Q. We had our house surveyed and sealed up recently, but we now seem to be capturing humidity in the attic that is freezing on the interior wood surfaces. This can’t be good. I was thinking of putting a vapor barrier up on the interior roof joists and spaces, but is that the best solution?
TIMOTHY P. KIRWAN
A. You’re not alone. Many people are reporting frost on the underside of their roofs. The frigid temperatures we experienced were making it prevalent. The short answer is that there is too much warm, humid air escaping from your home and into the attic, where it is condensing and freezing on the underside of your roof sheathing. The frost itself doesn’t do any damage, but when it melts, things will get wet. Melting frost can lead to deteriorated roof sheathing, mold, wet insulation, and water stains on ceilings.
I’ve written extensively in the past on air leaks, insulation, and attic ventilation. Frost gets into the attic from air leaks: attic hatches, wire and plumbing holes, recessed light cans, HVAC, chimney penetrations, and uninsulated bath and dryer pipes.
Your best bet is to seal off the leaks. Beefing up your insulation alone will not solve this problem. The problem with air sealing is that the leaks are underneath your attic insulation, and it will be very difficult to fix this without removing it.
In summary, reduce humid air in the attic by sealing air leaks, adding insulation, and ensuring adequate ventilation. Sounds easy, right? It’s not!
Q. We live in a condo that was recently gutted down to the studs and remodeled. Our unit is two stories: the garden level and first floor. During the colder months, we get a lot of condensation on our windows, especially on the garden level. Our developer told us to keep the HVAC fan running downstairs, but that doesn’t help. Some days we wake up and there’s an inch of ice on the inside of the window. Is there anything we can do to prevent this from happening? It seems to be ruining the inside of our windows and will be a hotbed for mold if we don’t clean them often.
A. A lot of people are experiencing what you are describing; warm, humid air is condensing on the windows and freezing on the glass. The crazy cold days we had were mostly the cause.
Are your windows double insulated? If not, do you have storm windows that are closed? Do your windows have aluminum frames? If yes, they may conduct the cold more. It’s also possible that your windows are older, underinsulated, and may have air leaking in around them. In that case, upgrading your windows will help.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to firstname.lastname@example.org or tweet them to @robertrobillard. Subscribe to our newsletter at pages.email.bostonglobe.com/AddressSignUp.