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Re: GSBN:re: Moisture Problem (Addendum(b))
Rob, Dan and all,
Sorry for my slow response.
The rafters are regular old lumber (a); 2x12's if my memory is
correct. The poly/cellulose is retained by strapping, to which the
drywall is attached. The ventilation space is exactly what is
created by Proper Vent-(not very permeable, thin foam tray) say, 1.5
inches?, with openings at soffit and ridge.
I should add that the ice was only on the outer 4 feet or so of the
sheathing, and that it didn't occur at all in areas of the south roof
that are over large windows with no bales above.
Also, Dan Smith said:
How are the inside joints between wall and ceiling sealed?
The answer is- not very well. A structural timber separates the wall
and ceiling planes, and there was clearly massive air leakage at
these joints. The joint between timber and plaster was backed with
15 lb felt, but it was not sealed in any effective way to either the
ceiling poly or the beam. I'm pretty sure that most of the moisture
in the roof cavity came from this point, though I'll be nothing short
of thrilled if Rob can demonstrate otherwise. Nonetheless, this
doesn't explain why the moisture level got so high throughout that
outer 30-50 mm zone of the wall, even in areas that had very little
exposure to rain, and why people are experiencing seasonal damp
patches in houses that should be well beyond the drying of their
Thanks again for all of your thoughtful responses!
Scooz 'eh Moi;
In his previous message, that dodo Stronzo di Nord forgot to ask:
"Were the rafters (a) solid lumber (or TJIs)
(b) Scissors or parallel chord trusses ?"
"What sort of a ventilation space was provided over the insulation in the
rafter bays of the cathedral ceiling and what arrangement was used to
provide exhaust capability for the ventilation space ?"
=== * ===
Kanata, Ontario, Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff from my edress in your reply)
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