A vapour barrier is an important component in building construction.
Roof vapor barrier details.
The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system.
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.
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.
The function of a vapor barrier is to retard the migration of water vapor.
This vapor if left unchecked can wet the insulation and over time will reduce the r value of the insulation and lead to mold.
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.
The vapor barrier protects the roof insulation from the vapor included in the interior air.
The inner surface in colder climates and the outer surface in hot humid climates.
Vapor barriers are not typically intended to retard the migration of air.
A vapor barrier can be loose laid or fully adhered.
Hence on large roofs with very few penetrations this type of membrane can be very economical to install.
Vapor barriers are usually best installed on the side of the wall that experiences the hotter temperature and moister conditions.
There is often confusion between air barriers and vapors retarders.
That reduction of air and moisture infiltration can then help improve roof longevity.
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.
Everyone knows that water in roof systems is never a positive.
In existing spaces oil based paints or vapor barrier latex paints offer an effective moisture barrier.
The purpose of vapour barriers.
Options for above and below grade applications are available.
Most epdm sheets are black although white sheets are available.
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.
Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful.
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 retarder when discussing air barriers roofing membranes and the building envelope another important topic comes to mind.
A loose laid vapor barrier is just a big sheet of 6 mil plastic that is rolled out prior to the insulation layers.
