Modified bitumen membranes were originally developed in Europe, where they have enjoyed widespread success since the early 1970s.
Modified bitumen technology developed out of attempts to widen the serviceability range of conventional oxidized roofing asphalt.
In the manufacture of modified bitumen membranes, one or more reinforcing plies, typically composed of fiberglass, polyester, or fiberglass/polyester composite, are encapsulated in polymer modified asphalt of varying weights. Sheets may then be surfaced with mineral granules or metal foils, or remain unsurfaced. The result is a membrane that combines the multi-layer benefits of a built-up roof with the installation advantages of a single-ply membrane.
Two main types of modified bitumen:
SBS (Styrene-butadiene-styrene) formulations perform well in cold weather applications, possess superior elongation and recovery properties, and are quite versatile in their application in that they can be mopped in asphalt, torched, or installed with cold adhesives. Mineral granules and metal foils are generally used in surfacing this type of membrane, as resistance to ultraviolet light is somewhat limited.
APP (Atactic polypropylene) products are more suited to application in hot weather, are resistant to weathering and aging, and are more resistant to ultraviolet radiation than are the SBS membranes. The method of application is generally limited to torching. However, cold adhesive applications have been introduced by a few manufacturers. These membranes are generally manufactured without a surfacing; although granule surfaced products are available. We recommend that protective coatings be installed and maintained on the unsurfaced sheets to provide additional ultraviolet resistance and to achieve the required fire rating.
Neither APP nor SBS membranes are well suited to applications in ponded conditions.
- Johns Manville