Design & Use Of Modified Bitumen Roofing Systems
Modified bitumen roof products can be used in various system configurations, depending upon the roof requirements. For small projects such as decks, additions and porches, two-ply systems comprised of a base and cap sheet may be appropriate (in conjunction with flashing membrane as specified by the manufacturer). For larger residential roofs and commercial applications, three-ply systems comprised of a base covered with mid ply and cap are recommended.
The advantages of self-adhering membrane are ease of application, minimum of installation tools or equipment needed, cleanliness, and the fact that no hot asphalt or torches are required for installation. View CertainTeed’s Modified Roofing Selection Guide.
Roofing manufacturers like CertainTeed, recommend the use of a base in conjunction with all self-adhering membrane roof installations. The base can be mechanically attached to nailable substrates or applied using hot asphalt (non-nailable substrates). For non-nailable substrates where use of hot asphalt to adhere the base sheet may not be appropriate, a mid ply may be used in lieu of the base to surfaces properly primed with an approved primer.
However, note that without the use of a base sheet, the membrane may be difficult to later remove (if necessary) and certain UL and FM listings for the products may not apply. Prior to application of any roof products, ensure roofs have adequate slope and drainage. Consult the local building official for minimum slope and drainage requirements.
Use Of Modified Bitumen Accessories
There are a few accessories needed for proper installation of a modified roofing system. Listed below are a few of those accessories and where they may be needed:
• Flashing Adhesive “Trowel Grade” Used around penetrations and at terminations. General comes in a 3 ½ gal. pail.
• Sealant Also used around penetrations and at terminations. Available in 11 oz. tubes.
• Asphalt Primer Required to prime concrete, aged wood, masonry, and metallic surfaces prior to application of the self-adhering membranes. For systems using a base sheet, application is recommended prior to the application of the base sheet for best results. Apply only over dry, dust free surfaces. Must be thoroughly dry to the touch before applying the self-adhering membrane. General comes in 5 gal. pails.
Water Base Vertical Primer Acrylic, latex-based, and specially designed to prime vertical substrates prior to the application of Base Sheet, Cap Sheet, or APP Cap Sheet. It offers superior bonding performance and can be sprayed, rolled, or brushed on almost any acceptable vertical substrate. The primer is non-flammable, non-toxic, and affords contractors a wide application temperature range. The texture is similar to latex paint so the primer applies easily and smoothly for fast installations and containers can be re-sealed without set taking place. Available in 3 ½ gallon pails only.
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