[Greenbuilding] epdm vs. tar geen roof

[JOHN SALMEN]

I would agree about 2 ply bitumen as a decent option at least from
durability and recycled content. I disagree about simpler methods for
stormwater retention - which is probably one of the most redeeming features
of a green roof (adding stormwater quality to that). Most other methods are
ground invasive and require a different and costly level of engineering and
technology (even a good porous parking lot is difficult to do well).

-----Original Message-----
From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of John
Straube
Sent: August-29-11 8:32 AM
To: Rob Tom; Green Building
Subject: Re: [Greenbuilding] epdm vs. tar geen roof

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


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