Planning on using the vapor barrier, gravel/sand, and 2" thick foam board for insulation under the slab. Will have 2" foam around the sides as well. I'm planning on installing the radiant heat system myself (with help of friend who did his own garage), then bringing in the guys to pour the slab.
Take some pics of the tubing layout before you pour the concrete. You may never need it, but it's better to document what you have. Ask the guy I told almost 30 yrs ago to use an electric pencil to mark the location of his septic tank lid on the frame of his mobile home when installing. He had to dig it up to pump out at one time (even with regular maintenance, sometimes this has to happen. With less maintenance, more likely), and called me to see where we etched it!
About the insulation under the slab. Good idea. Keep in mind that even the cheap white foam coated with the foil backing will do a good job. Key items here are 1) thermal brake (foam), 2) vapor barrier (you are doing this) 3) reflection (foil backing)
With these things you are addressing conduction, convection, and radiation (thermal, not the geiger counter stuff
)
If I had my choice, I'd use even the cheaper constructed foam to get the foil over the denser foam without foil. Of course, they make dense foam with foil, too, but diminishing returns on cost
Have you thought how you are going to hold the tubing in place while pouring and what pattern you are going to use? (You know there should NEVER be any joints or fitting under the slab, unless you leave an access hole)
Why is holding it important? First is to keep your layout for efficiency. But the more important is so the pipe does not come to surface while pouring, leaving too little concrete on top, or (gasp!) breaking the surface. It's easy to do, but it's also easy to avoid if you plan ahead.
And of course, you are going to use oxygen barrier tubing and all that jazz and make sure you don't leave it exposed to the sun while waiting to be installed (UV damages most PEX)
And you will be pressure testing your tubing with (compressed air?) after laying and before pouring the concrete.
And being careful your turns are sweeping enough not to kink and rolling the tubing off the roll so it lays flat naturally.
You probably know all this, but it never hurts to restate it. Better than letting it slip your mind. (easy to do, with all the other things you gotta be thinking about).
On our bigger projects-especially those done in pieces over a long period of time- I like to keep a project book. It's just a binder separated into sections with diagrams, research info, permit/regulations, equipment/technologies being considered, potential vendors, anything else important for the project, and finally documentation of how it was actually done (as-builts).
The book is very helpful when your help shows up and you are giving them an overview of what you are looking to accomplish and the key points. I've found that people (helpers) are more likely to pay attention to the important details if they are drawn out and explained ahead of time.
We do a lot of DIYs of our own between a number of families, and this certainly helps there, too. They tend to stretch out over a number of years, as time and money become available and other projects are finished.
Done right, you'll love radiant floor heat.
Oh- and think about your drains. I ran a 4" main line down one side and ran laterals out to each of the 3 sections, then put an additional trap at the end of the main line where it joins the outside drainline (outside the concrete base in case of clogging).
Garage floors often have the problem with the water evaporating out of the traps and leaving the drains exposed to sewer gases and cold air inflows. This way you only have to use any one of the drains occasionally to keep that trap filled.
Just some tips to help you get the best setup you can. Most of it is effort and planning, not expense. No sense wasting what I've learned, may as well pass it along
- JC
