Metal Roofing Underlayment
UNDERLAYMENT
Metal roofing should be installed without dependence on the underlayment beneath it. However, metal roofing can develop condensation on its bottom side during certain climatic conditions. Therefore, it is jeopardizing the durability of your roof system to use a product which does not specify a quality underlayment such as 30-pound felt or one of the new polyethylene-based underlayments. If you're in an area prone to high humidity or salt air and fog give special consideration to rust-free metals such as aluminum, copper, and zinc. Weather conditions can create the retention of condensation between the panels and the underlayment. Particularly with steel products which rest on or near the substrate such as standing seam, 5-V crimp, and low-profile steel shingles, this condensation can cause them to rust from underneath. Keep in mind that failures with steel roofing occurs from cut edges on the back side of the metal and rarely from the front weather side.
Both traditional and modern metal roofing systems are well suited for breather membranes. Traditional metal roofs suffer from condensation generally at the level of the felt underlayment or the slip sheet. A breather membrane can act as both a waterproof secondary roof and a slip sheet. Modern composite metal roofs suffer from internal condensation that can eventually compromise the insulation and even possibly the securement. Breather membranes allow water vapor to escape by condensing on the underside of the metal roof, dripping back onto the underlayment and draining to the eave.
Metal roofing should be installed without dependence on the underlayment beneath it. However, metal roofing can develop condensation on its bottom side during certain climatic conditions. Therefore, it is jeopardizing the durability of your roof system to use a product which does not specify a quality underlayment such as 30-pound felt or one of the new polyethylene-based underlayments. If you're in an area prone to high humidity or salt air and fog give special consideration to rust-free metals such as aluminum, copper, and zinc. Weather conditions can create the retention of condensation between the panels and the underlayment. Particularly with steel products which rest on or near the substrate such as standing seam, 5-V crimp, and low-profile steel shingles, this condensation can cause them to rust from underneath. Keep in mind that failures with steel roofing occurs from cut edges on the back side of the metal and rarely from the front weather side.
Both traditional and modern metal roofing systems are well suited for breather membranes. Traditional metal roofs suffer from condensation generally at the level of the felt underlayment or the slip sheet. A breather membrane can act as both a waterproof secondary roof and a slip sheet. Modern composite metal roofs suffer from internal condensation that can eventually compromise the insulation and even possibly the securement. Breather membranes allow water vapor to escape by condensing on the underside of the metal roof, dripping back onto the underlayment and draining to the eave.