Building Science Insights By Herman Kwok, Normac Depreciation Report Coordinator
A recent addition to the Normac team, Herman has assumed the role of Depreciation Report (Reserve Fund Study) Coordinator. Herman has a Bachelor of Applied Science from UBC with a specialization in Materials Manufacturing and Performance. In 2013, Herman obtained his Master of Engineering degree from BCIT in the field of Building Science. Herman applies his deep technical knowledge in his everyday work here at Normac. His graduate dissertation was titled “Experimental Investigation of Moisture Transfer between Concrete Foundation and Sill Plate.” Below is an excerpt from his final project.
The main functionality of a shelter, essentially a house, is to keep ourselves and our assets protected. The environment outside can be very harsh at times and we want to stay warm and dry. Not surprisingly, the building assembly itself, other than the exterior enclosure, is best to be kept warm and dry as well. Moisture problem has always been the number one issue that can affect the performance of a house. Performance includes the durability and integrity of the house structure.
Precipitation is one of the most common moisture source building constructions encounter. However, as much as water is coming from top-down, it can also come from the bottom up. Although foundations are sometimes constructed out of pressure-treated lumber, most of the time it is poured concrete. The foundation of a house, often below-grade, is under continuous contact with moisture. This is mainly due to wet soil in a wet climate zone, high water table, or combination of both. The wood frame structure then sits on the foundation with the sill plate in constant contact with the damp concrete. This creates a risk of rot growth and decay for the wood components. The building code requires the sill plate to be pressure-treated if it is located less than 8” above grade. The treated sill plate has resistance against rot; however, it doesn’t stop or retard moisture movement.
My research study quantitatively examined the necessity of sill gaskets and their effectiveness against moisture transfer on top their functionality as an air barrier. A customized experimental wall panel was built and erected at the state-of-art building science research facility at the British Columbia Institute of Technology in Vancouver, British Columbia. The test panel is fitted with thermocouples and insulated moisture pins that calculated moisture contents based on measured electrical resistance and local temperature. These pins are located at different depths on the sill plate as well as different heights on the stud. Different methods used by the industry to address foundation to wood-frame structure interfaces are experimented in test wall. The use of sill gaskets is one of them; however, it is only required by code as part of an air barrier system. Preliminary experimental results suggested that the use of damp proofing and sill gasket helps restrict moisture transfer. Sill gasket is the most effective in limiting moisture migrations and fluctuations between the sill plate and foundation. It is positive to conclude that sill gaskets, supplementary to being an air barrier, functions very well as a moisture barrier.