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Roofing and Siding since 1985
Sat, May 16 2026,12:07pm [ Login ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 1, [2], 3 ]
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Date Posted: Wed, Nov 27 2002, 7:00am
Author: Chip Natrin
Subject: Water Traveling Uphill

I added a relatively flat 80 ' lg. porch to a house, new construction. It is a plywood deck with a slope of 3/4" per foot, run of only 8 ft. I installed a GMS roof, where I nailed on a drip edge, nailed down the underlay to the plywood, then glued the GMS to the underlayment. Here's the problem and I can't seem to fix it. When it rains, most of the water runs off the edge of the roof. But some of it rolls around the edge of the roofing, then travels uphill on the underside of the GMS and goes under the underlayment. This get the fascia, edge of plywood, and rafter tails wet. I tired caulking the GMS down with a commercial sealant, but it wasn't sticky enough and didn't help. Now I am thinking of pulling off the edge strip amd replacing it with a piece od sheetmetal, which I will run up between the GMS and underlayment about 3", caulking the top edge of the metal to the underside of the GMS and nailing on thru the fascia. Does this sound like it will work? This is driving me nuts! I'm ready to tear off the roof and try again, but I don't know what I did wrong! Any advice will be appreciated!

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Replies:

[> Re: Water Traveling Uphill -- A Roofer, Thu, Nov 28 2002,12:05pm

CertainTeed makes Flintastic GMS and that is a Modified Bitumen roof. I suppose it is the granulated stuff also.

"then glued the GMS to the underlayment." You attached this product with some sort of adhesive? Thats a new one to me.

"When it rains, most of the water runs off the edge of the roof." Sound like you didn't run Gravel Stop on your gables.

Here's how I install torchdown products.
- First the whole deck is papered in with a cap sheet using simplex nails.
- All metal has to be primed with an asphalt primer or the Modified Bitumen will not adhere to it.
- A starter metal is installed to the bottom edge of the roof deck.
- I then take small strips that I cut out of a non-granulated torchdown and and run them down the gables sealing them down.
- I then nail down the gravel stop on the gables over the stip that I ran down earlier for a good seal. Gravel Stop has a edge on it that keeps the water from running over the edge of the gable.
- I now install the product. Torching the product down to the prepared deck surface.

Note: The manufacturer claims that the bottom surface of the product must reach 420 degrees for it to properly adhere to the surfaces.

From everything I've read about your post I think you will have to try again. Try to educate yourself a little better on the proper installation procedure for this product before you go at it again so that you won't have to do it a third time. I recommend hiring a experienced professional.

Sorry to hear about your problems,
Tim Soth / A Roofer


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