During an addition to my contemporary cape in NH, a bathroom ceiling fan was installed and vented into the soffit on the north side of the home. Within the last several months, I have noticed the paint on the ceiling cracking and brown stains developing on the ceiling. I inspected the space above the bathroom ceiling and found what appeared to be mildew or mould on the greenboard. The vent lines servicing the fixtures appeared to be watertight, and the insulation showed no signs of mildew or mould. I didn’t see any stains on the sheathing on the roof, so I think I can rule out a roof leak. The ridge vent appears to be functional. I suspect it could be condensation on the ducting for the vent fan. Any other thoughts on the cause of these stains?
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My guess.
You're running A/C and blowing cold air through the duct that goes into the warm attic = condensation.
Eric
I Love A Hand That Meets My Own,
With A Hold That Causes Some Sensation.
[email protected]
Thanks for the quick response Eric. Unfortunately, like many homes in New England I don't have A/C.
My guess is that humid room air is escaping to condense in the cold winter attic. When spring comes, the ice melts and keeps the ceiling wet long enough to grow mold.Fanatical air sealing is needed. It wasn't clear from the initial post if the fan vents into or through the soffit. It has to be ducted fully THROUGH the soffit, evin though you may have soffit vents galore.Bill
"and vented into the soffit on the north side of the home"
INTO or THROUGH the soffit?
It needs to be vented outside.
Is the ducting over or under the insulation? Add more ins'ln on top to keep the moist air wqarm until it hits the o/s, this will help stop moisture condensing if there's a chance of it. You haven't mentioned vapour barrier.
Query "into the soffit" - best get it thru and out. And make sure the duct slopes downward towards the o/s.
You also didn't say that the mold was where the fan and duct is - we deduce that - but is that the location, or all over?
cheers
***I'm a contractor - but I'm trying to go straight!***
To Bill, Bill Hartmann, and Pico...Thanks for the input. The fan ducting isn't insulated at all, and the exhaust is simply butted on top of the soffit, not through it. Additionally, the ducting itself has gaps in it...am considering pop riveting (with similar metal rivets to prevent galvanic corrosion) and sealing the gaps with metal tape. After that, I concur that more insulation is needed. I shall ensure that at least a slight pitch of the duct toward the outside of the home is added. The mould/mildew was not in the same rafter bay as the fan and ducting...it was in the adjacent bay. Again, the yellow fiberglass insulation showed no signs of mould/mildew growth. Venting into the soffit seems to be an unsatisfactory method of exhausting warm, moist air, especially in this climate, and particularly since the warm air would probably re-enter the attic space through an adjacent soffit grille. I plan to replace the greenboard ceiling drywall. Any other thoughts/hints/suggestions for a quality repair?
To Bill, Bill Hartmann, and piko...no vapour barrier present. Should plastic sheeting be stapled to the strapping before applying the greenboard ceiling drywall? Looks like another shortcut done on this job. Older and wiser now...?