Trying to warm up an uninsulated concrete garage floor
Kenora Ontario Canada P9N0E7
Climate zone 7
Background- I have a 24 x 30 ft garage with 2×6 wood framed walls (R20 fiberglass batts in stud bays) and a raised heel truss attic (8 ft walls) the ceiling has R50 blown fiberglass.
The man door is located on the south wall and the two 7×9 insulated overhead doors are on the north wall…the ridge of the 6/12 pitched roof runs E-W.
The concrete pad is a 4 inch thickened edge slab over 6 inches of compacted stone; the earth is well drained and slopes away rapidly in all directions.
I use 1/2 the building for parking and 1/2 for a shop.
I don’t heat it during the winter but would like to…keeping it just above freezing (say +5c) unless I have a project to do then raising the heat to a tolerable level (say +18c) for a day or so at a time.
I know from previous experience working in an unheated shop with a concrete floor that the heat gets sucked out of your feet and laying on the concrete is out of the question.
With those things in mind I wonder….
Q- Can I put a layer of EPS or XPS (I have LOTS of reclaimed EPS and XPS) down (say 1 1/2″) on either the whole garage floor or at the least the workshop side (1/2 the space (workshop on e side, vehicles on w side) and cover it with pressure treated plywood? This would give me a warm(er) floor and be easier to walk on than concrete.
The reason I ask is i fear this could do nasty things re frost heaving…. fwiw i can excavate around the exterior and add verticle foam if this would help a frost issue.
Thanks for any guidance… if need be I can forgo the insulated floor but would really like to do it if it won’t compromise the structure.
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Replies
Not sure how to edit the above post... I meant UN-INSULATED...damn spell correct!
With the building unheated, adding the insulation would help reduce the potential for frost heaving--worst would be leaving the garage door open on a cold day. So no worries there.
With the insulation, you have to wonder whether it can support the weight of the vehicle. It's probably OK--if it's rated 25 PSI, and the vehicle tires are pumped to 35 psi, that sounds bad, but the plywood over the top should spread the load more widely. Or you could get higher density EPS. You could leave the vehicle area uninsulated, but then you have the trip hazard of the transition.
I'm not sure whether PT plywood is the best choice. Although it's not as toxic as it used to be, I wouldn't want that as the wear surface of my floor, so that any dust created by the wear would have the biocides in it. I've heard of using cement backer board as a utility floor material over foam, but I have doubts about that as well. I'll be interested to hear what others suggest for that. You could certainly use a conventional floor material over the top of the plywood, but that seems expensive for a garage. Maybe just ordinary plywood would work, in two layers with the seams offset.
Another possibility might be to use rubber or foam-rubber mats, which are sold for enhancing comfort on garage floors or exercise room floors. Unlike polystyrene foam, they bounce back after being squished. But they are relatively thin and don't come with rated r-values. And they are often made of soft PVC, which, unlike vinyl siding and plumbing, contains nasty plasticizers.
Tim - If I'm following your description accurately, the first thing to do would be to build an insulated stud wall between the garage portion and the shop area. Then just get a good powerful heater that would heat the space up when you wanted to work in there. Unless you plan to work there a lot, it's hard to imagine insulating the floor would be cost effective. With the walls and ceiling reasonably well insulated,it should work fine. Rubber mats as suggested by Charlie sound like a good idea if the floor seems too cold once you've got the space isolated. Insulating the garage portion sounds like more trouble than it's worth, again, unless you plan to work there a LOT.
Kevin... I thought about that as well... Dividing the interior... However I wonder if having a half heated ....half stone cold building would cause me more potential frost grief potential?
Since I have the foam and it sounds like putting it on the floor... Even half the floor... Might actually reduce the likelihood of frost heave I'll explore that some more.
For those that haven't had the pleasure of laying under a vehicle on a piece of concrete that's -30 or so I can tell you it removes your will to work real quick!! Even warming the floor on the workshop side would be a good thing. Additionally with the floor insulation I should be able to heat it for far less... I would think!
Thoughts.... Please keep them coming!
The cheapest and simplest approach is to just lay down some old, worn carpet. You can probably get it for free. The carpet has almost no insulating power of course, but it will improve your comfort by having a higher surface temperature and much lower radiant heat transfer potential. The reduced radiant heat transfer effect is huge and under-appreciated. I do this in my own unheated garage that's used as a workshop. You can walk on it and cars can drive on it, no problem.
Tim - I'm not convinced with Charlie's assertion that the floor insulation would reduce the likelihood for frost heave. That MAY be true if it is totally unheated, but certainly not if heated - the escaping heat would warm the floor. You could divide the space with a stud wall, leave it uninsulated but fairly airtight (drywall on the garage side), place some thermometers, and see how cold the garage side gets. If it stays above freezing, you're good, and the shop side will still heat up much more readily when needed. If too cold at times, you could open the door some from the heated portion.If the garage side stays too warm, you could then insulate the wall, but I'm guessing you won't want to. I live in Maine, zone 6, and I am quite sure that this plan would work here. But you may get a lot colder. Other than this experimentation, you'd need a heat loss analysis that may or may not be totally accurate as you'd have to guess on how often you'd heat the space. Good luck!
Tim,
You've been given several options for ways to proceed. Here's one more: you can install vertical rigid foam at the perimeter of your slab to reduce heat loss and raise the temperature of your slab. If I were you, I would excavate the soil to permit the installation of 2-foot-wide strips of rigid foam; then backfill.
You can protect the above-grade rigid foam with metal flashing, pressure-treated plywood, or stucco. You'll also need Z-flashing at the horizontal joint between the bottom of your siding and the top of the rigid foam.
I wouldn't be overly concerned about frost heave. The pad and drainage characteristics you describe seem to be working for the unheated garage now and you won't be making the situation worse. The perimeter insulation seems like an excellent choice for added frost protection and for reducing heat loss for your future comfort in the shop. If it is practical, I would recommend partitioning off the shop area and building up the floor in the shop only. If a permanent partition isn't practical, even a well fitted curtain-wall of removable canvas will help a lot.
If your climate is like mine in Wisconsin, our cars are constantly importing lots of snow, ice and salt that melts from the vehicles underside and pools on the floor. Its hard to imaging a plywood/foam buildup that is going to deal with that type of punishment for long, therefor I would leave the car bay floor as is. In your shop area I suggest that you lay down high-density (25 psi or greater) XPS and cover with a 3/4" or thicker tongue and groove sub-floor plywood. There are numerous products available that claim to be extremely moisture tolerant and have a nearly finish-grade veneer topside. The tongue and groove configuration is important since the sheets would otherwise be likely to curl and make a mess of you floor. I would also add a few biscuits to the edges without the t&g. This "floating floor" should stay flat, add to your comfort and provide an adequate base for any loads you are likely to impose in a shop. The final addition of an electric heating mat ( http://healiohealth.com/products/index/3149 ) located in front of your workbench will work wonders. This flooring system is what I have in my shop and it has worked out very well. Its amazing how comfortable you can be if your feet are warm, even at fairly low air temps. The inverse is equally true.
Excellent ideas... I was unsure if it could be done without compromising the structure but feel confident now.
I will be adding perimeter insulation and a partition wall of some!e sort with the heat in the shop paying particular attention to air sealing the whole building.
Cheers from Kenora