Help! I’m adding two rooms to my own house, one of those “spare time” jobs that drag on forever. Anyway, I got everything framed up and dried in before winter set in, and I insulated all the ext. walls with fiberglass batts. I’ve spent most of the winter completing one of the rooms, and now am starting the other. I am just hanging the drywall and peeked behind the insulation to find mold and very damp sheathing. It seems to be mostly in the stud bays where the batts had to be trimmed to fit and weren’t stapled off. I can find no sign of a leak above the wall or from the outside siding. Could this just be humidity from the warm room getting through the slim insulation gaps and condensing on the inside of the ext. sheathing? When I hang the drywall will that take care of the airleaks or do I need to take down all the insulation and get rid of the mold first? Thanks for any suggestions.
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Replies
Yep humidity and condensation.
Get rid of fiberglass batts, attend to mold. Go to search in lower left of this screen after scrolling down.
Type 'insulation' in the search bar you'll see there.
Click on those threads until you are satisfied you know enough to deal with it.
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Take out the f/g insulation. Spray the mold with 1:4 bleach to water, and let everything dry thoroughly before you cover it up.
You did not say if this space is heated or how, but if you have no exterior leaks, then the moisture is likely from interior humidity and/or air leakeage through the wall.
Kraft face F/G does not make a good vapor barrier, unless very carefully installed. You also did not say what your exterior finish was. We would need to know more about the whole assembly to give reasonable advice.
Go to http://www.buildingscience.com for information on how wall systems work for your area. They also cover mold developement, prevention, and remediation.
BTW, welcome to Breaktime
Dave
Edited 2/12/2005 5:16 pm ET by DAVERICHESON
Thanks. The exterior is OSB T-111 type siding over housewrap over 1/2" OSB sheathing. Interior is tied into central heating and has been heated for about 3 months. Some of the stud bays have no mold at all. Mold is mostly in odd size bays where I had to trim the f/g batt to fit and no longer had the stapling flange to secure to the stud. Also, the upper part of the bays under the window sill.
You need an interior vapor barrier before the sheetrock goes up. The kraft face isn't doing the job.Beat it to fit / Paint it to match
You have described the reason why a vapour barrier is essential. Humidity from interior is condensing when it meets cold exterior sheathing surface, then is trapped in the insulation, allowing mould to form. Vapour barriers prevent moist air from reaching cold surfaces. It's important to meticulously seal everywhere - lapped joints in the vapoir barrier material, and around any penetration of the interior face of framing: electrical boxes, windows, doors, etc.
Remove the insulation and aggressively dry the stud spaces. You need both heat and air circulation to achieve this. Once the moisture levels drop sufficiently, mould will not continue to grow. There are industrial filters available for rent that circulate the air and filter out mould spores to prevent outbreaks should moisture levels climb again.
Wally