Pre-slab preparations - part 2.

I ended my last post about the foundation on the day that the rigid foam had been installed and the decision to omit the 10 mil poly was made. The following day was when the concrete guys were to come out and install the steel reinforcing for the slab, which proceeded as planned with no problems. For reinforcing, a 10 mm rebar grid was laid out on 12" centres and tied together. With hindsight, I know this is over-kill and if I were to do it again, I would have argued for lighter gauge reinforcing in my plans. My concrete contractor kept joking that if I ever needed any extra cash, I could open up my basement to do heavy-duty mechanic work since I would now be able to park a bulldozer or excavator on the slab. Live and learn.

The last big task to accomplish prior to pouring the slab was to install the PEX tubing for the radiant floor heating system. As I write this I have no plans to actually use the radiant floor system to heat the house, but I decided to install the tubing anyway since I wouldn't be able to change my mind later. The first step to installing the PEX was to layout the location of all the basement partition walls using fluorescent paint. Working off of a map that I had made for myself, I used nylon "zip-ties" to fasten the PEX directly to the rebar. One advantage to the heavy gauge reinforcing was the wider 12" spacing which made estimating the tie points for the PEX tubing easy. The most difficult aspect of installing the PEX was simply getting it uncoiled without kinking it.

The PEX layout consists of three zones, each of 300' of tubing. Note the orange lines that indicate the basement partition walls. I avoided running tubing directly under partition walls except to cross them at a perpendicular angle. By doing this, I hoped to minimize the risk of puncturing a tube when fastening the partition walls to the concrete. As it turned out, I used adhesive to secure the partition walls to the concrete thereby rendering this strategy moot.

Each run of PEX (one continuous run per zone) begins and ends at the same spot in what will be the utility room. I connected the beginning and end of each zone to the set of manifolds that I had constructed and pressure tested earlier. Once the tubing was connected to the manifolds, I also connected my home-made pressure tester to the manifolds using a long piece of 3/4" poly pipe. The manifolds and poly pipe were supported in an upright position by cantilevering a 16' 2x4 from the slab edge forms.

My "pressure testing rig" allowed me to apply pressure to the tubing and manifolds so as to check for any leaks. The system was able to hold at 20 psi overnight which convinced me the PEX was in good shape and there were no bad connections. By using a long piece of poly pipe, I was able to "remote" the pressure tank which allowed me to keep pressure on the tubing and manifolds during the actual slab pour. I'm not sure this is absolutely required, but it didn't seem like a bad idea.

In this picture you can see how the three separate zones come together at the manifolds. You may notice that there is a fourth pair of tubes that have not been connected to the manifolds. Those extra tubes run to what will be an attached sun room on the south wall. My intention is to eventually use this run to circulate warm water to "warming beds" - for seed starting. Next to the manifolds (on the left) is the coil of 1" poly pipe that is the main water line from the cistern. 

Lear and Burn - The Sheepdogs