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Low slope roof

Posted by GreenDog194 (My Page) on
Wed, Apr 11, 12 at 16:40

Has anyone applied a roof with 2" - 3" river rock ballast over a membrane on a low-pitched roof? Does it look good? Is it a pain to maintain (I suppose I don't mind moss -- could become a green roof here in misty Seattle). Do the stones gunk up the downspouts?

Here is the background:

We have a vintage 50s's house with a single layer torch down roof well-maintained with silver paint (probably asbestos). The original blue prints called for "marble chip" roof, so presumably this roof is not the original roof. We are doing a remodel and would like to add insulation to our roof (our roof is also our ceiling, which is exposed cardecking). There is no attic. We also live in a neighborhood with view covenants, so that 6 inches of rigid insulation had to be approved by the neighborhood board. Our pitch is just a bit more shallow than what you need for a standing seam metal roof, which I think is our first choice (looks nice and our roof is what you see the most of coming down the hill approaching our low-slung house. Perhaps metal is still an option, but either it would go over a membrane roof (paying for two roofs), or the metal would need to be folded over at every seam very tightly.

I don't like the look of the light grey TPO. If we had to do a TPO or PVC, I would want it to be very dark. In Seattle that extra absorption of heat from a dark roof might work to our benefit for most of the year.

So, should we even consider a ballast river rock roofing system?

I love this forum, thanks for your input!!

Follow-Up Postings:

RE: Low slope roof

What is the slope of the roof? What does 2" - 3" refer to? Are you considering an exposed synthetic single-ply membrane as well as a ballasted one? A good black membrane is EPDM (synthetic rubber).

The best membrane under metal roofing is self-adhering modified asphalt (ice & water shield) rather than a single-ply membrane.

RE: Low slope roof

I had to look up river rock ballast roof and I think I get the idea. All I can say is, are you sure those rocks are going to stay put?

When we moved into our home, which was 3 years old at the time, we had a gravel roof on our low pitched roof (between 3 and 4 in 12). Every time it rained we had gravel on the sidewalk around the house. Every time we had a good wind, we had gravel on the sidewalk. It was supposed to be stuck to the roof! Not nice at all. At the first opportunity we changed out that roof; since money was tight, we lived with it for several years. Maybe you could visit some houses with this type of roof and see if the roof rocks are decorating the ground or staying up where they belong.

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