Our aging building stock provides tremendous opportunities to reduce our overall environmental footprint through upgrades to the exterior enclosure. Buildings with solid or load-bearing masonry walls typically employ interior insulation retrofit strategies as these buildings often have heritage significance that preclude work from the exterior. Insulating from the interior may result in accelerated masonry freeze-thaw deterioration, embedded metal corrosion and/or embedded wood joist rot.
A limit states design approach compares factored loads to factored material resistance to assess resulting safety factors against reaching a limit state or failure threshold. Loads that are considered when insulating solid masonry walls include external/internal moisture and temperature. These can be measured through weather stations and sensors or predicted through models that incorporate weather files. Pertinent material resistance limits/thresholds include the Critical Degree of Saturation (Scrit) and the temperature/relative humidity levels where metal corrosion or wood rot progress. Scrit is obtained through frost dilatometry testing where brick or stone samples are subjected to freeze-thaw cycles at various moisture saturation levels to determine the limit/threshold where internal damage may occur.
This paper describes applying a limit states design approach for two case studies: an institutional facility in southwestern Ontario and a museum in northeastern Ontario. Expected climate conditions from numerical models are compared to Scrit values (obtained from testing site specific brick/stone samples) and to typical corrosion/rot thresholds. Findings show low freeze-thaw risk to the insulated brick and stone for these specific facilities but increased risk for embedded steel corrosion and wood rot. Strategies to control metal corrosion and wood rot are presented.
Note: This paper was presented at the 14th Canadian Conference on Building Science and Technology. It is copyrighted by the authors and is published with permission.