EPDM Sheet Attachment

 
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Old 08-14-2017, 01:41 PM   #1
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EPDM Sheet Attachment


I'm using EPDM on a flat portion of my own home and am looking for advice from anyone who has worked with EPDM over time and know how it can move or shrink.

We are fully adhering the roof with contact adhesive directly to about a 12' x 12' plywood roof deck. We have a change in pitch at two opposite sides of our flat roof where the deck plain turns upward to a 6:12 roof and transitions to composition shingles 4" to 8" up from the flat roof. Detail drawings I’ve found on the internet show a russ, batten, and quickseam on the decking at the transition under a continuous sheet above. This makes sense to keep the sheet taught in the plain of the flat roof, thus preventing the valley from lifting over time. In our case, because the EPDM is fully adhered with contact glue, I’m not sure that lateral shrinkage would be an issue if we just placed the top sheet up the slope without a tie down at the transition.

If this work were on a client's house, I would not even consider doing it any other way than whatever the manufacturer recommended - the manufacturer's details I've found call out bonding adhesive and not contact. I just don't know how much EPDM will/can move when it is fully adhered with contact adhesive directly to the plywood deck. Anyone have experience with this situation?

Last edited by hausfxr; 08-14-2017 at 01:56 PM.
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Old 08-14-2017, 08:50 PM   #2
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Re: EPDM Sheet Attachment


Quote:
Originally Posted by hausfxr View Post
I'm using EPDM on a flat portion of my own home and am looking for advice from anyone who has worked with EPDM over time and know how it can move or shrink.

We are fully adhering the roof with contact adhesive directly to about a 12' x 12' plywood roof deck. We have a change in pitch at two opposite sides of our flat roof where the deck plain turns upward to a 6:12 roof and transitions to composition shingles 4" to 8" up from the flat roof. Detail drawings Iíve found on the internet show a russ, batten, and quickseam on the decking at the transition under a continuous sheet above. This makes sense to keep the sheet taught in the plain of the flat roof, thus preventing the valley from lifting over time. In our case, because the EPDM is fully adhered with contact glue, Iím not sure that lateral shrinkage would be an issue if we just placed the top sheet up the slope without a tie down at the transition.

I
If this work were on a client's house, I would not even consider doing it any other way than whatever the manufacturer recommended - the manufacturer's details I've found call out bonding adhesive and not contact. I just don't know how much EPDM will/can move when it is fully adhered with contact adhesive directly to the plywood deck. Anyone have experience with this situation?

I usually take off several courses of shingles and run the EPDM way up and glue it. There is then several courses of shingles acting as the termination bar. Not sure if that is the situation you are talking about or not.

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Old 08-14-2017, 09:03 PM   #3
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Re: EPDM Sheet Attachment


Frank, it's the change in plain that I'm referring too - I agree that running the EPDM up under the composition shingles should hold the top in place.
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Old 08-14-2017, 09:42 PM   #4
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Re: EPDM Sheet Attachment


Bonding adhesive is a contact adhesive so I am confused what you are referring to to as contact.

If the transition from flat to steep is framed well the rubber should have no problem with you described installation.

The movement of buildings combined with wind uplift and potential shrinking of the membrane make the details prescribed by the manufacturer necessary as a specified standard. It does not preclude the product from functioning in a "modified" installation. IOW, your installation technique is a reasonable modification to the standard in your situation. The manufacturer just prescribes something different and wouldn't be on board with it "technically".

If the membrane does shrink over time, the result would likely only be a void under it local to the pitch change.
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Old 08-14-2017, 11:59 PM   #5
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Re: EPDM Sheet Attachment


Skip the batten strip, that is for a mechanically fastened system
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Old 08-15-2017, 12:01 AM   #6
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Re: EPDM Sheet Attachment


I would also at the very least throw down a layer of celotex. Cheap insurance
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Old 08-15-2017, 02:29 PM   #7
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Re: EPDM Sheet Attachment


When I look at your diagram, I see two batten strips. One at the top, under the shingles. That one appears to be the standard termination bar.

The second that is under the rubber, I have a question on it. They show it, so you need it, but what kind is it? They make a batten strip that goes under the rubber. When you get your rubber to that point, you pull off the protective paper, stick the rubber to it, then continue on.
It is used because the rubber will shrink and pull up from the corners first. When I say corners, I mean inside corners.

As far as how much shrinkage you will experience, no one can say for sure, and it's only a 12' x 12' piece.
What I know from experience, is that it will shrink and pull away from the inside corners.
You will be able to go up there, in a few years, and the rubber will be spanning over the inside corners, a few inches.
This doesn't happen in every single instance, but I see it alot. It could be, I'm seeing it because almost anyone can get rubber and install it.

You are using the contact cement to install the rubber. That doesn't matter. It will still shrink and pull apart at the contact cement. Or Bonding cement, whichever you want to call it.

Even when it does shrink, the roof won't leak and it won't really be a problem for many years.

I know of a roof that was done 25 years ago. It probably pulled away from the parapet wall, about 20 years ago. The owner doesn't want to spend any money to fix it. It still doesn't leak. I'll bet it's lifted up and spanning at least 6" over the deck, near the corners.
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Old 08-15-2017, 04:20 PM   #8
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Re: EPDM Sheet Attachment


Thanks BuildItGuy,

That's the sort of advice I was looking for concerning experience with shrinkage.

We'll install aluminum termination bars per the detail.

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