why do they put rocks on flat roofs

I assume you re not talking about rocks meaning boulders, but rather the layer of small stones you see not just on gas stations but on many flat roofs. Ideally the stones are river gravel, which has smooth edges and won t cut into the roof when somebody walks around on it. Talk to ten roofing contractors and you ll get ten answers on what the gravel is for, but this seems to be the consensus:
(1) Stabilization. In a typical tar-and-gravel roof (which, by the way, is gradually being supplanted by gravelless roof systems), you put down a layer of tar paper, then tar, and finally gravel.


Tar has a low melting point. In the summer it gets pretty soft and if left to its own devices would flow to the lowest point on the roof. The stones force it to stay put. (2) Protection. The gravel prevents sun, hail, errant baseballs, etc. , from damaging the membrane, the all-important moisture seal created by the tar paper and tar. (3) Ballast. The stones keep the tar paper in place and prevent it from buckling or blowing away in a high wind. That s all there is to it. My regards to mom.


Send questions to Cecil via The layer of gravel on a low slope / flat roof is used to help keep the underlay fabric secured and to provide some protection from the elements and human interference. This roof type is typically composed of overlapping layers of tar paper or rubber sheeting separated by tar. Putting a thin layer of gravel (usually river gravel for the smooth edges) on top of the top tar layer will keep the tar from running as much during hot weather thus reducing the risk of a leak developing. It also provides a safer, cleaner, more stable footing for anyone on the roof, as well as protecting the roof from that person s weight.


It keeps hailstones, errant baseballs, etc. from damaging the waterproof seal created by the paper and tar, as well as helping to keep the layers in place. Flat roofs in my experience are seldom totally flat. Most of the ones I have been up on had a tiny bit of slope to them to feed water to the edges for removal. Source: Carried more than a few rolls of felt paper up those steep ladders back in the days of my youth.

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why do you put gravel on a flat roof
why do they put rocks on roofs
why do they put rocks on flat roofs
why do they put gravel on roofs
why do they put gravel on flat roofs
why do they put gravel on flat roofs
why do they put gravel on roofs