Vapor Retarders For Membrane Roofing Systems

Vapor retarders do just as they are named they reduce vapor diffusion but not all vapor retarders are equal.

Vapor retarders for membrane roofing systems.

There are 3 classes of vapor retarder materials as shown in the figure. It appears now when vapor retarders are needed more than ever the design community seems to have lost interest which is not good considering how codes and standards altered through concerns for energy savings have changed how buildings are designed constructed and operated. Most roof membranes are class i vapor retarders. When discussing air barriers roofing membranes and the building envelope another important topic comes to mind.

Everyone knows that water in roof systems is never a positive. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful. Colvent 180 tg is a partially adhered heat welded elastomeric modified bitumen base ply for use in approved multi ply membrane and flashing assemblies or as a vapor retarder. Gaf sa vapor retarder is an sbs modified bitumen vapor retarder for use in approved gaf roof assemblies.

Vapor retarder primer sb is a solvent based primer vapor retarder primer sb us is a solvent based primer used to prime wood concrete lightweight concrete approved gypsum boards and gypsum decks prior to the application of sika s self adhered vapor retarders or sarnafil g 476 sa self adhered waterproofing membrane. Vapor retarder sa 31 is a 31 mil 0 8 mm thick self adhesive vapor retarder air barrier for use within sarnafil and sikaplan insulated roofing systems. There is often confusion between air barriers and vapors retarders. The fiberglass reinforcement provides high strength to the membrane which guarantees an excellent mechanical performance.

The firestone v gard vapor control membrane is designed to be used as vapor control layer in firestone roofing systems. The lower the perm rating the less diffusion occurs through a material. Vapor retarder sa 31 can also serve as temporary roof protection in areas limited to light construction traffic. Gaf sa vapor retarder is composed of a proprietary formulation of elastomeric styrene butadiene styrene sbs polymer modified bitumen in combination with a high tack self adhesive.

The need for use and design of a vapor retarder in the design of a roof system used to be a hotly debated topic. The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system. That reduction of air and moisture infiltration can then help improve roof longevity. A roof design that includes an adhered roof membrane with multiple layers of insulation with board joints offset and staggered over a vapor retarder air barrier helps lower the risk that air and the moisture it carries will infiltrate the roof system.

It can be left exposed for up to two 2 months.