Hey everyone, I have a question for the hive-mind regarding my garage that I am currently finishing. I am in Edmonton, AB Canada so I believe that’s climate zone 7a.

The building is a two-car detached garage with a “storage attic” – 1.5 story building with knee walls and a ceiling joist in the trusses. The builder (garage construction contractor) installed two passive roof vents and vented soffits to what is standard/code here.

My primary concern is actually keeping the attic storage space cool-ish during the summer months. When we have our summer days with >30°C the direct sun on the asphalt shingles raises the attic temperature to the point where LDPE items stored up there have deformed (I haven’t measured to be certain, but what I’ve read suggests the plastic deforms around 50°C).

I would like to keep this space cool enough to be useable, but I’m not looking to fully condition it as it is above where our cars are parking after driving around in the snow/rain/whatever and is not connected at all to our house.

I’ve read on here (and other sites) that simply installing more attic vents won’t help. I have also been advised (by the garage building contractor) NOT to fully insulate the garage in our climate unless I am going to install some conditioning control (electric heating, small gas furnace etc). Does that sound correct? I can understand not wanting to seal in the dampness from the vehicles if they’re parked wet or snow-covered and I obviously don’t want any issues with ice dams!!

So should I try and just “shield” the rectangular inter-truss space with some kind of foil lining on the interior of the roof sheathing? Or is there something else I can do that would be a better way to keep those temperatures down?

I’ve attached a pic from one of the articles here showing the construction, and location of the roof vent on the roofline.

thanks!