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Old 03-20-2013, 07:54 AM   #1
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


Hi ,
I am trying to decide on which product to put on a section of low slope roof.
Would like to get some opinions based on actual experience with these products which will be put in a low slope area on a shingled roof with 2 valleys that run into the low slope valley(3 sloped areas run into the low slope area)

1)GAF weather watch under GENFLEX .6 mil TPO-no seams
installed over 1" x 8" plank boards

2)2-ply MULE-HIDE self-adhering mod. bitumen SBS installed on 1/2 " plywood on top of framed cricket to be built to bring to 2/12 pitch -# seams to be determined by installer

3)CARLISLE EPDM .6 mil installed over 1/2" insulation board-no seams

Also, what other questions should I ask in regards to installation?

Thank you for your help!

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Old 03-20-2013, 11:26 AM   #2
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


Tried and true - epdm for flat/low slope roof. Best bang for the buck and will serve you well.

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cgeorgette (03-20-2013)
Old 03-20-2013, 12:19 PM   #3
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


60 mil EPDM no seams and 1/2 Dens deck not 1/2 fiberboard or ISO.
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Old 03-20-2013, 01:06 PM   #4
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


With that much slope to drain I would go with the two ply SBS self adhered with the addition of a ASTM 4601 type 2 Glass base sheet screwed to the plywood with roof deck screws and 3 inch plastic plates. I usually like metal plates, but they can cause thermal bridging, especially with no insulation package. The glass base gives you a shear plane between the plywood and the membrane, and a two ply SBS gives you a very tough roof membrane, resistant to missiles like branches and hail. I do not know the mule hide products but if they have a glass reinforced first ply, and a polyester reinforced granular cap ply that's the way to go. Make sure the SBS goes up the steep slope about a foot, strip in the top, then bring the felt and shingles down over 6 inches.
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Old 03-20-2013, 01:37 PM   #5
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


Quote:
Originally Posted by gordieax View Post
Tried and true - epdm for flat/low slope roof. Best bang for the buck and will serve you well.
Why do you prefer EPDM other than price? Have you seen the other products fail more often in your experience?
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Old 03-20-2013, 01:50 PM   #6
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


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Originally Posted by jagans View Post
With that much slope to drain I would go with the two ply SBS self adhered with the addition of a ASTM 4601 type 2 Glass base sheet screwed to the plywood with roof deck screws and 3 inch plastic plates. I usually like metal plates, but they can cause thermal bridging, especially with no insulation package. The glass base gives you a shear plane between the plywood and the membrane, and a two ply SBS gives you a very tough roof membrane, resistant to missiles like branches and hail. I do not know the mule hide products but if they have a glass reinforced first ply, and a polyester reinforced granular cap ply that's the way to go. Make sure the SBS goes up the steep slope about a foot, strip in the top, then bring the felt and shingles down over 6 inches.
I have some concerns about the seams in the sbs self adhered. Is this glass base sheet that is screwed in addition to the 2-ply base layer & cap sheet that is with the SBS self-adhered modified bitumen? I was under the impression that this SBS had adhesive backing. Should I request "insulation package" (what does this consist of?)
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Old 03-20-2013, 01:58 PM   #7
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


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60 mil EPDM no seams and 1/2 Dens deck not 1/2 fiberboard or ISO.
What is dens deck? Is insulation board a generic term for one of the 3 above?
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Old 03-21-2013, 02:45 PM   #8
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


EPDM because transitions are easier with it. It's not necessarily cheaper any more, TPO is actually cheaper for some of the material cost. EPDM has a better track record. easy to repair ect.

Dens deck is a Gypsum roof board, think drywall for a roof. Will provide a good solid surface to adhere the EPDM to. Wood Fiber board (think black jack on the sides of houses) Tends to absorb a good amount of moisture if the membrane is punctured. Dens deck will not well it will but not as bad, it also will help with puncture resistance. And it's much better at keeping the nails from popping up unlike fiberboard.


I personally would not use a self adhered SBS in a low slope valley like this, Front porch, rear sun rooms sure but I distrust the product on anything with minimal slope, plus some people just don't know how to do the details correctly. Now if it was a moped down system then I would fully support it.
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Old 03-22-2013, 09:08 AM   #9
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low slope roof/epdm,tpo,or self-adhered mod. bitumen sbs


Hi Georgette.

1. DensDeck is a high density gypsum board with a fiberglass facer. I think it is being recommended for its puncture resistance. A particular type of deep well insulation plate is required for its use if you go with a single ply, and I would demand flat head square drive (Robertson Head) screws, as you do not get burrs with them.

2. An insulation package is rigid board insulation located above the structural deck, in your case the plywood. When I say Package, I mean a thermal insulation like Isocyanurate foam, topped with a cover board like DensDeck, wood fiber board or other cover board. If you have insulation in your ceiling joists like fiberglass, you do not need, or want insulation above your roof deck. All it will do is heat age your roofing system.

3. Wood decks move quite a bit. That's why you want a shear plane just above the deck. They move a lot when there is no insulation package above them. Consider a sunny day, wherein a thunderstorm pop us. The roof may go through a 100 degree temperature change.

4. A 2/12 slope is more than enough for modified bitumen. I will not use it on a roof that ponds, but for your purposes it is ideal. It is very tough, and you can get it in many colors. I like Siplast, and Soprema, but I do not know who makes the sheet for mule hide. They are a second tier roof supplier.

5. I would NOT use TPO if I were you. If you use Fully Adhered EPDM, use 60 mil, unreinforced, and coat it with Firestone Acryltop Acrylic coating. You can take the coating to home depot and get it tinted to match your steep roof. You can also roll the roof coating on Mod bit, if you use a sanded cap sheet, instead of granular. I think That is what I would do. That roof will last forever.

Regardless of which system you use, install either a cover board, or a shear plane between the wood deck and the membrane.

As in all trades, a good, quality oriented contractor can make a marginal product work well, and a bad, make money fast contractor can screw up even the best product so badly that it has to be torn off. Keep this in mind. If the guy you are using does not know what NRCA, or SMACNA stands for, dont use them.

Get the manufacturers installation instructions and go over every step before the contractor starts. Roofing is sequential, and it is very difficult to go back and fix things that are screwed up. The result is that you usually end up settling for less than you really want.

Last but not least, you may need to use an FR granular surfaced Mod Bit, or fire resistant EPDM to satisfy your home insurance policy. God forbid you have a fire, and they refuse to pay or insure you due to your not having the correct fire resistance classification.

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Last edited by jagans; 03-22-2013 at 09:11 AM.
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