A plan for keeping water out of worskhop
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 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
Dabbler -
From the sounds of your program, it appears you're anticipating investing no small amount of time, energy, and .... money in this project. All's the better. My suggestions -
I wouldn't compromise the headroom. I'd remove the existing concrete floor. You say it has a "pier" foundation which I read as posts sitting on pier blocks. No mention of what part of the country you're in but if this is the case, it's doubtful that the pier blocks are below the frost line if you live in an area that experiences four distinct seasons. I'd consider adding some kind of actual footing around the perimeter. Remove the existing slab and excavate a foot in order to put in gravel drainage under an new slab.
In my opinion, a 60amp sub feed seems a little on the light side. If you have the capacity in your house panel, I'd go for a 100amp feed to the shop.
Are you in love with a wood floor? I have concrete in my shop and while there are several people who find bare concrete uncomfortable, I'm not one of them. Lots easier to sweep up.
For power islands out in the open part of the floor, install short lengths of unistrut type channel along side of an EMT (Electrical Metalic Conduit) feed from the panel to the outlet location. This would be cast into the slab, whichever way you decide to go. Once the slab is finished, the outlet box is mounted to the unistrut and the wires pulled from breaker to box. Thus the outlet is ~not~ located in the floor. You don't want this arrangement anyway. The box should be installed on some kind of pedestal above the floor. You want to do a very careful layout of your equipment so you get this or these outlets in the right place the first time.
If you can figure out a way to install a moisture barrier, a 6" minimum layer of washed pea gravel and a 2" layer of polyiso rigid insulation then a 4" reinforced concrete slab, I can almost guarantee you that you'll have a dry slab. Unless the water table in your area is less than 10" below grade.
But then it's pretty easy for me to spend your money! (grin)
From Beautiful Skagit Co. Wa.
Dennis
Dennis,Thanks for your reply. You were extremely helpful. One of the coolest things about flying into Seattle is the way the plane holds its altitude until it clears the North Cascades east of Bellingham and then turns south, dropping altitude quickly to make the runway at SeaTac. If you’re on the port side of the plane, the view going in is fantastic.I like your ideas about pouring a concrete perimeter and installing unistrut channels. I live in Connecticut, a short drive away from Taunton Publishing. Code here specifies that foundations be laid at least 3 feet beneath grade. The piers I refer to are just Sonotubes filled with concrete. Mine seem pretty stable, so I think they go down 3 feet. No posts atop that, just 2x4 framing. The mudsill is just lumber anchored to the top of each pier. The wall hangs over an inch or so of open space. It’s basic barn construction.As for an entire concrete slab, I don’t know. It would certainly get rid of any vibration. But no matter how warm the shop, I fear the cold in the floor would conduct straight through my shoes and numb the legs.I had never planned to install outlets flush with the floor. I had envisioned some kind of pedestal. Maybe the unistrut would take care of that.The 100-amp feed sounds great but my entire service is 100 amps. (Not that that mattered to previous owners of my house. I counted all the breakers in the main panel and came up with a total of 245.)
With regard to the electricity: you might want to bring in a new feed to the shop, and run the house off that to upgrade your power.
Yep, the whole Skagit and Whatcom county area is really wonderful. You should see it from ground level, too! (grin)I'm really concerned about limiting the headroom in your shop. I think even if you're only an occasional hobby level woodworker you'll come to find in a short time that anything less than 8' is a headache. Literally! If you can get more, all the better. I have a 10' ceiling in my shop and sometimes wish I could have made it higher still. But once you go above 8', lighting becomes an issue. I've got high output flourescent lighting, quite a bit of it, but still not enough.Yes, a concrete floor is colder than a wood floor, I can't argue that. But if you can go to the extent that I described, gravel drainage, rigid insulation then the concrete slab, it's not really too bad. Also you can install PEX tubing in the floor and rig up a heat exchanger in an old wood stove, get one or two used but serviceable water heater tanks for hot water storage mass, a couple hundred bux for misc. controls and a pump and you've got a warm slab! The nice thing about unistrut is that most electricians are accustomed to working with it. I haven't done it yet but my game plan is to mask off the outlet boxes, make a small form to surround the box(es) and the unistrut and pour pedestals around them all. This is more for housekeeping than anything. But if you were ever to see the manner in which I go about housekeeping in my shop you'd understand why that's not done yet. (grin)I agree with the suggestion of running a separate service to the shop. With a separate meter you'd be able to use the power bill as a tax deduction in the event you're doing this for more than a serious hobby. You'd also have the option to run it underground. Like the headroom thing, I just think that while you're in the process of doing it, might as well make it as right as you can. I put a 200amp panel in my shop with a 100amp subfeed from my 400amp house panel. The reasoning behind using a 200amp panel was that there's a lot more space for breakers in the larger panel. So long as the sub panel is protected by the 100amp breaker in the house panel, it was legal here in WA state. Your mileage may vary in Conn. so be sure to check. But what the hey! if you go with a whole new service to the shop you can make it 200amp all the way!Less isn't necessarily more in every case!...........
From Beautiful Skagit Co. Wa.
Dennis
Although I did not convert a garage into my shop, the floor system you describe is very similar to what I built.
Mine started with compacted gravel, which I covered with two layers of 6-mil polyethylene, overlapping, but not taping, the seams. Then the treated sleepers and treated joists. (I made sure that the polyethylene did not extend beyond the outside of the sleepers.)
Note -- I can use sleepers here, since there is virtually no frost line. Your use of piers does not change the moisture resistance of the floor system.
I insulated between the joists, then put down two layers of 3/4 ply -- the first layer is treated, the second is tongue and groove subflooring. The feltpaper between layers might help with moisture, and will certainly stop any squeeks.
My shop stays bone dry. There has never been a feeling of moisture coming up through the floor.
My shop is small, and I have a 50 amp/220v breaker as the main. The table saw is wired for 220. Everything else now, and planned, runs on 110. I have heat in the winter, and a window air conditioner in the summer.
Your biggest regret will be the ceiling height. Mine is an inch short of 8 feet, and I'm kicking myself for not going to a 10 foot ceiling. My former shop (basement in Ohio) had a ceiling that was a bit shy of 7 feet, and it was unbearable.
Now if I could just find room for all of the tools that I bought since building the new place....
Unless you're the lead dog, the view just never changes.
Yes'm:Thanks for your reply. I’ve gotten good feedback, including a bit that recommends a concrete slab. But your experience with joists over gravel gives me some reassurance. I definitely could not use sleepers over gravel. Freezing would toss them all over the place. That’s why I envisioned a deck-like structure independent of the ground beneath. In any case, the gravel layer would have to be deep to keep water from pooling. Also, it appears I will need to address underlying drainage situation, which is poor. Everyone has commented, it seems, on the low ceiling height. So I will do something about that. One person recommended replacing overhead joists with collar ties on the rafters, but then I’ve heard that engineers no longer deem collar ties reliable at countering the outward force of the rafters. So go figure.
Your plan sounds pretty good. To offer a different perspective on the concrete floor, if I didn't already have compromised headroom, I would put sleepers down in my basement shop, to get a floor with more give. I've put down anti -fatigue mats and they help, but are not the solution for me. We are planning to relocate, and I am determined that my new shop will have a wood floor.
I am not an electrician, but here is my $.02. I would suggest that you consider two 15 amp circuits for your lighting. As long as these circuits are supplying your ceiling receptacles for lights only i.e. not readily accessible as defined by the NEC , you do not need to protect them with GFCI's. The reason for two is so that you can keep some lights on should you need to modify one circuit or the other. I would also suggest two 20 amp circuits, GFCI protected for your shop 120 v receptacles, spaced no more than 4 feet. This is what I did in my shop and I really like it. Working by yourself, that probably is overkill, but if you are doing the work yourself, the extra wire and receptacles are fairly cheap. The 240 v receptacles need GFCI protection and yep there are such critters. I think you could GFCI the whole panel, but I have no experience with that application and have no idea if you would be plagued with nuisance trips. Any circuits below the floor, I would treat as a "wet" location and provide cable or cable and conduit accordingly.
As long a you are working by yourself, running one or two machines at a time, I think (but have not verified by looking it up) that your service will be fine- assuming you garage is close to your house - make sure it is 4 wire, two hots, neutral (grounded conductor) and ground (equipment grounding conductor). I don't think THHN is suitable for wet location which is what your underground service is. However, in conduit it may be, I would have to look it up in the NEC.
I didn't see your post over at breaktime - you can get some truly excellent professional advice over there.
My bottom line advice on the electrical if you are not experienced as you say, is that you get a competent, qualified professional to at least review exactly what you want to do on your site, if you don't get them to do it. The other parts of your plan, the worst that can happen is that you may be cold, have dampness in the shop or a mold problem to deal with. With the electrical, you can end up dead.
Barry
FWIW. You should consider posting this at BT. Since most contractors (not all) hang out there. Lots of good advice. It can be a little rough there sometimes but everyone means well.
Couple of concerns. While trying to seal out the weather make sure to allow for ventilation. If you trap moisture it will rot out your structure in no time.
If your a novice, I would recommend you get an electrician. Electrical code is sometimes tricky. Or a least get an electrician to look over your plan.
BTW. You can buy a GFI breaker that protects your outlets. I have one installed on my spa.
Good luck, sounds like you have the makings of a great shop.
Edited 2/22/2005 10:27 pm ET by Len
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