Perm Rating Of Building Materials

Using Asphalt Felt as Building Wrap Asphalt roofing felt has a perm rating of around 5 and moderately good water resistance making it suitable for use as a sheathing wrap. A vapor permeable material permits the passage of moisture vapor.

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Vapor Permeable Class III Vapor Retarder 1perm 5perm 10 perm.

Perm rating of building materials. Thats short for permeance which means that it already factors in the thickness. With paints however adding a second coat more than halves the water vapor transmission. Sheet metal flashing and 6-mil polypropylene.

Vapor permeability is dependent on paint - with latex paint generally in the 2-3 perm range. Vapor barrier has a perm rating approaching 00. A membrane with a permeance of 5 perms or more is classified as vapor permeable in accordance with the 2006 IBC and IRC.

A high perm rating of a building material indicates it is very permeable and allows more vapor diffusion. However unlike plastic housewraps asphalt felt will absorb water when wet. For high moisture build-ings such as those housing swimming pools or.

This is a summary report written specifically for the Roof Consultant Institute 2005 Symposium on. Using Procedure A dry-cup of ASTM E 96. Properties as variable as the material but almost always has relatively high vapor permeability.

Four categories are established. Perm rating of OSB also increases as it gets wet but less so than plywood. Given the combina-tion of high RH indoors and very cold weather outside measurable amounts of water vapor will pass through 6 mil polyethylene.

Water Vapor Permeability perm. 01 perms or less. The vapor permeance characteristic of the sheathingcladding assembly is defined by the effective wet cup permeance of both the cladding and sheathing combined.

It is a standard measure of the water vapor permeability of a material. 01 perm or less. Building materials are separated into four general classes based on perm ratings.

The higher the number the more readily water vapor in. Local building materials suppliers trade associations and union apprentice programs have provided additional assistance. Vapor impermeable vapor barriers have a perm rating less than 01.

When youre studying the properties of materials to use in construction youll often see a perm rating. If 1-inch of a material has a perm rating of 20 then for 2 inches the perm rating would be 10. There are four commonly accepted classifications to describe vapor permeability of construction materials.

27 rows Building materials with a perm rating of less than 1 are considered resistant to moisture. In other words two layers of a mate-. Materials such as rigid foam insulation reinforced plastics aluminum and stainless steel are relatively resistant to water vapor diffusion.

Material but water storage capacity is always very high. The most widely used vapor barrier is 6 mil polyethylene which has a perm rating of 006. 10 perms or less and greater than 01 perm.

What is a perm rating. 57 rows Material. Generally doubling material thickness halves water vapor transmission.

The perm ratings given are for stated thicknesses of materials. They also serve as effective air barriers. The property of having a moisture vapor permeance rating of 5 perms 29 x 10-10 kg Pa s m2 or greater where tested in accordance with the desiccant method using Procedure A of ASTM E 96.

Thinner membrane types come in rolls or as integral parts of building materials. Materials with higher perm ratings allow greater passage of water vapor. The permeance of a material is inversely proportional to its thickness.

These types of vapor diffusion retarders are usually mechanically fastened and sealed at the joints.