Remediating high moisture levels in the wall cavities of preserved wood foundations
Onysko, D., Rijn, G. V., Gates, D. and Fugler, D.
2005 10th Canadian Conference on Building Science and Technology, Ottawa, May 12-13
Onysko, D., Rijn, G. V., Gates, D. and Fugler, D., (2005), "Remediating high moisture levels in the wall cavities of preserved wood foundations", 10th Canadian Conference on Building Science and Technology, Ottawa, May 12-13.
Abstract:
There are thousands of preserved wood foundations (PWF) in Canadian housing and, in most cases, the wood bottom plate has a moisture content over 20%. The wood preservatives prevent wood rotting caused by this relatively high moisture content. However, while the wood is protected from decay, the high moisture levels may lead to mold growth on oth er materials in wall cavities.
This CMHC research project involved a house where mold growth in the wall cavities affected the occupant's health. The residents disassembled the inside finish on the foundation wall, discarded the fibreglass, and cleaned out the mold, but they needed advice on how to rebuild the wall safely to prevent further health effects. A consortium of experts recommended that, as a least-cost first-step intervention, the lower part of the wall cavity be left empty and that it be vented by an exhaust fan, both to aid in drying and to isolate the occupants from potential biological growth in the cavity. The rest of the cavity was filled with cellulose insulation and finished with drywall. Monitoring of wood moisture levels and cavity conditions was carried out from mi d-winter to early fall.
Results showed that the cavity depressurization strategy worked well at isolating the occupants from air in the wall cavities. Bottom cavity ventilation brought the moisture content of the wood framing back to drier conditions when increases occurred because fresh basement air was being provided. If this technique were to be applied to other PWF houses, there would have to be some optimization of wall cavity leakage, exhaust fan sizing, and installation proce dures to ensure efficient and effective operation.