Vapor diffusion ports (VDP) that are drilled in the exterior sheathing of wood-frame walls are commonly used in wood-frame construction in the coastal region of British Columbia with the intention to improve the drying capacity of wood-frame exterior walls. This practice was originated following the systematic building envelope failures due to rain penetration that occurred in this region around 1985-1995. A previous laboratory study carried out by FPInnovations found that the diffusion ports provided substantial improvement in the drying rates of Oriented Strand Board (OSB) sheathed walls, but not for plywood sheathed walls (Hazleden and Morris, 2001). A more recent laboratory test (Wang, 2018) using wood-frame walls with higher insulation levels in compliance with the current more stringent energy code found that VDPs did not significantly improve the drying rates; On the other hand, the provision of VDPs may allow moisture ingress into the wall assembly instead in a damp environment. The difference in these two studies in terms of test wall sizes, moisture sources, and test conditions may have attributed to the different findings. To provide a more comprehensive and systematic evaluation of the effect of VDPs, hygrothermal simulations using Wufi-2D are carried out in this study. The Wufi-2D model is firstly validated by comparing simulation results to the test results provided by Wang (2018), which tested the effect of VDPs under laboratory conditions by using a wetted wood block installed inside each wall assembly as a simulated moisture source. The simulation results agree well with the measurements. The Model is then used for sensitivity analysis with different levels of rain leakage with and without VDPs using yearly weather data. The variables included are types of exterior insulation, types of sheathing (OSB versus Plywood), and types of sheathing membrane. This paper presents the validation of the model and simulation results under transient conditions with rain leakage. General conclusions on the effect of VDPs are provided.

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Due to global climate change, the world has been experiencing significant increases in average temperatures and the frequency and intensity of extreme weather events such as heatwaves. The overheating problem in indoor spaces of buildings has become a concern to the comfort and health of building occupants, especially vulnerable populations such as the elderly, children, or the sick. A field monitoring network consisting of rooftop weather stations and indoor sensors has been set up on 11 buildings of different types in Montreal, Canada. This paper presents the results of field measurements of indoor thermal conditions of six school buildings to assess the risks of summertime overheating. These six primary school buildings were built in 1930-1966 with window-wall-ratios between 10-30% and limited mechanical ventilation. The indoor dry-bulb air temperature, relative humidity, and CO2 concentrations are measured by indoor wireless sensors. The weather conditions, including dry-bulb temperature, relative humidity, solar radiation, rainfall, wind speed, and wind direction, are measured by rooftop weather stations. Measurements presented in this paper are collected from July to September 2020, which include four different time intervals: (a) during two heatwaves, (b) during summer break when schools were closed, and (c) when schools were reopened, and windows were intermittently opened. Data analysis shows that the indoor and outdoor temperature difference has a strong linear correlation with the outdoor temperature observed for all school buildings. This correlation is also affected by building operations, such as opening windows, closing blinds, and the micro-climate of their surroundings.