Abstract
The objective of this study was to assess the potential effects of climate change on the moisture performance and durability of typical Canadian wood-frame walls using hygrothermal simulations, with a particular attention to the risk of condensation. To reduce the risk of condensation, the National Building Code of Canada (NBCC) recommends a maximum air leakage rate of 0.10L/sm2 at 75 Pa in buildings with interior relative humidity not greater than 55%. This leakage rate was evaluated in five cities across Canada for a wood-frame wall having brick cladding, with and without outdoor insulation and both walls meeting the minimum insulation requirements given in NBCC. It is found that the risk of condensation will be reduced in the future in all 5 cities analysed. The reduction in the risk of condensation is slightly higher for the wall with no exterior insulation than for the wall with exterior insulation. This reduction in the risk of condensation means that the limit of 0.10L/(sm2) for building having a warm side relative humidity of less than 55% may be reconsidered in the future. There may however be some risks associated with the increase in rain in some cities.
Highlights
In cold climates, air leakage through the wall assembly, especially air exfiltration during the heating season, decreases the energy efficiency of the building [1], but significantly, can lead to condensation within the wall that may cause premature deterioration of building envelope components [2]
The majority of moisture problems resulting from condensation of water vapour in walls, ceiling and attic spaces are caused by the leakage of warm moist interior air into these spaces rather than by the diffusion of water vapour through the building envelope [3]
To minimize moisture problems associated with air leakage, the National Building Code of Canada (NBCC) [3] states that air leakage must be controlled to a level where the occurrence of condensation will be sufficiently rare, or the quantities accumulated sufficiently small, and drying sufficiently rapid to avoid material deterioration and the growth of mould and fungi
Summary
Air leakage through the wall assembly, especially air exfiltration during the heating season, decreases the energy efficiency of the building [1], but significantly, can lead to condensation within the wall that may cause premature deterioration of building envelope components [2]. To minimize moisture problems associated with air leakage, the National Building Code of Canada (NBCC) [3] states that air leakage must be controlled to a level where the occurrence of condensation will be sufficiently rare, or the quantities accumulated sufficiently small, and drying sufficiently rapid to avoid material deterioration and the growth of mould and fungi This can be achieved by using an air barrier system in opaque insulated portions of the building with an air leakage rate not greater than 0.15, 0.10, and 0.05L/(s.m2) at a reference pressure of 75 Pa when the warm side relative humidity (RH) is less than 27%, between 27 to 55%, and greater than 55%, relatively [3]. Global warming in effect with more frequent and intense extreme climate events [4], there is a need to assess the resilience of wall assemblies to the risk of the formation of condensation, moisture uptake and the possible presence of mould growth in components or decay fungi in wood
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