7/13/2012 components of green roof design - apwa · patios, fountains, ... american society for...

7/13/2012

1

Components of green roof designEric French

The first and most important component of any green roof is its design. Green roof design is typically initiated under two circumstances:

1) The owners of a structure desire to adda green roof to their existing building.

2) The owners of a building in the design stage are interested in a green roof and ask the design team to include the green roof in the design.

Beginning with the first scenario, adding a green roof to an existing structure poses a special set of design challenges that must take into considiteration:

1. Available excess load for the green roof.2. Age and condition of existing membrane.3. Existing mechanicals and utilities on the roof.4. Access needed for future building maintenance.5. Access to roof for installation purposes.6. Condition and efficiency of roof drains.

An onsite roof inspection is a critical first step.

7/13/2012

2

•Get on the roof to assess the conditions first hand. Do not rely on someone else.

After our site inspection, we need to calculate the excessload available for a green roof. These calculations must be done by a licensed structural engineer. The calculation looks something like this:

Structural load capacity minus dead loadminus live loadminus snow load

Equals the allowable weight for a green roof

It is critical that we keep the weight of the green roof under the allowable excess load for the roof.

The other important factors to consider when looking at an existing roof are the age, type, and condition of the existing waterproofing membrane.

Roof membranes older than three years are consideredtoo old to receive a green roof. Some manufacturers will nullify their warranty if a green roof is added overan existing membrane without their consent and input.

It is critical to inspect every aspect of an existing roof to determine its condition before you agree to add a green roof.

7/13/2012

3

Often you will find HVAC units and their associated utilities on an existing roof laid out in a seemingly random manner. These units need to be maintainedon a regular basis and access to them must be designed intothe green roof to avoid damage to the green roof plants.

Access is also needed for other building maintenance activities such as window washing and lamp bulb changing.

Allowances need to be made for existing utilities such as gas lines, power lines and condensate piping so not to bury them in the plantings.

Common items to inspect are:

• Seams and flashings • Drains, valleys and crickets

• Future access requirements

• Patches and variations in elevation

7/13/2012

4

• Penetrations • Utilities

Access to an existing roof is often more complicated than one under construction. Sometimes it becomes necessaryto use large cranes for hoisting materials to the roof. Gaining access for large cranes in the urban environment will often require street closings and off peak work hours.

If a roof can be designed using fewer components or faster installation systems, substantial savings can often be accomplished.

Working in the city requires a lot of upfront planning and coordination with public safety agencies.

7/13/2012

5

Using bulk planting mix saves considerable time and expense, if you have the room to set up the equipment.

The final item we want to verify on an existing roofis the adequacy of the existing drains to assure wateris not ponding on the roof during storm events.

If the roof has a history of ponding, additional roof drains may need to be added before installing a green roof.

A green roof is not intended to become submerged because the additional weight to the roof of standing water is problematic. If insufficient drainage can not be rectified then the building is not a candidate for a green roof.

• This is not a well designed drain.

7/13/2012

6

•Designing a green roof for a new structure is vastlysimpler than adding a green roof to an existing structure.

•Work backwards with engineering once the type of roof desired determined.

•Selections can be made regarding roofing materials and methods to optimize both efficiency of maintenanceand cost of installation.

•Construction access is often much easier and hoisting is less of a problem.

After we determine if our structure can accept a greenroof and what excess load we are working with, we need to start our design process.

Green roofs are made up of the following components:

•Waterproofing membrane and associated flashings•Root barrier to protect the waterproofing membrane•Drainage layer to allow the growing medium to drain•Growing medium - typically light weight engineered media•Vegetation

These are the very basic requirements.

Additional components of a green roof can be:

• Supplemental insulation / contouring foam• Water drainage channels• Water retention mats• Gravel vegetative free zones with edgings• Stepping stones / access paving• Irrigation

Additional amenities are often:

Patios, fountains, railings, lights and furniture.

7/13/2012

7

Preliminary designs can be done in SketchUp for impact.

Regional building codes must be taken into considiteration. The city of Pittsburgh now has a green roof ordinance:

§ 912.04. I Extensive Green Roofs

Extensive Green Roofs are lightweight veneer systems of thin layers of droughttolerant self-seeding vegetated roof covers.

(1) Extensive Green Roofs permitted by-right shall not have more than five (5)inches of soil medium.

(2) All Extensive Green Roofs shall have at least a one (1) foot perimeter ofvegetation-free zone around the edges of the roof and around all roof penetrations(i.e. skylights, pipes, etc).

(3)For Extensive Green Roofs with projected live loads of higher than fifteen (15)pounds per square foot, consultation with a structural engineer is a requirement.

§ 912.04. J Intensive Green Roofs

Intensive Green Roofs are heavier than Extensive Green Roofs. For the purposesof this code the term means any Green Roof with soil mediums greater than five(5) inches.

•A consultation with a structural engineer is required for all Intensive GreenRoofs.

•Vegetation Height on Intensive Green Roofs shall not exceed five (5) feet over themaximum height of the zoning district.

(3) All Intensive Green Roofs shall have at least a one (1) foot perimeter ofvegetation free zone around the edges of the roof and around all roof penetrations(i.e. skylights, pipes, etc).

7/13/2012

8

No uniform or national building code exists for green roofs in the United States.

American Society for Testing and Materials (ASTM) has developed the most comprehensive set of guidelines in the US.

The German Society for Landscape Research,Development and Construction, the

Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau(FLL)

has created a German national standard for green roof construction and performance which is used in the US as the reference standard.

First we can discuss roof membranes. There are manytypes of water proofing systems used today. The only systems that are suitable for green roof applications are water impermeable membranes:

1. Fluid applied membrane such as coal tar or asphalt2. Polymer Modified Bitumen or MB 3. Single Ply Membranes

1. Thermoplastic: TPO, PVC, and PVC alloys2. Thermoset: Most commonly EPDM

It is highly recommended that any single ply membranes be fully adhered to reduce leak migration.

7/13/2012

9

This is a fluid applied membrane going down on a roof along with the reinforcement layer.

Photo courtesy of American Hydrotech

Once a membrane has been installed it should be thoroughly leak tested either by flood testing or electronic vector mapping to assure the integrity of the waterproofing.

Chain of custody is critical at this point to assure no damage occurs to the waterproofing. The green roofcontractor should start installing the green roof as soon as the leak test has been completed.

Root barrier should be immediately installed along with the drainage layer. The drainage layer can be as simple as a synthetic wicking layer to a multi functioning all in one composite layer.

7/13/2012

10

After installation of the root barrier over the waterproofing membrane and the drainage layer is installed, installation of the vegetation free zone typically occurs.

Photo courtesy of American Hydrotech

Foam contouring occurs on top of the drainage layer if variations in elevations are desired.

Installation of the green roof media occurs after the contouring foam is covered with another layer of fabric.

7/13/2012

11

After the soils are in place it is time to install the plant materials. These are plugs ready to go on the roof.

Plugs require regular watering after planting and require 18 to 24 months to fully grow in.

• Sedum sod is a roll out pre-vegetated mat providing an instant green solution for an extensive roof.

7/13/2012

12

• Sedum Sod requires immediate regularwatering for the first month or two.

Pre-vegetated trays are a great option for small projects and require almost no transitional maintenance.

Green roofs are everywhere. Sometimes where we least expect to find them.

7/13/2012

13

There are may ways to build a green roof.Have fun, be creative, innovative but….

Remember everyone is watching:

We need to get it right the first time!

7/13/2012

1

Allegheny County Office BuildingGreen Roof Demonstration

John K. Buck and Darla Cravotta

October 4, 2011

Speaker Introduction

Darla CravottaAllegheny County

John K. Buck, CPSScProject Manager, Civil & Environmental Consultants

2

Project Information

Client:

� Allegheny County, Pittsburgh, PA

Location:

� Allegheny County Office Building

542 Forbes Avenue, Pittsburgh PA, 15219

Support From:

� Penn State Engaging Pittsburgh

� Pennsylvania Environmental Council

� Conservation Consultants, Inc.

� 3 Rivers Wet Weather (www.3rww.org )

� USDOE and Federal Stimulus funding (ARRA)3

7/13/2012

2

4

5

Green Roof Benefits

What is a Vegetated Green Roof?� A roof intentionally designed to support the long-

term growth of plants on its surface

Why a Green Roof?� Environmental Benefits

� Financial Benefits

� Looks cool, is cooler

6

7/13/2012

3

Green Roof Benefits

Societal

� Reduced Stormwater

Runoff

� Reduced CSOs

� Cooler Urban

Environment

� Improved Aesthetics

� Parkland on Rooftops

� Carbon Sequestration

7

Financial

� Extended Roof Life

� Lower Energy Costs

� Lower Stormwater

Management Costs

� Image (e.g. LEED)

� Property Value

� Green Space Incentives

Project Information

Allegheny County Program Goals:

� Reduce CSOs by speeding adoption of green

infrastructure

� Public

� Private

� Demonstrate Benefits of Green Roofing

� Lead by example

� Support optimized design

� Support educational initiatives

8

Project Information

Selection Process

Project Execution Team:

� Allegheny County – Darla Cravotta, Dan Onorato

� Cuddy Roofing (A Scalo Company) – Prime

Contractor

� Eisler Landscapes – Green Roof Design and

Installation

� Civil & Environmental Consultants – Monitoring

System, Engineered Soil Design

9

7/13/2012

4

Green Roof Benefits

Combined Sewage Overflows (CSOs):

� Sewage and stormwater are combined into one

pipe, all sent to [or toward] sewage treatment

plant

� In wet weather, what can’t be treated gets

dumped directly into the river – a Combined

Sewage Overflow (CSO)

� Green roofs and other green infrastructure reduce

stormwater volume, intensity, and CSO pollution

10

CSOs

11

Green Roof Runoff Reduction

Reducing CSO Pollution with Green Roofs:

� Mechanism: Soil acts as “sponge” to soak

up rainfall that drives runoff and CSOs

� Some succulent plants also behave like

sponges (e.g., Sedum spp.)

� Commonly 20-100% runoff

reduction

12

7/13/2012

5

Green Roof Heat Island Benefits

Urban Heat Island Effect:

� Impervious surfaces absorb heat by day, re-

radiate heat day and night

� Re-radiated heat make cities hotter

� Re-radiated heat increases cooling costs

13

Cooler Surface and Subsurface Temperatures

14

Peak Summer Surface Temperatures: Green Roof 35-60oF Cooler

Building Peak Building Peak Temp. DelayTemp. Delay

BuildingBuilding CityCity

• Intensive green roofs are generally elaboratelyplanted and commonly used as habitable spaces.

Aesthetics

Carnegie Mellon University

7/13/2012

6

ACOB – Structural Limitations

Types of Green Roofing

IntensiveSemi-IntensiveExtensive

2 ½ - 4” Depth 5- 8” Depth 8”+ Depth

Leak Detection (EFVM)

7/13/2012

7

Click to edit Master title style

Monitoring: Demonstrate Benefits

Overview Web Site

Allegheny County Office Building

Green Roof Project Overview:

www.alleghenycounty.us/alleghenygreen/COBroof.aspx

20

Allegheny County Office Building Green Roof

Monitoring Program

Overview:

� 8,400 SF of 20,200 SF converted to

green roof in June 2010

� Remainder conventional “control”

roof

� Monitoring weather, temperature

and water relationships using 95

sensors linked to internet

21

7/13/2012

8

22

Details of Allegheny County Office Building

Green Roof Monitoring Program

Green Roof Types:

1. Tray Extensive (4” soil, pre-grown sedum)

2. Extensive (4” soil, sedum sod)

3. Semi-Intensive (~6” soil, plugs and pots)

4. Intensive (>8” soil, plugs and pots)

Green Wall – to hide cellular switchgear

23

H

Extensive (4”) H

HHH

L

LLL

L

L

L

Intensive (8”)

Semi-intensive (6”)



24

7/13/2012

9



25

Climate and

Microclimate

Legend

Climate

Control Roof

Green Roof

Extensive Extensive Sod Roof (4”)Sod Roof (4”)

Extensive Extensive Sod Roof (4”)Sod Roof (4”)

Tray Extensive (4”)Tray Extensive (4”)Tray Extensive (4”)Tray Extensive (4”)

Intensive & Intensive & SemiSemi--IntensiveIntensive(~6(~6--10”)10”)

Intensive & Intensive & SemiSemi--IntensiveIntensive(~6(~6--10”)10”)

26



Monitoring System Features:

� Microclimate and design differences considered

� “High” and “Low” slope positions monitored

� 95 temperature, moisture, and weather sensors

monitored

� Real-time internet-accessible data

� Transfer relevant data to inspire, educate, advance

state of art

27

7/13/2012

10



28

Sheltered

Sheltered

Exposed

Before

29

Installation of Drainage Mat

30

7/13/2012

11

Drainage Wetness Sensor

31

Lateral Drains to Roof Drains

(Over Composite Drainage Blanket)

32

Sensor Wires

in Conduit

33

7/13/2012

12

Closed-Cell Styrofoam

for Lightweight Contouring

34

Wire Shelves to

Support Microcosms

35

Crane Lifting Engineered Soils

36

7/13/2012

13

Crain Lifting Engineered Soils

37

Filter Fabric and Soil over Filter Fabric and Soil over

Styrofoam MoundsStyrofoam Mounds

38

One Year Later (6/10/11)

7/13/2012

14

Before40

After 1 monthAfter 1 monthAfter 1 monthAfter 1 month 41

After one yearAfter one yearAfter one yearAfter one year 42

7/13/2012

15

L

H

H

1 Month After Planting

43

One Year Later (6/10/11)



Microcosms Comparisons in Same

Microclimate:

� Highly-monitored miniature green roof

alternatives

� Set in same microclimate

� Interpretive display value

45

7/13/2012

16

46

10”6.5”

4” Control



Microcosms Comparisons in Same

Microclimate:

� Measure:

�Percolation to drainage blanket (runoff)

�Soil Moisture (3 depths)

�Soil Temperature (3 depths)

�Solar radiation, air temperature, rainfall

47

7/13/2012

17

Runoff Over Soil

Roof Drainage Through

Soil

Microcosms

50

Soil Drainage Soil Drainage LysimeterLysimeter (to (to rain gauge)rain gauge)

Soil Drainage Soil Drainage LysimeterLysimeter (to (to rain gauge)rain gauge)

Soil Surface Soil Surface Runoff (to Runoff (to drain tube)drain tube)

Soil Surface Soil Surface Runoff (to Runoff (to drain tube)drain tube)

Soil Drainage Soil Drainage (to drain tube)(to drain tube)Soil Drainage Soil Drainage (to drain tube)(to drain tube)

51

7/13/2012

18

52

53

Sensing and

Sampling Area

54

7/13/2012

19

One Year Later

(6/10/11)

56

ACOB Microcosms

57

7/13/2012

20

Dielectric Soil Moisture Sensor (Decagon EC-5)

58

Dielectric Soil Dielectric Soil Moisture Moisture SensorSensor

Dielectric Soil Dielectric Soil Moisture Moisture SensorSensor

Soil Soil Temperature Temperature

SensorSensor

Soil Soil Temperature Temperature

SensorSensor

Soil Sensors

59

Sedum Sod Monitoring

60

7/13/2012

21

Control Temperature Monitoring

61

Roof Surface Roof Surface TemperatureTemperature

Solar Solar RadiationRadiation

Air Air Temperatures Temperatures

at 6”, 18” at 6”, 18” a.g.la.g.l..

Roof WetnessRoof Wetness

Control Roof Measurements

62

40oFCooler!

Cooler Roof Temperatures

63

7/13/2012

22

Cooler Surface and Subsurface Temperatures

64

Peak Summer Surface Temperatures: Green Roof 35-60oF Cooler

Building Peak Building Peak Temp. DelayTemp. Delay

BuildingBuilding CityCity

H

Extensive (4”) H

HHH

L

LLL

L

L

H

Intensive (8”)

Semi-intensive (6”)

CMU Heat Flux Comparison (Wang and Becker, 2011)

65

Hea

tFlu

x C

ompa

rison

ACOB Heat Flux Analyses (Wang and Becker, 2011)

Carnegie Mellon Univ. Student Analyses of

Temperature Flux Differences (Wang and Becker, 2011, David Dzombak, Ph.D. Advisor)

� Considered insulation components and temperature gradients

across green roof and control roof layers to calculated heat

flux

� Found Greatest Energy Benefit in Warm Weather – Cooler

Roof Temperatures Reduce Heat Gain to Building (75.3%

difference in heat flux (gain) between green and control roofs

in June-August)

� Found Modest Energy Benefit in Cold Weather (8.2%

difference in heat flux (loss) between green and control roofs

in November 2010-April 2011)

7/13/2012

23

Heat Loss or Gain at ACOB, MJ/M2

(Wang and Becker, 2011)

67

Green Roof Hydrologic Monitoring

Forecasting Stormwater Capacity:

� Monitoring green roof soil moisture

and roof runoff

� Can forecast how much stormwater

green roof soils can absorb

68

Water Balance Monitoring

Monitoring Rainfall & Runoff vs. Soil Water Content

69

7/13/2012

24

Green Roof Soil Moisture Storage Relationships

Monitoring Green Roof Soil Stormwater Storage

70

Rainfall (blue), Roof Drainage (red) and Soil

Volumetric Moisture Content with Depth

Runoff DelayRunoff Delay

Run

off R

educ

tion

Run

off R

educ

tion

7/13/2012

25

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

0.2

0.4

0.6

0.8

1

1.2

1.4

8/31/11 0:00 9/10/11 0:00 9/20/11 0:00 9/30/11 0:00

So

il W

ate

r S

tora

ge

(v

olu

me

tric

)

Inch

es

of

Ra

infa

ll o

r R

oo

f D

rain

ag

e

Date / Time

Rainfall, Roof Drainage, and Soil Moisture Relationships

Total Rainfall During Rain Event

Total Roof Drainage During Rain Event

Total Apparent Soil Water Storage (0-7" BGS)

74

4.46

5.75

4.1

1.92

3.13

4.36 4.4

3.89

0

1

2

3

4

5

6

Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11

Rainfall and Roof Drainage

Main Roof Microcosms (inches) Rainfall

(inches)

4" Soil

Roof

Drainage

(inches)

6.5" Soil

Roof

Drainage

(inches)

10" Soil

Roof

Drainage

(inches)

4.46

5.75

4.1

1.92

3.13

4.36 4.4

3.89

0

1

2

3

4

5

6

7

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Mar-11 Apr-11 May-11 Jun-11 Jul-11 Aug-11 Sep-11 Oct-11

Runoff Reduction - Main Roof Microcosms

4" Soil %

Runoff

Reduction

6.5" Soil

% Runoff

Reduction

10" Soil %

Runoff

Reduction

Rainfall

7/13/2012

26

Summary

Green Roofs:

� Reduce stormwater volume and

intensity, prevent water pollution

(CSOs)

� Keep buildings and neighborhoods

cooler

� Save money

76

Questions???

Darla CravottaAllegheny [email protected]

John K. Buck, CPSScProject Manager, Civil & Environmental [email protected]

78

7/13/2012 components of green roof design - apwa · patios, fountains, ... american society for...

Documents