Why Do Flat Roofs Have Rocks On Them

This is for a roofing membrane that is not fully adhered to substrate and the pebbles are essentially acting as a paperweight.

Why do flat roofs have rocks on them.

It has a very low slope between 1 4 to 1 2 inch per foot so that it drains water. A flat roof is a roof which is almost level in contrast to the many types of sloped roofs the slope of a roof is properly known as its pitch and flat roofs have up to approximately 10. Flat roofing is not actually flat. 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. The gravel provides a better grip for foot traffic when conducting maintenance or repairs. If the roof is what is called a ballast roof it is not fastened or adhered down throughout the whole 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. Roofing ballast is usually the little pebbles you see on a flat ish roof.