Hi, All:

I am a newcomer to this site and new to woodworking. Because I am not an architect, engineer, electrician, framing carpenter or general contractor, I need some feedback. I am trying to locate my workshop in my garage, which is separate from the house and sized to fit about 2½ cars. The problems are the cold winters (it can drop to 10 below here) and the garage’s pier foundation, which admits light and moisture under the sheathing and makes the garage as damp as a leaky basement. In fact, the “half” part of 2½ cars has no slab at all — it’s just dirt with a wood platform above it.

My plan is to insulate the garage against moisture and cold by extending a reinforced deck across the entire garage (the existing concrete has cracks and dips due to frost heaves). I first would place over the concrete and dirt a plastic vapor barrier and nail (with stainless steels nails) a perimeter of pressure-treated 2-by-6’s on edge around the garage. I would caulk along the base of the perimeter to keep water from riding in over the vapor barrier. I would then connect to the perimeter a joist-like deck structure of treated 2-by-6s spaced 12” on center. I would put blocks of expanded polystyrene along the walls in between the studs to block air from coming up from underneath the walls. I would lock them in place by spraying polyurethane foam around all the seams.

In the bays between the joists I would fit two layers of 2-inch-thick polystyrene and spray-foam the seams. I would leave open a channel to run electrical and a branch of 4-inch-diameter galvanized ducting, to be connected later to a dust-collection system. I would nail atop the joists two layers of “¾”-inch plywood. The first layer would be pressure-treated, the second layer CDX. I am thinking of slipping a layer of roofing paper or adhesive rubber waterproofing (called Water and Ice Shield?) between the plywood layers as moisture insurance. Maybe priming the CDX would be enough. The floor would be painted with an epoxy or latex laden with grit or crushed walnut shells or something similar to prevent slipperiness. There would be two or three openings in the floor for electrical and dust collections ports. The rest of the garage would be insulated conventionally, with fiberglass batts (maybe polystyrene under the roof where warm air would condense).

The platform would compromise headroom. There would be just 7 feet from the new floor to the joists overhead. Enough for me but maybe not for some as-yet unpurchased bandsaw. (Lighting would be recessed between the joists.)

The electrical service would come from a subpanel inside the garage. I would run #6 THHN through PVC conduit underground from the house. That would originate with a 60-amp breaker in the main panel. I plan on having three 240V outlets, each on its own circuit. But no two would be in use at the same time. (Well, I should qualify that. Some dust collection systems run on 240V and might need to be on the same time as the 240V table saw). I’d like two of those outlets to be floor-mounted to keeps cords from stretching across the room. I’d have regular 120V outlets spaced along the wall and overhead to accommodate fluorescent lighting. I haven’t decided yet on how to heat the place. The garage already has a wood stove, but I’m sure a wood stove sitting atop a wood platform would never meet code, and I cannot devote floor space to a brick hearth.

That’s it. Is this plan adequate? Is it overkill? Is it illegal in 48 states? Any and all comments are welcomed. I am especially concerned about the place getting enough juice and the safety of that service. For example, NEC requires that garages have GFCI-protected outlets. But I have never seen a 240V GFCI outlet. Also, I have yet to find any housing made for locating an outlet on the floor. If such a thing exists, it has to be watertight.

Thanks.