A slab sits on its insulation, so the foam under it has to carry the load. EPS comes in compressive strengths from 10 to 60 psi, so you can match the foam to the job: a garage floor, a heated pole barn, or a commercial slab with radiant tubing.
Source Mountain Supply supplies EPS sheets for under-slab and radiant floor work in the thicknesses and facings you specify, faced or unfaced, and we arrange local and jobsite delivery. Not sure which psi to order? Our density and compressive strength guide explains the choices, and we will go over your numbers with you before you order.
EPS sheets are made in compressive strengths from 10 to 60 psi. Strengths of 25 psi and higher are available for slabs that carry heavier loads.
Faced EPS has a laminated facer that adds jobsite durability. Unfaced EPS is the lowest-cost option. We quote either.
Custom thicknesses, sizes and densities are available, so you can use fewer layers and waste less.
R-value by compressive strength and the thickness you need for common R-value targets, at 75°F mean temperature, from the Atlas ThermalStar thickness selector.
| Compressive strength (psi) | R per inch | R at 2 in | R at 2-5/16 in | R at 4 in |
|---|---|---|---|---|
| 10 psi | 3.9 | 7.8 | 9.0 | 15.6 |
| 13 psi | 3.9 | 7.8 | 9.0 | 15.6 |
| 15 psi | 4.2 | 8.4 | 9.7 | 16.8 |
| 25 psi | 4.4 | 8.8 | 10.2 | 17.6 |
| 40 psi | 4.4 | 8.8 | 10.2 | 17.6 |
| 60 psi | 4.5 | 9.0 | 10.4 | 18.0 |
| Target R-value | 10 psi | 13 psi | 15 psi | 25 psi | 40 psi | 60 psi |
|---|---|---|---|---|---|---|
| R-5 | 1-5/16 in | 1-5/16 in | 1-3/16 in | 1-3/16 in | 1-3/16 in | 1-3/16 in |
| R-7.5 | 2 in | 2 in | 2 in | 2 in | 2 in | 2 in |
| R-10 | 2-9/16 in | 2-9/16 in | 2-3/8 in | 2-5/16 in | 2-5/16 in | 2-5/16 in |
| R-15 | 4 in | 4 in | 3-9/16 in | 3-9/16 in | 3-9/16 in | 3-9/16 in |
Typical values for molded polystyrene insulation, not a specification. Your plans and engineer set the psi and thickness. Sources: Atlas ThermalStar thickness selector and Insulfoam R-Tech data. Download the R-value and thickness selector and the Insulfoam R-Tech 10-60 PSI sheet.
Foam under the tubing keeps heat in the slab and out of the ground.
Insulated floors for shops, garages and agricultural buildings.
Higher-strength EPS under slabs that carry traffic and loads.
Insulation under basement floors and along slab edges. See below grade insulation for foundation walls.
Tell us the slab size, the load and the R-value you need. We will quote the psi and thickness.
It depends on the load. Light floors such as a garage or shop floor use lower strengths, and heavy commercial slabs use higher ones. EPS under-slab sheets are available at 25 psi and higher. Your plans or engineer have the final say, and we can go over the numbers with you.
Both are used under slabs. Faced sheets have a laminated facer for jobsite durability, and unfaced sheets cost less. We quote either. Check your plans for the requirement.
It depends on the R-value you need. As a guide, about 2-5/16 inches of 25 to 60 psi EPS gives R-10, and about 3-9/16 inches of 15 to 60 psi EPS gives R-15. See the tables above.
Yes. EPS under heated slabs is a common use. Ask us about the thickness and psi that fit your radiant system.
Call 920-382-0382 or send a request with the slab size, psi, thickness and delivery address. We arrange local and jobsite delivery.
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