Radiant Slab on Grade Install Diary

Radiant Floor Heating Thermal Break/Moisture Barrier

This how-to was a garage project. The floor was prepared, as you would normally prepare a floor for any slab. Soil or gravel is compacted and leveled according to plan. Any necessary drainage is put in place to avoid problems with water touching the slab. The next step is to create a thermal break and moisture barrier. The idea is to avoid letting any heat transfer into the ground below or the adjacent footer.

We began by laying the Low-e slab shield rolls on the floor. Allow extra at the end and sides, so it will come atleast an inch or so above the pour. The Low-e can be trimmed after. If the slab is in a cold climate, foam board can be inserted around the perimeter for extra insulation. The rolls are then taped together with seam tape, to create a continuous membrane. The Low-e is both a thermal break and moisture barrier. Corners are easily formed and then taped well. We are now ready for welded wire or rebar. This is also the time you want to mark your pour height. This can be done on the footer wall.

 

Radiant slab on grade install - rolling out the Low-e Slab Shield

Radiant slab on grade install - rolling out the Low-e Slab Shield

 

 

Radiant slab on grade install - applying seam tape to create a continuous membrane

Radiant slab on grade install - applying seam tape to create a continuous membrane

 

 

Radiant slab on grade install - Low-e Slab Shield is in place

Radiant slab on grade install - Low-E Slab Shield is in place

 

Radiant slab on grade install - positioning the rebar

Now it is time to place our rebar and welded wire. In this application structural rebar was required and welded wire, 6x6 inch square, will be placed as a grid on top. This will allow the even attachment of PEX later.

 

 

Radiant slab on grade install - positioning the rebar

Radiant slab on grade install - positioning the rebar

 

Manifold and PEX Positioning

Once the rebar is in place the wire is zip tied over. This is also when we place our manifold. Careful thought should be put into where the manifold goes. Supply water, outside walls, easy access and a protected area are all concerns. Laying the tubing begins with placing PVC bends and attaching the PEX to the manifold. The tubing is then zip tied to the welded wire or rebar. The spacing of the PEX depends upon the desired BTU output.

  

Radiant slab on grade install - manifold and PEX positioning

Radiant slab on grade install - manifold and PEX positioning

 

 

Laying Out the PEX

Unreel the PEX, do not pull the PEX off so it coils like a phone cord. This will make things much more difficult and could result in kinks. A PEX un-coiler can be purchased or made if you don’t have enough hands.

 

Radiant slab on grade install - Laying Out the PEX

Radiant slab on grade install - laying out the PEX 

 

 

Radiant slab on grade install

Contouring to bump outs and irregular shapes is easy. The perimeter runs will dictate how this happens. The key is to have even loop lengths for even flow. Once you calculate your loop lengths cut the PEX and start your layout. Extra PEX can be put closer together on the edge. Small shortages can be compensated for by wider spacing in the center of the floor.

 

Radiant slab on grade install - Even loop lengths = Even flow

Radiant slab on grade install - Even loop lengths = Even flow 

 

Finished PEX Tubing Layout Here is a picture of the finished pattern.

The loop lengths are even, spacing varies very little. Note the tubing is closer together at the edge, where heat loss is greatest. When creating a garage slab a thermal break should be used at the apron. We don't want heat sneaking under the door and outside.

 

Finished PEX Tubing Layout

Finished PEX Tubing Layout

 

 

Radiant slab on grade install - ready for pressure testing

Radiant slab on grade install - ready for pressure testing 

 

 

Pouring and Leveling the Concrete

Once the concrete is poured the screed process begins. We are not concrete experts, so we will not try to reinvent the wheel. Follow your concrete contractors instructions and level the pour. Note there are 1 inch PEX supply lines in the background. They will supply the water to the manifold. We rented afloat, making the work much easier. There are many options when finishing concrete. You should always consult a concrete specialist

Radiant slab on grade install - leveling the concrete

Radiant slab on grade install - leveling the concrete

 

 

Pouring and Leveling the Concrete

Radiant slab on grade install - Pouring and Leveling the Concrete

 

 

Trimming Extra Slab Shield

This close-up shows the slab shield corner and the extra slab shield to be trimmed. The foam is trimmed after the concrete cures. There are several caulking products available to cover the foam and prevent water, insects and anything else from getting into the foam. 

Radiant slab on grade install - Trimming Extra Slab Shield

Radiant slab on grade install - Trimming Extra Slab Shield