Roof Ballast Rock

Next the membrane is rolled over the insulation 2.

Roof ballast rock.

A ballasted roof means that the roof membrane is not anchored or adhered in any way to the decking material. In windy areas ballast stone can actually blow off the roof creating projectiles below. Ballast is commonly used with roofs made of tar and gravel roof alternatives including ethylene propylene diene monomer epdm polyvinyl chloride pvc and thermoplastic polyolefin tpo single ply flat roofs. When the concept first came to the u s plenty of roofers scratched their heads and wondered how the roof stayed on without being anchored especially during high winds or storms.

Ballast stone can crush the underlying insulation creating weak spots in the roof membrane. Single ply roofing materials aren t self adhered nor are they sealed together in any way. The buildup is ballasted with a gravel layer of at least 50 mm and 80 kg m 2. Gravel ballasted roofs with sikaplan or sarnafil single ply membranes are conventionally installed.

Despite the positive qualities associated with a ballasted roof system there are some challenges. Stone ballast is no longer allowed by many building codes. The single ply membrane and other roof components including thermal insulation are loose laid. The gravel top coat is also extremely resilient to heavy foot traffic and high wind scenarios.

Over time the stones move around creating bald spots where the system isn t held down at all. The ballast is used to keep the roofing system cool and of out of the sun s harmful rays thus keeping energy costs down. It is however ballasted generally with gravel.