Subfloor over Concrete

[Angelfire]

Hiya,
I'm beginning to turn my attention to flooring in my wood shop side of my garage. Ultimately, I'm looking to go with wood flooring. I've got a slab on grade. Living in NM where humidity is pretty much non-existent, there was no vapor barrier placed below the slab. Having done a number of moisture tests over the years prior to installing glued down hardwood in the house, I know there is no moisture coming up through the slab. I'll test the garage just to be sure but am not anticipating any issues. I know that glued down hardwood works here but I'm actually looking to build a subfloor over the concrete to make things more comfortable while working so have been looking at installing a subfloor. I'm also looking to minimize the height of this subfloor just to preserve as much ceiling height as I can.

So with all that said, I've been researching about products such as Delta FL, Platon, and Delta MS (have heard its the same technically as the Delta FL but just happens to be made from recycled plastic vs new....and is cheaper). It appears you can lay this "membrane" out, cover it with 3/4" T&G plywood tapconned to the concrete and then install the finished floor on top of this. This would give me a total height increase of 1 3/4" or so vs a height increase of 2 1/4"+ for a sleeper/ply setup. One advantage of the sleeper/ply route would be filling in the voids with rigid insulation but honestly, we really don't get that cold here in the winter and the slab was already insulated under the concrete with rigid insulation so it's really not a major benefit for me.

I've seen as well, the panel systems that are out there such as Drycor. While these look to be a good option, they are a bit taller and significantly more expensive vs. the "membrane"/ply route.

Just curious if anyone has used one of these membrane type systems for a subfloor and what your impressions/concerns/ease of use/etc.... was?

Thanks very much.
Cheers,

 

[astroracer]

I think you are making it too difficult.
With no moisture or insulation requirements a simple sheet of 3/4" OSB glued to the concrete should suffice. If you want to get the OSB off the floor anyway run 1 x 3 sleepers on 12" centers and screw and glue the sub-floor to those.
Height increase... 1 1/2".
I did the same thing in my Michigan shop (with vapor barrier and insulation) 25 years ago. No issues yet...
Mark

 

[Angelfire]

Thanks.

The point of building up a subfloor was to give a bit of cushion to the floor on those long work days. In terms of sleepers, I was thinking 2x4 but 1x 3 would work. The membrane system I'm asking about would give a total height increase of 1- 3/4" whereas a using 1x3 sleepers would be at 2 1/4". So only 1/2" difference but it might be worth it considering I need to mate up to other spaces.
Cheers.

 

[astroracer]

Do you really need the membrane system? What does it do for you that the sleepers and T&G OSB won't? That's the point I'm trying to make. The sub-floor in my shop has worked well in Michigan for 25 years and I just used plastic sheeting and foam board. The 1 x 3 sleepers are laid flat so, with 3/4" OSB on top you only lose 1 1/2" in ceiling hgt.
Mark

 

[Angelfire]

With the 1x3 sleeper system as you've described, I will lose 2 1/4" vs. the membrane system at 1 3/4". Only 1/2" but I do have a transition to another room and a door threshold (that I still need to measure) to work around. This is what got me thinking about the membrane as it essentially replaces the 3/4" sleepers with 1/4" membrane. I'm sure your suggestion would work just fine and once I get my measurements, I may very well go that route. Was primarily asking about the membranes to find out how they've worked for other people in case that 1/2" makes a difference for me.

 

[astroracer]

With the 1x3 sleeper system as you've described, I will lose 2 1/4"

You're not doing the math right. A 1 x 3 is only 3/4's of an inch thick. Laid flat the 1 x 3 is 3/4". Throw the 3/4" OSB on top and that adds up to 1 1/2 inches...
Mark

 

[Angelfire]

You're forgetting the 3/4" hardwood on top.

 

[astroracer]

You're forgetting the 3/4" hardwood on top.

Yes, yes I am... I just painted the OSB in my shop, that's why I didn't think about it.
Mark

 

[stillsteamn]

In my Minnesota basement I used DriCore 2'x2' OSB tongue-and-groove panels that have plastic vapor barrier/standoff feet built in. This provides some air flow to the concrete but a vapor barrier to the room above. The whole assembly is about 1" thick. It goes together easy, almost like tongue and groove flooring which is essentially what it is. In my basement I then put carpet in some rooms and cork flooring in other rooms, on top of the DriCore. In a garage or shop, you might just stop with the Dricore and be done. http://dricore.com/nw/index.php Now I see that you mentioned Dricore in your original post. Anyway, I like the Dricore for various reasons.

 

[Angelfire]

Thanks. Just had another look at the Dricore when you mentioned it was about 1" thick. I had seen another of their products that was signicantly thicker so it's a possibility to go this route. Since I'll be putting hardwood flooring on top, how thick is the OSB? I see the panels aren't quite 24" square....did you just figure your square footage and divide by 4 anyway to get the number of panels needed? I'd have to order this in so would want to get the correct number on the first time. Thanks for the inputs!
Cheers.

 

[stillsteamn]

I'm pretty sure the OSB is 3/4", and the plastic feet/panel on the back is 1/4". Specs should be on their website. They should also have a formula for required square footage. It would basically be /4 like you say, plus maybe 5% or 10% to account for waste around the edges.

 

[Angelfire]

Thanks. Got into a chat with them as their OSB thickness was not on their site (or I couldn't find it). For the 7/8" panels, the OSB is 5/8".
Cheers.

 

[James-W]

I have heard that some people put down 1X4's a foot apart and then put rigid insulation in between them. You put the hardwood flooring on the 1X4's so you only take up 1 and 1/2 inches of space. The idea is that with the 1X4's and the rigid foam the whole floor is supported and you do get some insulation value, although the insulation part isn't really needed where you are.

 

[Angelfire]

Thanks. Another option to consider.
Cheers.

 

[TractorJeff]

I wouldn't worry about moisture as stated "slab was already insulated under the concrete with rigid insulation so it's really not a major benefit for me."

 

[yeldogt]

I used Drycore for my office space -- walk out basement slab. The product works as long as the slab is flat .. mine moved a bit and I shimmed. I'm sure with a nailed floor on top it would be solid -- I did industrial carpet. A basement floor is not as cold as a slab on grade in PA.

What are you going to be doing in the space (weight of equipment) and what type of finished floor?

I have built many wood floors over slabs using 2x4 on the flats w/ VB and plywood or Warmboard if I'm doing radiant heat -- strip flooring on top. In my area the 1.5 thickness allows for rigid insulation between. But, this is going to need 3". This is also inside a home .. not a shop. You don't want a polished wood floor in a shop.

Being in PA we have access to inexpensive hardwood -- I have actually installed 5/4 x 6 oak boards (no t&g) directly to the concrete with a VB under it ... it was a lot of work (nailing) and if I did it again I would use 3/4 boards as nailers (and glue) to eliminate the nail gun use. They sell the 5/4 oak around me for use w/o subfloors -- it's a popular look when you want the wood exposed as a ceiling bellow .. so it reasonably priced. I did nothing to it and used two coats of oil varnish.

I have never done it -- but don't discount glue .. people glue down wood strip flooring all the time. Full glue coverage is a VB and the glue today is strong/strong/ strong.

 

[Angelfire]

I did glue down in my house and that has worked out very well. In one room, I needed to remove the floor as we were doing an addition and that was an utter nighmare getting the floor up. The glue really works well. A nightmare to work with but when done, you're done!

I'd do glue down again but am really looking for just a little spring in the floor so hence the subfloor questions. This is for my woodworking shop and will have my cabinet saw, jointer, etc... so while not overly heavy, there is some weight to it.

I'd love to just put down straight planks on top of something but unfortunately here in NM, I'm not going to find any hardwood that fits that bill at a reasonable price. Pine is king around here and any hardwoods need to be "imported". So I'm currently looking at what's available/costs but haven't decided on anything just yet.

Cheers.

 

[yeldogt]

I wonder how much a hardwood floor gives vs concrete as far as standing/walking -- it's often discussed. Concrete is colder -- I don't find my radiant concrete floors as uncomfortable as when standing on unheated concrete. Obviously I would rather drop a glass on the wood floor ... even in the summer my concrete floors are colder vs my body .. I really think that's why they are uncomfortable.

That said .. I can tell the difference when walking from the heated wood floors in my old house to either the kitchen/ sunroom (wet bed tile) ... or the addition -- Warmboard on sleepers on a slab.

My new house is all engineered floor joists w/ Warmboard --- even without the 3/4 flooring .. it's firm.

 

[Angelfire]

Yeah, I'm sure having warmer floors definitely helps on the comfort....nothing's worse than cold feet!

I have a small cabin in northern NM which is wood planks over joists....I can definitely feel a bit of give in the floor vs. the hardwood glued directly to the concrete at my home. Not a ton mind you but it's there. The planks are a pine of some sort (not sure if SYP or ???) so that may be contributing a bit.

If nothing else, by adding a subfloor, it will allow me to possibly add some insulation/thermal break which might help with the cold concrete concerns.

Cheers.