Butyl rubber sheeting is, in fact, not made from rubber but is a synthetic copolymer.
As well as being used for roofing membranes, Butyl sheet is used as pond liners. The effective application of butyl for roof membrane needs considerable care and experience. Butyl sheet is heavy to manipulate on site. The edges need to be weighted down as the butyl is laid to ensure that wind does not lift and wrinkle the sheeting as it is spread out in position.
Butyl is often “loose laid” over the greater parts of flat roofs with only the edges and upstands being glued down; the concept being that the weight of the butyl will keep the membrane in place.
Leaks in butyl rubber roof coverings are often the result of the failure of edge adhesion leading to water building up under the loose butyl and causing raised “blisters”. Under freeze/thaw stresses the trapped water can cause the degradation of the butyl from the underside as well as impacting upon the structural integrity of the roof’s substructure.