Location of pex and rebar / mesh in slab
I’m in the (hopefully final) design stages of my new 30×50 shop. It will be heated by radiant in-floor pex. I’m mulling over a 6 inch slab vs. a 4 inch slab, but in any event my question is about the same.
Where in the slab should the pex be? At the bottom over the insulation, or at some mid-point? Usually I see recommendations to tie the pex to mesh, but if the mesh is at the bottom of the slab, it isn’t doing a ton of reinforcement……use both mesh and rebar?
This is also tied in to a concern about expansion joints. I’d prefer to cut them in later, but obviously the pex in the slab is a concern. How deep should expansion joints be as a general rule? If I’ve got the pex at the bottom of a 6 inch slab, I’m a lot less worried about cutting than if it is in the middle (and likely floating up a bit…) Your help appreciated… –Ken
Replies
Hey Ken.
Rebar should be in the bottom 1/3, mesh in the top 1/3. Expansion joints should be 1/4 depth.
Rebar and mesh can both move to 1/2 depth without too many problems unless you have a highly engineered solution.
The closer PEX is to the top the faster the response time.
So, If you use a 6" slab with 3 1/2" chairs for the mesh and tie the PEX to the bottom of the mesh, a standard 1 3/8" deep expansion joint will optimize your setup as much as possible. A 6"slab is really 5 1/2" and a 4" is 3 1/2".
Assuming you don't need the structural strength of rebar. WW mesh is not for structural use.
SamT
my 6 inch slabs are true 6 inches but then we don't form with 2x's
Not structural at all. Just a shop/garage floor. I'll probably put rebar in it anyhow. --Ken
I did mine with 2" rigid extruded foam over VB and compacted fill. The PEX was stapled to the foam, rebar laid over that, and then a 4" pour. Came back three days later and cut the slots. No penetrations, and even though the PEX in down at the bottom of the slab, you can feel heat striping during acceleration. Running 100 * water in, comes out at 85* - 95*. 30 X 24 with set point slab sensor.
How deep did you cut the slots?
use zip strip when you pour. no saws next to the pex.
About 1/2"
Some photos and/or video of the floor/pex/rebar before the pour might prove useful down the road.
I am certainly going to document fully, and will likely try to line up the "runs" with scribe marks on the mudsills. My nephew works for the local gas company and says the "locator wire" they place on gas mains would likely work w/in the slab. Just normal 14 gauge wire, I think. I'd need one of those electronic gizmos to "excite" the wire and read its location, but as long as my nephew works for the gas company, I think I know where I can find one.......