Standard Condensation Control in Building Practice

The principles and measures of condensation control described in scientific reports and applied in the standards have found their way to building industry, designers, contractors and builders through a variety of technical recommendations and commercial publications. Design guidelines may vary from coimtry to country, and range from simple to more differentiated. 

The most commonly applied vapour retarder materials in lightweight envelope parts are polyethylene film and bituminous or aluminium kraftpaper. In flat membrane roofs, the bituminous membranes applied for water-tighmess are also used as a vapour retarder. A new 

Roof slope Cavity width, cm Ventilation area Diffusion thickness of the layers at inside of cavity, m 

4 pd 200 m Bituminous membranes with metallic foil reinforcement, multi-layer membranes 

In the Belgian design guides, four vapour retarding classes have been developed, depending on the resistance to water vapour diffusion of a vapour retarder (expressed as the diffusion thickness or equivalent air layer thickness pd). Table 4.2 gives the boundaries of the vapour retarding classes, and some examples of materials. 

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