Roof Vapor Barrier Details

Everyone knows that water in roof systems is never a positive.

Roof vapor barrier details.

That reduction of air and moisture infiltration can then help improve roof longevity. A vapour barrier is an important component in building construction. A vapor barrier can be loose laid or fully adhered. Most epdm sheets are black although white sheets are available.

The vapor barrier protects the roof insulation from the vapor included in the interior air. The purpose of vapour barriers. Damage from water condensation due to water vapour movement called water vapour drive can wreak havoc on even the sturdiest of built structures and threaten the effectiveness of insulation. The sheets are typically available in widths of 10 20 and 45 or 50 feet 3 6 and 14 or 15 m and lengths up to 200 feet 61 m.

Vapor barriers are not typically intended to retard the migration of air. Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions. Details about air vapor barriers carlisle boasts the industry s most comprehensive line of air and vapor barrier products including self adhering sheet membranes spray and roller applied air vapor barriers and fluid applied vapor permeable air barriers. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful.

A loose laid vapor barrier is just a big sheet of 6 mil plastic that is rolled out prior to the insulation layers. The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system. This can be done by applying vapor barrier paint over the interior surface of the low density spray foam or by installing a material layer that has a vapor permeance of 1 perm or less. 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.

The function of a vapor barrier is to retard the migration of water vapor. Vapor retarder when discussing air barriers roofing membranes and the building envelope another important topic comes to mind. Options for above and below grade applications are available. Where it is located in an assembly and its permeability is a function of climate the characteristics of the materials that comprise the assembly and the interior conditions.

Its purpose is to help prevent water vapour from reaching building walls ceilings attics crawlspaces or roofs where it can condense and cause building materials to rot or grow mould. This vapor if left unchecked can wet the insulation and over time will reduce the r value of the insulation and lead to mold. 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. In existing spaces oil based paints or vapor barrier latex paints offer an effective moisture barrier.

There is often confusion between air barriers and vapors retarders.