Val Varga, M.Eng. 2014
Supervisor: Rodrigo Mora, PhD
Mould growth in the attics of wood frame residential construction is often publicized in the media, industry publications and professional conferences and seminars in BC. The occurrence of mould growth appears more frequent (and a more prevalent systemic problem) in Greater Vancouver area, in part because of the population concentration, but also because this region is exposed to the mildest tempered oceanic climate in Canada. With a mean annual temperature of 9 degrees celcius, a summer mean of 15 degrees celcius, and a winter mean of 3.5 degrees celcius, the climate of the Lower Mainland of Vancouver has the potential to favour mould growth almost year-round. The annual precipitation in this micro-climate ranges from an annual mean of 850 mm in the west end to 2000 mm in the eastern end of the Fraser Valley, which also creates consistently high RH, frequently hovering around 80-90%, in turn proving even increased risks of mould growth.
Mould growth is routinely observed to occur in sheltered (but freely ventilation) spaces such as carports, garages, sheds and closets. These spaces are protected from direct rain, and openly ventilated, an in some cases, subject to conditioned indoor air. However, mould growth still occurs, which led to the following local professional debate:
How could attics (which have limited ventilation), be protected from mould growth, when mould occurs ubiquitous in other spaces with free air flow and ventilation, such as carports? The scientific polemic expanded, with professionals arguing that ventilation does not have the potential to prevent mould growth in attics, due to the high RH year round. Various sides of the polemic suggested various solutions. Some argue that ventilation should be discouraged, others that it should be increased. Scientific papers from other corners of the world suggest a combination of both, with mechanical adaptive ventilation as the solution. Other papers suggest the complete de-coupling of the attic from the environment, by sealing the attic to the outside conditions (cathedral ceiling). However, some others, including a few local Vancouver municipalities, seem to discourage or disallow cathedral ceilings.
The current research project aims to provide a review of a large number of attics, and to draw conclusions with respect ot the follwoing factors:
- Statistically, is mould a systemic problem in the attics of wood frame buildings in Vancouver’s Lower Mainland?
- If so, what factors seem to influence, aid, and favour or discourage mould growth in the attics?
- Is the current code required current natural ventilation rate adequate to best protect against mould growth in the attics of Vancouver’s Lower Mainland?
The research project concludes that mould is a systemic problem in wood frame construction in the Lower Mainland, that orientation of the roof (exposure to daytime sun radiation) is the most important factor in preventing mould growth, and that the current code required natural ventilation rate appears to be the most optimal (although not a strong deterrent) for preventing mould growth (the research project observes that it is more likely to observe mould in attics which have ventilation rates in excess, as well as below, the code required rates).