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Home Builder Magazine, 21, 5, p. 34, 2008-09-01
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Fighting condensation inside walls
Maref, W.
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A version of this document is published in / Une version de ce document se trouve dans: Home Builder Magazine, 21, (5), pp. 34, September 01, 2008
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Fighting Condensation Inside Walls
By Dr. Wahid Maref
NRC-IRC develops evaluation protocol for innovative vapour barrier
Poor vapour control between the interior and exterior environment of a building can have expensive consequences from the build up of condensation inside walls. This can cause materials to deteriorate, lead to occupant discomfort, and increase energy consumption.
To prevent these problems, builders normally install a vapour barrier (see sidebar 1) as a control on how much water vapour can diffuse through the surface enclosing a space and as a way to prevent moisture from travelling to a point in the wall where it may condense.
Vapour barriers were originally intended to keep building assemblies from getting wet, but they can sometimes end up preventing assemblies from drying out. An innovative new product to manage moisture accumulation in the building envelope, however, may be able to address both issues: while the product acts as a vapour barrier under most conditions, it also allows excess moisture to escape.
The Canadian Construction Materials Centre (CCMC) set out to determine whether this product can serve as a vapour barrier and an air barrier system and whether it conformed to the intent of applicable building code requirements. In collaboration with NRC-IRC researchers, CCMC developed a testing protocol for its evaluation, which was based on laboratory testing requirements for vapour diffusion, air leakage control and durability. Because of the product’s varying water vapour permeance, CCMC also required computer modelling to verify compliance with the National Building Code.
For the computer modelling, researchers in NRC-IRC’s Building Envelope and Structure program provided the expertise, using their hygrothermal modelling tool, hygIRC 2-D. This tool creates a computational model of a building and subjects it to hourly temperature, relative humidity, solar radiation, and wind and rain variations on the outside, and temperature and humidity variations on the inside. It then simulates the building’s responses to the changing environmental conditions, producing information on temperature and relative humidity distributions within the envelope assembly and how they will change with time.
The researchers were able to demonstrate that the product performed well in all locations (they simulated a wood-framed stucco wall system, exposing it to the climate of four separate Canadian locations, both coastal and non-coastal), and in interiors with both high and low relative humidity. One problem it uncovered with the product occurred when it was used in
conjunction with acrylic paint on indoor walls. Latex paints are recommended to capitalize on this material’s variable properties.
Based on NRC-IRC’s experimental and modelling research results, CCMC has published an evaluation report (CCMC 13278-R) on the product, known as MemBrain™, for consideration by building officials.
The report provides CCMC’s opinion, the test results on which the opinion is based, and usage conditions and limitations for the product. It stipulates that the product can serve as an alternative to polyethylene film and be used both as a vapour barrier and as an air barrier system within a building’s exterior walls—except in buildings with high indoor relative humidity such as saunas and swimming pools.
For more information, contact Dr. Wahid Maref at 613-993-5709, fax 613-998-6802, or e-mail
wahid.maref@nrc-cnrc.gc.ca. The complete results of the CCMC evaluation are also available at
