I have a 35 year old house in Minnesota. Last winter we noticed large amounts of frost built up on the bottom side of the roof sheating. He are using a ridge vent and soffit vents where ever possible. The house has a 4/12 pitch which doesn't leave much room above the top plate and roof sheating to allow for insulation and a vent chute. At one time we had the normal tin roof vents about every 6-8 feet near the peak of the roof. They worked fine but we found in a wind driven snow storm snow sifts in through the vent and collects on the attic insulation. Hence the reason we went to the ridge vent. But now it doesn't seem to be getting rid of enough of the humid air causing it to freeze to the underside of the roof sheating. The ceiling does not have a poly vapor barrier. Is the frost caused by a lack of venting or lack of insulation? We have about 7-9 inches of cellulose, and would like to add fiberglass batts over it. Looking for ideas.
You probably have a ridge-vent with a filter in it. Filters trap moisture, restrict air flow and clog with dirt. Ridge-vents made without an exterior baffle design don't work very well. You must have a ridge-vent with an exterior baffle design in order to move the air out of the attic. 99% of all moisture problems in the attic, as well as snow in through the roof vent, is caused by lack of proper soffit venting. Soffit vents on existing homes become clogged with dirt, paint etc. many time there simply aren't enough vents installed in the first place. This is the number one cause of heat and moisture build up in the attic. Go to www.lomanco.com and you can learn all about how to properly ventilate
Hi. Just a comment on the Minnesota attic. I found it interesting that you recommended the Lomanco product website. I too had a low quality, filter type ridge vent. I was talked into installing it over the standard roof vent hoods when I had a new roof installed. That winter I had exactly the same problem the Minnesota fellow experienced. Long story short, I had the entire roof and the ridge vent replaced due to the poor installation and my legal threats. I chose the ridge vent ... again ... on the advice of the new installer. He highly recommended the Lomanco Ridge Vent Product. It's 36' in length. I have 32 Grille type 4 x 16 placed @ the eaves - actual openings 3 x 16. The shoots/baffles are positioned properly and they're open. Plus, I made certain the top plate of the walls @ the edge were covered with batt pieces. I re-did the entire attic insulation and re-sealed all voids, holes, plumbing stacks ... etc. with foam. As with the Minnesota scenario, I too do NOT have a vapour barrier. The original installer didn't recommend it given the age of the house and there was concern it could create a moisture problem in the aged house between the living area ceiling and the attic. So I laid R-12 batts between the joists and re-spread the loose fill on top for a layer depth of approx. 16". Yet ... even with the new Lomanco Product with the outside baffle, I'm still experiencing high humidity. Now I've read that Ridge Vents don't work well without wind. Moreover, I'm beginning to think there's too much intake venting ... I'm still working on it. My point is to be careful what you choose and do your homework ... 'cause the decisions you make now can come back to haunt your attic. I'd love to hear what anyone has to say about this ...