In floor heat foundation Prep

[MNMike]

HI Guys,

I've been lurking for awhile now to get some ideas on my 26x30 detached garage build. Unfortunately I will not be building anything close to the amazing shops you guys have. This garage will be more for storage and Man Cave.

I am in the beginning stages of planning and had a contractor come out to the site yesterday to bid the concrete slab. After reading tons of articles about in-floor heat my understanding is this. Vapor barrier, insulation, wire mesh, pex and pour.
My guy said that I would not need a vapor barrier and that we will do a grid with rebar and not have the wire mesh. So his construction style is: Insulation, pex, rebar and pour.

Most everything I have read says that I need a vapor barrier and the pex goes on top of the rebar/mesh. This guy does a ton of work in the area and is highly respected. The reason he says I do not need a vapor barrier is because we have extremely sandy soil.

I'm confused, Any thoughts?

Thx,
Mike

 

[forAK]

I'd do the vapor barrier->insulation->pex->rebar->pour. Sandy or not, it's cheap insurance and also slows the water down when the pour happens, keeping the slab moist.

 

[kj_mustang]

rebar on chairs with pex on top gets it close to the top of the slab and a little dicey for control joint cutting. Agree that you need the vapor barrier.

 

[forAK]

Depends on how thick the pour is. I've seen the rebar placed directly on the pex.

 

[Chris705]

One reason most concrete guys don't like vapor barriers is it does slow down the setup and ability to get on it to finish it.....I agree if you are planning on heating or ever adding any top coat finish to the slab then stick to your guns and insist on the vapor barrier....AND don't allow it to become Swiss cheese, so place it under the insulation board. If the base is good and firm go ahead and place the wwm on the insul and tie the pex to the mesh....it gives you the ability to place accurately with the 6x6 grid.

Good Luck!!

 

[MNMike]

Thanks Guys,
I will be installing the vapor barrier, insulation and pex, they will do the rebar and pour.

I'm super stoked to get this project going, I've been putting it off for a year or so. We have a three car attached and my little shop is jammed with ****, I have to go outside to turn around.

Thanks for the input.
Mike

 

[73RR]

Rebar is a better choice than the 6x6 mesh since the mesh usually gets trampled and pushed to the bottom of the slab where is does no good.
If you can afford some extra concrete then go thicker (5½). It will give some added depth above the PEX. Although the PEX could be tied under the steel it would be a major PITA. The extra concrete would be cheaper.
In lieu of saw-cutting the slab, the finishers could trowel a joint which would not harm the PEX if they hit it.

 

[MNMike]

They did mention they were going to trowel the joints and go thicker.

 

[theoldwizard1]

I'd do the vapor barrier->insulation->pex->rebar->pour. Sandy or not, it's cheap insurance and also slows the water down when the pour happens, keeping the slab moist.

CONCUR ! Rebar is overkill in most case. Wire mesh (4x4, 6x6 ?) is adequate in most cases.

If you live in a cold climate or where foundation wall is required under the edge, you should have insulation there, down to the frost line.

 

[PWC Repair]

I just did this a couple months ago. Look at the last page of my thread in my sig.

 

[73RR]

They did mention they were going to trowel the joints and go thicker.

Excellent! Is this a FPSF?

 

[ScaldedDog]

Every word out of a contractor's mouth is to advance his interest, not yours.

I'll never have a slab less than 6" or without rebar again. If you are insulating with 4x8 sheets, make sure they sit perfectly flat on the compacted base. Air under the insulation = cracks in the slab.

Mark

Sent from my SM-G935V using Tapatalk

 

[rburke65]

Yes Vapor barrier. Especially if you have sandy soil as the sand will **** the water right out of the concrete. Trowel the cuts? Not a fan of that. I had my floor cut as soon as they could walk on it after the power troweled the floor. NOT the next morning. If you will not have an epoxy finish then spray a concrete sealer/curing compound on it the retard the drying. If your going to do an epoxy floor than maybe just keep it wet with water for a week to cure.

 

[Randy in Maine]

The only thing I might add would be to isolate the heated slab floor from the non heated concrete walls using 2" of the same foam insulation as is under the slab. Give yourself a good thermal break.

 

[MNMike]

73RR,
You got me on this one, what is FPSF?

 

[73RR]

Frost Protected Shallow Foundation

http://www.greenbuildingadvisor.com...ost-protected shallow foundation detail 3.jpg

 

[MNMike]

73RR,
yes, but around here it is called a floating slab and the "footings" only need to be 12"

Thx,
Mike