In floor heating base, sand or class 5 ?

[UpNorther]

Planning on infloor heat:

Whats a good base and thickness for under the concrete polystyrene ?
Sand or class 5 ? And how thick ?

I live in central Minnesota, have a 40x50 polebarn. Already have 2" styro going 2' down on perimeter. Just figuring out fill needed inside.

 

[Randy in Maine]

Mine is just a good compactable base using a good gravel with fines that packs down really well. They compacted it about every 6" of lift placement.

 

[like2wheel]

I believe for the best performance of your insulation, it needs to be a washed gravel that won't capillary up moisture.

Sand does not meet that requirement.

 

[pstnbly]

I believe for the best performance of your insulation, it needs to be a washed gravel that won't capillary up moisture.

Sand does not meet that requirement.

A moisture barrier (sheet plastic) should be installed as well as the insulation.

 

[rburke65]

I used clay. Sand never dries out and the clay raised my footprint of my build. They make dams from clay to hold back water, so that's what sold me when that was suggested. Clay was like concrete by the time I had the floor placed. Vapor barrier, foam board, wire, pex, then concrete.

 

[Jess]

You should have a capillary break under the insulation to prevent moisture wicking up. Spend some time a seal the poly all around the footing and you will have a dry floor and no concerns about moisture especially if you want to apply a coating to the concrete now or later. I'm in the process of having a building (not a shop) built by a contractor. The design for the floor calls for 4" of crushed stone, 4" of foam insulation, 10 mil poly and 4" of concrete on top. We are placing Hpex pipe for future hydronic floor heating.

 

[klrdiant]

x3 (or 4) on the moisture barrier .. water under your slab can wick the heat out faster than you can put it back in