Adding Soffit Vents
Attics and Basements, Interior, Repairs and Installation by Ben Erickson
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.
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 amount of vent space 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. Ideally, half the vents should be located in the soffit at the bottom of the roof and half in gable or ridge vents near the top. Divide the vent area by the opening in each vent to come up with the number of vents needed. For example a vent with a 6”x12” opening would equal 0.5 sq. ft. Space soffit vents evenly around the bottom of the low sides of your roof.
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?
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! If half the vent space is near the top of the roof in ridge or gable vents, that would reduce the number of soffit vents at the bottom to 50.
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?
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.
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.
February 22nd, 2008 at 9:21 am
My mistake and thanks for the clarification.
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?
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.
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.
May 19th, 2008 at 10:57 am
Ben,
I used your formula to do my house (38×60), and had planned on using soffit vents with three 2″ round holes on them-until I realized that I would need a crazy amount of holes. So here’s my question-if i modify the hole to make it bigger, is there any such thing as too much ventilation when it comes to attics?
Ben Erickson Says:May 19th, 2008 at 12:02 pm
Paul,
While you can have too little venting in your attic, you can’t really have too much. Keep in mind that it’s best if half the venting is in the soffit at the bottom of the roof and the other half at the top in gable or ridge vents to allow outside air to flow through the attic. Depending on local building codes, the venting may be reduced to 1 sq. ft. of vents for every 300 sq. ft. of attic area if the house has an adequate vapor barrier and the venting is balanced between the top and bottom of the attic.
May 20th, 2008 at 10:17 am
I remember hearing or reading somewhere that soffit vents should not be installed directly above windows (and doors also?), though the picture here shows one squarely above a window
I’m adding soffit vents to my home, and the ones I’ve got are currently evenly placed, except for above windows. Any truth behind this?
Thanks!
Ben Erickson Says:May 22nd, 2008 at 1:14 pm
Hi Adam,
I see no problem with locating a soffit vent above a window or door. Many houses have continuous soffit vents which go all the way across the house. The only reason I could think of not to put a vent over a window would be in the unlikely instance that a downdraft caused hot air to come out of the vent and in an open window. However, since hot air rises, under most circumstances the soffit vent would be drawing cool air in rather than letting hot air out.
June 9th, 2008 at 1:40 pm
Danny:
I have a run the numbers on my vents and I am a little short on the total vent opening space, I think. I have about 3,400′ of floor space in the attic and 26 soffit vents that are about 8″ X 16″ and maybe 60% open (the efficiency is eaten up by loovers and screens. Then on the roof I have six wind turbins that are about 12″ (when i measure the inside diameter they seem like they don’t quite measure 12″ but are more than 10″. If I did the numbers right I have enough soffit vent but need a little more venting higher up. I live in Texas and when the outside temp is 100F the attic temp is arond 135F. I had read once that if the attic were properly ventilated the attic temp should be around 105 if the outside temp is 95. What are your comments on this? Do I need more vent space and if so, where? Is it really reasonable to expect to get the attic temp down to 105 with an outside temp of 95 with natural ventilation?
July 13th, 2008 at 11:52 am
Would it be a problem to install soffit vents near or over an A/C? Also, when I install my bath vent out through the soffits, will that interfere with the attic soffit vents? Should I vent thebath out the roof? I have a roof with a ridge vent and gable vents, but no soffit vents. I can install some easily on one side, but the other side has the problems outlined above. This side also has half the soffit length because of an addition with a torch-down roof. Maybe I can get some venting through the torch-down roof soffit by cutting a hole in the roof to allow the air to flow.
Thanks for your help
Ben Erickson Says:July 14th, 2008 at 10:28 am
Gary,
Since AC units expel quite a bit of heat, putting a soffit vent directly above one wouldn’t be the best place for it. Rather than taking up one of your existing soffit vents with a bath vent, perhaps you could cut a separate hole in the soffit for it, or run it out the gable if it’s not too far away.
August 3rd, 2008 at 3:20 pm
where can i purchase that vent cover? i have 3 2″ holes inline every 2 feet all around the house - most of the screens are missing & need to cover them. thank you.
August 5th, 2008 at 2:19 pm
When installing soffit vents, do you install them with the vents facing the house or with the vents facing away from the house?
August 18th, 2008 at 8:16 pm
fyi regarding direction of vents
September 14th, 2008 at 7:22 am
ATTIC VENTILATION FOR HOMES
B. R. Stewart
Agricultural engineer-environmental control ~ Agricultural Extension Service ~ Texas A&M University
http://www.factsfacts.com/MyHomeRepair/ventilation.htm
September 19th, 2008 at 2:19 pm
per http://www.diynetwork.com/diy/he_home_insulation/article/0,,diy_13895_2275822,00.html
vents point toward the house