Under-slab radon mitigation insulation layer

Posted by

KanataEcoBuilds

May 29, 2026

On March 12, 2026

TECHNICAL INFORMATION

HEAT-SHEET HEAVY. UNDER-SLAB RADON MITIGATION INSULATION LAYER

Specifications

Heat-Sheet® Heavy Panels are offered by the manufacturer in two thicknesses - 3-1/4” (R-10) and 4-1/4” (R-14).

Heat-Sheet® Heavy’s tubing channel system provides proper, multidirectional placement of 1/2”, 5/8” or 3/4” I.D. tubing with 4” on-center points.

Heat-Sheet® Heavy Panels are made with expanded polystyrene (EPS): a tough, high-density, closed cell foam insulation that is engineered to a minimum compression strength of 25 psi to support the weight of cast-in-place concrete (Higher compression strengths are available upon request.)

SIZE & PACKAGING CHART

*1Refers to thickness of the panel minus the nodules (grid height per image).
*2Refers to thickness of nodule plus nominal panel thickness.
*3In accordance with ASTM C578 and CAN/ULC S701 at 750°F (240°C). R-value is determined based on weighted average R-value of nodule and panel profile.
*4Meets water vapor barrier/retarder in accordance with the National Building Code of Canada and the International Residential Code.
Confirm with local bylaws.
*5 Panels per bundle may vary. Contact your local Heat-Sheet® representative to confirm.
*6 When made with Graphite Polystyrene this product will provide an average R-Value of 16.1.
*7Based on compressive strengths at 10% deformation.

Applicability As An Under-Slab
Radon Mitigation Insulation Layer

Tested per NRC’s Radon Infiltration Building Envelope Test System (RIBETS) to be able to serve, when when placed with the nodules facing down, as an under-slab radon mitigation insulation layer that is 50% more permeable than 4” (0.1m) of clean granular material. (Report No.: A1-21580) Test results available upon request.

Other Applications

Heat-Sheet® Heavy radiant floor panels, when placed “nodules up”, can be used in all underconcrete radiant floor applications, including: + Slab-On-Grade Applications + Sandwich Slab Applications + Snow-Melt Applications + Retrofit & Overlay Applications

Estimating

1. Measure the length and width to determine the size of the area in which you want to install Heat-Sheet® Heavy Panels.
2. The panels are 8 sq. ft. each. Divide the area by 8 to get the number of
panels you require.
3. Heat-Sheet® Heavy Panels come bundled in varying quantities as shown in the Size & Packaging Chart. When ordering your panels, round up to
the nearest whole bundle.

FOR CREATING AN UNDER-SLAB RADON MITIGATION INSULATION LAYER

Installation Steps

(Refer to the the Under-Slab Radon Mitigation Insulation Layer Installation Guide for the complete instructions)

1. Level and compact the base material, as required.
2. Install Heat-Sheet® Heavy, “nodules down”, on the base material.
Heat-Sheet® Heavy acts as the sub-slab ventilation layer, so no additional gas permeable layer, such as granular fill, is required. : (Granular fill
acceptable under Heat-Sheet® Heavy, but not required).
3. Since Heat-Sheet® Heavy panels interlock, taping joints is not required.
4. Cut a circular hole in the foam layer with a hole saw or utility knife to accommodate the radon exhaust pipe.
5. Apply spray foam between Heat-Sheet® Heavy and the exhaust pipe for gaps 1/4” or greater.
6. Install an air and vapor barrier layer on top of Heat-Sheet® Heavy, such as 6 mil polyethylene sheets or a peel-and-stick membrane.
7. All joints and any penetrations through the air and vapor barrier layer must be sealed with flexible caulking or tape. The air and vapor barrier
must connect to the air and vapor barrier in the foundation wall.
8. Cut a hole in the air/vapor barrier to accommodate the exhaust pipe. Must be sealed to air and vapor barrier with flexible caulking or tape.
9. Install exhaust pipe with a sealed cap that is labelled radon. Exhaust pipe must be located in the centre of the slab or placed off to the side with a
pipe under Heat-Sheet® Heavy extending to the centre of the slab.
10. Seal the perimeter with acoustic sealant between the air/vapor membrane and the foundation wall, grade beam or slab and ensure the slab air and vapor barrier connects to the air and vapour in the foundation wall.
11. Pour the slab