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mk1st · 10-26-20, 11:29 AM

Any mold growth means you have a water problem.
It will either be a 1)water leak or 2) condensation (in rare cases it could be both)

1) A water leak will usually be pretty easy to determine and the mold will be confined to only that area: is the roof in poor condition?, is there a flashing penetration such as a vent or chimney that's failing. The damage may not show up though right under the leak as water can wick along framing members. Fix the ongoing leak and the mold won't be able to grow. Old mold, once it's inactive, is not harmful to most people and if you don't go in the attic I'd not worry about it. Definitely DON'T try to "kill the mold" with bleach!!

2) If you see mold over a wide area of the underside of the roof and framing members then you have a condensation problem, most likely because you have air leaks from your living space up into the attic. In the winter the warm moist air from below will condense on all of the cold surfaces in the attic (insulation won't stop the air movement) Air sealing the attic floor is the solution. Get an energy audit (mainly that's a blower door test with infra red imaging) and you'll get a good idea as to how much air sealing is needed. Once the air sealing's done then you can insulate with confidence.

I know roofers will beat me up over this but this problem (if it's condensation) is NOT because you don't have enough attic venting. A properly air sealed attic needs very little venting - really just to allow expansion and contraction of the air in there when it changes temperatures. Good attic venting is fine but it's not the fix-all that roofers would have you believe (partly because roofers never go in the attic and want the easy work of adding vents).

Now....off to set up my blower door.

10-26-20, 11:29 AM	#4
mk1st Friend of Entropy Join Date: Feb 2010 Location: Fort Atkinson Wi Posts: 17 Thanks: 1 Thanked 5 Times in 2 Posts	Any mold growth means you have a water problem. It will either be a 1)water leak or 2) condensation (in rare cases it could be both) 1) A water leak will usually be pretty easy to determine and the mold will be confined to only that area: is the roof in poor condition?, is there a flashing penetration such as a vent or chimney that's failing. The damage may not show up though right under the leak as water can wick along framing members. Fix the ongoing leak and the mold won't be able to grow. Old mold, once it's inactive, is not harmful to most people and if you don't go in the attic I'd not worry about it. Definitely DON'T try to "kill the mold" with bleach!! 2) If you see mold over a wide area of the underside of the roof and framing members then you have a condensation problem, most likely because you have air leaks from your living space up into the attic. In the winter the warm moist air from below will condense on all of the cold surfaces in the attic (insulation won't stop the air movement) Air sealing the attic floor is the solution. Get an energy audit (mainly that's a blower door test with infra red imaging) and you'll get a good idea as to how much air sealing is needed. Once the air sealing's done then you can insulate with confidence. I know roofers will beat me up over this but this problem (if it's condensation) is NOT because you don't have enough attic venting. A properly air sealed attic needs very little venting - really just to allow expansion and contraction of the air in there when it changes temperatures. Good attic venting is fine but it's not the fix-all that roofers would have you believe (partly because roofers never go in the attic and want the easy work of adding vents). Now....off to set up my blower door.