Venting & insulating garage roof in Colorado

[av8bpilot]

Howdy. I was hoping to get some advice for venting my roof (or not) before I sheetrock everything over and blow in the insulation (closed ceiling). This is a detached, 2.5 car garage in the Denver area. I'm in the process of finishing it off with R19 in the walls, drywall, and an 18K mini-split. Currently, the roof only has two box vents on the north face and no 'intake' side for a ventilation system. Heck, they couldn't even manage to cut the box vent holes large enough. The soffits are OSB/Hardiboard and open on the inside, but have no external vents.

What kind of venting do you think would be sufficient for this? I was thinking something simple like 4" vents every other rafter span or something. I do not want to rip out and replace all the soffits. Thanks.

 

[couch67]

4" would work, maybe even 3", would be easier to drill them, just drop more of those in. I think the general rule is 1/150 venting for sq footage of the garage, but maybe research that more for your area . So for every 150 sq ft, need 1 sq ft venting, between the roof and soffit vents.

 

[tarmy]

I did what you are doing about 2 years ago…the vents I used work great due to the typical afternoon breeze and the direction it faces…

 

[75gmck25]

You might also want to get a price for sealing the "attic" area and applying foam to the underside of roof deck. We did this with our house a few years back and it has been really efficient. It works even better because our A/C unit was in the attic, and now the entire system is in conditioned space.

You have lower humidity than we have in Virginia, so that may be a factor, but I really like how ours worked out. We used Icynene open cell foam and on the roof deck they applied about 8-10" thick. Attic temps are within a few degrees of the temp in the house.