[Greenbuilding] epdm vs. tar geen roof

[John Straube]

Practical experience with EPDM roofs is that they do not have great durability.  This is one reason they, and TPO, are almost never used in green roofs. I would also assume you would be specifying a protected membrane roof in any case you care about durability.  Worry about which membrane uses more or less oil or energy seems completely misplaced if there is a trade off with durability which there will be with roofing products. Pick the most durable, or nearly the most durable, roof membrane and save environmental impact on the life-cycle. 
Tar roof is not sufficiently specific to make judgements.  There are many types.
I would always recommend either a two-ply modified bitumen roof, or liquid applied glass matt reinforced hot rubberized asphalt if all you cared about was durability.

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).   A fair comparison is to compare a green roof to a protect membrane roof (PMR) with white balast (pavers or river rock).  When this is done the energy savings and durability benefits of a green roof essentially vanish.  The benefits of dust removal, stormwater retention remain.  There are cheaper ways to retain stormwater than a green roof.  The reason for a green roof is mostly because they are beautiful to look at relative to the options, and in intensely urban areas they add to biodiversity (they don't do much in rural settings).



On 2011-08-29, at 10:20 AM, RT wrote:

> On Sun, 28 Aug 2011 23:13:45 -0400, Gennaro Brooks-Church - Eco Brooklyn <info at ecobrooklyn.com> wrote:
> 
> 
>> So....over 30 years.
>> Tar roof - $40, more petro chemicals consumed, more waster created.
>> EPDM + green roof - $40,
> 
>> Your thoughts? How do my numbers look?
> 
> 
> I'd say that the numbers look like they were "cooked" by someone who might have done creative book-keeping for Tony Soprano et al.
> 
> But aside from that, all or most of the benefits in the comparison are due to the Green Roof component and a Green Roof can be installed over any waterproof membrane and provide the same benefits.
> 
> Without actually checking the actual numbers (not my job, eh ?) I have a gut feeling that the embodied-energy of a hot-mopped tar membrane is lower than that of an EPDM.
> 
> But using Gennaro's numbers for life expectancy -- 30 years -- I'd say that that's pretty ?!$$-poor performance (PPPP or 4P).
> 
> Any Greenie worth their chlorophyll would shun asphalt shingles as a sloped roofing option largely because of their short service life (30 years max) and their high waste factor (ie not recyclable for the most part) so it's curious that one would consider a 30-year tar or EPDM membrane as viable options for a flat roof.
> 
> That is to say, perhaps third, fourth or fifth non-petro options might be considered for the membrane (the Green Roof being a "given" if for no other reason, because it extends the life of the membrane, like IRMAs).
> 
> The other benefits are quantified in Dr. Karen Lui's report (if the IRC at NRC) which I've cited here numerous times in the past.
> 
> -- 
> === * ===
> 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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Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com