[Bldg-sim] Modeling a Green Roof

Drury B Crawley dbcrawley at gmail.com
Fri Jun 25 07:24:56 PDT 2010

EnergyPlus has a model for green roofs built in -- based on experimental
measurements and experience of researchers at Portland State University,
Prof David Sailor:  http://web.cecs.pdx.edu/~sailor/

---------- Forwarded message ----------
From: Jeremy Poling <jpoling at epsteinglobal.com>
Date: Fri, Jun 25, 2010 at 10:04 AM
Subject: Re: [Bldg-sim] Modeling a Green Roof
To: Jason.Boehning at ricegardner.com, bldg-sim at lists.onebuilding.org

 Penn State University (http://horticulture.psu.edu/cms/greenroofcenter/)
and Michigan State University (http://www.hrt.msu.edu/greenroof/) both have
significant research programs on green roofs.  I would recommend looking at
the results of the Penn State study on energy transfer in Green Roofs (
In general, green roofs handle energy through the insulating effects of
soil, the cooling effects of evapotranspiration in the plants, and water
flows within the green roof assembly.  This means that a calculated R-value
will be different depending on the amount of plant material participating in
evapotranspiration, the wetness of the soil, and whether the roof is
intensive or extensive.  A straight R-value approach is very simplified and
should be used with the understanding that model results are much less
likely to be accurate.  The Penn State study gives a review of published
literature showing extensive green roofs have R-values between 1.8 and 4.8
while intensive green roofs have R-values between 5 and 20.

In general, the average R-value of soil is 0.25 per inch, so for a 12” soil
depth the R-value of the soil would be R-3 excluding assumptions on soil
wetness and evapotranspiration.  We typically go conservative and just model
the R-value of the additional soil since you would need a TRNSYS or MatLab
model to take into account the other energy benefits of a green roof.

Associate Vice President,

Senior Sustainability Analyst
Strategic Services
*Site Solutions | Operations | Sustainability*


*Epstein is a firm believer in sustainability. We ask that you please
consider the environment before printing this e-mail.*

*From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Fareed Syed
*Sent:* Friday, June 25, 2010 8:05 AM
*To:* Jason Boehning; bldg-sim at lists.onebuilding.org
*Subject:* Re: [Bldg-sim] Modeling a Green Roof

I heard from our director of sustainability to use R-5 for a typical green
roof. It was confirmed by few senior architects.



*From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Jason Boehning
*Sent:* Friday, June 25, 2010 8:46 AM
*To:* bldg-sim at lists.onebuilding.org
*Subject:* [Bldg-sim] Modeling a Green Roof


Has anyone modeled a green roof? I have a standard roof with 12 inches of
soil and grass. I have been searching the web for thermal properties such as
U values, thermal absorptivity and so on. Are there any good references to
find these values or does anyone have tips to model a green roof? I
appreciate your help.

Jason Boehning, EIT

Mechanical Engineer

6161 Savoy, Suite 1212

Houston, Texas  77036

 v.  713.482.2322

 f.   713.482.2314

 e. Jason.Boehning at ricegardner.com

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