New Radiant Slab Questions

[husker77c]

My 30X56X10 pole barn is going up in a few weeks, first garage i've had in my life, only took 47 years haha. The contractor is not pouring the floor, as i have several friends that pour concrete for a living so I will be pouring the floor in early fall. Shop is in northern PA, i envision using the floor to keep the garage at 40ish degrees in the winter and using a supplemental heater to raise it up if i need to work or hang out. R19 walls and R30 ceiling, pole barn batts most likely.

I will be prepping the floor myself to save money, then I'll use my friends for the labor and experience for the actual pour.

1) For under slab Insulation i am seeing multiple different types. The normal green or pink board from a box store, or specific radiant heating insulation from various specialty manufacturers with dimples or similar for running the tubing. I will have to use wire mesh in the slab anyway, so I'm not seeing the advantage to using the more expensive application specific insulation, unless there is something I am missing of course. It seems it is more cost effective to use pink board and zip tie the tubing to the mesh and call it a day. The specific foam board actually puts the tubing directly on top of the insulation and from what I've read you want it closer to the surface than you do the bottom of the slab.

2) I am planning on 2" under the slab and 2" on the perimeter up against the grade board and posts, what do you do for the garage door openings? if I'm wanting to have a concrete apron in front of the garage doors how do i create a thermal break between the shop slab and the apron outside? My thought was to use 1" insulation for an expansion joint type thing. Is that necessary or am i over thinking it and should just use an actual expansion joint.

Thanks for the help.

 

[jack stand]

IMHO the dimpled foam is not worth it especially when using 6x6 wire mesh. It's also "coffee cup" Styrofoam, the lowest r/inch of all of the foams.
Isolating (thermal break) your apron and the rest of the perimeter involves more foam.
Describe your foundation/slab.
You should search "frost protected shallow foundation". It will show you the simple principles of keeping the cold out from under your slab and the heat where you want it.

 

[husker77c]

Pole building so no foundation to speak of, 4-5" slab poured installed inside the building. I would think 2" foam completely encapsulating the bottom and sides of the slab would be the most i could do for this application, aside from going to a thicker insulation.

 

[jack stand]

There are examples I've seen of foam being placed in a vertical narrow "ditch" around the perimeter, ideally down to your local frost depth. Another variation is outside of the perimeter burying horizontal foam outward (with a slight pitch away from the building) several feet. 4' would be ideal.
Remember that radiant or not, keeping the cold away from your slab, the thing that your trying to heat is pretty beneficial and there's no easy "re do" once it's poured.

 

[dscheidt]

IMHO the dimpled foam is not worth it especially when using 6x6 wire mesh. It's also "coffee cup" Styrofoam, the lowest r/inch of all of the foams.

It's worth pointing out that the actual aged insulating value of polystyrene foams is all very nearly the same. XPS has a higher claimed R-value because it's tested when it's new, and is still full of the blowing agent. The blowing agent used in XPS in the US has a very high GWP, and it all will defuse out over a much shorter time period than the manufacturers want you to believe. After that happens, the insulating value is the same as XPS made with a lower GWP blowing agent (as is done in most of the rest of the world) or EPS. EPS is cheaper, and available in better grades than what is used for packing materials. So for most of the life of the building you get the same performance as the cheaper material. Whether two or three years of slightly higher performance is worth the cost is up to you, but it isn't on a total cost basis.


The special radiant foams selling poing is they save time at installation. I doubt it's enough time to make it worth using on a small building, especially if you're doing it yourself.

 

[husker77c]

It's worth pointing out that the actual aged insulating value of polystyrene foams is all very nearly the same. XPS has a higher claimed R-value because it's tested when it's new, and is still full of the blowing agent. The blowing agent used in XPS in the US has a very high GWP, and it all will defuse out over a much shorter time period than the manufacturers want you to believe. After that happens, the insulating value is the same as XPS made with a lower GWP blowing agent (as is done in most of the rest of the world) or EPS. EPS is cheaper, and available in better grades than what is used for packing materials. So for most of the life of the building you get the same performance as the cheaper material. Whether two or three years of slightly higher performance is worth the cost is up to you, but it isn't on a total cost basis.


The special radiant foams selling poing is they save time at installation. I doubt it's enough time to make it worth using on a small building, especially if you're doing it yourself.

I appreciate that info, my only concern with using EPS would be the possibility of it getting damaged during the pour. It seems the pink or green board would be more durable when walked on and such. For money we are talking half the price though for EPS. The quotes i got for the special radiant foam was $3800. I'm seeing box store prices are $3k for XPS and $1400 for EPS.

 

[billconner]

For the apron to slab, I would look at a detail with chamfering the top of a vertical piece of foam 45 degrees and then topping that with a piece of galvanized angle. Inside overhead door just. Top flat leg of angle flush with slab. Apron poured to leave a 1/2" vertical or angle. Will stop any water from blowing in under door.

Just FYI Rockwool's Comfortboard can be used under slabs. Another product I'm interested in for this is Glavel. Recycled glass "expanded" that is both insulation and base for slab. You can use spray foam also. Last, consider looking for rigid foam used. I see a lot of it from large reroofing jobs, mostly polyiso. Around 1/2 price usually.

YMMV

 

[Mattilac]

Here's what I did: https://www.garagejournal.com/forum...-40x64x16-garage-in-new-england.492458/page-5

I had some of the same questions as you with regard to what foam to use as well as what to do in the garage door openings. One major difference is that my slab is inside a foundation though.

 

[dscheidt]

I appreciate that info, my only concern with using EPS would be the possibility of it getting damaged during the pour. It seems the pink or green board would be more durable when walked on and such. For money we are talking half the price though for EPS. The quotes i got for the special radiant foam was $3800. I'm seeing box store prices are $3k for XPS and $1400 for EPS.

Around here, the box stores have type 1 EPS. It's the cheapest, least dense, least insulating, and weakest EPS sold as insulation. It's the reason people think EPS *****, because this stuff does. It works fine above grade, but for underslab use, you'd want to use type II or type IX, or maybe one of the even denser versions. They're denser (ICF blocks are usually type II, if that's a useful reference for what it's like), stronger, and do not absorb water. these cost more, but not all that much, and it's still cheaper than XPS for a given R value. If I remember right, type 1 is 1 lb/cu ft, type II is 1.5, type IX is 2. type 1 is 10 PSI comrpessive strength, type II is 15 psi, IX is still higher. R value goes up with density, too, but hugely.


you might also see if you can get reclaimed foam (most of it is from commercial flat roof replacements). It's cheaper, the GWP of it is already a sunk cost, and it will perform just fine under a slab, whether you end up with XPS or EPS.

 

[dscheidt]

[QUOTE="billconner, post: 11257345, member: 430968]Last, consider looking for rigid foam used. I see a lot of it from large reroofing jobs, mostly polyiso. Around 1/2 price usually.

YMMV
[/QUOTE]

Most polyiso shouldn't be used below grade, because it absorbs moisture, and loses much insulation value. There is polyiso sold for below grade use, but you're unlikely to find it used, because it probably had concrete poured on it, and wasn't on a roof. Also, newish polyiso has much worse cold weather performance than advertised. (the non ozone depleting blowing agent used condenses, or something.) That's probably not a problem for a heated slab, but something to keep in mind.

 

[fitter30]

In prep for the pour put air pressure of 30 psi on the tubing till it setup.

 

[ConCretin]

Since your overhead door mounts to the inside face of your wall framing, this is where your door contacts the floor and is where you want your thermal break. Otherwise a section of heated slab sticks out beyond the doors.

Since you plan to do approach aprons anyway, this is pretty simple. Bond out your main slab just inside the face of your door and tracks. Install your thermal break before placing your aprons. You could use beveled rigid insulation or 1/2" expansion joint to keep the joint to a minimum.

Don't forget to pitch the aprons away from the doors a minimum of 1/4" per foot. If you place the apron slightly lower than the main slab, it will create a lip that provides even more protection again wind driven water getting in.

Check out my Guide to Floor Slabs in the link below for some additional thoughts on placing your slab and congrats on the new digs

 

[PoorUB]

What ever foam you use, just make certain it is rated in in ground use.

As for tying the tubing to the netting, it is a royal pain to do that compared to stapling it to the foam. You are on your knees, kneeling on netting, hunched over. by the end of the day your knees all be screaming and your fingers will be sore. With staples you stand upright and walk along. I have done a fair amount of floor heat and I would staple it to the foam, no hesitation!

As for the tubing closer to the surface, I don't know. I have read info on both ways and as long as you have decent insulation the heat has no choice but to go up. It is pretty hard to screw up floor heat.

 

[tricountytrail]

My 30X56X10 pole barn is going up in a few weeks, first garage i've had in my life, only took 47 years haha. The contractor is not pouring the floor, as i have several friends that pour concrete for a living so I will be pouring the floor in early fall. Shop is in northern PA, i envision using the floor to keep the garage at 40ish degrees in the winter and using a supplemental heater to raise it up if i need to work or hang out. R19 walls and R30 ceiling, pole barn batts most likely.

I will be prepping the floor myself to save money, then I'll use my friends for the labor and experience for the actual pour.

1) For under slab Insulation i am seeing multiple different types. The normal green or pink board from a box store, or specific radiant heating insulation from various specialty manufacturers with dimples or similar for running the tubing. I will have to use wire mesh in the slab anyway, so I'm not seeing the advantage to using the more expensive application specific insulation, unless there is something I am missing of course. It seems it is more cost effective to use pink board and zip tie the tubing to the mesh and call it a day. The specific foam board actually puts the tubing directly on top of the insulation and from what I've read you want it closer to the surface than you do the bottom of the slab.

2) I am planning on 2" under the slab and 2" on the perimeter up against the grade board and posts, what do you do for the garage door openings? if I'm wanting to have a concrete apron in front of the garage doors how do i create a thermal break between the shop slab and the apron outside? My thought was to use 1" insulation for an expansion joint type thing. Is that necessary or am i over thinking it and should just use an actual expansion joint.

Thanks for the help.

I did all the work on mine check out my thread https://www.garagejournal.com/forum/threads/the-new-shop.410461/

 

[HoosierBuddy]

I was able to get the correct foam for underground use under concrete from the concrete company. They had the mesh I needed and the foam as well.

 

[old_smokey]

I used a combination of three types of foam in my shop. I had a thickened-edge monolithic slab. Under the main slab, I used a product called Heat-Sheet Heavy, R15, which was over 3" thick, plus the dimples. In hindsight, I probably wouldn't have bothered with the dimples. It did work, but was easy to damage and, in general, kind of finicky to work with. The panels interlock together, though, which was nice. No taping required, and it acted as a vapour barrier. It was a type-3 EPS, good to 25psi.

Under the thickened edge, I used a product called Halo Subterra. Also 3". Type 3 EPS, 25psi. This was a graphite-infused GPS/EPS foam with a really tough fabric face.

Around the perimeter of the slab, I used 3" blue XPS, only because I had a bunch laying around.

At the doors, I fastened a 2x6 to my forms to create a pocket in the concrete. After curing, I pulled the 2x6 out and fit a replaceable wood threshold into the pocket that was cantilevered out over the 3" of foam surrounding the slab. This way, I have no concrete thermal bridge at the doors. My apron is not pinned to the shop slab either. I poured it a bit lower, so it has room to move if needed.
Oh, and I surrounded the whole shop with 2' of 3" EPS as well before backfilling, sloping away from the slab. I would have liked to do more, but had no access.

 

[mrhemi426]

OP, not sure what building code requirements you have in your area, but I will relate my experiences and opinion based of what I did for my house & shop approx. 12 years ago. I have radiant infloor heat in both the basement and the shop floors. Since by our applicable building code, a vapour barrier is required for infloor heating. In the basement of the home, I chose spray in polyurethane as it provided the vapour barrier and the insulation in one product, albeit at a greater expense. Wire mesh was utilized on top of the foam. In the shop, I used 2" blue styrofoam with poly vapour barrier on top. It was vary difficult to get all of the voids from underneath the foam sheets. Voids were not a problem with the spray in product. I wish I had spent the extra for the spray foam product in the shop as well.