CONTENTS

Typical slab on grade detail

Typical staple-up detail

Alternative Details

1) Suspended floor using sleepers
2) Suspended floor using concrete
3) Slab over existing concrete floor

Links to related resources on this subject

Typical slab on grade

Typical staple-up

1) Suspended floor using sleepers
In this case, insulation (R-19 to R-38, depending on climate) is generally placed between floor joists beneath the subfloor. A radiant barrier is always placed on top of the lower subfloor, beneath the sleepers, to reflect most of the heat upwards. Metallic heat transfer plates are placed between the sleepers to hold the tubing in place and spread the heat horizontally (Fig 1-1).

It's also important to insulate around the perimeter edge of the floor (Fig. 1-2) with 1.5" to 2" rigid insulation. When the tubing installation is complete, an upper subfloor is then placed on top. It is important to maintain your tubing under pressure (with air) while nailing the upper subfloor in place, and to be very careful to mark nailing locations from above to avoid nailing anywhere close to the tubing.

There are also commercial products made for this purpose, retailing for about $1/sf, such as Thermaboard (Fig. 1-3)

2) Suspended floor using concrete
In this case, a thin layer of standard or lightweight concrete is poured over a wood floor system. A vapor barrier is generally required. When using lightweight concrete (Fig 2-1), tubing installed on top of wood or insulation board may be fastened down with plastic u-nails or a stapler made for radiant tubing (electric or manual tubing staplers are available, using 5/8" to 1 1/2" staples with 3/4" to 1" crowns).

3) Slab over existing concrete
In this case, a thin layer of standard or lightweight concrete is poured over an existing concrete floor (Fig 3-1). A vapor barrier is generally required (if one has not already been installed), as well as 1" to 2" thickness extruded polystyrene insulation . The amount, thickness and placement of the insulation depends upon the climate and the depth of the slab above/below grade. The tubing can be attached to the existing slab with tubing straps by power nailing directly into the concrete with a ram set. Or, if rebar or welded wire mesh is used to reinforce the slab, the radiant tubing can be attached to the steel with plastic ties.