Radiant Slab on Grade Install Diary

Click the above link for install images.

This project was part of a weekend class taught by HouseNeeds and held by a local design build school, Yestermorrow.

HouseNeeds is here with more how to. This time we are looking at a radiant slab for a garage. If you are going to make the effort to pour a slab, why not lay tubing in it for added comfort and value. Homes with radiant heat are generally valued higher and differentiate themselves on the market. At HouseNeeds we make slabs easy. There are Slab Packages ready for your floor and layout patterns in our Heating University.


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.

Rebar and Welded Wire Mesh
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.


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.

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.

Even Loop Lengths = Even Flow
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.

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.

Pressure Testing
The PEX is fully attached to the manifold and ready for pressure testing. There is more info on our site about 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.

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.