Vegetated Roof Presentation

A Preliminary study of the Water RetentionPerformance of an ExtensiveVegetated 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
Vegetation
Growing Medium
Slab/Sheet rock
Retention Fleece
Waterproofing membrane
Drainage Mat
Insulation

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.

Preliminary Study Goals
Get model up and running properly
Gather data from at least 3 storm events
Determine whether data seems reasonable
Estimate 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:
Construct model of roof
Collected data from 10/14/09 - 11/14/09 (32 days) (however ..data collection is on going)
Used RL-Loader 2.2.1 (a RainWise program) to export raw data into excel for analysis.
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.
Compared runoff data and precipitation data with graphs and

Model
A vegetated roof model was used to study the main roof because it was difficult to access and control the drainage on the main roof.
Vegetated Roof runoff capture system with RainWise tipping bucket
Adjacent rainfall Gauge RainWise tipping bucket

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)

Data Summary
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

Data Summary: STORM 1 10/24/09

Data Summary

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…
Potential future work:
Continued runoff volume data collection
Water quality analysis
Temperature data collection
Lessons Learned:
Drainage mechanisms should pierce the waterproofing layer
Don’t assume things have been installed correctly

Questions?
Special Thanks to:
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

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