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Adding Soffit Vents

Attics and Basements, Repairs and Installation, Interior Published 08/15/2007 by Ben Erickson

Adding Soffit Vents

Keeping your attic cooler in the summer can increase the life of the roof as well as saving money on your air conditioning bill. To effectively cool the attic, outside air needs to circulate through it. One solution is to bring fresh air into the attic through soffit vents under the eaves.

There are several different types of soffit vents available including continuous, circular, and perforated vents made for vinyl siding. We’ll discuss the easiest to install, standard 8″ x 16″ vents.

First mark off the space where you want the soffit vents to go, spacing them so they fit between joists or rafters.
Cut the hole slightly smaller than the vent itself with a circular saw or a saber saw. Don’t forget to wear eye protection.
Check to be sure that the hole vents into the attic and isn’t blocked by insulation or other obstructions.
Screw or nail the vent into place.

The fresh air the soffit vents draw in should be expelled near the peak of the attic through vents in the gables, ridge vents in the roof, wind turbines, or power vent fans.

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13 Comments to “Adding Soffit Vents”

milt Says:
August 30th, 2007 at 11:59 am

Can a 8″x 16″ be install between each rafter and both side of roof.
Ben Erickson Says:
August 30th, 2007 at 3:09 pm

Milt,
The rule of thumb on the number of soffit vents needed is approximately 1 sq. ft. of vent space for every 150 sq. ft. of attic area. So if your attic is 1,500 sq. ft., you divide that by 150 to get 10 sq. ft. of vent area. Then divide the vent area by the opening in each vent to come up with the number of vents you need (for example a 6”x12” vent opening would equal 0.5 sq. ft, divide that into 10 sq. ft. and you get 20 vents). Space them evenly around the bottom of all the low sides of your roof. You should also have a way for the hot air to escape near the top of the attic, such as a vented ridge, gable vents, or vent fan.
B. Hanson Says:
November 8th, 2007 at 1:19 pm

I am ready to do this plus add styrofoam ventilation channels. I am wondering if the ventilation channels go only where the soffit vents are or must I do all the roof rafters with the channel vents?
Bob Says:
December 26th, 2007 at 10:14 pm

My house is 22×60 the attic is about 4ft from attic floor to the peak not a walk up attic i want to install 4in soffit round holes how many do i need. thanks
Ben Erickson Says:
December 27th, 2007 at 4:52 pm

Bob,
Using the formula above, you would need 8.8 square feet (or 1,267 square inches) of vent space in your attic. Since each 4” diameter hole would have an area of 12.56 square inches (3.14 x r²), you would divide 1,267 by 12.56 to come up with 101 vents. That’s a lot of holes to cut!
Don Severson Says:
February 10th, 2008 at 7:03 pm

Does it matter whether the vent holes face
away from the house into the wind or should they face away from the wind toward the side
of the house so they dont clog?
Brad Kendell Says:
February 13th, 2008 at 8:27 pm

I have a 28 X 24 garage with 24″ centers of rafters.

I went with a plywood eave. The ceiling is insulated, and it is cold up here, 25 degrees f for a few months of the year.

I was going to put an 8″ x 16″ soffit vent on every second rafter in the front, starting with the outer most ’space’, between rafter 1 and 2. On the rear I was going every second one, but alternate by starting between rafter 2 and 3.

I thought that would give better ventilation that mirroring front to back.

Also, do I need them in the ends of the garage, where the peak is?

Thanks.
Chris Says:
February 21st, 2008 at 10:42 am

Just a quick comment in regards to Ben Erikson’s response to Bob dated December 27, 2007. Apparently, Mr. Erikson did not double-check his math. According to the formula, Bob’s attic area would be 1320 sq ft not 1267 sq ft. Dividing 1320 by 150 gives a vent area of approximately 9 sq ft which would interpert into 9 4″ soffit vents or 10 if you like even numbers.
Nicholas Roussos Says:
February 21st, 2008 at 6:21 pm

Chris, I think you’re confusing sq feet and sq inches. They’re not the same thing. For instance you say he needs a vent area of 9 sq ft and that 9 four inch soffit vents would do. But 9 four inch holes does not equal 9 square feet.
Chris Says:
February 22nd, 2008 at 9:21 am

My mistake and thanks for the clarification.
chargerplates Says:
February 29th, 2008 at 2:33 am

My garage floor shows a crack in it. It appears to come from the outside wall about half way in the garage. Also, lots of water comes off the trucks wheels from melted snow or just rain water. What is the best thing to do in this case?
rick kellum Says:
April 6th, 2008 at 8:52 am

We live in a 50’s style ranch and over the years the soffit vents have been painted over while painting the overhang. We would like to replace or restore these, but haven’t been able to find the size we need to replace them. Any ideas would be appreciated.
Mark Says:
April 15th, 2008 at 11:15 pm

Rick,

It doesn’t have to be exact. Just get one that is larger then your existing as they just nail or screw over the cut out opening.