Vapor Retarders For Membrane Roofing Systems

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.

Vapor retarders for membrane roofing systems.

There are 3 classes of vapor retarder materials as shown in the figure. 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. 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. The need for use and design of a vapor retarder in the design of a roof system used to be a hotly debated topic.

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. Colvent 180 tg is composed of non woven polyester reinforcement. The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system. The fiberglass reinforcement provides high strength to the membrane which guarantees an excellent mechanical performance.

Most roof membranes are class i vapor retarders. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful. The firestone v gard vapor control membrane is designed to be used as vapor control layer in firestone roofing systems. It can be left exposed for up to two 2 months.

When discussing air barriers roofing membranes and the building envelope another important topic comes to mind. There is often confusion between air barriers and vapors retarders. Vapor retarders do just as they are named they reduce vapor diffusion but not all vapor retarders are equal. 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.

Gaf sa vapor retarder is an sbs modified bitumen vapor retarder for use in approved gaf roof assemblies. Vapor retarder sa 31 can also serve as temporary roof protection in areas limited to light construction traffic. The lower the perm rating the less diffusion occurs through a material. 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.

A vapor retarder is a material or system that is designed as part of the roof system to substantially reduce the movement of water vapor into the roof system where it can condense.