If moisture damage to drywall and framing is not that bad, blowing in a few cans of expanding polyurethane foam to fill the gap should do the trick.
QUESTION: We are in the process of renovating our home and removing carpets to be replaced by a floating floor and repainting.
The problem exists in our bedroom. It has a bay window near the centre of the room facing the north side. The other exterior wall of the bedroom faces the east side. The problem is the northeast corner of the bedroom shows moisture on the floor, especially when the temperature outside gets colder. This was never evident before because of the carpet.
We have removed furniture from the corner as well as all the carpets in the room. The corner has no obstructions blocking it. The floor heat vent is situated in front of the bay window which is recessed 16 inches from the straight line of the wall. The corner is more than six feet from the floor vent, measured in a straight line.
We think the heat is not being circulated in the problem corner. We have used a fan to circulate the air and we have put a heater in the corner. We have caulked the small opening under the drywall at the bottom plate of the two exterior walls. The basement room underneath is insulated and finished and the ceiling is lay-in tiles. The house was built in the mid-'70s.
Should we open the wall in the problem corner in the bedroom and re-insulate? We should mention also that we have opened the ceiling and the floor in the bay area to re-insulate. Could you please give us your experienced thoughts on this matter? Thank you, Rose Couts
ANSWER: I recently saw a similar problem in a house of about the same age, so I have a good idea of the cause. While poor distribution of heated air in the room may be a contributing factor, the original construction is the real culprit.
Houses built in the '70s are often fairly well-insulated, with decent air/vapour barriers, but there are sometimes a few areas where that is not the case. The corners of the exterior walls, where the wood framing of perpendicular walls meet, often has a void between the studs. This void can be about three to five centimetres in width and extend from the bottom to top wall plates.
In modern homes, this void is normally even wider but is filled with insulation before the walls are joined together. This may not be the case in your home.
While the polyethylene air/vapour barrier should bridge this gap on the inside of the walls, minimizing air leakage, it will not fully prevent warm air from the home entering this cavity. In the winter, this cavity can be at a considerably cooler temperature that the interior of the wall but also lower than the surrounding walls. If the rest of the walls are reasonably well-insulated, the temperature may not be low enough for any warm air that leaks into them to condense. But in the uninsulated corner, condensation is almost a certainty.
When the weather is well below freezing outside, this condensation will freeze and turn to frost or ice. As the weather warms, or when the sun hits this corner of the building, the frost will melt and slowly wet the area below.
If you're lucky, this moisture will leak along the exterior of the house through the bottom of the wall assembly and dry out in the warmer months. In your home, some of this moisture is making its way inside the home and wetting the bottom of the wall, the floor sheathing and the old carpet.
Improving air movement in the corner of the problematic wall will help the wet material dry quickly, probably preventing a major problem, but will not be a complete solution. As you have suggested, removing a portion of the drywall in the corner will be required. This should be done mainly to expose the corner and see if my theory is correct, but also to see if the there is any major moisture damage. If this has been going on for several decades, there is likely significant rot in the studs, and certainly the bottom wall plate, that will need to be repaired.
The polyethylene may be saving the drywall from becoming wet and mouldy, but there could be hidden damage on the backside requiring it to be discarded. Removing a small section of drywall on either side of the corner should be enough to see how bad the damage is.
If the moisture damage to the drywall and framing is not that bad, adding proper insulation to the void in the corner may be enough to stop a reoccurrence. Blowing in a few cans of expanding polyurethane foam to fill the gap should do the trick. If the studs, bottom plate or floor sheathing are rotten and need to be replaced, more conventional insulation could be installed prior to reframing the corner.
I recently saw a similar situation in a bedroom closet of a home. When I looked in the closet, there was excessive storage on the floor and clothes hanging from the bar were filling up the back of the closet. When I reached in to pull the clothes back, they were damp. I saw a thick layer of frost on the inside of the corner of the closet walls. Since these were exterior walls, my conclusion was that insulation was missing in this area.
In both this case and yours, the lack of proper airflow may have been the straw that broke the camel's back, but the underlying cause is missing or improper insulation.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the president of the Canadian Association of Home & Property Inspectors-Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
