New Garage – Design Considerations
I am in the preliminary design phase of a detached garage, around 34×48 (1632 sq ft) with 12-14 ft ceiling. The size could go up or down a bit, but that’s pretty close to what it will be. Location is Montgomery County Maryland, mixed-humid. We get a few weeks of nice weather in the spring and fall, and otherwise it is too cold or too humid and hot. I have dealt with working in that for a lot of years, but now I want to remedy that.
The usage of the garage is a shop. While I may park a daily driver inside, that same space would be used for something like washing and detailing, working on project cars, side work, storing some older cars, and some woodworking and metalwork equipment would be in the same space. At least one two-post life will be installed.
So, to summarize, I want this garage to be comfortable year around, warm in the winter (around 50-60 degrees – I’m too old to deal with working in cold shops like I used to), comfortable in the summer (humidity control is really important, and temps under 80), and not have me equipment or old cars passively rust from humidity. Also, want to make environmentally responsible decisions, which also means less expensive to heat/cool. I probably have 20 years left to enjoy what I build, but someone else will inherit it, so 20 year payoff is not critically important (although will be considered).
I definitely don’t need to meet passive house standards (garage doors prevent that), but I am thinking of “pretty good house” standards. Thoughts now are towards 2×6 walls or maybe ‘post-frame’, raised heal truss, and a slab with insulation underneath. Possibly hydronic heat (current intention, unless costs are prohibitive), that would make my time in the shop nicer, but for 3 months of time maybe I can go without? I still don’t want a cold floor.
My open ended question to all of you is what should I be asking? If you were in a similar situation, what would you consider, and what have you done? What have I missed?
Thank you for looking at this post, and responding (all feedback is appreciated).
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Replies
Pretty-good house standard is the right direction.
I would put my money into the best doors you can get. Maybe even have them custom made, or use french doors meant for living space. You want this space to be sealed and insulated like a house and that's just not going to happen with a conventional garage door. Be very suspicious of r-value claims by garage door manufacturers, there's a lot of shenanigans there.
If you must have a roll-up door I would consider having it in a separate bay that is treated like unconditioned space and is insulated and sealed from the rest of the building.
A 1600 square foot open plan building with PGH insulation screams out to me for a mini-split. If you're only heating to 50-60 probably a pretty small unit.
I'm nearby in DC, the last Manual J I had done said we're cooling-dominant, so an uninsulated slab contributes more cooling in summer than the heat it requires in winter. So insulation under the slab isn't need, which is good because it simplifies the footings for your lift.
The only thing I would put in that is garage-specific is high-capacity ventilation, so that if you're painting or sanding you can flush it all out. I'd have makeup air inlet vents, and I'd put filters on them to keep outside dust out of the shop. If you're gong to have cooling you need some sort of air handler inside and I'd put high-capacity filters on that so it doesn't get clogged with dust you kick up. It may be worth getting a ducted minisplit even though you won't need ducts, just so you can put better filters on it.
If you're going to be working on cars and running the engine you should have a hose to run the exhaust outside. And a carbon monoxide sensor.