GAFGLAS® Stratavent® Perforated Venting Base Sheet is a premium-grade roofing felt constructed around a strong glass fiber mat and high-quality asphalt. The bottom of the sheet is granule-surfaced to provide positive venting of any trapped gases under the roof membrane. GAFGLAS® Stratavent® Perforated Venting Base Sheet is a venting base sheet designed to be used in various GAFGLAS® built-up and RUBEROID® modified bitumen roofing systems. It can be used over both nailable and non-nailable substrates, including certain existing old roof surfaces and isocyanurate foams.