Sheena Noce
1/31/2014
Hello, We built a 2 story home nearly a year ago with a metal roof. When we experience a thaw, a lot of condensation builds on the underside of the roof in the attic. So much so, that it has begun to mold/rot the trusses and some of our ducts/fire alarms will 'drip'. We are also having some drywall damage starting... The inside of the attic is very wet. We have vapor barrier, approx 24" of blown in cellulose insulation, the styro foam in the soffits, and I feel plenty of ventilation at the ridge cap and end gables (you can feel air movement throughout and see sunlight at the end gables as well as a gable vent at each end) We think that the issue may be that we have our 2nd story heating/cooling ductwork running through the attic with drop down venting into the 2nd story rooms. I am not sure of the R-value, but the ducts are wrapped in a black plastic and thin insulation. There seems to be about 2-4" of cellulose on top of them, but in several places there is frost/ice buildup on the actual ducting trunks. The wettest area is the end of the attic in which the main ducting trunk comes up. Any ideas if this is in fact the cause? And if so, what is the fix? We were thinking more insulation, maybe batts this time wrapped around the ductwork? Could it be another issue? Thank you!
Todd Miller
Isaiah Industries, Inc.
1/31/2014
First of all, I am never a fan of residential metal roof installations without decking. You mentioned soffit vents, ridge vents, and gable vents. Have you tried closing off the gable vents? I am concerned that air is flowing from the gables vents to the ridge. This means that you're not getting good air circulation in the attic. The best circulation will be from the eave to the ridge. The gable vents are short circuiting that, it would seem to me.
Eric Novotny
An informed customer is the Best Customer!
1/31/2014
Air seal, air seal, air seal. That is a bunch of moisture and I agree with Todd that metal without sheathing must be supremely vented and over a very tight structure. It is a recipe for failure most times. Insulating the ducts additionally will not stop the moisture and air loss. You have to air seal the attic floor, add additional insulation, and seal up the duct work. The radiant loss of energy isn't moving the moisture...the air loss is. If you can't seal up the duct work (i.e. bad flex lines) plan on having rigid duct lines installed that can be properly sealed up.
Guest User
2/2/2014
Thank you for your replies. We used spray foam throughout the house in the walls, at R24 (4.5" of 2 pound closed cell soy base) and the attic floor is code R50. we have added R40 batts around the flexlines. We did not have gable end vents until last week when we noticed the problem, so they are recent. before that, we did have good flow.... but added them out of desperation when we saw the moisture issue. We are at the top of a hill with plenty of air movement. We do have vapour barrier on the attic floor, is there something additional that we can do to air seal further to avoid heat loss? Now that the cellulose is damp, will it dry? or does it need to be replaced?
Eric Novotny
An informed customer is the Best Customer!
2/3/2014
Cellulose in the attic and Fiberglass around the flex lines are not stopping the loss of conditioned and moisture laden air into the attic either via the penetrations of the attic floor (top plates, can lights, electrical drops, etc.) or the HVAC connections. What do you have on the attic floor that is a vapor barrier? Air loss is your biggest issue in this attic. The cellulose will dry out once you remove the moisture source.
Guest User
2/3/2014
We have a poly vapour barrier. It is taped around all of the lights, hvac etc. and there is acoustic caulk at all of the joints.
Eric Novotny
An informed customer is the Best Customer!
2/3/2014
How is it tape around the lights? They should not be taping the plastic to any recessed lights regardless if they are Insulation Contact (IC) rated or not. They should have fireproof enclosures built around them. Is the home on a crawlspace? Regardless, the answer is that too much moisture is getting into the attic. SPF in this case is both a blessing and curse. The home is supremely tight in this case and the air in the home is making it up into the attic.

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