Shop Building with heated floor

[Cap07]

I'm designing a shop building which will have a radiant heated slab on grade. I've attached a jpeg which shows the foundation configuration. I have a couple of questions:

1)I'm showing the insulation under the slab and around the perimeter. Someone told me that it's also required that the insulation be placed underneath the footing. This is the first radiant heated floor design I've done, so I'm not familiar with the insulation requirements. In most of the details I've found, insulation is not shown under the footing. Is there rigid foam board insulation that is rated for the load the footing would impose on it?

2)For placing the tubing in the slab, I was going to specify either WWF or rebars and then tie the tubing to that. The contractor wants to attach the tubing to the rigid insulation that is going under the slab, then pour the slab over it. Has anyone done it this way? In all the details I've seen, the tubing has been supported by WWF or rebar.

Thanks for your help.

 

[SlideRuleEra]

1: Typically 100 psi, maximum.

http://www.dow.com/PublishedLiterat...foam/pdfs/noreg/179-02548.pdf&fromPage=GetDoc

You may want to look around the manufacturer's website for additional recommendations:

http://building.dow.com/na/en/applications/building/foundations/cs.htm

2: The final location is important, not how (within reason) it got there. With that said, suggest that you have the contractor provide explicit details (in advance) of what he wants to do since his proposal varies from your experience. If what he proposes is reasonable, let him do it.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Cap07]

Thanks SlideRuleEra, that is very helpful information.

Regarding item #2, I found something today in ACI 302.14-04 (Guide for Concrete Floor and Slab Construction) that seems to indicate that the way the contractor is proposing to place the tubing is not recommended. See excerpt below:

"3.4.3 Radiant heating: piped liquids—Slabs can be heated by circulating heated liquids through embedded piping. Ferrous, copper, or plastic pipe is generally used with approximately 2 in. (50 mm) of concrete cover (not less than 1 in. [25 mm]) under the pipe and with 2 to 3 in. (50 to 75 mm) of concrete cover over the pipe. The slab is usually monolithic and the concrete is placed around the piping, which is fixed in place. Two-course slab construction has also been used, wherein the pipe is laid, connected, and pressure tested for tightness on a hardened concrete base course. Too often, however, the resulting cold joint is a source of distress during the service life.

Insulating concrete made with vermiculite or perlite aggregate or cellular foam concrete can be used as a subfloor. The piping should not rest directly on this or any other base material. Supports for piping during concreting should be inorganic and nonabsorbent; precast concrete bar supports (Section 3.2.4) are preferred to random lengths of pipe for use as supports and spacers. Wood, brick, or fragments of concrete or concrete masonry should not be used."

 

[CarlB]

I've seen several different versions of
insulation/tubing/sand/mesh/concrete.
For example this installers handbook shows attaching the tubes to insulation:

http://www.roth-canada.com/caf/pdf/Can_Snowmelt_Inst_Handbook.pdf

 

[Cap07]

Thanks for the link Carl, I appreciate your input.