[PDXhomeowner]

I’ve been looking at ways to make my garage cooler in the summer. It is ~450 square feet with open rafters. It has a peaked roof that kicks out a little at the bottom, creating these very small soffits. One side is 3.5” wide, the other is 8” wide. There are four roof vents, two on the roof at each end. No gable vents. The previous owner added cedar bead board material in the soffit area. The rest of the house has wide soffits and the same cedar material was used, but with a continuous venting strip added as well.

Eventually I would like to put in a drywall ceiling to be able to better condition the space below. I have insulated the walls in the garage area.

What should I do to increase proper venting for the garage attic space? There isn’t much room to add venting. I was thinking I could put some kind of small vents along the narrow soffit on the North side of the garage, and add larger vents on the wider soffit on the South side of the garage. Or remove all the soffit on the narrow side and replace with a wide soffit vent?

Or, am I missing something? Is there a reason why the previous owner put all this nice cedar up instead of adding soffit vents?

Photos of:
-wide(r) soffit
-narrow soffit
-wide attic detail
-narrow attic detail
-roof vents

 

[Nealtw]

This 2x4 didn't have to be there, but getting it out might be tricky, could likely drill some 2" holes into each bay

 

[PDXhomeowner]

This 2x4 didn't have to be there, but getting it out might be tricky, could likely drill some 2" holes into each bay

Fortunately that’s not a 2x4, it’s the thinner cedar beaded planking. Only a few inches wide, it could be ripped out and replaced with some kind of continuous vent?

 

[Nealtw]

Fortunately that’s not a 2x4, it’s the thinner cedar beaded planking. Only a few inches wide, it could be ripped out and replaced with some kind of continuous vent?

That would do it. :wink2:

 

[huesmann]

Your wider soffit looks like you have room to get a circular saw in there to rip a strip out (blade depth set to soffit thickness).

 

[PDXhomeowner]

Your wider soffit looks like you have room to get a circular saw in there to rip a strip out (blade depth set to soffit thickness).

I guess the trick is finding what’ll work with the 3/4” thick cedar? I’m thinking of cutting out rectangular holes for some 16x4 soffit vents on the wider side. The narrow side is tricky, it would be nice to find a continuous vent of some sort that could fill the strip there. If I try fitting the standard continuous vent, it’s a little narrow and lower profile than the 3/4”. Maybe rip all of the thin strip of cedar out, attach the continuous venting strip to the rafters, then add trim strips to cover the edges?

Or can I add more vents on the wider south side and just add less area of circular cutout vents on the north side?

 

[Porsche986S]

Can you use round soffit vents ? Pick the largest diameter that will fit the narrow area maybe 3 " ? Get a hole saw and start drilling you already know your rafter tail spacing from the attic . If you were to put two 3 " vents in each soffit/rafter cavity on both sides that would provide a decent amount of incoming air . So drill a hole , pop in a vent and drill the next hole . Not sure how much they cost but every box store and hardware/lumber store sell them .

In my opinion adding intake volume at the soffit is half the battle , you have to have enough exhaust outlet . I'm not smart enough :biggrin2: to know what " enough is " but I don't think you currently have enough :smile:

 

[Once Upona Hack]

It's a garage so it has a garage door and it probably leaks air pretty well already.


Adding soffit vents seems like the right thing to do according to theory, but truth is likely you won't get much, if any, benefit from them. Volume of passive air movement in constricted spaces is very minimal. Put in a powered, thermostatically controlled, roof vent (round saucer type) and you will move a good amount of air without any soffit vents. Add the soffit vents if you like, but don't expect any appreciable difference. Probably a hole saw and a drill, combined with the largest round vents you can fit in the soffit, one per bay, is the best you can hope for without fully removing the soffit and installing a continuous strip vent.

 

[PDXhomeowner]

I should add that part of the inspiration for doing this is to prepare for insulating and finishing the garage ceiling. Hopefully I seal that enough to minimize the draft from the garage door!

The roof vents are 8” dia., so approx 50 square inches of area each. x4=200 sq. in.

My 450 sqft garage needs ~3 sqft of venting(432sqin)

Ideally there would be another roof vent, but it’s close.

So I need to add 200 sqin of soffit venting. Those circular vents are easier but don’t offer much actual vent area. I think I’ll add some 4x16 vents on the wide side and then see if I can find a good circular vent option. Hmmm

 

[Bud9051]

For the narrow side they make 8' long strips about 3" wide, maybe a bit less, but you can drill many holes in a row and cover with the strip.

Remember the calculations for recommended vent area refer to net free area (NFA) not necessarily the opening size. When there are bug screens in there that NFA can drop to 50%.

And you are correct, those pop-in round vents do not provide a lot of NFA.

Get as much as you can easily get as the guidance is really an industry WAG (Wild Ass Guess) that got written into codes. Fortunately it has worked for over 50 years so no one has bothered to do better. But there is a lot of wiggle room.

Bud
https://www.homedepot.com/p/Air-Ven...ld-in-50-Pieces-Carton-Only-SV351WH/308306211

Ignore the price they can be found in singles.