Shop flooring question -- Advantech osb over concrete without sleepers

[Peter Franklin]

Hi,

I'm just at the stage in my shop build of deciding on flooring. Appreciate all the info I'm getting on this forum and others and reading that people who use OSB usually recommend laying it over sleepers with foam panels.

Am I shooting myself in the foot if I skip the sleepers and panels and just use Advantech OSB over poly over concrete? I can use leveling concrete to get out any big dips that may be an issue, so hoping that solves one potential problem. And I can a use dehumidifier during summer if the poly doesn't keep down moisture enough. And bite the bullet on higher heating costs in the winter without an insulated floor.

But curious if I'm missing something. Sleepers would add cost and time and I don't have the height for my front door so would need a ramp or something. All in all I'm just not keen on going in that direction unless using Advantech on it's own is just a bad idea.

FYI, converted by 2 car garage to a shop and bumped it out an extra bay. Very well insulated and soundproofed walls and ceilings but the floor is concrete. 1/3 of the floor was poured 6 months ago over poly. The other 2/3 I'm not sure if it was poured with a poly underlayer. The house was built in the mid 70's in the NE and I read it wasn't common to use poly back then. So likely nothing.

Any advice much appreciated!

[Jim Becker]

I'd personally use the sleepers even if they have to be relatively thin. Why? Leveling the floor so your sheets of Advantec seat together well. It also allows you to actually level the floor since most garages are sloped. You can leave small wells at any doors to accommodate them and make a portable ramp to use when wheeling things in and out if that's necessary. You can then stick some thinner iso insulation between the sleepers to further increase comfort in the shop. You don't have to raise the floor a lot, but having a little structure can help. As an alternative...put a thin layer of iso insulation over the polyethylene and then float the floor on the foam. Again, it's only raising it a little, but it will even out pressure and provide some additional comfort.

[Peter Franklin]

Thanks. I hadn't really considered leveling the slope of the floor. What's the downside with leaving as is? It doesn't seem like that big a slope and any the few machines I have on wheels can be locked down. Am I missing something?

Also, wouldn't i then need tapered foam panels?

[Kevin Jenness]

If the slab conducts any significant amount of moisture you may regret not using pressure treated sleepers. As Jim points out, that also allows for insulating between the sleepers and levelling the floor, compensating for the inevitable dips as well as any intentional slope in the slab. Untapered foam panels will be fine. You might consider raising the door to flush out the sill with the new floor. It does all take time and money- I found it worthwhile.

[Jim Becker]

Thanks. I hadn't really considered leveling the slope of the floor. What's the downside with leaving as is? It doesn't seem like that big a slope and any the few machines I have on wheels can be locked down. Am I missing something?

Also, wouldn't i then need tapered foam panels?

If you only lay foam and float the floor, it's not going to get leveled. Getting tapered foam would be a pretty expensive proposition. With sleepers, you can taper the wood and just use the least common denominator for the insulation...it doesn't have to be in contact with the Advantec where things are "deeper".

Leveling is personal preference. My previous shop had a sloped floor. I dealt with it, but for some tools, it required careful orientation. The slider for example, had to go across the slope and I then leveled it in the perpendicular dimension. Because of how the floor was in that space, the wagon side, which was facing the "down" slope had to be raised over .75" to be level. The CNC also had to be shimmed level, but fortunately, in the area where that was, it only required about .375" in the front to make it happen. Now those are tools that are not and shouldn't be mobile. Most other tools care less about level. But I have to tell you, having a level floor like I do now is a really nice thing...

[Peter Franklin]

Just to clarify, do you mean regret not using pressure treated vs regular wood for sleepers or not using sleepers to begin with? If the later, what is the problem moisture would cause on using foamboard without sleepers?

[Kevin Jenness]

I think you would be ok putting Advantech over foamboard w/o sleepers, although it may be a little spongy in hollow areas and not as level as it could be with sleepers. When you said "skip the sleepers and panels and just use Advantech OSB over poly over concrete?" I assumed you meant poly sheeting. If the slab and underlying soil are damp whatever sits on the concrete, even over poly, could get wet in which case pt sleepers might be a good idea.

[Bill Dufour]

I make my shop doors open outward so the floor can be were ever it need to be. Just seems more logical to me and more secure as well. No way can they be kicked in just at the lock.
OP climate. I get no condensation unless the shop goes below 45 or so. I have never heard of condensation on the floor in summer. You must have a leaky pipe under there.
Bill D

[Ned Otter]

Peter - I had a similar situation for flooring, though my shop is not a garage. But it's completely unlevel over the entire length, as it's an 1860 shed with stone flooring and 1/2" concrete over the stones (and the concrete is in pretty bad shape).

Based on feedback from this forum, I put down 1" foam core, and then Advantech over that. No sleepers, as my head already almost hits the header for the doorway, also not enough concrete depth to attach the sleepers to. The Advantach can be completely unlevel where it meets the next panel, but that hasn't been an issue for me. I use a pallet jack to move equipment around if required, some of it 1,500 lbs.

I think I will eventually sand down the high spots between panels.

Ned

[Cameron Wood]

I've made a floor over existing old concrete slab (no VB) with poly sheeting, 1 1/2" foam insulation, and two layers of 1/2" plywood, one on the bias & screwed together. Still working fine- 20+ yrs.

[Peter Franklin]

Peter - I had a similar situation for flooring, though my shop is not a garage. But it's completely unlevel over the entire length, as it's an 1860 shed with stone flooring and 1/2" concrete over the stones (and the concrete is in pretty bad shape).

Based on feedback from this forum, I put down 1" foam core, and then Advantech over that. No sleepers, as my head already almost hits the header for the doorway, also not enough concrete depth to attach the sleepers to. The Advantach can be completely unlevel where it meets the next panel, but that hasn't been an issue for me. I use a pallet jack to move equipment around if required, some of it 1,500 lbs.

I think I will eventually sand down the high spots between panels.

Ned

That's great to hear, thanks!

By any chance, did you notice a change in humidity levels in summer when you added your floor? I just had a new HVAC system put in my house, including ductless splits in the workshop. The house is reading low 50% humidity while the workshop is low 80%. I'm thinking that must be due to the concrete slab as everything else was constructed with lots of insulation and very tight for sound proofing reasons. Hoping the poly over the slab and foam board will solve that problem, though in one of the two rooms I have I can only have 1/2" foamboard, unless I pull out the front door and reframe, which I really don't want to do.

[Peter Franklin]

I've made a floor over existing old concrete slab (no VB) with poly sheeting, 1 1/2" foam insulation, and two layers of 1/2" plywood, one on the bias & screwed together. Still working fine- 20+ yrs.

Thanks. Was the poly sheeting 6 mil? Or thicker?

[Cameron Wood]

Thanks. Was the poly sheeting 6 mil? Or thicker?

I'm pretty sure it was 6 mil, but now I have a roll of 15 mil. It's good but the roll is big, heavy, and expensive. it's sold for use under concrete slabs.

[Ned Otter]

That's great to hear, thanks!

By any chance, did you notice a change in humidity levels in summer when you added your floor? I just had a new HVAC system put in my house, including ductless splits in the workshop. The house is reading low 50% humidity while the workshop is low 80%. I'm thinking that must be due to the concrete slab as everything else was constructed with lots of insulation and very tight for sound proofing reasons. Hoping the poly over the slab and foam board will solve that problem, though in one of the two rooms I have I can only have 1/2" foamboard, unless I pull out the front door and reframe, which I really don't want to do.

My shop is uninsulated, so temps and humidity fluctuate wildly --

[Peter Franklin]

If you only lay foam and float the floor, it's not going to get leveled. Getting tapered foam would be a pretty expensive proposition. With sleepers, you can taper the wood and just use the least common denominator for the insulation...it doesn't have to be in contact with the Advantec where things are "deeper".

How close together would you run the sleepers? And if there are gaps in places where the insulation isn't butting up against the 3/4" Advantec, won't that cause sagging when you're walking or rolling a heavy machine over?