Task Force observed and concluded:
1. Most panels that stayed wet exhibited fungal growth.
2. Permeability was the most significant factor in drying.
3. "The use of exterior sheathing materials with a very
low permeability to water vapor in combination with wet framing
lumber or insulation materials having a high moisture content, puts
walls to a high degree of risk of moisture problems."
4. "If drying is protracted over a long period of time,
rot-causing fungi may become established in the wall cavity. Once
established, rotting may continue even though no moisture is added."
Test hut location had little effect
"The climate or geographical differences of the site in this
experiment had little effect on the final structural moisture content
values" (OBOE Engineering LTD., Consultants to the CMHC/CHBA
Joint Task Force).
Other independent tests performed in Ottawa, in 1988, confirmed
the Joint Task Force's findings.
Ottawa drying tests results
After 60 days in a professionally controlled test environment, wall
studs in the fiberboard sheathing test panel dried from 30% moisture
content to 7%, and showed no signs of fungus or decay. The batt
insulation in the wall cavity was dry.
Wall studs in an identical test panel, but with waferboard sheathing,
were still at 20% moisture content after 60 days, and showed definite
signs of fungal growth. In fact, the upper area of the batt insulation
in the waferboard test panel was so wet that water could be squeezed
out by hand.
Comparison of wall drying performance of
fibreboard and waferboard sheathing
Fibreboard sheathed walls dry quickly!
Fibreboard sheathing is so permeable, that wall systems
using fiberboard will dry in a few weeks, without decay.
This chart shows clearly why moisture can escape so quickly through
fibreboard sheathing, compared to waferboard or extruded polystyrene.
- - Canadian Fiberboard Manufacturers' Association