Penn State Green Roof Research: Research

Stormwater runoff

All research buildings at Rock Springs have enclosed connected to runoff barrels (capacity 208 L) fitted with pressure transducers (Omega PX26 Series) to measure runoff. Pressure transducers were connected to a Campbell 21X data logger (Campbell Instruments, Logan, UT). Data have been collected every min and averaged every 5 min.

Building energy use

Buildings are insulated with 3in of household fiberglass insulation on all sides. Paneling (.25in thick) covers all interior surfaces, over the insulation. Buildings were equipped with space heaters (1 kW)) and air conditioners (3 kW), Each building is fitted with a household watt-hour meter that is read daily.

Building heat flux

All buildings are fitted with thermisters in the floor, walls, and ceilings to gather data on heat flux. These are probably the only buildings of their kind in the US where the effects of green roofs on heat flux are being examined.

Water quality

Water quality has been determined by analyzing a composite sample for several selected rain events from each building from October, 2002 to June, 2003. Analysis of Variance (CoStat, CoHort Software, Monterey, CA) has shown differences between roof type and rain events. Runoff samples have been analyzed for several environmental parameters including pH, turbidity, and nitrates. pH was measured using a Hanna Instruments model HI9813, nitrate was measured using a HACH DR890 (Loveland, CO) colorimeter using the cadmium reduction method (Method 8039) and turbidity was measured with a HACH pocket turbimeter model 52600-00. A weather station (Watchdog model 500, Spectrum Technologies, Plainfield, IL) sited atop one of the buildings provided rainfall, temperature, solar radiation, and wind data.

Evapotranspirational model development

This is being done in cooperation with the USEPA. Small (4.5sq ft) greenroof modules are hung from load cells in the greenhouse. Half of the modules are vegetated with Sedum and Delosperma and half contain only the greenroof medium. The object is to determine the contribution of plants to the greenroof systems ability to absorb and transpire water. Preliminary estimates suggest that plant, exclusive of the medium, can absorb up to 25% of a rainfall event.

Roof membrane testing

Roof membrane testing: The PSCFGRR is presently negotiating with a major manufacturer to begin evaluations of American roof membranes using the widely accepted German FLL membrane testing procedures.

Media analysis

The Penn State Soil Testing Lab has recently installed new equipment and is setting up procedures that will allow us to duplicate the German FLL medium testing procedures.

Interaction of medium depth and drought stress on the establishment of succulents.
This is the basis for an MSc thesis by Ms. Christine Thuring. Drought stress was given early in the summer and late. Preliminary results suggest that early drought stress is particularly harmful. However, some succulents appear to withstand drought stress imposed by medium depth much better than others.

How long can Sedum cuttings survive on a roof without irrigation yet root when irrigated?
This seemingly simple project has suggested that sedum cuttings can remain turgid for 3 weeks yet still develop adventitious roots when placed in a rooting environment. Tough customers!

Additional research areas being examined at the Penn State Center for Greenroof Research include:
• Plant competition analysis
• Plant hardiness evaluation
• Media evaluation including the effect of various amounts or organic matter on plant growth

Plant growth and spread

Objective: Determine how rapidly Sedum and Delosperma taxa cover the medium surface.

Materials and Methods: On May 23, sedum plugs (72’s that were 1.5” wide x 3” deep) were planted into circular pots in a highly porous, expanded clay-based medium (dry bulk density = 42lbs/cubic ft.) suitable for green roofs. Pot dimensions were 14” wide and 5” deep and were originally designed as hanging basket containers. After the plugs were transplanted planted, each pot received 10 g of surface applied Osmocote 14-14-14 and were watered in.

				Plant varieties are as follows: Delosperma aberdeenense Delosperma nubigium ‘Basutoland’ Sedum acre ‘Aureum’ Sedum album Sedum album ‘Murale’ Sedum floriferum ‘Weinenstephaner Gold’ Sedum reflexum Sedum sexangulare Sedum spurium ‘Fuldaglut’ Sedum spurium ‘Roseum’
				There were 10 plant varieties, each with 3 replicates. Pots were arranged in a completely randomized experimental design. On May 20, and at 2-week intervals each pot will be photographed. Photos were transferred to Adobe Photoshop, sized, printed, and the outline of each plant cut out and weighed to determine a relative growth rate for each taxon.

Stock beds and hardiness evaluation

Ten 4' x 8' test beds were constructed. Each bed has a bottom that is sloped (1:12), covered with a drainage mat and is 3.5" deep.

Modeling roof runoff

Green roof test buildings

The facilities at the Penn State Center for Green Roof Research consist of 6 buildings, 3 with green roofs and 3 with conventional, non-green roofs. The green roofs are a modified layer system utilizing an Enkadrain drainage layer overlain with 4" of an expanded clay-based growing medium, and covered with PEPP (Porous Expanded Poly Propylene). The PEPP sheet has 1" diameter holes on 3" centers into which we inserted rooted cuttings of Sedum spurium. Roofs were watered several times to promote establisment, but we do not expect to provide further irrigation.

A weather station that collects data on rainfall, solar radiation, temperature, and wind speed and direction serves to collect ambient environmental data for all buildings.

Extensive heat flux, storm water runoff, and nutrient filtration data are being collected from each building. Each buildings is fitted with thermisters in the walls, roof and floor. Each green roof is fitted at each of 4 locations with 7 thermister sensors in a vertical array. Thus each green roofed building has 39 total sensors and each non green building has 14 sensors. The thermisters in each building are connected to a Campbell Multiplexer In turn, each Multiplexer is connected to a Campbell 23x data logger in the data collection building. Sensors are prompted every 30 minutes and data are collected continuously. Each building is fitted with a heater and an air conditioner whose energy consumption is recorded by a watt-hour meter installed in each building. These data will be utilized to evaluate, modify, and enhance existing (German) technologies and new green roof system technologies for use in North America. Basic research projects will include development of storm water management computer aided design tools for green roofs and standard testing protocols for roof systems and components suitable for North American construction techniques and climatic conditions. Energy balance, including heating and cooling requirements, will be measured for green roof systems and computer models developed. Drought, and high and low temperature tolerant plants will be evaluated and physiological, biological, and ecological factors influencing plant survival and roof function will be studied. The Penn State Center for Green Roof Research will involve both graduate and undergraduate students in these research projects to provide workforce training

Above: Green roof building structures at the Russel Larson Agricultural Research Center

Right: Graduate Student Julia Denardo at the data collection station

Building heat flux

Stormwater management

Summary of a Rainfall Event Green roofs retain and detain (slow down) stormwater runoff. The graphs below are a compilation of data from research buildings (3 greened and 3 non-green) at the Center for Green Roof Research at Penn State located at Rock Springs, PA. Spring, 2003 was very wet and cool.

Start	5/31/03 4:33 AM
End	6/1/03 10:33 AM
Duration (hrs)	30
Interevent interval (hrs)	51.75

	Inches
Total rain	1.11

Runoff non-greened	0.984 ±.075
Runoff greened	0.746 ±.018

Peak runoff	inches/5min	% of rain
Rain	.05	100
Non-greened	.041	82
Greened	.011	22

Percent runoff
Non-greened	88.65%
Greened	67.21%

Percentage retained
Non-greened	11.35%
Greened	32.79%

Amount retained (in)	0.364
Cumulative (5/23-6/1)	inches
Total rain	2.21
Total retained by green roofs	1.045	47.29%

Rainwater nutrient amelioration

Neutralizing acid rain

Do green roofs remove pollutants from rainfall? This photo illustrates some of the renovation power of plants. Most green roof media have organic matter (OM) incorporated into the mix at 15-20 % by volume. When water passes through green roof media, humic acids contained in the OM are washed through. Humic acids occur naturally in great abundance in runoff from swamps which contain large quantities of organic matter. Humic acids do no harm when they are conveyed away from the roof in storm drains, but may slightly discolor a new concrete sidewalk below the rain gutter downspout. Even if plants were grown in media that contained no OM, humic acids would be present due to the natural buildup of OM in the system and to the break down of plant parts, especially roots, which die and form humus. Studies are currently underway at Penn State to better characterize root recycling in sedums most commonly used as green roof plants.

Financial Support

Alcoa	Solite Corporation
Big River Industries	US Hydrotech
Colbond, Inc.	Scott’s Landscaping
Emory Knoll Farms	US Environmental Protection Agency
Garick, Inc.	PA Dept of Environmental Protection
Laural Valley Farms	Penn State Institutes for the Environment
Roofscapes, Inc.	College of Agricultural Sciences