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Alto 06-19-2010 04:44 PM

Ridge Vent Size
Is thee a recommedned minimum length for a ridge vent to be effective?

seeyou 06-19-2010 05:33 PM

If your vents are split between ridge vents and intake vents, the minimum requirement is 1 square foot of ventilation or net free area for every 300 square feet of attic floor space.

Alto 06-29-2010 12:27 PM

I am back to working on my roof and the question of rdige vents has come up again. Seems to me like one of the most important things is venting. Sorry to say but i am so new at this i don't understand your answer here. Do you mean that a ridge vent 20 feet long by as many inches in width that the opening of the riodge vent is --the square footage of the opening of the vent; let's say 20 feet X 8 inches- should be a functioin of every 300 square feet of attic space?

Right now I have two or three pretty small -- probably less than a foot across -- passive round vents coverend with a metal "bublble" . Good soffit boxes all around the house. I have been told not to keep these passive vents with a ridge vent. I also understand that these alone would not necessarily work today because the roofing material is not as good today as it was 40 years ago when they put on my present roof.

Wouldn't the surest thing to do be to close off the passive vents and put in two electric ones?

seeyou 06-29-2010 01:03 PM

Each brand/model of ridge or any other type of vent has a specific sq in/sq ft free air rating. So if you have a 300 sq ft attic, you need 1 sq ft (144 sq in) of inlet/outlet combined. So you'd need 72 sq in of inlet and 72 sq in of outlet. If you use a ridge vent that gives 9 sq in of free air per foot, you'd need 8 lin ft of ridge vent. These are minimum requirements.

If you're venting to reduce the temperature in your living space, you'd be better off increasing the insulation. Vent to remove moisture from the attic.

Alto 06-29-2010 02:17 PM

I am going to have to do the measurements. I have received an interactive table from Owens cornings that gives measurements. But it seems like I am going to need a whole lot more venting than I have space for. What do you do in this situation? is this when you go to the elctric vents and how do you figure square footage per one of them?

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