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Fiberglass for roof valleys

Posted by julienola (My Page) on
Tue, Jul 13, 10 at 16:45

Can anyone tell me about the use of fiberglass for roof valleys? I've only heard of using copper or galvanized metal. There's a long (over 35 feet) and deep (about 1 foot at the start) section where the two sections of my roof meet. Unfortunately, I wasn't home when the roofer inspected the project and wasn't able to ask questions. I can't even picture what the material might look like.


Follow-Up Postings:

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RE: Fiberglass for roof valleys

He might mean asphalt/fiberglass roll roofing but it would be a poor choice. How steep is the roof?


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RE: Fiberglass for roof valleys

The roof itself is steep, but I don't know the specifics. The 35 foot valley between the two roofs has very little slope.

Why is fiberglass roll roofing a poor choice? Could it be possible that he's talking about that corrugated material that you see on the sheds and sunrooms?

We think that the valley was originally part of a rain water collection system that emptied into a cistern that was (and still is) inside the house. Sounds crazy, I know.


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RE: Fiberglass for roof valleys

Two steep roofs can't intersect to form a low sloped valley. Perhaps you are talking about some other part of the roof.

Asphalt coated fiberglass roll roofing is thin and brittle. If a valley is low sloped it can have Ice & Water Shield as a base flashing and then the asphalt shingles can weave back an forth across the valley or one side can extend over the valley and the other can be cut back near the line of the valley.

You should talk to the roofer. He was probably talking about something else.


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RE: Fiberglass for roof valleys

I'd have to take a photograph to make the situation clear, but there is almost no slope to this valley--imagine two houses joined together side-by-side and a valley in-between where they connect. The valley goes from the front of the house to the back.

It's a family-owned property and someone else already gave the roofer the go-ahead. I wanted to get some independent opinions before I put my two cents in.

Thanks for responding.


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RE: Fiberglass for roof valleys

Sounds like a low cricket. If so it's a very poor way to connect two roofs. Good luck with it.


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RE: Fiberglass for roof valleys

The roofers ended up leaving the corroded metal flashing and roof roll that I had put on as a temporary measure three years ago. On top, they applied Hydrostop. Macv, do you know anything about that product or system? I know it's too late to change anything, but I'm curious.


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RE: Fiberglass for roof valleys

It's a liquid acrylic waterproofing material that is applied over a non-woven polyester fabric. It's primary benefit is that it can go on top of old roofing which makes it a favorite of budget-minded owners.

The roofers probably think the polyester reinforcement is fiberglass fabric and that there is some kind of resin in the waterproofing.

This stuff was originally called "Cool Roof" in the 80's for DIY roof patching. I used it and thought it found it to be worthless. After the company was sold maybe someone figured out how to make it work. If they gave you a warranty keep the paperwork in a safe place.


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RE: Fiberglass for roof valleys

I hope it works. They charged $3,800 and the job didn't involve re-shingling or anything extra.


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