I have a reproduction victorian house with a 12 in 12 hip roof. There is only about 50 ft of vented ridge for about a 1000 sq. ft footprint. The soffits are vented with 3 in diameter vents about every 32 inches.
Problem: Every winter I get some mildew and frost on the sheathing on the north facing side near the eaves. I’ll be due for a new roof nest year and I know I’ll need to replace plywood. I’m considering two options when I reroof. 1) cut vents and vent the hips. or 2) put a doghouse dormer at the peak with a louvered vent and a fan.
Need opinions on this. Are there other options? Should I add more soffit vents? The house is 17 years old. The ceiling openings are pretty tight and ceilings well insulated. I’m in upstate NY.
Replies
Add roof warts or the more attractive Louvered doghouse.
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First, you need to control the source of the moisture. Is there a damp/wet crawlspace or basement? (Most likely source, at least in my area.)
Or bath fans venting into the attic.
I did a few rough calculations based on some assumtions.
Standard venting req is 1' for every 300' of foot print You need about 3.5sq ' of venting minimum. Your ridge venting should roughly equal your soffit venting.
If your house was a 32' square you have approx 48 3" vents at 7.1sq" each that equals 2.36sq'
Ridge vent varis but some is 12.5sq" per linear foot @50' thats 4.34sq'
The soffit appears to be OK based on these #'s but a bit more wouldn't hurt.
Have a good one
Edited 8/13/2006 1:16 am ET by diesel
When you re-roof, you can use a vented drip edge instead of the traditional drip edge. You just need to be certain that your fascia boards are not tight to the roof deck. Otherwise you'll get no air flow through the drip edge up to the roof. It looks a lot better than soffit vent in my opinion.