[Greenbuilding] epdm vs. tar g(r)een roof

[John Straube]

Whatever the motives of researchers almost all compare Green roofs to exposed membrane black roofs. 
The reason the conventional roof is conventional is because it is cheap. Eg EPDM on polyiso for $2 per square foot installed! Hard to find green roofs under $20. 

I like green roofs. I have one on my own apartment. But the studies do not justify the cost premium any more than they justify granite in the lobby: I personally paid the premium to have a good looking roof. I know cheaper and better ways to safe energy control stormwater protect the membrane etc etc. But I try to keep the science clear and I can't honestly explain green roofs on economical or technical grounds. 


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-----Original Message-----
From: RT <Archilogic at yahoo.ca>
Sender: greenbuilding-bounces at lists.bioenergylists.org
Date: Mon, 29 Aug 2011 15:11:22 
To: GBioEL<greenbuilding at lists.bioenergylists.org>
Reply-To: archilogic at chaffyahoo.ca,
	Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] epdm vs. tar g(r)een roof

On Mon, 29 Aug 2011 11:31:37 -0400, John Straube <jfstraube at gmail.com>  
wrote:


> Speaking of cooking the books, Dr Lui's report, like most you will find,  
> over sell the performance benefits of green roofs.  They do this by  
> comparing an excellent green roof design with the dumbest low slope roof  
> we know how to build (an exposed membrane black roof).

I don't know if this is a fair criticism.

The first study that Dr. Lui did used a conventional roof that was  
available on the NRC campus, and she simply installed a rudimentary Green  
Roof over one half of the roof and then monitored what the two did over  
the course of a year or so.

I think that was a fair comparison that highlighted the benefits of a  
Green Roof over a "conventional" one because the "conventional" is a  
fairly common type throughout North America.

At the time, I suggested to Karen that to be fair, her next study might  
involve an IRMA (for comparison of thermal benefits) or a PMR and she  
agreed,  while at the same time wincing and rubbing the fingers and thumb  
of an up-turned hand together indicating that acquiring funding was the  
biggest problem. I don't know if Karen ever got the funding to do further  
studies.

A PMR would of course provide similar protection for the membrane and  
perhaps a similar reduction  in the cooling load (my guess is most likely  
"less" due to minimal contribution via evaporative cooling) but then the  
Green Roof goes further and provides additional benefits which in an urban  
core setting, extend beyond financial.

Do Green Roofs make much sense in a climate like Canada's where greenery  
is either dead or dormant for a third or a quarter of the year ?  Nyeh.

-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
(manually winnow the chaff from my edress if you hit "reply")

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