[Greenbuilding] epdm vs. tar

[Michael O'Brien]

Hi, all--

I wonder if the assessment of EPDM still applies when it is used in a green roof, where the plants and medium shield it from UV exposure and reduce the expansion and contraction due to day/night temperature swings?

Most of the leaks that have occurred in green roofs here in Portland have resulted from incorrect or inadequate detailing, such that water gets into joints where membrane meets edges. For example, architects use internal roof drains on commercial buildings, and they seem more likely to get blocked up for unanticipated reasons, like snow piling up. I have yet to hear of any membrane failures per se, although we are only about ten years into building green roofs. 

BTW the next building code cycle in Oregon will include green roofs as a standard application.

Best,

Mike O'Brien


On Sep 10, 2011, at 2:30 PM, jfstraube wrote:

> I have idea who Gennaro is taking to, or what "layers of torch down" means, but anyone with any experience in roofing will tell you that a twp-ply modified bitumen (perhaps this is what you mean) will last twice as long as 60 mil EPDM. 
> In fact, in a all federal government buildings, the design standard explicitly does not allow single-ply membranes like EPDM, and strongly advises two ply mod-bits or multi-ply liquid-applied hot rubber roofing based on their track record of hundreds of buildings over several decades.
> 
> But, hey, if some local roofer tells you EPDM is the way to go, you could believe them.
> 
> 
> On 2011-09-10, at 11:49 AM, Gennaro Brooks-Church - Eco Brooklyn wrote:
> 
>> Michael,
>> That sounds like a bombproof roof. My thought would be that maybe you
>> could get away without doing the two layers of torchdown.
>> I have asked some other green roofers and they agree that EPDM is a
>> good first choice. It performs two functions - waterproofing and root
>> barrier. You can do torchdown but then you have to install a solid
>> root barrier, and we're not talking those cheap rolls of black felt
>> you buy in garden centers. It has to be the kind that is used to keep
>> tree roots and bamboo from spreading, which at that point you might as
>> well just do the one step EPDM.
>> I have seen torch down roofs laid with plastic and then the green
>> roof, but the roofers I've spoken to agree that you are not creating a
>> long term root barrier.
>> Gennaro Brooks-Church
>> 
>> Cell: 1 347 244 3016 USA
>> www.EcoBrooklyn.com
>> 22 2nd St; Brooklyn, NY 11231
>> 
>> 
>> 
>> 
>> On Sat, Sep 10, 2011 at 1:06 AM, Michael O'Brien <obrien at hevanet.com> wrote:
>>> Hi, Gennaro--
>>> 
>>> We used two layers of asphalt torchdown over plywood to seal the roof, and then we laid EPDM over that, mainly to create a root barrier as plants can get through asphalt. Our roof is sloped so we installed perforated metal dividers horizontally to prevent our planting mix from sliding on the EPDM. Four years on, seems to be doing fine.
>>> 
>>> Best,
>>> 
>>> Mike O'Brien
>>> 
>>> 
>>> 
>>> On Aug 28, 2011, at 8:13 PM, Gennaro Brooks-Church - Eco Brooklyn wrote:
>>> 
>>>> Let me be more clear. I install EPDM roofs and green roofs on top of
>>>> that because I think it is better than a simple roll on tar roof. So I
>>>> get a lot of clients coming to me wanting me to explain why they
>>>> should do EPDM (and maybe a green roof) instead of roll on. I'm
>>>> looking for substance from you all to add to my explanation. I'm not
>>>> sure I have my facts right or maybe I'm leaving something out.
>>>> 
>>>> Here is what I say more or less.
>>>> Tar roof - lasts 10 years, $10 to install (for argument sake)
>>>> EPDM - 20 years, $20 to install
>>>> Green roof - extends EPDM by 10 years, $20 to install
>>>> 
>>>> Tar roof needs to be cleared off every three layers - $10 to clear off.
>>>> 
>>>> So....over 30 years.
>>>> Tar roof - $40, more petro chemicals consumed, more waster created.
>>>> EPDM + green roof - $40, not including cooling savings (any guess on
>>>> this?), quality of life, no heat island effect, reduced water run
>>>> off...
>>>> 
>>>> Your thoughts? How do my numbers look?
>>>> 
>>>> Gennaro Brooks-Church
>>>> 
>>>> Cell: 1 347 244 3016 USA
>>>> www.EcoBrooklyn.com
>>>> 22 2nd St; Brooklyn, NY 11231
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Sun, Aug 28, 2011 at 8:35 PM, Gennaro Brooks-Church - Eco Brooklyn
>>>> <info at ecobrooklyn.com> wrote:
>>>>> Hi,
>>>>> Does anyone have life span of EPDM vs. typical tar roll on roofs?
>>>>> Gennaro Brooks-Church
>>>>> 
>>>>> Cell: 1 347 244 3016 USA
>>>>> www.EcoBrooklyn.com
>>>>> 22 2nd St; Brooklyn, NY 11231
>>>>> 
>>>> 
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>>> 
>>> Mike O'Brien Photography
>>> 1905 N Alberta Street
>>> Portland, Oregon 97217
>>> 
>>> 
>>> 
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>> 
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> 
> John Straube
> www.BuildingScience.com
> 
> 
> 
> 
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