A research program conducted at Forintek Canada Corp.’s western lab in Vancouver, Canada, the Envelope Drying Rates Analysis Experiment (EDRA) Group A, has evaluated the relative drying rates of typical wood-frame wall assemblies under controlled laboratory conditions, (Forintek Canada Corp & HouseWorks Building Science Inc., 2001). Five of the typical test wall panels (of Group A) have been re-tested (Group B) after being modified by the addition of vapour diffusion ports. The objective of the test was to determine if the vapour diffusion ports would add substantially to the drying rates of the test wall panels. Test conditions included Vancouver wintertime drying only. Test panels incorporated polyethylene vapor retarder and sealed poly air barrier construction. The research ranks test wall panels in terms of their relative drying capacities, and assesses the differences in drying performance of test wall panels with and without vapour diffusion ports. The Group B tests indicate that vapour diffusion ports have a substantial improvement effect on the drying rates of OSB sheathed panels and no substantial effect on the drying rates of plywood sheathed panels.