moisture on vaulted ceiling

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  #1  
Old 02-02-03, 11:41 AM
Christopher G.
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moisture on vaulted ceiling

We have recently purchased a 7-year old two story home. The living room/kitchen area is vaulted with scissor truss construction. We began noticing moisture lines at the drywall joints in various spots on both sides of ceiling. I recently cut a hole in the drywall from a second floor landing to get a view of the cross-section of the truss system. The fibreglass batts sit on the drywall vaulted ceiling between the truss members. Their is approximately a 18-24" air space over the insulation to the under side of the roof plywood. I can see light coming in along the ridge vent but cannot see if the insulation is jammed against the soffet vents.
The air space is very cold (we live in the mountains). I see no evidence of moisture infiltration from rain or snow. All the scissor trusses and plywood are dry with no water marks. It seems the only time we notice the water stains on the living space side of the drywall ceiling is when we have a warm day after a very cold spell. The ceiling gets very damp along some of the drywall joints but of course the previous owners say they never had a problem!
Any suggestions as to solutions to this problem outside of a lawsuit???
 
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  #2  
Old 02-03-03, 08:35 PM
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Join Date: Nov 2001
Location: USA
Posts: 1,873
CONDUCTIVE HEAT TRANSFER

Trusses have been noted to have several problems concerning ceilings, especially the expansion and contraction of the trusses. Most manufacturers are aware of these problems and the best advice is for you to contact them. They will more than likely have a solution for you or at least aleviate the problem.

Conduction, in this case the mechanism is diffusion, is how heat transmits through solid materials. The problem with scissor trusses is that a relatively small portion of the truss is buried in the insulation, while a good portion is not and even touching the underside of the roof. This allows heat to transmit through the truss quickly causing the portion of the truss buried in the insulation and touching your ceiling to lose temperature rapidly. The result is dew point temperature is reached on the ceiling where the trusses touch it.

Again, I will advise you contact the truss manufacturer.
 
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