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Evaluation of vapour diffusion ports on drying of wood-frame walls under controlled conditions

Hazlen, D. G. and Morris, P. I.
CMHC, Technical Series 02-130

Hazlen, D. G. and Morris, P. I., (2002), "Evaluation of vapour diffusion ports on drying of wood-frame walls under controlled conditions", CMHC, Technical Series 02-130.
As part of the effort to address the leaky condominium problem in British Columbia, it is necessary to understand how walls manage moisture. A 1998 best practice guide indicates that walls require four features for effective moisture management: deflection, drainage, drying and durability. Of the four, drying has received little attention. For this reason, the Building Envelope Research Consortium (BERC), an industry and government group formed by Canada Mortgage and Housing Corporation (CMHC) to address the condominium problem, undertook an Envelope Drying Rate Analysis (EDRA) experiment as part of its program.

Typically, permeance is used to calculate drying rates. However, the effective permeance of a wall may be several times greater than the calculated permeance. Efforts have been made to improve the effective permeance of walls. One approach involves creating one or two holes 75 mm in diameter in the sheathing at the top and bottom of stud spaces; a concept initiated in the BC lower mainland by Vancouver architect Brian Palmquist, of ProPacific Architecture Ltd. These holes, known as vapour diffusion ports (VDPs), allow vapour in the stud space to contact the sheathing protection membrane directly.

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Author Information and Other Publications Notes
Hazlen, D. G.
Morris, P. I.
Wood Preservation Scientist, Composites and Treated Wood Products, Forintek Canada Corp., Vancouver, BC, Canada
  1. Criteria for unacceptable damage on wood systems
  2. Designing for durable wood construction: the 4 Ds
  3. Limiting conditions for decay in wood systems
  4. The influence of design on drying rates in wood-frame walls under controlled conditions
  5. Understanding biodeterioration of wood in structures  

CRDBER, at CBS, BCEE, ENCS, Concordia,