Insulating Garage Floor?

[MattN03]

I'm getting ready to build a 40' x 40' pole building next month that will store my truck, tractor, offroad toy, mower, and provide a general area for vehicle/equipment maintenance as a home owner. I was wanting to spray foam the floor with the intention of spray foaming the rest of the shop down the road. The cost is to prohibitive as we're needing to remodel our home and something needs to give. Instead of spray foam, can foam board be used around the perimeter of the slab only or is there any real benefit of using foam board under the entire slab? The builder will be using bubble wrap insulation on the ceiling and walls so if I ever decide to spray foam it, a metal panel would be easier to replace if damaged.

How is everyone insulating their slab on a budget if your using your shop as a weekend hobbyist? I'm located in central KY so our winters are relatively mild. There are no plans to heat/cool the shop currently. Any suggestions are appreciated.

 

[Buckgnarly]

Everyone up here uses 2" board under the slab..... I've never heard of anyone spray foaming under a slab.

 

[BruceMc]

Everyone up here uses 2" board under the slab..... I've never heard of anyone spray foaming under a slab.

It's gaining popularity in high latitudes, especially in areas with permafrost where you don't want to transfer any heat to thte ground, but it's not cheap. And serious overkill for KY.

Foam board is relatively cheap and you can't go back later and install it if you change your mind. It's a one-shot deal.

 

[dave_dj1]

We use it (2"-3" blue foam) under slabs up here in the northeast but we also use 4' frost walls. I'm trying to wrap my head around having posts 4' in the ground and a slab that "floats" on the surface. How does it hold up long term?

 

[K'ledgeBldr]

Granted, you're doing a pole barn- but your slab detail will still be practically the same-

 

[rburke65]

As pictured above. Pretty much EVERYBODY on this site is on a "budget", but it's all subjective. Bubble wrap isn't worth the effort. There is a ton of reading on here about sab insulation. All insulation is beneficial.

 

[Prestonwv]

I'm just about to start a 28x36 motorcycle room/shop and spec'd 2" foam board under the entire slab to make the floor more comfortable and the building a little easier to heat. The next best thing would be to focus on the edge making sure to have a thermal break of foam board between slab and block, and place 2' of foam board just around the perimeter which I've seen done.

 

[6768rogues]

I am in western NY and I have several buildings without any floor insulation. No problems and heating bills are reasonable. If I were to insulate the floor, I would run insulation vertically at the wall line to below the frost depth, then leave the floor itself uninsulated. I have seen concrete floors that had insulation board under them where frost went down outside, under the floor, and heaved the floor.

 

[wssix99]

I was wanting to spray foam the floor with the intention of spray foaming the rest of the shop down the road. The cost is to prohibitive as we're needing to remodel our home and something needs to give.

Spray foam under the slab will compress. You'd need to use boards. Boards are also pretty expensive. One way to achieve a similar effect with less material is to do a frost protected foundation:

Just insulating the foundation is not as efficient as doing the floor and foundation (note, the horizontal board outside the foundation is really important) but if you're long term plan is just to heat the space to around 50 degrees in the winter - I think you would be fine. Insulating the foundation only will still keep a heat bubble in the dirt below the building, but if you are going to heat the building to the 50's, you are going to be around the equilibrium point for the ground - so I wouldn't think insulating the floor would give you a payback. (It might make it "feel" warmer, but I wouldn't expect you'd see it in your heating bill.)

If you plan to heat the space to a normal living temperature, then you'd probably want to find a way to insulate the floor.