Power Roof Vent Fan & Soffit vent spacing

Old 05-19-02, 07:04 AM
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Power Roof Vent Fan & Soffit vent spacing

Im having my house re-roofed and theyll be installing ridge vents and vented aluminum soffit (soffit vents). Two questions:

1) Does every roof joist cavity need to be vented and if so, should I have them use continually vented (perforated) soffit material or is it sufficient to have a band of perforations every 8 10? (I dont really like the look of the continually perforated soffit but will use it if its needed).

2) Should I also have them install a roof mounted, thermostatically controlled vent fan or is that overkill?

Note: I live in the Chicago area so I deal with winter ice dams and a couple months of hot weather. The attic space is unfinished and unusable (no storage).

Old 05-19-02, 08:01 AM
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You do not need to vent every joist cavity unless you have a Cathedral ceiling. It's not good to install two types of exhaust vents ( ridge vent & power vents) it will cause a short circuit in your ventilation. Air will follow the path of least resistance and you will not be venting your attic properly. Air should enter the attic at the lowest point, move up through the attic and exit at the ridge. In other words use one type of exhaust venting.
Before you have the aluminum soffit panels installed you should check with the manufacturer to make sure that they provide sufficient net free area per linear foot to balance the ventilation system. Also make sure your existing intake system is not blocked by paint or dirt and just covered up with the new aluminum panels. You should have at least a 50/50 balance between your intake and exhaust vents. Ridge vents will give you 18 square inches per linear foot which means you should have 9 square inches per linear foot of intake vents on each side of your roof.
If you decide to go with a power vent system look for a fan that has both Thermostat and Humidistat controls.
Old 05-19-02, 09:21 AM
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Just a suggestion for an alternative to aluminum soffit. There is a vinyl soffit product that is perforated continuously in the side of the rib where is it not even noticable unless you look closely. It is super-strong and easy to install. I'm not advertising for the company, but do install a lot of it and consider it one of the best. If you would like more info let me know.

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