I’ve got a 40 yr old ranch house that is getting mold due to condensation on the interior walls (at the ceiling). It happens at soffit vent locations, the power entry, and plumbing vents. The upper 8 inches of the wall is above the soffit height. What are suggestions for insulating these locations and will I have to tear out the drywall to get rid of the mold?
Some other info : I plan to put more soffit vent in, when the roof was replaced ridge vent replaced 2 square vents; the walls are 2 x 4 construction, ~same size as vents not much room for insulation.
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You need to figure out what's causing the problem. Poor insulation is likely part of it, but it could be that there is too much humidity leaking into the attic in the first place. Several hours spent in the attic sealing around wire/pipe penetrations is well worth it.
Another very likely source of leakage into the attic in your situation is the raised ceilings -- this may be leaving the tops of stud cavities open to the attic. So dig through the insulation, and if you can see into any stud cavities, apply rock (or maybe housewrap or plastic sheeting) over the openings.
Likely the edge right adjacent to the eaves is going to be a problem, though. It may be that you'll have to remove the soffits to gain access to the area to seal the stud cavities.
When insulating, keep in mind that "naked" fiberglass is just about useless. But of course you don't want a vapor barrier on the outside of the fiberglass, so consider something like housewrap to cover it and keep air from infiltrating it. Or use some other type of insulation.
Having sealed and insulated as much as you can, probably the getting as much air movement as you can will be sufficient to prevent further trouble. Double up on the soffit vents (if using the 8x16 metal vents, use at least one every 4 feet). The ridge vent, if properly installed (check from the inside to be sure it's not blocked) should be sufficient.
Make sure that insulation doesn't block soffit vent air flow. Install vent channels against the roof deck as needed. If you have to take the soffit down install the channels even if you don't think you need them -- it will be good to have them if you get some more insulation blown in or some such.
You could also take some steps to reduct the relative humidity of your house. That way there will be less moisture available to get through any gaps in your air sealing...Dehumidifier is my least preferred idea since they cost a whole bunch of money to run.Ventilation in your house is what you need.Make sure that any point sources of moisture (bathrooms and kitchens) have proper exhaust fans which do not end up spewing water into your attic. Out the roof or out the wall (and only out the wall if it is sufficiently low down that your soffit vents won't pick it all up).You may need to consider some kind of supply ventilation as well but I would start with making sure the kitchen and bathroom were taken care of.Its funny. Last year I knew next to nothing on this subject until I discovered a need to know the hard way. The first big chunk of information I got on it was from this forum and I haven't turned back since.Amazing how much information is available on the subject.If my house wasn't a 100 years old... there would go a really fine hobby.
A 40-year-old ranch is unlikely to be so tightly sealed that high moisture inside the house is a problem, but you were right to point out a detail I missed -- make absolutely sure that any vent fans, etc are dumping the air OUTSIDE, not into the attic. Seal joints in the fan ducts, etc, to eliminate any leakage into the attic.One other problem a 40-year-old ranch could have, though, is slab leaks, if it's built on a slab. Small leaks in the water pipes buried in the slab can contribute considerable moisture (without an obvious leak), causing what would otherwise be a "dry" house to turn into a swamp.So if there are water (not drain) pipes in the slab, they need to be checked for leaks (a daunting task I'll leave to someone else to help with).