Adding a Wood Floor in the Garage

[Torch02]

(Cross-posting from my blog for a wider audience)

I'm in the planning phase of putting a wood floor into my garage, following the plans laid out in FWW 216.

The basic idea is a frame of pressure treated 2x4s surrounding rigid foam insulation, covered by 3/4" T&G OSB (see the blog post for more details).

The questions I have are:

1. 1. Given that I’m sealing the concrete with an epoxy, do I need sheet plastic anywhere as an additional moisture barrier?
   2. Do I need to do any taping and/or spraying to seal the pressure treated 2x4s to the rigid foam?
   3. In the FWW article, the author nailed the 2x4s to the concrete with a powder-actuated nailer. Is this really necessary?
   4. I plan on running some branch circuits to the center of the room. I was thinking of just routing a channel through the 2x4s and rigid foam to run the wires. Is that a good approach or is there something else I should do?
   5. Having the OSB sheets line up in the center of the 2x4s means I’ll have 1 3/4″ between the end of the first sheet of OSB and right wall. What should I do here? Should cut this first 2×4 in half so the OSB is against the wall? Maybe add a 2×4 “baseboard” on end and shift everything over 1/4″ to the right?
   6. This garage, like most, slopes down towards the front. Should I shim the front of the subfloor so the final floor is level? I’m leaning towards yes, but am open to contrary opinions.

1. Any answers/ideas? Thanks.

[Beechwood Chip]

4. I plan on running some branch circuits to the center of the room. I was thinking of just routing a channel through the 2x4s and rigid foam to run the wires. Is that a good approach or is there something else I should do?

In general, a horizontal beam has most of the force carried along the top and bottom surfaces, with very little force in the middle. That's why you see beams with an I shaped cross section instead of a rectangular cross section. So, if I have to run a wire or pipe through a beam, I try to cut a hole through the center of the beam rather than notching the top or bottom.

If the 2x4 is supported along it's length, this is not be a big deal.

[DeGauss]

Hi Torch,

I added a similar wooden floor to my garage and it was one of the best things I have done for the space.

1. I did put down the plastic sheet but I am confident it would have been fine without it.

2. No attaching was necessary for me

3. My floor just floats and is not attached to the concrete. My thinking was that I might someday want to sell the house and some fool would want to park a car in there. It has been 5 years and once you put a 1000+ pounds of tools on it it is not going anywhere.

4. I ran 2 circuits around just above the base board and use extensions out to the tools. If I where to run it in floor I would put in a conduit under the plywood and surface mount a box.

5. I would just butt two 2x4's together at the end and make one wide sleeper for the edge and cut a small piece of ply to go over it. Also I did not use OSB I used T&G plywood. I do not think OSB would hold up well to the task of flooring.

6. I built my frame first and then shimmed and leveled it before I put the plywood over the top. Has worked great no issues.

Hope that helps.

-Gary

[Dave H]

They make 3/4" OSB T&G subflooring, and it is a fine product very stable, and moisture resistant it has to be sometimes when your building a house it's subjected to the elements for weeks & weeks, and holds up just fine. I think the epoxy should be enough vapor barrior, but poly sheeting is pretty cheep insurance. Routing through the 2x4's for the wireing should be fine as long as you add support down to the concrete on either side of routed area, if you decide to level the floor you would already have a channel under the 2x4's. If the shop is always heated I could see the ridgid foam, but if its only heated when your working I'm not to sure your gaining anything if it's for moisture control you've already addressed that issue with epoxy, and possibly poly sheeting.

[CJC5151]

I think the rigid foam is more to make the floor more solid and not necessarily for heat loss. If im thinking of the fame aritcle, This is why you can space your 2x4s with 2 feet between them and still load heavey tools on the floor. it helps limit the flex

[davionics]

Torch,

So how did the floor end up? I'm curious what you put on top of the floor, paint, epoxy?

Dave

[CJC5151]

I think they just left it bare. The name of the product they used was advantex. Its a much more ridged/water resistant 3/4" t&g flooring. you dont need to finish it but i assume any garage floor paint would work, something flexible

[Torch02]

Torch,

So how did the floor end up? I'm curious what you put on top of the floor, paint, epoxy?

Dave

I ended up just leaving it bare. We'll see how wise of a move that was in due time :-)

[logan.newman]

Any thoughts on just putting the OSB T & G down by itself with no 2X4's under it? I'm thinking of doing that to save on overhead space (ceiling joists are only 7.5 feet above

[Bobby Slack]

Here is my take. You are going to invest a lot of elbow grease, time and money. The plastic barrier is not going to break the bank and will guarantee success in your project.

I am not saying that is going to be necessary but .... what would happen if? ...

My style is to overbuild as much as possible to eliminate bad outcomes.

Good luck with your project. I am about to do the same thing. In Southern California we don't need insulation so my approach will be ...

1. plastic barrier

2. t&G osb

3. Leftover hardwood flooring.

All the best

[sbarton22]

I'm an architect, so I'm going to give you the CYA, so I don't get sued, answers. Then you know the "rules" and you go from there.

Pressure treated wood contacting concrete is standard residential construction. I would bet every sill plate in your home is like that. With that said, I always run plastic between any wood and concrete. The reason I do that is a belt and suspenders approach. Concrete actually never finishes curing. It will always accept moisture and always seek some level of equilibrium... basically meaning the water will weep within the concrete as long as there is enough to go around. Now, the older the concrete, the less it will interact with moisture, but it always will. Even pressurized/ treated wood is susceptible to rot. Like it has been said before, it is the cheapest insurance you can buy...and not insurance against rot, but really, insurance against mold.

So, your epoxy sealer is intended to create a barrier so that the moisture cannot weep completely through. Usually, you do not do this on green concrete because it will cause cracking if the concrete cannot cure consistently throughout. Most manufacturers will specify a maximum moisture content or will not warranty their product. This is the greatest point of lawsuits for flooring failures. Assuming you apply the epoxy correctly and you don't have a brand new home, you probably don't need another moisture barrier...but again, plastic is super cheap insurance.

Now, the one thing that you are thinking about that has me concerned for you is running electrical in, what is essentially, a raised floor. In normal condition on the interior of the building, this is a GREAT idea. Bravo for going there. However, you are doing this in a garage. Garages have very specific rules for electrical outlets. If you are going to get a permit for this keep reading. If not, you are on your own and forget we had this conversation. If you are going to get a permit, or concerned someone might turn you in (and people do all the time....for what reason I do not know), then you need to speak to your local building authority.

USUALLY, by the International Electrical (or Fire, I forget) Code, you cannot have any outlets lower than something like 42". I don't know the exact number because I haven't done it in a while. And they must have a GRCI on the first outlet of the circuit. The reason that code asks for this is because people wash their garage floors with their hoses. Now, you and I both know you aren't going to do this with a wood product laying on the floor, but code is there to protect the idiots from themselves. They are also there so if you should ever leave that house for whatever reason, some idiot who doesn't know any better doesn't move in and do something stupid. I do know my city has this requirement because I just ran some circuits in my basement and I went through this with the city twice to make sure I would be ok to locate them near the floor. It is a rule that is very specific to garages.I don't know if conduit and specialty outlets are allowed.

That is the CYA answer.

Other than that, I would shim the grid to level as the first thing. Don't need your tools rolling all over the place. Do you want to shim/taper your rigid? Up to you, but if you are counting on it for "structural" help, then you are best to do something there. You may have up to an inch gap near the door if you do not. Tapering insulation is pretty simple. I would actually recommend adding additional studs in areas where you plan on locating the big boy tools. Depending on the size of the specific point load, you could even make a steel base(eventually removable) or concrete pad (less removable) in certain zones. I don't know what kind of tools you are thinking, so this might be overkill.

Just some ideas to think about.

[kaiser]

(Cross-posting from my blog for a wider audience)

I'm in the planning phase of putting a wood floor into my garage, following the plans laid out in FWW 216.

The basic idea is a frame of pressure treated 2x4s surrounding rigid foam insulation, covered by 3/4" T&G OSB (see the blog post for more details).

The questions I have are:

1. 
   
   1. 
      
   2. Given that I’m sealing the concrete with an epoxy, do I need sheet plastic anywhere as an additional moisture barrier?
      
   3. Do I need to do any taping and/or spraying to seal the pressure treated 2x4s to the rigid foam?
      
   4. In the FWW article, the author nailed the 2x4s to the concrete with a powder-actuated nailer. Is this really necessary?
      
   5. I plan on running some branch circuits to the center of the room. I was thinking of just routing a channel through the 2x4s and rigid foam to run the wires. Is that a good approach or is there something else I should do?
      
   6. Having the OSB sheets line up in the center of the 2x4s means I’ll have 1 3/4″ between the end of the first sheet of OSB and right wall. What should I do here? Should cut this first 2×4 in half so the OSB is against the wall? Maybe add a 2×4 “baseboard” on end and shift everything over 1/4″ to the right?
      
   7. This garage, like most, slopes down towards the front. Should I shim the front of the subfloor so the final floor is level? I’m leaning towards yes, but am open to contrary opinions.
      

Any answers/ideas? Thanks.

1: No plastic needed with epoxy, just make sure you epoxyup the walls./

2: Taping the rigid foam will help with thermal break.

3: Nailing down the sleeper joists not totally necessary, you can float the floor.

4: Put wiring in conduit tomake sure it is not punctured by flooring nails.

5: Hook you tape onto the 2x4 on the wall and measure 14 1/4" and go with you first joist and than 16" for there out. This will make a full sheet go up against your wall and break half on you sixth joist.

6: Unless the pitch is so great that it gives you dementia, don't bother.

And my 2 cents on osb................don't use it especially where there will be temperature swings. It does not hold nails well (flooring nails that is) and with great temperature swings there will be level of condensation acquired and osb does not react well to it.

[Frankengruvin]

On the topic of insulation, I believe in that article (by David Pekavich?) he lives in Vermont or someplace like that with some pretty nasty winters, which is why he insulated his floor. He just didn't want the heat to be leached out of his space by the cold conrete. I would say unless you're worried about that, don't worry about the insulation. He did count it as structural as well, however, which is one reason he went with 24" OC sleepers under his T&G plywood.