‘Mod-Bit’ roofs are essentially ‘pre-manufactured built-up-roofs’ made from plies of manufactured plastic, glass-fiber, or fibrous reinforced (0.04-0.16″) sheets and Polymer-Modified bitumens.
These modified bitumens are most commonly APP (atactic-polypropylene) or SBS (styrene-butadiene-styrene) which increase cohesion, durability, and flexibility. Modified-Bitumen roofs are commonly seen in residential low-slope roof applications, but are also seen in commercial as well. Similar to a built-up-roof, Mod-Bit roof sheets are bonded in the field by:
-hot-mopped (SBS common installation method)
-Bonded modified bitumen sheets create a multi-ply system (commonly 2-3 plies thick).
First a base sheet/ply is attached to the insulation or other substrate.
Then the plies (often 3′ wide rolls) may be adhered to eachother and the substrate in a few different ways: torch applied with an open flame to the underside of the sheet; hot-mopped with a hot asphalt binder between the sheets; cold applied adhesive; or a self applied membrane with an adhesive side coming direct from the factory. Then a top sheet or cap-sheet is surfaced with mineral granules, metallic laminates, or asphaltic/elastomeric coating for UV/wear/fire resistance.
Pipe boots for mod-bit roofs are typically lead or copper and installed by the roofing contractor (except for non-MEP penetrations). Galvanized pipe boots will not adhere to asphalt membrane roofing. Cap sheets with white coatings to achieve a ‘cool roof’ standard may also be available. Flashings are then installed to complete the watertight roofing system. Essentially, modified bituminous roofs provide the strength and durability of Built-Up-Rooofing with the quality and efficiency of pre-manufactured, single-ply high-quality sheets, increasing the total plies while greatly reducing on site labor. Mod Bit Roofs account for 20-30% of all low-sloped roofing systems. Life and warranty depend on the number of layers and can vary between 10-20 years. The following is a general rule of thumb for warranty:
-1 Base layer, 1 surface layer – 10 year
-1-2 base layers, 1 surface layer, reflective coating – 12 years
-2 base layers, 1 layer granulated surface layer – 15 years
-2 base layers, mid ply, surface layer – 20 years