How to Prepare Radiant Heat Subflooring

Radiant heat.
  • 15-30 hours
  • Advanced
  • 10,000-25,000
What You'll Need
Tile backer board
Insulating material, such as foam
Double-sided tape
Concrete trowel

Radiant heat is a popular device in Europe, and as it becomes clear that it is very fuel-efficient, many homeowners are wondering how to install radiant heat systems in their own homes. One of the best varieties of radiant heat is the underfloor radiant heating method. It is relatively easy to install, or have installed. If you are planning to install radiant heat underflooring yourself, you need to correctly prepare the subflooring in order to support the extra weight. This is not easy, but with a few simple steps, you should be able to make the subflooring secure within a few hours.

Step 1 - Install the Backerboard

You should first work out exactly what you will need to complete the preparation of your subflooring. Take your plans along to a local home improvement or hardware supplier and discuss the preparation with them. Once you have your materials, begin by installing the backerboard. Place the board on the bottom of the exposed floorboards in the subfloor, and using a staplegun or drill and screws, fix the backer board in place. You should add a very thin layer of mortar over the top of this.

Step 2 - Add Insulation

After installing the backerboard, you can place on top a layer of insulation that will help keep the radiant heat traveling upwards. Insulation can be made from anything you wish, although typical foam is the most commonly used. Lay this down and use a layer of card, or another layer of backerboard, above it in order to deflect any concrete run-off. You should smooth the card over with a layer of mortar, and then place a sheet of polythene over the top. The latter will prevent any water damage, and also keep later concrete applications from touching the wall.

Step 2 - Add Cabling and Mats

Lay whatever cabling you will need, and then place the mats evenly over the cabling and backerboard. You will need to make sure that these are placed carefully next to each other, so that there are no gaps, and then the mats are stuck in place using double-sided tape. Once they are firmly positioned on top of the backerboard, you should place another later of mortar over the top, making sure that it is completely flat using a standard concrete trowel. Don't apply too much pressure when laying the mortar, as the cabling can become damaged.

Step 3 - Lay Tiles

Laying tiles on the top of your subflooring adds an extra layer of insulation. Leave at least 6 inches of space between these tiles and the top of the subfloor. Aside from tiles, wood, or vinyl makes suitable subflooring covers. Once the tiles are on the subfloor, you can add your radiant heat tubing and lay the concrete flooring. It is important to remember that everything which the concrete touches will subtract from the warmth collected by it, so consider what the concrete is next to when laying your subfloor. Leave enough room for the subfloor to move during changes in humidity.