



→ Water Retention Experiment at BCIT

Generic green roof growing medium

Proprietary green roof assembly

=> Measure dry weight



→ Water Retention Experiment at BCIT

Submerged for 24h…

Dripped for 2h…

=> Measure saturated weight



→ Saturated Weight and Water Retention

DryWeight

SaturatedWeight

Water Retention

(L/m2)Generic Extensive GRS

46.3 kg/m2

9.4 lb/ft2

74.3 kg/m2

15.0 lb/ft2 28.0

Proprietary Extensive GRS

24.6 kg/m2

5.0 lb/ft2

49.8 kg/m2

10.1 lb/ft2 25.3

Comparison 53% 67% 90%




1. Introduction2. Green Roof Materials3. Green Roof FAQ4. Standards and Guidelines5. Green Roof Research at BCIT



→ Standards and Guidelines

Materials standards

Installation standards

Guidelines



→

Runoff increases with roof slopeMinimum 2% for extensive GRS to allow proper positive drainage

>5%: use growing medium with high water storage capacity and vegetation with low water demand

special considerations to protect GRS against shear and sliding for steep slopes

Maximum 45o to avoid danger of sliding

GRS on pitched roof (XeroFlor)

FLL Guidelines – Roof Slopes



→

Roots can penetrate membrane

Use protective sheeting or special treatment

Use multiple root-penetration barriers if necessary

Avoid plants with aggressive roots such as bamboo and variety of Chinese reeds

Resistance to root penetration should be tested by standard test

bamboo

FLL Guidelines – Root Penetration



→

Maintain proper drainage

Roof outlets should be permanently accessible and not covered by greenery or gravel

Inspection shaft should be installed in outlets that are located within the planted areas

Avoid plants to grow into the gutters and block drainage path

Avoid hanging plants that block gutters at eaves on steep slopes

Roof drain and inspection chamber (HydroTech Membrane Corp.).

FLL Guidelines - Drainage



→

Dried plant materials pose fire risk

Use growing medium that meet a composition and depth requirement

Select vegetation that has a low fire load (e.g. succulents instead of grasses)

Allow spacing between vegetation areas and any roof penetrations

Incorporate irrigation systemSedums – low fire load

FLL Guidelines – Fire Resistance







→ Green Roof Research at BCIT

Green Roof Research Facility at BCIT, Great Northern Way Campus



→ CAGRT’s Partners

Roofing Systems

Firestone Building ProductsHydroTechMembrane Corp.IKO IndustriesSarnafilSiplastSoprema

Other Industry

Detec SystemLinnaea NurseryNATS NurseryNilex/J-DrainQuad-LockStream Organics Management

Green Roof Systems

Elevated Landscape TechnologiesXeroFlor CanadaZinCo Canada

BCIT-CAGRT

Agency

NSERCWDREFECGVRD –SILG



→

• Comparativeperformancedata

• Quantitative3rd partyverification

• Increasedmarketconfidence

Roof Evaluation Module (REM)

Roof Evaluation Modules at BCIT



→ Regional Infrastructure Network

City of White Rock Operations Building, White Rock, BC

• Electronic Arts, Burnaby

• White Rock Operations Building

• Elevated Research Platform, BCIT



→ Education

Open House Every 3rd Thursday of the month, 3-5 pm555 Great Northern Way

Green Roof CoursesGROW 0001 workshop (4h)GROW 1000 part time (18h)GROW 3000 full time (45h)

Visit our web site: www.greenroof.bcit.ca



→ CAGRT Research Team

Maureen Connelly Research Program Head

Karen Liu Acting Program Head

Kerly Acosta Research Faculty

Janet Snell Research Faculty

John Compton-Smith Research Analyst

Anita Green Education Coordinator

Claro Dejeres Community and Industry Liaison

Thank You!

Documents

Sustainable Building Envelope â€“ Green Roof Technology