# Correct Substraight for EPDM roof.



## Warmsmeallup (Apr 2, 2008)

We install a snow and ice melting system under asphalt or metal roofs. We have an application where we are to be on top of a fiber board that is the substraight for a .60 EPDM roof. Is this the correct substraight for under EPDM? Have any of the roofers out there ever applied a membrane in this fashion? What are the benefits or negatives, if any?

Thanks in advance...


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## tekwrytr (Sep 11, 2007)

Warmsmeallup said:


> We install a snow and ice melting system under asphalt or metal roofs. We have an application where we are to be on top of a fiber board that is the substraight for a .60 EPDM roof. Is this the correct substraight for under EPDM? Have any of the roofers out there ever applied a membrane in this fashion? What are the benefits or negatives, if any?
> 
> Thanks in advance...


You are going to put the snow and ice melting system on TOP of the fiberboard, and UNDER the EPDM? Are you leaving something out about the installation? And has anyone (like an engineer or architect) considered the coefficient of linear expansion of the EPDM under varying temperature scenarios that might occur with such a system?
Thanks


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## Warmsmeallup (Apr 2, 2008)

The subject of the posting wasn't the installation of the snow melting system so I left nothing out. However, yes, the element goes between the substraight and the EPDM. We prefer laying 1/4" plywood over the top of the element to protect it for the time in the future when the EPDM needs replacement and the element doesn't. The removal of the plywood with the EPDM will allow continued use of the element.

Look up Zmesh under non-metalic surfaces. Then, if you'd like to answer the original question, I'll keep an eye out for it.

Is fiber board preferred to plywood under the EPDM as a sub? If so, why?


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## Gilby (May 15, 2009)

*Hmm*

With an EPDM roof it can be tricky. It also would depend on whether it is a Ballasted roof system or just pressure bared down. I feel that it would depend on whether the heat would expand or contract the EPDM material. In my personal opinion i feel it wouldnt be a good thing.


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## Warmsmeallup (Apr 2, 2008)

This is a non-ballasted, fully glued down (contact glue on both surfaces) application.


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## apehangeralfy (Oct 26, 2008)

How are you attaching the plywood?

1/4" could have some cupping and is not up to code here...


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## Warmsmeallup (Apr 2, 2008)

UUMM...let's change the tact....

Is a 1/2" fiber board substrate the correct application (instead of plywood or OSB) under a fully adhered Carlisle .060 EPDM roof?

This fiber board looks like ...compressed horse hair, for the lack of a better description, but it's not horse hair. When it cut with a knife, you can cut full through by hand and bend it to break it from there. Little "fibers" blow in the wind when it's cut. 

Our concern is that the glue will only adhere to the surface of the board and since it can be broken by just bending the board in half, the membrane could lift off with the top layer in high winds...like that are near a major international airport on the East coast.


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## Warmsmeallup (Apr 2, 2008)

Gilby said:


> I feel that it would depend on whether the heat would expand or contract the EPDM material. In my personal opinion i feel it wouldnt be a good thing.


The radiant system does not get hot, perse'. It will bring the EPDM up to ...maybe 40 degrees. Just enough to keep the snow from building and allowing it to flow off the roof and down the spout to the ground. So the issue is not really with the radiant system. It's with the possibility that the EPDM will lift off the fiber board and take the element with it.


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## BULLHART (Oct 14, 2006)

To answer your question, yes fiberboard is preferred to plywood/osb. But both of these substrates are at the very bottom of the list.


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## tekwrytr (Sep 11, 2007)

Warmsmeallup said:


> The radiant system does not get hot, perse'. It will bring the EPDM up to ...maybe 40 degrees. Just enough to keep the snow from building and allowing it to flow off the roof and down the spout to the ground. So the issue is not really with the radiant system. It's with the possibility that the EPDM will lift off the fiber board and take the element with it.


 
40 degrees will keep the snow from building? We are talking about flat roofs, not sloped roofs. Have you ever installed this system on a flat roof? Unless it someone's porch, or a flydeck, you may have some problems with generating enough heat to facilitate drainage after a bit of snow. The new snow would tend to chill the surface faster than the element would warm it. 

The issue with recovery board as an adhesive base is well taken; EPDM roofs in high wind areas can peel, because the "fully-adhered" part is only stuck to the surface of the recovery board. There is little or no penetration of the adhesive beyond the surface of the recovery board. That is, a "fully-adhered" EPDM roof is almost as easy to strip as a ballasted roof with the ballast removed. 

BTW, "substrate" is the commonly-accepted spelling. Same root as strata. 

Thanks


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## Warmsmeallup (Apr 2, 2008)

tekwrytr said:


> 40 degrees will keep the snow from building? We are talking about flat roofs, not sloped roofs. Have you ever installed this system on a flat roof? Unless it someone's porch, or a flydeck, you may have some problems with generating enough heat to facilitate drainage after a bit of snow. The new snow would tend to chill the surface faster than the element would warm it.
> 
> The issue with recovery board as an adhesive base is well taken; EPDM roofs in high wind areas can peel, because the "fully-adhered" part is only stuck to the surface of the recovery board. There is little or no penetration of the adhesive beyond the surface of the recovery board. That is, a "fully-adhered" EPDM roof is almost as easy to strip as a ballasted roof with the ballast removed.
> 
> ...


Sure, lot's of flat roofs. As long as there is a way for the water to get off the roof in the rain (drainage or slope to a drip edge), 40 degrees is plenty warm enough to melt the snow on contact, preventing it from building up. Our element does just that. The system activates within the first 2 minutes of snow fall. It warms the surface preventing snow from building at all.
 
The problem we're having is that the roofer is claiming that the membrane won't adhere where ever our element is and it will prevent adhesion. Our element is a screen that allows the glue to pass through it to adhere to the base below. My point is exactly what I've mentioned here and you concurred. I don't believe that a recovery board is a good base for adhesion in the first place.

In fact, our element, that is in this application, nailed down and through the 'recovery-board' to the plywood substrate below it, will actually create a better bonding surface for the EPDM's adhesive.

"SUBSTRATE"  Yeah, I got that yesterday! Thanks.


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## apehangeralfy (Oct 26, 2008)

I'd make a call to the manufacture of both companies involved...


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