Bison House Wrap, Bison Permeable Roofing Underlay and Bison Vapor Control Layer (Bison VCL) are designed to jointly form a permeable system of P-marked, air and water tight membranes. With the Bison System, good air and water tightness is achieved for wall and roof constructions. You get a so-called bidirectional vapor transport which, for example, prevents possible construction moisture.

Our permeable and P-labeled membranes are designed to work together to form a wall or roof structure that is air/water tight and at the same time allowing the structure to breathe. To achieve optimum insulation houses should be built wind and water proof. The problem is that houses then also become vapor proof, which in many cases leads to moisture problems. By using permeable membranes from Bison your building becomes wind and water proof but still open to vapor.

Wall construction: Bison House Wrap – Bison Vapor Control Layer (VCL):

By using Bison House Wrap on the cold side and Bison VCL on the warm side an optimal diffusion ratio is achieved. You then get a ratio with a five times as tight membrane on the inside compared to the outside (equivalent to guideline for wall constructions). A wall construction with this ratio is allowing moisture in the walls to be transpor-ted in both directions.

Roof structure: Bison Permeable Roofing Underlay – Bison Vapor Control Layer (VCL):

In roof structures Bison Permeable Roofing Underlay can be combined with Bison VCL which also achieves an optimal diffusion ratio. The ratio is a ten times as tight membrane on the inside compared to the outside (equivalent to guideline for roof structures). Such a design with forgiving membranes ensures that moisture doesn’t stay in the roof.

Why use a permeable roofing underlay?

With Bison Permeable Roofing Underlay no air gap is necessary, the membrane is placed directly against the insulation. Low weight, covering large areas and double adhesive edges on the roll makes installation easy and quick. Bison Permeable Roofing Underlay belongs to the new generation of permeable roofing underlays. By so-called Monolithic technology, our product has many advantages compared to other permeable roofing underlays. Examples are better UV resistance and better resistance to hard rain and incoming snow.

Why use a vapor control layer?

There are many advantages to using the Bison VCL compared to using a vapor tight foil on the inside of the structure. For example, it minimizes the risks of moisture from the construction phase leading to moisture damage. Bison VCL is well suited to most structures but is particularly beneficial for holiday/seasonal housing, where the heating occurs periodically. Also works great with cellulose insulation (insulation of organic material). Even in sanitary room exterior walls the Bison VCL is recommended.

To achieve good air tightness and moisture protection of wall and roof joints and penetra-tions, these materials should be sealed with approved jointing aids. Use an approved tape; Bison Flex Tape, with very good UV-resistance and adhesion.