Frost in the heated garage

Stewzallu

What is the cause of frost in my garage? Here's the scenario:
House and garage were built less than 2 years ago, 2 car attached garage 26x26 x 10 ft(2x6) walls, fully insulated, vapor barrier on ceiling and walls, accousta sealed, 20-24" blow-in Insulation in attic w/ insulation stops on all rafters, radiant floor heat, drywalled (not taped/mudded), no ceiling fan or anything
Here's the problem:
In various locations along the top edges and worse in corners there is frost build up causing wet spots in the drywall. Also, heavy ice build up on windows. I put a dehumidifier in there a few days ago and it seems to have helped the windows a bit, still lots of frost in the walls/ceiling.
Do I need an hrv in the garage?

Thanks for any help or suggestions!

joecaption

Cold unheated garage, warm wall in house for one thing.
Air leaks around garage door, Uinsulated garage door. No foam or vaper barrer under the garage floor.
Just guessing.

jklingel

Stating the obvious, frost forms where it is cold. Why is it cold in corners and top of wall? Possibility for the corner: Poor or no insulation. Just because you have 5.5" walls does not mean that the insulator did a good job; corners take having someone who GAFRA construct them. I've seen 3 or 4 studs in a corner on a few houses, some having small gaps, and at least nowhere to insulate. Wood's R value is well below good insulation, so the corners get cold. Possibility for the top edges: The attic insulation does not extend beyond the corner, or at least enough. Some folks don't have enough truss height over the walls to accommodate sufficient insulation and an air space. That leaves a cold corner up there. Or, the insulation job in the wall was fiberglass batts (not very good product) and they were not detailed accurately; some batts are short, and a person needs to fix that, not just run poly over it and move along. Those would be my first guesses. Sorry to hear.

Stewzallu

Thanks for the info. I did use fibreglass batts in the walls. I may have rushed putting them in , so I may have to remove some drywall and vapor barrier. One of my building friends said that I probably didn't get enough blow-in close to the very edges of the wall and this will cause cold spots . I wonder if once these issues are resolved I will still need an hrv or at least a dehumidifier? 2 vehicles out in -25 to -30 Celsius brought into a warm garage are gonna cause a lot of moisture, and with nowhere to go is probably going to cause a lot of humidity.

Stewzallu

There is 1 1/2 Rigid SM and vapor barrier under the heated garage floor "radiant floor heat" I think I put. The overhead doors are insulated and air leaks around the garage door would cause frost build up around the garage door. But I do appreciate you trying.

jklingel

Ah, so YOU'RE the contractor who cut corners! Kidding. Corners can be a nasty. I would absolutely dig in and remedy the problem if at all possible; the truss height deal may be tough. Closed cell spray foam may be very helpful, but that will likely have to wait till it is warmer. Yes, those cars are gonna wet the hell out of the place. After 30-some years in Frb, we are going to have a garage to park in soon, and I am curious about that very issue. I will be running a fan for 20 minutes when the garage doors open (for fumes) and an HRV will be run as well. I may have to bite the bullet and run one of these small and spendy "mini-HRV's" I've read about; if I could recall the name I'd tell you, but I think they are made in Canada. They are just fans w/ heat recovery grates in them; I know nothing more. I believe I read about them on greenbuildingadvisor.com, if you care to investigate.

biggles

check out "holmes on homes" youtube he has a bunch of draft videos and always starts with the garage ceiling seems any space above the insulation will cause infiltration of cold air into the heated spaces

antlerdancer

Check that Your roof vents (ridge vents) are open. When blowing in 2 feet of inslu.,the dust will clog the screens on said vents. I have seen it happen alot. Good Luck

Stewzallu

Hey! I don't know what you're talking about...but I'm no contractor! Hahaha. All kidding aside I read that cardboard baffles hold moisture and that the blow In Should be touching the top plate! Wish I woulda known that before I stapled the edge completely over the top plate?! That's how they seemed designed to fit! Now I think I'll go in the attic, trim whatever I can from the baffles on the top plate, make sure they're well sealed and then make sure I got lots of insulation packed tight in the corners. A lot of F-ing around! Goes to show a person not to rush anything unless you've done it a million times....or ever before!

Stewzallu

Thanks I'll check the vents as well to make sure they are clear.

Donnig

Check your radiant heat. If you have a heated garage floor you should not have freezing at all unless you have huge gaps. do you have the radiant set at 40 to 45 degrees. also check if you develop a small leak in the radiant in the floor it will leach moisture into the garage big time concrete is very porous Do you have a way to check your water levels or loop pressure of your radiant to make sure your not losing any water?

MJW

I think you found your problem, but you have to remember that the concrete will give off plenty of moisture for a long while. The dehumidifier will help, so keep it going.

Your main problem is the lack of insulation in those areas. I'm sure you figured that out by now.

Stewzallu

Problem was that I Installed the cardboard insulation stops wrong. Definitely paid for it though! Was up there all day laying on my face mucking around in 2' of blow in insulation fixing them so wind would not get underneath them (which it did!) and blow away the insulation from the top plate(which it did!) haha.
Haven't had any issues since then, but I still got the dehumidifier blasting all day and night.
Thanks for all the help folks!