I live in the northwest and was looking at a house today when I noticed stains on the ceiling. The house has a hip roof and the living room and dining room are two stories tall, approximately 18 feet from floor to ceiling. The stains were dark enough to notice when you looked closely, but not black. The house is 4 years old and the stains appeared to be located at each truss. The stains were about 2-3 inches wide, and extended about 8-10 inches from the outsidewall. There was also a dark circle about 24 inches in diameter about two feet from the outside wall. I suspect that it is somehow related to lack of insulation where the trusses sit on the wall, since it is probably all wood from the ceiling sheetrock to the roof sheeting that close to the outside wall. The trusses are 2×4 and the wall studs are 2×6. Could the differences in temperature between the wood trusses and the insulation cause this type of problem? Does anyone have any ideas or experiences with this type of problem, and how to eliminate it? The circle stain has me completely baffled.
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very common
Colder material at the wood trrusses allows condensates to form on the sheetrock. Sometimes water vapour that feeds mildew, sometimes smoke fro cigs, fireplace, or candles.
Circle could be an old leak
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The "shadow" staining is from smoke -- fireplace, candles, cigarettes, etc. The circular stain is from a roof leak, possibly fixed, if the stain looks old and dry. (Or the circular stain could be from condensation due to ductwork in the attic, though not likely in that area.)
If the problem area on the winter prevailing winds side of the home- usually northwest around to northeast?
The circle is definitely from water. It may have been from melting snowwater (blown up through soffit venting) finding a place down through the poly AVB. The blowing snow phenomenon may not happen every winter and may vary from very little causing no visible effect to what you have.
The other problem would be wind blowing along side the bottom chord of the truss and under the insulation. This happens if there is no outer airtight wind-deflecting baffle to cover the end of the insulation at the wall-soffit. Infrared images of this are quite telling. It happens in most houses but can be defeated easily at the building stage.
Thanks for your reply. It is on the east and south side of the house, but the house is on a hillside in the Columbia River Gorge, which can get extremely strong winds. It is on the side of the house of the prevailing winds. We don't get a lot of snow here, but it rains a lot in the winter. The house has a low pitch roof, probably about 4/12, so it could be blowing through the blocking vents and under the trusses if it is not sealed well where the siding, trusses, and blocking meet. Very few houses out here use sofffits, but I understand why we always used them in Michigan where I grew up. Starts to make more sense.
Edited 6/11/2006 1:54 pm ET by Deschutes