Detached Garage Insulation and Venting Query
brandon!
| Posted in General Questions on
Following up to my previous post, Attaching 1″ Rigid Foam Under Hardie Plank Lap Siding. I’m seeking advice on my insulation approach for a Zone 5 (Chicago) detached garage with a ridge vent. In particular, are rafter vents required (see attached photo) if the attic space remains open and unconditioned; e.g., we do not build knee walls or finish/seal the rafters?
Our garage will be similar to the photo in that our main/lower space will be conditioned as I use the garage as my DIY wood/workshop year round. However, we are not planning to build out the attic space. Instead, we’ll simply lay OSB/Plywood over the joists to allow for storage (e.g., sleds, camping gear, etc.) My current insulation plan is as follows:
- Roof (Completed)
- None. Builder wasn’t flexible on this.
- Ceiling
- Drywall
- Rockwool batts (R30) in the joist cavity
- Walls
- 1/2″ fire rated drywall and/or plywood (French cleat system)
- 2×4 studs w Rockwool batts (R15)
- 1/2″ OSB (Completed)
- WRB (Completed)
- 1″ rigid foam board (R5) (Completed)
- Hardie siding (Completed)
- Heat
- Comfort Zone Ceiling-Mounted 7,500-Watt Fan-Forced Industrial Heater
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Replies
In zone 5 your choices are vented attic or conditioned attic you need to pick one.
Add the vents or move the insulation to the roof line.
If it were my shop I would add the roof vents and a heat pump set to the lowest heating set point its software allows. Plus keep the 7500 Watt heater hooked to a app based control. The HP will heat the garage using ¼ of the electricity that the shop heater will and give you AC if you chouse to run it. The HP keeps the shop at say 55° when you want to use the shop you turn on the shop heater remotely and it quickly heats the shop to a nice temp before you arrive.
Walta
Thanks Walta. If I’m understanding you correctly, my current approach is considered a vented (unconditioned) attic and is OK, e.g., the attic will be entirely open from the soffit vents to the ridge vents. The ceiling insulation is for conditioning the main garage space, not the attic. While I plan to place OSB over the joists to allow for storage in the attic, they will not extend over the soffits. In other words, they will NOT impede their venting function.
Thanks for the heat pump tip. I’ll investigate it though it may be more than I need – I’m used to working in an uninsulated, leaky, unheated garage...
I'm in zone 2A and am planning a conditioned/unvented detached garage attic with 3" of polyiso on the roof deck. If you're only insulating the ceiling then you'll want to vent every thing as Walta says.
I'm also planning to condition with a heat pump (haven't decided on conventional/ducted vs. mini split yet) but I'm not sure how long the recovery time will be without the resistance heater. I may need to plan ahead on the winter and summer days I want to use the shop space.