Radiant Floors

We installed radiant floors in our basement. Radiant floors are also called 'heated floors' and can be heated using various techniques. In our case, we ran 1/2" diameter PEX (that's the tubing that is generally used now for water piping) inside the new concrete slab. But, before getting to the point of laying out the PEX, one has to prep the ground below it! Here is our recipe for radiant concrete floors:

1. Excavate down far enough to allow for some compacted gravel (3-4" will do), 2" of extruded polystyrene insulation (R-10, this is a code requirement), another 1-2" of sand so that the concrete doesn't crack right away, and 4-5" of concrete. In our case, the concrete is our finish floor material, so from the top of the floor to the bottom of the existing ceiling joists, I maintained 7'-1" clear. Code calls for 7-ft. ceilings in livable spaces, and with 1/2" of sheetrock below the joists, I cleared it with 1/2" to spare!

2. Backfill the gravel and compact. Beware that the compactor machine will fill the whole house with gas vapors! Stinky! (and hazardous, potentially) Be careful around water pipes! You don't want to compact them and break them!

3. Lay a 6-mil. moisture barrier over the whole thing and duct tape the seams.

4. Lay your R-10 insulation boards and duct tape the seams. Part of all of this duct taping is to keep moisture out, but another part is to keep radon gas from penetrating the floor. In the Alameda neighborhood of Portland, many houses are exposed to radon. We tested our house in 2004 after we bought it, and found elevated levels. Long term exposure to radon can cause lung cancer, so it is smart to test for radon gas and mitigate for it if you find it.

5. Spread sand over the insulation board.

6. Install a rebar grid or some wire mesh over the sand, using something to prop the rebar up an inch or so. Small chunks of concrete work well, or rocks, and there are several products you can buy at concrete stores. I recommend Mason's Supply in Portland if you need concrete materials. Go to the one out by the airport - the guy working there is really nice and helpful.

7. Now you are ready to lay the PEX. PEX is actually short for 'cross linked polyethylene' and it was developed in the 1930's if you can believe that! It is now commonly used for water supply piping. But I digress! Laying the PEX is a little like herding cats. The stuff is packed in a nice loop, and it wants to stay that way! It takes a lot of coaxing, cursing, and patience to get the stuff to lay flat on your rebar.

8. Now your PEX has been installed, and you feel ready for concrete, right? Not yet. Go around and take lots of pictures and some measurements to make sure you know where those precious pipes are. After you frame up the walls, and when you get ready to anchor those walls to the concrete floor, you'll know why!

9. Put the PEX under pressure and call the inspector. You need to get the piping and rebar approved before pouring your slab.

10. Finally, if you intend to use an integral color like I did, go to Davis Colors and choose a color. Your contractor should be able to provide you with a printed brochure, but if not, you can call me and I will probably be nice enough to give you mine... I can always order another one.