Radiant Slab Detail

Peter_4

First time poster here, and radiant heating novice.

Getting close to starting a 3500 sq.ft. garage/shop. Been reading all I can get my hands on , and asking the concrete contractors who are bidding the job but I'm getting different opinions concerning slab detailing. I'm getting more confused as I go...not the best way to start.

specifically:

Wire mesh or fiber...or both? <p>
Best insulation, blanket or foam board?<p>
Tie PEX to wire mesh or foam or ? if using blanket.<p>
Sand on top of insulation?<p>
Vapor barrier below insulation?<p>
Pull mesh up into slab when pouring?<p>
Leave mesh on bottom?<p>
Insulate perimeter at foundation wall?<p>
Insulate Perimeter of slab only?<p>
Ideal substrate under slab?<p>
Radiant reflective barrier?<p>

Sorry for the barrage, but my research has raised as many questions as it's answered. Perhaps a case of a little knowledge being dangerous!
I'd sure appreciate y'all's experience and recomendations. I really don't want to get it wrong... planning on living here forever and it's not so easy to go back and fix later.

Peter

Unknown

I'll answer what I can and leave the ones I am not positive on

Use foam board, not blanket insulation. Blanket is better than nothing, it is not as good as foam board however.

Raising tubing in the slab can decrease response times but isn't a crucial detail if you are controlling the system adequately. so raised mesh is preferred, but you can usually get away with stapled to the foam as well.

Insulate EDGES and perimeter of slab at least. If your soil is rocky, wet, clay or if you have a high water table, insulate under the entire slab. Otherwise the outer 5' and the edges will do if necessary (also your climate affects this). Insulating the entire slab will decrease response times as well even if it's not needed from an "excessive heatloss" standpoint.

No reflective barrier. They are useless in direct conduction with a slab.

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Andy_14

> First time poster here, and radiant heating

> novice.

>

> Getting close to starting a 3500

> sq.ft. garage/shop. Been reading all I can get my

> hands on , and asking the concrete contractors

> who are bidding the job but I'm getting different

> opinions concerning slab detailing. I'm getting

> more confused as I go...not the best way to

> start.

>

> specifically:

>

> Wire mesh or

> fiber...or both? _p_ Best insulation,

> blanket or foam board?_p_ Tie PEX to wire

> mesh or foam or ? if using blanket._p_

> Sand on top of insulation?_p_ Vapor

> barrier below insulation?_p_ Pull mesh up

> into slab when pouring?_p_ Leave mesh on

> bottom?_p_ Insulate perimeter at

> foundation wall?_p_ Insulate Perimeter of

> slab only?_p_ Ideal substrate under

> slab?_p_ Radiant reflective barrier?_p_

> Sorry for the barrage, but my research has raised

> as many questions as it's answered. Perhaps a

> case of a little knowledge being dangerous! I'd

> sure appreciate y'all's experience and

> recomendations. I really don't want to get it

> wrong... planning on living here forever and it's

> not so easy to go back and fix later.

>

> Peter

Andy_14

I would use fiber mesh and a re-bar grid 2' on center throughout the entire slab. You will be very glad you did when the slab cracks and doesn't move anywhere.

Insulate foundation walls first

Use 6mil vapor barrier on grade next


2" ridgid foam insulation next

pex next

re-bar grid on 2" chairs next

All done, ready to pour

james barnett

info on vapor retarder location

some of this depends on your climate. In Seattle, I'm getting ready to do the same thing, and engineers are changing their specs as far as vapor barriers/retarders (a retarder is 6 mil visqueen, barriers are reinforced membranes with sealed overlaps) going under the 4"of well-graded 5/8minus. They were putting the 4" of 5/8"minus on top of the vapor barrier/retarder to act as a blotter, or to aid in the curing of the slab. Now they say, put the 5/8 minus on top of the vapor barrier/retarder only if will not get wet before your pour the slab. If it might get wet, put the vapor barrier directly under the slab, and reduce joint spacing and use low shrinking concrete mixture and "other measures".

Gordy

Radiant Slab

Peter,
Pertinent info. What is going in the new garage/shop as far as largest equipment? This may dictate some things on tubing,slab thickness and reinforcement of the slab. This would not change insulation requirements. If you are going to use wire mesh use "road mesh" 6x12 its heavier than the rolled mesh and comes in 8'x 20' sheets lays nice and flat.Fiber mesh is great but its harder to get the glass steel trowel finish.
Gordy

Peter_4

Thanks for the info, guys. Two things I should have included. I'm in Boise, southern Idaho... lots of clay in soil and moderately cold winters.
One part of the shop is large enough to house a motorhome, although I don't own one...(spending all the money on the building!). Max weight likely less than 22K lbs. Probably will install a two post car hoist in this area. I plan too talk to the hoist guy to get an idea what slab requirements are for that.

Cheers, Peter