Dealing with mold on the inside of OSB sheathing
Zip code 53951, south central WI, zone 6a.
Working in non-perfect situation - occupying unfinished house and can't afford to finish it up in timely manner. Heated by central air furnace with supplemental wood burning stove heat. Plan is to finish walls first and after we can afford to do the infloor heat, finish ceilings (2 stories to do)
Moved in early October, found mold about week ago (late February), when moved some fiberglass for new electrical box. Still recovering from the shock...
Here is wall profile, all new materials:
- (no siding yet)
- 1" polyiso foam, foil side to the house, outie windows, windows and ISO not taped yet (I doubted tape longevity in weather elements, wanted to wait to just before siding installation; I know that this could have added to the problem)
- typar housewrap
- 1/2" OSB
- 2x6 studs
- R-19 unfaced batts between studs
- at some areas we had 4mil plastic, to avoid contact with fiberglass (but mold is also in spaces without plastic, no rule or reason to mold); obvious rim joist areas wouldn't have plastic anyways.
- started removing plastic and installing 3/4" T&G wide plank flooring as wall finish
Before you say anything about drywall - we don't plan to have any in the house, other than maybe required firebreak from attached garage. All wall and ceiling finish will be 3/4" pine.
After extensive studying of the problem, I have figured out, that most likely mold was caused by "cold sheeting" problem, which is direct result of too little of exterior ISO vs interior fiberglass. I doubt if interior plastic/no plastic added to problem. Doubt if untaped ISO seams was a big factor in the winter, but I know it can be in the summer.
Questions I have now on exterior fix:
1. Would taping the joints and windows and adding 1 more layer of 1" ISO be sufficient? It's more economical to go with 2 more layers of 1" than 1 extra layer of 2". 1-1/2" is just little less than 2".
2. With outie windows on current layer of ISO, I would tape the flanges to the ISO, but what to do after 2nd layer of ISO is installed? Removing windows to box them out is out of question.
3. Siding will likely be a lapped cedar. After proper thickness of ISO is achieved, would it be better to go with 1x4 vertical straps or some kind of wicking membrane. In 2nd case, fastening would be a problem. I will likely not have enough funds to do #3 until later this year or even next year.
Now questions for the interior fix, would like to start with #5 after exterior fix is complete :
4. I will experiment with 4 following cleaners: boric acid and hydrogen peroxide mix, TSP, Spray Nine and Sporicidin. Plan to remove batts in 4 different bays, apply cleaners, let dry, observe performance, put insulation back in, check for mold reappearance in couple weeks.
5. After exterior fix is done, pick best performing cleaner and use it to clean all OSB sheeting.
6. Once OSB is clean, should I use any mold preventers/sealers like PermaGuard (Zinsser).
7. Should I spray perimeter of stud bays with foam or entire stud bays? 1" closed cell kit? (like 600 board feet kit)
8. Should anything I apply (sealer or foam) create a vapor barrier?
9. Fiberglass seems unaffected by mold and will be applied back into wall cavities.
10. No plastic to be used, 3/4" T&G installed as interior finish.
I appreciate all advice and ideas.
Posted Sun, 03/03/2013 - 01:02
Edited Sun, 03/03/2013 - 07:23
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