A PRELIMINARY STUDY OF THE WATER RETENTION

PERFORMANCE OF AN EXTENSIVE VEGETATED ROOF

USING A SCALED MODEL AT LAFAYETTE COLLEGE

How did this get started?

Spring 2008: Kney! can we have a roof garden?? Pleasee??

Summer 2008:Excel research to identify possible roofs. Attend GRHC workshop “Green Roofs 101”

Fall 2008: Select Acopian roof for the project, bring Spillman Farmer Architects into the project.

Spring 2009: Select vegetated roof material based on architects recommendation. Preliminary design for the model in CE 351.

Summer 2009: WOOT! We have a vegetated roof!

Fall 2009: Preliminary data collection

Why Vegetated Roof?

Filters water/air Retain water (reduce sewage

system loads) Act as a rain water buffer Extend the life of the roof: UV

and acid rain protection Lowers heating and cooling cost

(acts as an insulator) Increased property value Stores carbon Creates a habitat Helps maintain healthy

ecosystem

commitment to sustainability/reducing footprint

A pilot for future vegetated roofs new route for research which

could combine different discipline: geo, bio, eng, econ.

Easton has combined sanitary and storm water system, green roofs reduce run off into the system

Increases the life of the roof Energy cost reduction due to

better insulation Increased property value

In General: For Lafayette:

Vegetative Roof System

  The roof garden system used is a pre-vegetated mat from XeroFlor. The vegetation is primarily sedum and moss, which are both low

lying durable plants. This is an ultra lightweight system, weighing approximately 12 lb/SF

and only 3” thick. The waterproofing membrane will be a modified bitumen membrane. The system costs approximately $37/per square foot.

Growing Medium

Retention Fleece

Vegetation

Drainage Mat

Slab/Sheet rockWaterproofing membrane

Insulation

Preliminary Study Goals

Get model up and running properlyGather data from at least 3 storm eventsDetermine whether data seems reasonableEstimate retention for large roof based off data or other vegetated roof studies

Hypothesis

Average Vegetated Roof Runoff < Average Precipitation

By how much??

Other Expected Outcomes: • Runoff from green roof will form a smooth

hydrograph• Percent retained in the 25%-75% range• Runoff Peak is delayed slightly from

precipitation peak

Methods:

1. Construct model of roof

2. Collected data from 10/14/09 - 11/14/09 (32 days) (however ..data collection is on going)

3. Used RL-Loader 2.2.1 (a RainWise program) to export raw data into excel for analysis.

4. Adjusted vegetated roof runoff based on an area ratio. The area of the vegetated roof = 16SF or 2304 in2 compared to the

gauge 4 in diameter (50.265 in2). A ratio of .0218 was multiplied to the vegetated roof runoff data to normalize it.

5. Compared runoff data and precipitation data with graphs and

ModelA vegetated roof model was used to study the main roof because it was

difficult to access and control the drainage on the main roof.

  Model is made from recycled wood. Model is sloped towards the 2 inch PVC drainage pipe PVC pipe penetrates just above the waterproofing layer Tipping buckets record how many tips there are in 10 second

intervals (1 tip = .01 inches)

Vegetated Roof runoff capture system with RainWise tipping bucket

Adjacent rainfall Gauge RainWise tipping bucket

Data Summary

6:2

7:0

0 P

M1

1:4

1:0

0 P

M1

:18

:00

AM

9:0

9:0

0 A

M4

:44

:00

PM

4:5

4:0

0 P

M5

:04

:00

PM

5:1

4:0

0 P

M5

:24

:00

PM

5:3

4:0

0 P

M5

:53

:00

PM

6:0

5:0

0 P

M6

:18

:00

PM

12

:43

:00

PM

10

/27

/09

6:3

61

0/2

7/0

9 7

:41

10

/27

/09

8:0

21

0/2

7/0

9 8

:12

10

/27

/09

9:1

71

0/2

7/0

9 1

0:2

31

0/2

7/0

9 2

1:3

81

0/2

7/0

9 2

3:2

41

0/2

8/0

9 0

:41

10

/28

/09

2:4

81

0/2

8/0

9 3

:33

10

/28

/09

3:4

61

0/2

8/0

9 3

:56

10

/28

/09

4:1

31

0/2

8/0

9 5

:07

10

/28

/09

7:3

11

0/2

8/0

9 7

:41

10

/28

/09

8:5

11

0/2

8/0

9 1

1:4

01

0/2

8/0

9 1

3:0

91

0/3

1/0

9 1

8:5

51

1/1

/09

8:2

1

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120 Vegetated roof events 10/14/09 to 11/14/09

Time

Inches/inte

rval

SizeStorm size

(in.)Number of days

observedAverage

retention (in.)

Average percent retained

small 0.001-0.5 11 0.0943 97.11%

medium 0.5-1 4 1.2343 93.01%large >1 0 - -

There were 5 days with 100% retained

The 17 days with no rainfall were not included in

Vegetated roof runoff was less than precipitation in all rain storms recorded.

Data Summary

Weather.com precipitation is on the same order as the rain gauge, the difference might be accounted for in the distanced between the gauges.

Vegetated roof runoff is consistently lower than the precipitation

10/1

4/20

09

10/1

6/20

09

10/1

8/20

09

10/2

0/20

09

10/2

2/20

09

10/2

4/20

09

10/2

6/20

09

10/2

8/20

09

10/3

0/20

09

11/1

/200

9

11/3

/200

9

11/5

/200

9

11/7

/200

9

11/9

/200

9

11/1

1/20

09

11/1

3/20

090

0.2

0.4

0.6

0.8

1

1.2

1.4

Daily Rainfall/Runoff 10/14/09-11/14/09

weather Precip (in) Rain gage (in) Adjusted Vegetation (in)

Date

Rain

(in

ches)

Data Summary: STORM 1 10/24/09

4:33 PM4:55 PM5:17 PM5:39 PM6:01 PM6:23 PM0.00

0.10

0.20

0.30

0.40

0.50Storm 1 Runoff: 4:30pm-

6:30pm

Time

Vo

lum

e (

inch

es)

Data Summary: STORM 1 10/24/09

12:01 AM 1:51 AM 3:41 AM 5:31 AM 7:21 AM 9:11 AM 11:01 AM12:51 PM 2:41 PM 4:31 PM 6:21 PM 8:11 PM 10:01 PM11:51 PM0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09Storm 1

Precipitation

Adj. Runoff

Time

Volu

me (

inches)

Data Summary

12:01 AM3:31 AM 7:00 AM10:31 AM2:01 PM 5:30 PM 9:01 PM12:30 AM4:00 AM 7:30 AM11:00 AM2:30 PM 6:00 PM 9:30 PM0.000.010.020.030.040.050.060.070.080.09

Storm 2: 10/26/09-10/27/09

Precipitation Runoff

Time

Volu

me (

inches)

Data Summary: Storm 3

Comparing Our Results

Lawerence Technological University: 1,000 SF green roof. retained an average of 68.24% over the course of 21 storm

events. 9 were small, 8 were medium sized and 3 were large.

Penn State University: detention and retention abilities of green roofs between July

and October of 2002. 100% of storms less than 4mm (~.157in) were completely

retained by the green roof. 20-25% of runoff is retained for storms around 25mm (~.984

in.) North Carolina State University:

two different sites 2003-2004. The Goldsboro site had a 63% retention rate, while Raleigh had

a 55% retention rate.

Conclusions

Did the model meet expectations?Average Vegetated Roof Runoff < Average

Precipitation• Runoff –FIX this• Percent retained WAS NOT in the 25%-75% range

• The difference in Lafayette’s results most likely due to the size of the storms being observed. It may also be possible that water is leaking.

• Runoff Peak would require further study to determined if it is delayed slightly from precipitation peak

Due to issues setting up a procedure and constant adjustment to the model runoff collection system, not much data was taken. It is difficult to draw any conclusions with statistical confidence without further study.

Is the roof reducing runoff?If the vegetated roof retained 58% of the total rainfall, I estimate it could hold

106 gallons for small (.5in) storms and up to 200 gallons for medium storms (1in).

Final Thoughts…

Lessons Learned: Drainage

mechanisms should pierce the waterproofing layer

Don’t assume things have been installed correctly

Potential future work:

Continued runoff volume data collection

Water quality analysis

Temperature data collection

•Mary Wilford-Hunt, •George Xiques, •Salvatore Verrastro, •Prof. Anne Raich, •Prof. Arthur D. Kney, •Prof. Steve Mylon, •Prof. John Greenleaf,

•Anthony Belgiovine ‘12,•Joshua Sadlock ’12, •Jeffrey Shoemaker ‘10,•Diana Hasegan ‘10, •Tomas Concepcion ‘11, •Lindsey Getches ‘11, •Dan Miller ’11 •Dan Moran ‘11

Questions?Special Thanks to: