Why Do Flat Roofs Have Rocks On Them

Because the gravel holds and releases heat the layer of gravel on a bur flat roof can both help water evaporate and keep heat away from the underlying roof structure.

Why do flat roofs have rocks on them.

Ideally the stones are river gravel which has smooth edges and won t cut into the roof when somebody walks around on it. It has a very low slope between 1 4 to 1 2 inch per foot so that it drains water. If the roof is what is called a ballast roof it is not fastened or adhered down throughout the whole roof. Roofing ballast is usually the little pebbles you see on a flat ish roof.

Rocks are placed on commercial flat roofs for many different reasons. But such a low slope holds snow and water much longer than a steeply pitched roof and therefore needs a very different material to stay watertight. This is for a roofing membrane that is not fully adhered to substrate and the pebbles are essentially acting as a paperweight. Flat roofing is not actually flat.

Why not fully adhere. Talk to ten roofing contractors and you ll get ten answers on what the gravel is for but this seems to be the consensus.