Vapour Permeance

The vapour permeance properties of the materials installed on exterior walls are of capital importance to achieve long-term structural integrity and assure a healthy indoor environment. Many severe cases of health problems are being reported when stachybotris-atra (fungi) are involved.

Low vapour permeance intermediate sheathings restrict the evacuation of humidity migrating through the cavity and thus create a proper environment for growth and proliferation of micro-organisms.

All BP exterior Wood Fibre Insulation sheathings are classified as high water vapour permeable products. This is in fact the best protection you can get against the occurrence of mould in your construction. It is also why we qualify all our wall systems as ?anti-mildew? breather wall.

There have been many research projects relating to rot and structural deterioration of building structures with some major ones still under way. The undeniable test, however, is that of experience. With more than 50 years of true-life performance, thousands of houses built with Wood Fibre Insulation have been remodelled, (replacing siding, windows, doors...) and the proof is in the wall. It is dry. The wall cavity has not been affected by organisms that can cause deterioration in the structure and potentially cause health problems to humans.

NBC A-9.25.1.2.

Location of Low Permeance Materials.

"...If the material (low permeance) is located where the temperature is below the dew point of the interior air, the water vapour will condense and accumulate as water or ice. This reduces the humidity level and encourages the movement of more water vapour into the assembly. If this temperature remains below the dew point for any length of time, significant moisture could accumulate. When warmer weather returns, the presence of a material with low water vapour permeance can retard drying of the accumulated moisture. Moisture, which remains into warmer weather, can support the growth of decay organisms."

Section 9.25. of NBC

Heat Transfer, Air Leakage and Condensation Control Specifies in 9.25.1.2. that:

"...any sheet or panel type material with an air leakage characteristic less than 0.1 L / ( s.m²) and water vapour permeance less than 60 Ng / (Pa.s.m²) ? incorporated in a building? to be insulated shall be installed:
a) on the warm face of the assembly;
b) at a location where the ratio between the total thermal resistance of all materials outboard of its innermost impermeable surface and the total thermal resistance of all materials inboard of that surface is not less than required in Table 9.25.1.2."

All BP Wall Systems are based on the installation of an interior water vapour barrier material and the installation of a breather exterior sheathing.

EXCEL II