Attic ventilation is typically recommended for the removal of moisture build-up caused by air leakage from indoors in cold climates, however, it may also increase the amount of snow and rain penetration into the attic, especially in the extremely cold climates. In northern regions, extremely cold temperatures can cause snow particles to become very fine, which will penetrate vents or unsealed openings. The snow accumulated in the attic would melt at temperatures above zero and penetrate to indoors through the ceiling and cause moisture problems. One of the solutions is to add filter membranes along a ventilation cavity behind the façade to prevent snow from entering the attic. The ventilated attics with filter membrane had some success but there were instances with reported water leakages and moisture damages. There have been also attempts to use un-ventilated cold roofs. Un-ventilated attics prevent snow accumulation but do not allow for effective removal of moisture, which could be risky and prone to moisture damages.
In this thesis, three houses in northern Canada are investigated, two of them have ventilated attics with different filter membrane designs located in Kuujjuaq and another has un-ventilated attic located in Iqaluit. Field measurements are setup in these three houses to monitor their hygrothermal performance under different venting systems. Measured results indicate ventilated attic has reasonable hygrothermal conditions which moisture content level on attic sheathing is under 20% and un-ventilated attic has higher risk of moisture problems. At the same time, hygrothermal modelling using WUFI Plus, a whole-building hygrothermal simulation software, are performed and simulation results are compared with measurements for model validation. Validated models are also performed in other location to further verify their universality. Attic ventilation rate, air leakage rate, un-intentional air infiltration rate and indoor conditions are set as variable parameters in WUFI Plus to discuss their effect on the hygrothermal performance of attics.
This thesis is intended to provide documented evidence of the hygrothermal performance of ventilated and un-ventilated attics in extremely cold climate. Simulation models validated by field measurements can be used under other climates. Recommendations on proper attic design are provided for Canadian northern housing.