Hi, All:
I first posted this on the Fine Woodworking forum.
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 “¾â€-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 suspended 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.
I am posting a copy of this query on the Fine Homebuilding forum.
Thanks.
Replies
You've got some good ideas. Myself, I think two layers of 3/4" ply is overkill, as is the idea of tarpaper between the two layers. I might also say that using treated ply at all here is not necessary but it probably wouldn't hurt as long as you added a layer of 1/4" or 1/2" something over it.
No, you cannot put a woodstove on a wood floor, but it's simple to make a hearth platform of ceramic or cement or whatever you like.
As far as the 240 volt stuff goes, will it be hard wired direct or do you plan to use outlets?
At any rate, I'd send it through a 100 amp breaker instead of sixty, and upgrade the cable size accordingly. You may want the added capacity if you decide to use electric heat, and sometimes you may not be the only person operating in the shop? Nice to work with other people at times, each running machines at will. Plus the added security of knowing you aren't overloading the main is a good thing too.
You could solve the headroom problem by eliminating the ceiling joists and moving them up as collar ties, or using a few beams occasionally to keep the walls from spreading apart, assuming you don't use the space above?
Have fun. It seems like I've built enough workshops for other people but don't get to do my own too often.
Mad Dog,
Thanks for your advice. Somewhere I read that the ply underneath heavy woodworking machinery needed to be at least 1 inch actual. Hence the two-ply idea for 3/4.Each 240V outlet would have its own circuit and a separate breaker in the box. Any idea where to find a 100-amp breaker? What gauge THHN wire goes with 100?
#4 gauge copper or #2 aluminum for 100 amp. Easy to get breakers--if it's a square d or cutler hammer, you can get them at any big box store. Other boxes may require a trip to an electrical supply store.
WAAAY overkill.
If it were me, I'd first square up and pour a cement pad over top your dirt half of the floor. Dirt floors love to give off water vapor.
I then would paint all of the old and new concrete floors with a floor mastic...or use foundation tar, and then embed heavy mil plastic on top of that mixture.
After prepping the floor as described, I would use pressure treated 2x4s and install them flat on the floor, 16 in OC. Screw them down with tapcons, or better yet, use a powder actuated fastener gun (PAF).
Where the concrete floor heaves a little in spots, alter your 2x4 placement to accomodate or cut the 2X4 on the underside to accomodate. I would use 1-1/4 CDX , T&G subflooring plywood, and would glue and screw this down in place. This step eliminates doubling the floor with 3/4 ply and still gives you the overalll thickness you desired for strength.
Before installing this floor, I would cut and fit in between the 2x4 sleeper bays, 1-1/2 inch thick Dow (blue) insulation board.
Wherever you planned to install large heavy machinery ( such as an old industrial bandsaw you mentioned), dig out the old concrete floor first and pour a new, reinforced concrete punch pad, up to the new designated subfloor height. These machines can be bolted to the pads...wood subflooring is not needed in these locations.
After subfloor installation is complete, I would paint the new floor with a good oil base floor enamel...no sand, grit, or walnut chips...the floor will dull soon enough and will not be slippery.
I would install a 100 amp breaker in my main home panel box, run new feeder lines to the garage and set up a 100 amp breaker box in this location.
Your underground duct work for dust collection could be done with regular flat furnace ductwork instead of the 4 inch round.
There is no need to use treated plywood for your first layer of subflooring, and do not put a water membrane between the 2 layers of flooring if you go your intended 2 plywood floor layer system.
The plastic membrane you initially wanted to install on the floor should stop moisture from rising up...the ridgid insulation between the bays also is a moisture barrier...now if you lay down one layer of flooring and then sandwich waterproofng membrane between that flooring and your final "top" floor...you are inviting trouble.....it's better to let any moisture that may rise toward the floor surface to be carried out via evaporation. Water vapor stuck between wood layers will keep the bottom floor layer damp all the time . Even though you planned on using treated, a continually damp floor is still not a good thing.
In my suggested scenario, the mastic greatly stops water vapor...the plastic is added insurance and allows you to walk on top of it without getting the stuff all on your shoes and clothing. This step alone should prevent water moisture from rising. The ridgid insulation between the sleepers adds both warmth and ridgidity to the floor ; which enables you to space sleepers 16 inch OC instead of your planned 12 inches....thus saving you money. The 1-1/4 thick subfloor will handle anything you have...but the concrete punch pads will definately eliminate any other fears you may have in this regard. The 2X4 sleepers are less costly than 2X6s...you eliminate needing perimeter rim joists as well, and you gain headroom. Yet, your finished floor should remain warm and strong.
Pour a punch pad for your wood stove...or better yet, eliminate the stove, and buy and install a forced air gas or oil furnace with a self contained heat exchanger so no inside air (sawdust) has a chance to infiltrate the unit and cause an explosion.
A York, 90% efficient furnace sized for approx 60,000BTU would be a very good choice. The combustion air and the exhaust air are both funneled from outside the building envelope via 3 inch PVC piping. Put this baby on a thermostat and leave it set on low when away and turn up when working...garage will stay very warm.
No need for a large duct run either...just cut out some register openings in your plenum...this will suffice. I have a large, pleated filter ( Air Bear) on my return air, and I have a small furnace pump to transfer the liquid condenstae into a waiting, 50 gal, plastic trash can; that I simply dump outside in my yard from time to time because my garage has no water/drain lines...if yours is set up so..then run it into the drain.
Simply letting the condensate hose stick outside via a small hole is no good because the line can freeze up and then cause the furnace to back up and not operate properly. I empty my can about once every 2 weeks depending on my furnace's temperature settings...I just dump the water on my grass. It has never been a problem or cause any environmental problems.
Do insulate or at least cover your ceiling joists with either plastic, or insulation board, or luan, or drywall or something...you need to keep the heat from running out the roof.
Just my "long-winded" 2 cents.
Good luck on your project.
Davo