How To Insulate A Concrete Slab with Prodex Total

1. Unroll Prodex Total Under Concrete or Reflective Bubble White Poly WHITE SIDE UP
2. Overlap seams 2". Let the material go up wall 6".
3. Great for driveways, radiant floors and basements!
4. Seal seams with Under concrete tape.
5. Install wire mesh and piping system per manufacturer's recommendations.
6. Pour concrete.

Customer suggestion:

In my situation, after the 4” floor was poured we trimmed 1-3” off around the edges all the way around. Insulation really didn’t move any when floor was poured, just that contractor didn’t lay all the strips even. Had some running up the wall 5” an some 7”. If they would’ve had it all 6” evenly placed everywhere it would’ve required 2” trimmed all the way around before power toweling the floor.

So my theory on the advice of running 6” up the wall is for allowance for slight movement in the prodex so your end result is to have the cut off prodex edge right at the top of the finished floor on the outside walls. If gravel were used instead of packed fill sand like I used, I’m sure there would be even more movement from pouring, so the 6” recommendation is universal advice for both gravel and sand.

Hope this helps should any other customers inquire on the reasoning of running the prodex up 6” on the walls.
Thanks again for a GR8T product.

Tim Wright

Understanding Under Concrete and Under Slab Insulation

Adding under concrete insulation or under slab insulation beneath a concrete floor is one of the most effective ways to control heat loss and moisture migration in a building. Whether in a residential foundation, commercial slab, or garage floor, this type of insulation provides a thermal barrier between the ground and the structure above.

When installed correctly, it helps maintain consistent interior temperatures, reduces condensation, and prevents heat from escaping into the soil. Builders, homeowners, and radiant heating installers all benefit from the improved efficiency and comfort that proper under concrete insulation provides.

Why Under Slab Insulation Matters

Concrete alone is not an effective insulator. It absorbs and transfers heat quickly, which can lead to cold floors in winter and unnecessary energy use year-round. By adding under slab insulation, the floor assembly gains thermal resistance and moisture protection.

Key advantages include:

• Energy efficiency: Less heat loss through the floor.

• Moisture control: Prevents vapor from migrating into living spaces.

• Comfort: Warmer floors and more even room temperatures.

• Durability: Helps protect finished flooring and reduces stress from temperature swings.

These benefits are especially noticeable in buildings that use radiant floor insulation systems.

Radiant Floor Insulation and Heat Distribution

For radiant heating systems, insulation beneath the slab plays a critical role. Without radiant floor insulation, much of the heat from tubing or electric cables is lost downward into the ground.

By combining a reflective barrier with a closed-cell foam core—such as in Prodex Total Under Concrete Insulation (5M)—the system reflects heat upward into the living space, improving efficiency and comfort while reducing operating costs. 

How to Insulate a Concrete Slab: Step-by-Step Overview

If you’re wondering how to insulate a concrete slab, the process is straightforward:

1. Prepare the base: Level and compact the soil or gravel base.

2. Unroll the insulation: Place the material with the reflective surface facing down toward the ground.

3. Seal seams: Overlap edges by about 2 inches and seal with under-concrete tape to prevent moisture seepage.

4. Extend up walls: Run insulation 4–6 inches up the perimeter walls for continuous protection.

5. Install radiant system (if used): Position tubing or cables per your radiant design.

6. Pour the concrete: The insulation remains beneath the slab as a permanent thermal and vapor barrier.

Following these steps helps ensure long-term performance and a warmer, more efficient floor.

Choosing the Right Under Concrete Insulation

When selecting under concrete insulation, consider:

• Compression strength: Must withstand concrete loads without collapsing.

• Moisture resistance: Closed-cell foam and foil layers reduce water absorption.

• Ease of installation: Lightweight rolls simplify handling on job sites.

• Compatibility with radiant systems: Reflective surfaces enhance upward heat transfer.

For detailed specifications, see:
Under Concrete Prodex Total Insulation 5M 

Long-Term Benefits of Slab Insulation

Investing in quality under slab insulation reduces energy costs, minimizes condensation issues, and extends the lifespan of finished flooring materials. In climates with high humidity or large temperature swings, the payoff in comfort and durability is substantial.

A properly insulated slab foundation is an integral part of an energy-efficient building envelope—working in harmony with wall and roof insulation systems to maintain consistent indoor comfort year-round.