Spray foam under mono slab, will it work?

[backintheday]

Hey all,
I'm planning to do a 64 x 54 monolithic slab for my shop this spring and am curious on what everyone thinks about spray foam under the entire slab, the footers, floor and everything in between. I've seen it done on a couple builds on the GJ but I would like to get every ones view on if it will hold up over the years. The ground is hard mostly clay, rock and sand not to much rain but we get a lot of snow and can go weeks with -20 temps. The building will have 16' sips walls and a 4'' slab.
Thanks in advance and I respect the opinions of the members on this site.

 

[Bondo]

Ayuh,... Spray foam is a pretty generic term,...

If the foam used is dence enough, 'n of the closed cell varity,....
Ya, it oughta work just Fine,....

 

[BadgerBoilerMN]

Spray foam insulation is not rated for mechanical loads and should never be sprayed as a foundation for a slab-on-grade. It pays to ask the manufacturer with the notable exceptions listed below.

When installing radiant slab we don't get creative, shunning all gimmicks, like; insulating blankets, bubble foil or spray foam. The standard is 2" of 25 psi extruded polystyrene.

I used 2lb spray foam in nearly every square inch of my 1921 farm house remodel ,but rigid foam holds everything up!

 

[volleyball]

Spray isn't going to give you a very flat surface and will be expensive. You would have to use a 2 lb or greater foam. Premade boards will be a better choice.

 

[ADSR]

seen it done on here only once. looked costly!

 

[backintheday]

Thanks for the info guys. I used spray foam in my new house, highly recommend it. I thought it would be pretty slick under a mono slab since there are angles and it would make it 1 uniform piece of insulation. Guess I'll steer away from it since it hasn't been around very long to see how it's holding up over time. Hopefully rigid foam prices will go down with oil price but I'm not holding my....
Thanks again

 

[Concrete Homes]

You did not mention if you are going radiant or not. We carry one called EZ Floor out of Wisconsin. It is insulation, vapor barrier all in one, and has moulded in high spots to run your tubing in. That is made at the plant we get Fox ICF from in Post Falls, ID. We also have another one made up at Beaver Plastics in Chilliwack, BC. It does not have the vapor barrier built in, but a good vapor barrier is pretty simple. With that clay, be sure to get a good gravel compacted base. Depending on your loads, you may consider going a bit thicker than 4". I would also recommend fibers instead of bar or mesh.

 

[BadgerBoilerMN]

The EPS knob style EZ Floor and CreteHeat are certainly acceptable alternatives. One assumes PEX will go in the slab since everything else is a compromise.

 

[coldh2o]

Spray foam insulation is not rated for mechanical loads and should never be sprayed as a foundation for a slab-on-grade.

What is a "mechanical load"? I disagree, "spray foam" (recognizing that's a general term and the specs need to be appropriate for the application) can and has been widely used structurally under slabs.

That aside, I don't see much advantage over board insulation except a continuous vapor barrier less susceptible to damage during construction, and that's an incremental gain. In my neck of the woods board insulation is way cheaper, especially for a DIY project.

 

[backintheday]

I spoke with the local concrete contractor whom I trust. He will not pour a mono slab in this area, he said he has lost to much money having to repair cracked slabs, he won't pour a slab unless it's under cover. So it looks like I'll be pouring a footer and wall using ICF's. I was trying to avoid the added cost of the wall and ICF's but that's what seems to work best in this area. I poured my house foundation the same way, it was a piece of cake, my wife and I staked the ICF's like legos then I poured the wall by myself. I'll use foam board under the floor. Yes it will have radiant.
Thanks for the help everyone.

 

[James-W]

I would definitely go with the traditional method of insulating rather than try to do something different and have it turn out all wrong.

 

[volleyball]

Take some of those sheets left over from putting under the slab and put on the outside of the ICF's.
Are you going to have frame or ICF's as walls in living areas?

 

[backintheday]

ICF foundation then SIPs with 16' walls. 5/12 tusses. It will be a very efficient building. I plan to use geothermal water to water for the radiant. I should be able to down size the heat pump due to the sips, at least I hope. I still need to do more research on electric on demand or whatever is best with solar as the main power supply. Other than the floor I will do all the work.

 

[volleyball]

You can do water to water system for radiant and radiators. A heat exchanger for other areas.
You want to size your right but since I was in between, I went larger that had a variable speed output. Mine is water to air. Mine is also designed more for a northern climate. It helps so that the cooling season is much better. Mine pulls about 5 gallons of water a day dehumidification so it is well sized. I collect the water for watering plants so I know how much I get.

 

[Kogashuko]

I have seen it done many times. There are a number of retrofits and new constructions that do this in basements. They spray 2lb foam over the dirt instead of using foam panels. They then install the rebar on top of the foam off of the surface. They then pour the concrete over it. Of course this is done with the block walls in place first. Very efficient.

Since I dont want to sink the money into pouring concrete in my crawl I plan to spray 3lb roofing foam over the plastic at some point. I might even put some foam panels in first and put the wire over them to hold them down first. 3lb roofing foam is really hard and will create a rigid surface making it easy to roll around in the crawl on a wheeled creeper.

 

[backintheday]

You can do water to water system for radiant and radiators. A heat exchanger for other areas.
You want to size your right but since I was in between, I went larger that had a variable speed output. Mine is water to air. Mine is also designed more for a northern climate. It helps so that the cooling season is much better. Mine pulls about 5 gallons of water a day dehumidification so it is well sized. I collect the water for watering plants so I know how much I get.

Which model do you have? I'm looking for a diy friendly unit, I know there aren't many out there. I'm also looking for a calculator to help size the unit if you know of any. I might pay a geothermal specialist to size it, that's one thing I know very little about .
Variable drive is the way to go. I deal with them at work.

 

[mygarageone]

Which model do you have? I'm looking for a diy friendly unit, I know there aren't many out there. I'm also looking for a calculator to help size the unit if you know of any. I might pay a geothermal specialist to size it, that's one thing I know very little about .
Variable drive is the way to go. I deal with them at work.

I do not think you'll find anyone who will sell you the equipment , unless they can do the inspection and start up. Geo is not DIY friendly .

 

[volleyball]

I agree geo isn't something you want to tackle on your own. There isn't a lot to it if it is a straightforward retrofit. But you want a whole new system.
You really need someone who can calculate your HVAC needs. A calculator isn't much good if you don't know what numbers to punch in.
Besides planning the runs for the radiant, you will probably want to do A/C since you are installing a geo. That means ductwork.
You will want to have a geo guy to get it right the first time and to fix it if there is a problem. I had 2 problems. One was the drain backing up but that was my fault. And I made my own custom drain so that is no issue. The other one was an error which was due to the zone controller. He had a fix and up and running in hours. I contacted the mfg who had just designed new grommets. Problem permanently resolved.
I have years of knowing that I won't be too hot or cold for years.
For your space, it may be simpler but a good designer can make a much more comfortable space.
I have a Hydron Module unit.

 

[backintheday]

If I decide to install it my self I'll do my best at a write up. There are some kits on ebay through ingrams, need to do more research on them before I decide anything.
There will be no A/C. Doesn't get hot enough here for it.
Thanks again guys.