Under slab inslulation for heated floor in new Shop. Pex Panels?

bellinoracing · Jun 30, 2014

Can someone recommend an under slab insulation to me? Hopefully within a couple months I will have the cement poured for my new 2000 sq ft shop. I spent most of today researching trying to figure out what I need to put down first to have heated floors someday. The boiler I wont be able to afford for at least another year but I want to put insulation and pipes in the ground so that I can have the in floor heat someday. I maybe in trouble because I only planned on about $1500 for pipes and underground insulation and its starting to look like it is going to cost me about double that. I have seen and I really like the crete heat panels as well as a few other similar products but they are all out of my price range and they are not sold anywhere near me. I see amazon has rolls of what looks like a bubble wrap that is sold as a underslab insulation but I doubt that works very well. Any suggestions for a good product within my price range?

stonehaven · Jun 30, 2014

Rigid insulation panels?

Bill D · Jun 30, 2014

Under slab insulation is not needed in the center of the slab if the soil is dry, or solid rock. Depending on soil type etc you should put insulation around the outer 5-10 feet of the slab or vertical insulation surrounding the perimeter. Think about it, five or ten feet of dry dirt is as good an insulator as a few inches of anything. And, 7,800 miles of dry rock is an excellent insulator.
Honestly in most shops the outermost few feet of slab is covered by machines or storage so I wonder if any insulation is really needed at all.
Bill D.

dian · Jun 30, 2014

use foam glas gravel. it insulates, keeps the slab dry and provides an exellent foundation. put a vapor barrier on top of it (bitumen/aluminum).

Harold Mulder · Jun 30, 2014

I would recommend rigid styrofoam panels as well, possibly 2" thick. Look for the rigid blue or pink stuff from Dow Corning. To save money check out your local craigslist or other sale sites. Look for used panels that have been recycled from factories or buildings being torn down. Up here in Ontario you can find that stuff for at least 1/2price of the new stuff.
Good luck
Harold

kustomizingkid · Jun 30, 2014

My shop floor is over 2" pink styrofoam with pex heating tubes... Love the in floor heat. Just make sure you plan for whatever you need or want to bolt to the floor.

gustafson · Jun 30, 2014

Bill D said:
Under slab insulation is not needed in the center of the slab if the soil is dry, or solid rock. Depending on soil type etc you should put insulation around the outer 5-10 feet of the slab or vertical insulation surrounding the perimeter. Think about it, five or ten feet of dry dirt is as good an insulator as a few inches of anything. And, 7,800 miles of dry rock is an excellent insulator.
Honestly in most shops the outermost few feet of slab is covered by machines or storage so I wonder if any insulation is really needed at all.
Bill D.

No

Not when you are heating the slab

2 inches minimum of foam under and surrounding the slab.

More won't hurt

Ralph_P · Jun 30, 2014

2" rigid with a sheet of 1/8" rubber under it.

Toms Wheels · Jun 30, 2014

In the snow belt, code requires a 30" deep footing, and a perimeter wall above grade 8". What I did is put two layers vertical against the walls and two layers 4' from the walls. I would have liked floor heat, but a heat pump was a better choice.

This past winter was colder than usual, at -5° F the floor was 60° the shop at 68°.

Bill D · Jun 30, 2014

2 inches minimum of foam under and surrounding the slab.

More won't hurt[/QUOTE]

I agree that more insulation will not hurt, in heating season. I think our difference of opinion about insulating value of dry sand has to do with our climate. If it is really dry, likely in the desert, dry sand is about R 1 per inch. So if he has 24 inches of dry sand that the slab is sitting on top of that is as good as 3-4 inches of foam. Of course if he has to buy sand and have it trucked in etc. foam be cheaper. I just assumed, being in the desert, he was pouring a slab on top of several feet of dry sand to begin with.
Bill D.
Modesto, ca

PS: One of my Father's friends grew up in Montana on a ranch. She was probably born around 1915. She said, in the fall, her father would plow manure against the house to cover the foundation and almost up to the bottom of the window sills. This was to add extra insulation for winter

sfriedberg · Jun 30, 2014

Not all rigid insulation panels are alike. The panels recommended for direct under-slab insulation are different from the panels used in exterior walls. I've got either Highload 60 or Highload 100 from Dow under my shop slab.

I did insulate under my entire slab, not just the perimeter, as part of full six-face insulation. Been quite happy with the result.

gustafson · Jun 30, 2014

Bill D said:
2 inches minimum of foam under and surrounding the slab.

More won't hurt
I agree that more insulation will not hurt, in heating season. I think our difference of opinion about insulating value of dry sand has to do with our climate. If it is really dry, likely in the desert, dry sand is about R 1 per inch. So if he has 24 inches of dry sand that the slab is sitting on top of that is as good as 3-4 inches of foam. Of course if he has to buy sand and have it trucked in etc. foam be cheaper. I just assumed, being in the desert, he was pouring a slab on top of several feet of dry sand to begin with.
Bill D.
Modesto, ca

PS: One of my Father's friends grew up in Montana on a ranch. She was probably born around 1915. She said, in the fall, her father would plow manure against the house to cover the foundation and almost up to the bottom of the window sills. This was to add extra insulation for winter

still not going with it, first because the percentage of the world with actual dry sand as a base is small, and second, the sand has thermal mass, so while it may have insulating value, it also takes heat to warm it up throwing a monkey wrench into trying to control the temperature. Your points are valid for an unheated slab under those conditions, never for a heated slab.

I grew up with radiant heat in the northeast, with no insulation, so it can be done, but it is a huge waste of very expensive energy

Oh, and bubble wrap is a scam scam scam

lucky7 · Jun 30, 2014

Strongly suggest underslab insulation. This is based on real world experience in mid continent Canada, so if you're in a location that doesn't get freezing temps for any length of time it may not be as worth while. If you go without, you will be heating 6-10 feet depth underground and laterally. In my location the payback for underslab 4" rigid heavy duty foam is one year with an electric boiler. And electricity is way cheaper here than in the US. For info I regularly move 15,000 pound loads across this floor without cracking it. Been using for seven years now and love (!) in floor heat.

Lucky 7

paul39 · Jun 30, 2014

Bellinoracing,

Check with a LOCAL architect or someone who installs under floor heating in your area about insulation. Are you in Tucson or on the side of Humphreys Peak. It would make a lot of difference in how much insulation you need.

Some of the people giving advice about insulation live in places that you have to bury your water line 8 feet down to keep it from freezing.

This might help you:

Under-slab Insulation

Radiant Heat From Radiant Floor Company The Slab on Grade Installation

https://www.google.com/#q=radiant+heat+slab+insulation&revid=1006061197

https://www.google.com/#q=insulation+for+in+slab+heating

Paul

adama · Jul 1, 2014

I have just started building my conservatory, Being frugal, i have managed to aquire the alu clad 5" thick cellotex like panels cold stores are built from. After some simple loading tests involveing a 1.5 ton ish series landrover, (jacking the landrover up on it, from a central cross member till all 4 wheels are just of the ground) a flat piece of lawn and a load spreader of a thick 2' square paving slab i came to the scientific conclusion there was zero crushing risk in any thing i can install in a shop let alone a conservatory.

If you have a source of any alternative flooring insulation its real easy to load a given area and measure for any crush with the gear most of us have ready access to. To get the stuff to crush based on the 9 square meters of conservatory floor i have, i re-con its going to take a pile of series three land-rovers over 25 tall, which is not even remotely going to fit in a 3 meter conservatory. Thats a loading in-excess 4 tons a square yard.

SND · Jul 1, 2014

In arizona, why? is the ground that hot?

here I used 2" highload 40 under the shop slab, and regular 2" under house side. Currently starting work on the new shop, probably gonna use high load 40 again if price hasnt gone too insane but I'm not heating the slab in the new shop.

Gthphtm · Jul 1, 2014

When we built my shop we put french drains around the outside in the proper stone and fabric.After the fotting was poured = 4' down it was tared and 2" insulation on the outside with plastic over that. Then we put in pex tubing under the 5" of cement.First was a vapor barrier, then 2" #40 foam,standoffs holding the tubing 1" to 2" above the foam, Rebar above that.Then the cement.Do yourself a big Favor and (Take Pictures and make a Print showing where Every Tube is Located ). You do not want 1 continious run or one zone. Make it a number of zones depending on the size.
In the northeast on the side of a mountian , clay and rock soil and springs can pop up anywhere any time.
Nice and comfey all year long.

omrc7771 · Jul 1, 2014

Back in the mid 90s, I built several walk - in freezers. After much research on loads and insulation values, I used 6" of pink rigid board that extended 2'-0" beyond the perimeter, 6x6 wire mesh, 1/2" rebar on 2'-0" centers and fibermesh 6 bag mix. Concrete was 8" thick. This was all done for insulating value and to accommodate a very large forklift. I don't know why anyone here, willing to make this investment, is even talking about not using as much insulation as they can afford.

Under slab inslulation for heated floor in new Shop. Pex Panels?

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