[Insulation Advice] Detached Garage – First-Time Homeowner in Southern Ontario

Hey folks, I’m a first-time homeowner and looking for advice on insulating my detached garage. Hoping to make it usable year-round (I’m in Southern Ontario), and I’m trying to balance comfort with budget. Garage Overview: Home built in the late 1950s; garage was likely added in the 90s or 2000s (based on outlets/wiring). Detached garage with siding, soffits, and a black shingled roof sloped on all four sides. Single-panel garage door — has ~3–5 inch gaps at the top corners when closed. No roof vents. One small window on the right side. Wood framing, sealed with a fibrous MDF-like panel. Concrete slab floor. Current Issues: After a few hours closed in the summer heat (30°C+), the garage becomes insanely hot inside. I’ve got an old TV and PS4 set up, and I’m worried about electronics overheating. I'd like to reduce heat buildup and eventually make the garage usable in both hot and cold seasons. Ventilation Question: Would a roof vent and a front vent (for passive airflow) help reduce the heat when the garage is closed? Would it make a noticeable difference? I’m not expecting AC-level cooling, but even a slight drop would be worth it. Insulation Plan: Trying to decide between two insulation options: 1. Rigid foam board (1") ~$20/sheet locally. Doesn’t seem to require a moisture barrier? More expensive overall but simpler to install? 2. Owens Pink fiberglass $65/bag locally. Cheaper, but I’d need to install a vapor barrier and do more sealing work. My overall plan: Insulate walls and ceiling. OSB over the walls, painted. Gaps sealed with expanding foam. Rigid foam along the ceiling, leaving rafter space open for ventilation. Future upgrade: Replace the garage door with a multi-panel one. May turn the window into a door later. Using portable AC/heater units for now. Mini split planned for the future. Main Question: Given the goal of year-round use , which insulation type makes more sense for keeping the space reasonably comfortable? Would love any advice — insulation type, vent placement, passive cooling tips, etc. Happy to answer questions or clarify anything I missed. Thanks in advance! submitted by /u/Asgaard_Hunter [link] [comments]

Jun 27, 2025 - 15:12

Hey folks,

I’m a first-time homeowner and looking for advice on insulating my detached garage. Hoping to make it usable year-round (I’m in Southern Ontario), and I’m trying to balance comfort with budget.

Garage Overview:

Home built in the late 1950s; garage was likely added in the 90s or 2000s (based on outlets/wiring).
Detached garage with siding, soffits, and a black shingled roof sloped on all four sides.
Single-panel garage door — has ~3–5 inch gaps at the top corners when closed.
No roof vents.
One small window on the right side.
Wood framing, sealed with a fibrous MDF-like panel.
Concrete slab floor.

Current Issues:

After a few hours closed in the summer heat (30°C+), the garage becomes insanely hot inside.
I’ve got an old TV and PS4 set up, and I’m worried about electronics overheating.
I'd like to reduce heat buildup and eventually make the garage usable in both hot and cold seasons.

Ventilation Question:
Would a roof vent and a front vent (for passive airflow) help reduce the heat when the garage is closed? Would it make a noticeable difference?

I’m not expecting AC-level cooling, but even a slight drop would be worth it.

Insulation Plan:
Trying to decide between two insulation options:

1. Rigid foam board (1")