| Investigation
The objectives of the study were:
to study varying vent cavity depth
to study restriction of vents from the ventilation cavity to the exterior
to rank, by drying ability, different assemblies subjected to identical simulated steady state winter temperature and humidity conditions.
to assess drying under these conditions when the vapour barrier is omitted.
In addition, wood and vinyl siding were compared to stucco in a limited number of cases. Over 342 simulations of different walls were conducted.The model used was a modified version of WALLDRY, a program developed for CMHC in 1988, and subsequently modified to account for air infiltration and exfiltration, sorption isotherm algorithms for materials other than solid wood and vapour diffusion properties that vary with moisture content.
The model does not include liquid mass transfer by capillary diffusion. None of the simulations included air leakage. Although variations in resistance to vapour diffusion with different moisture contents are accommodated for some materials, thermal conductivity of materials is assumed constant, irrespective of moisture content.The model has not yet been compared with more comprehensive computer models. However, it has been compared with the field results of walls exposed to climate in the Atlantic provinces and Ontario. The conditions modeled for this report represent winter-like conditions in Vancouver without wetting of exterior surfaces by rain. One must keep in mind that walls that appear to perform well in the simulations (or in the laboratory) might experience problems in summer conditions depending on the climate and indoor conditions. | 