I’ve read and heard so many differnt techniques on venting roof rafters that share interior space…specifically the ratio of intake through soffits to the exhaust at gables or ridge? Any suggestions/feedback would be appreciated. Some say 50% of the exhaust area should suffice for intake…others say a cold roof with 3 1/2″ of air space through out the rafters to vent …and yet there are plenty of roofs seemingly unvented?
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Framing the floor inside a crawlspace foundation keeps a gable-end addition close to grade.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Fine Homebuilding Magazine
Fine Home Building
Follow
-
Fine Homebuilding
Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.
Start Free Trial Now -
GBA Prime
Get instant access to the latest developments in green building, research, and reports from the field.
Start Free Trial Now
Replies
Welcome to the vent wars!
The first thing to understqand is that venting is not done alone by itself. it is one part of a system that includes structure, insulation, vapour barriers, ( or not ) and other minutae of design. So tell us more about what you have and where you want to go. Sometimes no ventilation is needed and othertimes enough is never enough.
In direct responce to some of your questions - You do not ventilate rafters. You ventilate a roof or attic space. It is the space that might collect moisture that needs ventilation and not the rafter itself.
When a through ventilation system is part of the design, the ratio is always 1:1 in and out. It is not possible for the ridge to vent out more than the soffit can suck in.
Look at it this way - if there is only half as much in capacity at the soffit as out flow at the ridge, on a windy day, the ridge will be creating a vacumn/suction in the assembly. The only place makeup air can come from if provision is not made in the soffit, is from within the house itself, via the many little cracks that are bound to exist in all but the most excruciatingly performed work. That interior air will carry moisture and heat from the house into the attic and cause more of the problem the vent is designed to prevent.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!