Shop - Too Many Vents?

[desert4wd]

Well.....
Edited: Having a shop built and I was thinking it was going to have too many roof vents (static 12"x12"). About 24k cu.ft. and 17 vents. Since the post, I learned a few things about the build I didn't know but it still seems a bit extreme to have 17 of them.
Cheers!

Original post:
I'm having a shop built and it seems like it will have an excessive number of vents (standard size 1'x1'ft I believe). I've contacted the contractor as far as what is planned for insulation and exactly where but no answer yet. The shop is 36 x 42 x ~16ft (approximate) and also approximately, 24,000 cu.ft. There are 10 vents planned for the large side (R) and seven for the smaller side (L), 17 total. Everything I've read so far including calculators, address "attic" venting. This shop basically consists of two bays, the large bay just has open rafters and a peaked roof above it, the small bay has a stand up storage above, 20x12'. Besides the bays, it has several large windows, up and downstairs, plus man doors front and rear.
I'm more concerned with excess heat leaving the shop when it is cold out (ie. down to 10 degrees some years, but generally a fair amount of days below freezing every year.
Doe's this amount of venting insinuate a fully insulated shop, including the small "attic" locations in the peaks of the shop? My original thoughts didn't really include making the shop as comfortable as our house living room and this has kind of surprised me - lol.
Any insight into this would be appreciated.

- Doug
Willamette Valley, OR

 

[tomroblee]

I would guess that the number of vents in the roof depends on what the builder is trying to accomplish.

As a general rule, the free area of the exhaust vents should match the free area of the intake vents. I'm guessing that your intake vents will be soffit vents----but I suppose that you could leave the doors and windows open as well.

I would be interested in seeing what kind of vents the builder is intending to install over the holes. In my area (central Indiana) ridge vents are more commonly used when there is an adequate length of ridge to install the vents. My home has a hip roof, so there is only a very short ridge. The builder used something that looks like:

https://www.homedepot.com/p/Master-...le-Match-Weathered-Wood-SSB960ASMWW/100028379

The installation instruction specify a 10" diameter round hole, and the vents provide 60 sq. in. of free air flow.

It is possible that your builder intends to use a perforated soffit material something like this:

http://www.emcobuildingproducts.com/Aluminum-Soffit-Panels

The specifications show that the fully vented panels have 13.2 sq. in. of free air per foot length of the panel.

From your pictures and descriptions, it doesn't look like you will have enough soffit area to install sufficient soffit vents to match your 17 roof vents.

 

[Rusty Bolt]

Here is an engineer, Joseph Lstiburek, talking about venting. He has a PhD and researches venting. Lots of good info. It's been a while since I watched it, but IIRC, you want more venting down low than up high. He goes into some detail about why.

 

[desert4wd]

Thank you guys for your input on this, I am checking those links out and researching some other sources as well. The roof vents being used are static RCV stem vents (RV038) I can't tell what the diameter is at this point in time . The soffit vents are in the spaces between the trusses- these are apparently old-school, in my opinion, just screened vents placed over rectangular cutouts, perhaps 8"x2".

 

[tomroblee]

I'm a retired geezer, not a ventilation expert.

A few years ago the building codes seemed to specify free air flow attic venting requirement for an attic to be 1/150 of the square footage of the attic.

Your building is about 1500 sq. ft., so it should have about 10 sq. ft. of free air flow to vent the attic. This would be about 5 sq. ft. of roof vent and 5 sq. ft. of soffit vents.

I couldn't find much concrete information about "static RCV stem vents (RV038)", but assume that the RV means roof vent and the 38 means 38 sq. in. of free air flow. 17 vents would give you about 4.5 sq. ft. of free air flow. My best guess is that the vents would require an 8" diameter round hole to install. This would make your 12" square holes seem a bit odd.

If you are using 8" x 2" soffit vents, you will need a lot of them to balance the vent area of the roof vents. Soffit vents are normally screened to keep insects out. This screening restricts the free air flow by a significant amount. 40 completely open holes could supply the area you need, but I'm guessing that you will need many more once the effect of the screening is factored in.

 

[desert4wd]

First of all, Thanks Rusty Bolt. Nice and educational link, pretty long video but a good speaker that's easy enough to listen to. I appreciate that very much, it definitely helped me get more up to speed.

Tom, thank you for your information. I'm in the same Geezer club!
A couple of items I should correct or clarify. 1. Soffits are 10x2" which it looks like I have 30. 2. I described the roof vent holes incorrectly and their size is just a bit larger than the pipe diameter. Since the vents are on the roof I can't determine positively what that measurement is (I'm very much hobbled at the moment.... ok last two months)

Five sq.ft. of roof and five of soffit vents is right on, (720 sq.in. total) and with 30 soffit vents (600 sq.in. total)... (sans loss because of the screen) that puts the soffit flow about 120 sq. in. short (0.833 sq. ft.) or six soffits.

Im not so clear minded these days, even after checking things. I could be way off, but it looks about right to me. (six soffits sounds better than 120 sq. in.- lol).
I have to take a break and let the little brain rest a while so I'll let this be for now.
Thanks a ton!