Abstract: An improved membrane roofing arrangement is designed to eliminate the problem of "blistering" in prior art single membrane system.The membrane roofing arrangement comprises a perforated underlay sheet interposed between a single membrane and the roof, the perforated sheet preventing adhesion of the membrane to the roof at the non-perforated portions of the underlay sheet. In this manner, paths are provided between the membrane and roof for venting vapor to the edges of the membrane and/or suitable vents, thereby eliminating blistering of the membrane.