Frosty rooftop vents might mean trouble in the attic


by CCHRC Staff

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

Q: I have a cold roof. The other day I noticed frost on the vents that are high up on the end walls of my house.

What should I do?

Frost on roof vents of a cold roof indicate you might have air leakage and moisture coming from somewhere inside the house, more than likely through the ceiling. So you have warm air getting into the attic, then out through the vents where it condenses and forms hoarfrost. There are a lot of places this leaking can occur. You could have a chimney or plumbing penetrations going through the ceiling that aren’t sealed properly, poorly sealed can lights, holes in your vapor barrier, or bathroom vents and fans that are broken or not properly connected to the outside.

When it warms up, crawl up into the attic and take a look. If there is so much frost that it is building up on the outside, then there could be some moisture damage inside.

Q: Are there any cautions for replacing windows in the winter?

Flanged windows, especially vinyl ones, get brittle in the extreme cold, so handling them takes a bit more care. Also, expanding spray foam, used to seal the gaps between the window and the framing, doesn’t cure well in low temperatures. The can instructions are pretty specific in this regard, and if you install a foam backer rod into the gap first, which stops the airflow from the outside, then you can spray the foam and it should work.

Q: What are some general rules on when to plug in your automobile?

The rule of thumb that the Alaska Department of Environmental Conservations provides is to plug in for at least a couple hours when it’s 20°F or colder.

I think most of us have realized that if it’s 20°F, you can get by plugging in at a lesser amount and if it’s quite a bit colder you need to plug in longer. If you find you need to leave your car plugged in substantially longer before it starts smoothly, then you car may need some maintenance.

Q: I hear the word “retrofit” being used a lot in talks about fixing up an old house.

What’s the difference between retrofitting and renovating?

Renovating simply means restoring something, making it look new again, or repairing it.

Retrofitting is modifying something old with new technology. In a home, upgrading an older energy system, using a new technique to insulate walls or replacing outof- date windows with new ones are examples of retrofitting.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at You can also call the CCHRC at (907) 457-3454.