Insulation Under Slab

[pv74]

I am having a 24x36x12 pole barn built. The contractor is getting ready to pour the 4" slab, and I was thinking of adding a vapor barrier and 2" XPS 15 or 25 PSI insulation and possibly a radiant floor heating system.

I have a friend who has poured a lot of concrete and swears that the floor will crack if I put down foam insulation, especially if the surface is not perfectly flat. The ground surface is compacted road mix. I'm concerned as my contractor has no experience pouring over foam, etc...and want to avoid an expensive mistake.

The other concerns I have about a radiant floor system are heating the building almost full time (it would only be occupied for a few hours over the course of a week) and cost. Using Loopcad, I am calculating that it would cost me several hundred dollars a month using an electric boiler to just keep the building at 50 degrees (the building will have standard pole barn insulation which is good for keeping the drafts out).

I am beginning to think that I should just pour a standard floor and spend the extra money on further insulating the walls and the roof.

What are your thoughts?

 

[anthony666]

once your floor is poured you cant go back and add pipe .. spend the money, buy a good quality heat pex like uponor/wirsbo .. you can add a boiler later .. but infloor heat is amazing to work in

 

[Firebrick43]

I am having a 24x36x12 pole barn built. The contractor is getting ready to pour the 4" slab, and I was thinking of adding a vapor barrier and 2" XPS 15 or 25 PSI insulation and possibly a radiant floor heating system.

I have a friend who has poured a lot of concrete and swears that the floor will crack if I put down foam insulation, especially if the surface is not perfectly flat. The ground surface is compacted road mix. I'm concerned as my contractor has no experience pouring over foam, etc...and want to avoid an expensive mistake.

The other concerns I have about a radiant floor system are heating the building almost full time (it would only be occupied for a few hours over the course of a week) and cost. Using Loopcad, I am calculating that it would cost me several hundred dollars a month using an electric boiler to just keep the building at 50 degrees (the building will have standard pole barn insulation which is good for keeping the drafts out).

I am beginning to think that I should just pour a standard floor and spend the extra money on further insulating the walls and the roof.

What are your thoughts?

Well maybe it would it the sub base is not flat, but a slab of uneven thickness(due to uneven sub base) will crack to without insulation!

Why would you put foam down on an uneven base? With a good smooth sub base and a heavy plastic vapor barrier like stegowrap, and wet curing for a week, and decoupling from the post/ walls, you can possibly get a slab with out cracks. My basement slab(26x50) and garage(26x30 with 3" foam and pex tubing) have remained crack free. As they shrank the edges pulled up to a 1/4" away from the edges.

Both on #8 stone 8+ inches thick compacted in 2-3" lifts multiple times with no variance of more than 1/2".

 

[climb.on]

Where are you located? Put it in your profile so people can answer you better.

Yes put a vapor barrier AND 2" of rigid foam under your slab. Your friend is on crack - foam insulation will not make concrete crack. 2" of foam insulation is standard practice. It's not expensive and you only have one chance to do it. There are only 2 guarantees with concrete. 1. It will get hard and 2. It will crack (well probably, but not because of insulation). Proper site prep (drainage, compaction, etc) is your best defense against cracking. Do some searches here...almost anyone who pours slabs that has any intention of ever heating the building, puts insulation under the slab. I poured 4000 sq/ft of concrete over 2" of foam insulation.

Whether to do in-floor heat is quite debatable. I chose not to. It would have be "nice" but I can't say I regret not doing it. Because of the insulation under the slabs, my concrete really isn't cold...it's just not warm.

 

[pv74]

I'm in Boise, ID. The winters are fairly mild, with minimal snowfall... But we do get a few days where it can get down to -20.

Anyhow, I've spoken to a good friend installed several systems. I've also spoken to a structural engineer, and the staff at the county building inspection office. The county building guy seemed very supportive of it. From all the hard evidence that I can gather, it should work.

The ex concrete guy is the same friend that told me to nail down hardwood flooring to Redex (particle board subflooring) with no vapor barrier (a no no, according the manufacturer). I've ignored some of his advice before and I'm going to ignore it this time as well.

My contractor is supportive of the idea and the concrete guy will not guarantee his work (and I kind of expected that).

With all of the evidence and research that I have done, I've decided to go ahead with it. I'm going to put down a bit more road mix (sand gravel mixture) and level the surface as for a patio. Rent a compactor and compact it down well. Put down my vapor barrier, tape, then lay down 25 PSI Owens Corning Formular 250 XPS rated for under slab use. put down some 6" grid wire and zip tie my pex down. I've designed a 3 loop system using LoopCad. It may be 4-5 years before I get the time and money to install the rest of the system, but I think it will be worth it in the long run (like running more conduit that you need immediately when excavating).

 

[Firebrick43]

I would suggest using plastic staples to attach the tubing to the foam and then set the grid wire on top. This places the tubing and the wire in the proper location.

The stapler is pretty expensive but I did my 26x30 garage by using a flat blade screwdriver to "drive" the plastic staples into the foam. It took a few hours but beat buying a 220+$ tool. You are on your knees but it's on foam.

I would also suggest 4 loops as 288' long loops (if you use 1' of tubing per square foot) is a little long. Keeping under 250 foot is ideal. Also if you keep every loop exactly the same length you can for go fancy and expensive manifolds with flow controls(balancing valves) and use much cheaper manifolds with 1/4 turn ball valves.

 

[climb.on]

I'm in Boise, ID. The winters are fairly mild, with minimal snowfall... But we do get a few days where it can get down to -20.

Anyhow, I've spoken to a good friend installed several systems. I've also spoken to a structural engineer, and the staff at the county building inspection office. The county building guy seemed very supportive of it. From all the hard evidence that I can gather, it should work.

The ex concrete guy is the same friend that told me to nail down hardwood flooring to Redex (particle board subflooring) with no vapor barrier (a no no, according the manufacturer). I've ignored some of his advice before and I'm going to ignore it this time as well.

My contractor is supportive of the idea and the concrete guy will not guarantee his work (and I kind of expected that).

With all of the evidence and research that I have done, I've decided to go ahead with it. I'm going to put down a bit more road mix (sand gravel mixture) and level the surface as for a patio. Rent a compactor and compact it down well. Put down my vapor barrier, tape, then lay down 25 PSI Owens Corning Formular 250 XPS rated for under slab use. put down some 6" grid wire and zip tie my pex down. I've designed a 3 loop system using LoopCad. It may be 4-5 years before I get the time and money to install the rest of the system, but I think it will be worth it in the long run (like running more conduit that you need immediately when excavating).

Solid plan. Perhaps you've got this detail already but if not...I'd suggest getting more info on the concrete guy's "guarantees." Is the the foam insulation the reason the concrete guy won't guarantee his work? If it is...what exactly will he guarantee, if you don't use the foam. I've never heard of a concrete guy guaranteeing concrete won't crack, but my guy guaranteed cracks wouldn't exceed a certain size. I did get a few hairline stress cracks overnight after the pour, but they haven't changed since. I've even put epoxy floors over several and the epoxy hasn't even cracked. I was pretty pissed when I first saw them, but seeing as they haven't moved in 14 months now, I can live with it.

Good luck on your project!

 

[pv74]

How are expansion joints dealt with?

 

[Firebrick43]

How are expansion joints dealt with?

Take a piece of pvc that the floor tubing fits loose but not sloppy loose. Slide the pvc over the tube and place the center where saw joints or an expansion joint is. Tape the ends of the pvc to the pex so concrete doesn't get in with electrical or duct tape.

Make sure you mark the walls where saw cuts should be so you know when it's time to cut. It should be cut just after it sets up but unfortunately many concrete guys will not wait around that long and will come back the next day.

 

[pv74]

From my research, in a 4" slab, the saw cut is done at approx 1" and produces a controlled crack. This can be done with a saw or by hand troweling. I take it that a hand trowel would be the safest approach. Also, since my tubing will be lower than this, so I would guess that the expansion joint or crack wouldn't have any effect.

Debating on whether to suspend the tubing on re-mesh by at least an inch, but it doesn't seem very practical at all when the concrete guys will be walking all over it. A friend of mine tells me not to overthink it, and just lay the re-mesh on the floor and zip tie the lines down securely (leaning towards this as it seems simple). I also want to avoid the horror stories of pipe floating up through the concrete, although I think if it is tied to the remesh securely, it should be fine.

What does putting the lines in PVC pipe through where the expansion slits will be buy me?

I've ordred USA made Sharkbite Oxygen barrier Pex in 300' rolls. I believe it is classified as Pex C

 

[tricountytrail]

From my research, in a 4" slab, the saw cut is done at approx 1" and produces a controlled crack. This can be done with a saw or by hand troweling. I take it that a hand trowel would be the safest approach. Also, since my tubing will be lower than this, so I would guess that the expansion joint or crack wouldn't have any effect.

Debating on whether to suspend the tubing on re-mesh by at least an inch, but it doesn't seem very practical at all when the concrete guys will be walking all over it. A friend of mine tells me not to overthink it, and just lay the re-mesh on the floor and zip tie the lines down securely (leaning towards this as it seems simple). I also want to avoid the horror stories of pipe floating up through the concrete, although I think if it is tied to the remesh securely, it should be fine.

What does putting the lines in PVC pipe through where the expansion slits will be buy me?

I've ordred USA made Sharkbite Oxygen barrier Pex in 300' rolls. I believe it is classified as Pex C

I have the same Questions staple pex to foam (won't I lose some heat transfer from NOT being in concrete)
Zip tie to wire mesh with pex on top and lose reinforcement in concrete.
Or add wire mesh on top also and concrete guys will destroy it all anyways.

 

[Firebrick43]

From my research, in a 4" slab, the saw cut is done at approx 1" and produces a controlled crack. This can be done with a saw or by hand troweling. I take it that a hand trowel would be the safest approach. Also, since my tubing will be lower than this, so I would guess that the expansion joint or crack wouldn't have any effect.

Debating on whether to suspend the tubing on re-mesh by at least an inch, but it doesn't seem very practical at all when the concrete guys will be walking all over it. A friend of mine tells me not to overthink it, and just lay the re-mesh on the floor and zip tie the lines down securely (leaning towards this as it seems simple). I also want to avoid the horror stories of pipe floating up through the concrete, although I think if it is tied to the remesh securely, it should be fine.

What does putting the lines in PVC pipe through where the expansion slits will be buy me?

I've ordred USA made Sharkbite Oxygen barrier Pex in 300' rolls. I believe it is classified as Pex C

Stapling the pex down and laying the remesh on top puts both in an optimum placement. The tubing won't float, the remesh is well supported and won't end up on the bottom and is in the bottom third. Your friend that tells you not to overthink things isn't going to face the consequences. This does not mean that there isn't many successful installations with the Pex on top of the remesh. Just as many endeavors in life, you need to decide what risk your willing to be exposed to.

The PVC sleeves are recommended to protect the tubing if the slab shifts at the cracks and shifts a small amount at the crack/cut joint. That's all. It has nothing to do with the cutting process other than the cut forces where the crack will be if done correctly. A tooled vs cut joint is a decision you have to make. A cut joint is smaller and less obtrusive, especially if filled. A tooled joint ***** to roll hard and small casters over.

One thing to remember with Pex B and C is if the tube kinks, cut the kink out, and splice. If you use brass fitting to do so wrap well with electrical tape to keep the concrete from corroding it. Only PEX A can you work out kinks with a heat gun.

I have the same Questions staple pex to foam (won't I lose some heat transfer from NOT being in concrete)
Zip tie to wire mesh with pex on top and lose reinforcement in concrete.
Or add wire mesh on top also and concrete guys will destroy it all anyways.

You lose nothing in heat transfer of stapled to the foam. The tube will still be nearly fully encased as it will float slightly and cement will run underneath only where the staples are will the tube touch the foam. And what little heat that goes down(heat rises) will be reflected back up by the foam. That is the whole purpose of the foam.

 

[GYPSY400]

If your concrete guy won't guarantee the floor then get a new concrete guy.
A floor that size in my area needs to be done by engineer specs and yes it's fine to insulate under the pad ( I HIGHLY RECOMMEND THIS). You will also need some sort of reinforcement.

concrete will crack due to poor site prep, not the insulation

You insulate once.. you will heat it every day.

Sent from my SM-G903W using Tapatalk

 

[rburke65]

No.....insulation does not cause cracking. I graded my base pretty well. It was clay and was real hard at the time of the concrete placement. Vapor barrier, insulation, wire mesh then pex tubing zip tied to the mesh. I think it’s imparitive that the finishers saw cut joints as soon as they can walk on the concrete without making impressions on the surface. My finishers did so and ....TYJ.....no visible cracks on a 32’x56’ floor. If you look into a sawn joint you will see a hairline crack, but I’m not looking at it. I’m a happy guy. Don’t forget to slow cure it....water or sealer. Good luck

 

[pv74]

If your concrete guy won't guarantee the floor then get a new concrete guy.
A floor that size in my area needs to be done by engineer specs and yes it's fine to insulate under the pad ( I HIGHLY RECOMMEND THIS). You will also need some sort of reinforcement.

concrete will crack due to poor site prep, not the insulation

You insulate once.. you will heat it every day.

Sent from my SM-G903W using Tapatalk

Making sure that you do your homework on how things are supposed to be done and inspecting the work is about the best that you can do where I live... At least the contractor I hired has somewhat taken an interest in this project. Ground prep was very poor IMHO. I poured in 4 more wheelbarrows of roadmix, spent some time with a screed board and level and wacked it down with a compactor. The surface is fairly flat and level...about as much as it is going to get.

 

[pv74]

Also, I forgot to mention... I want a 2 post lift.
The plan is to leave a pit about 4" deeper, 3 foot wide by about 14' where the lift will be.
I am planning to leave the bottom of the pit with no insulation, just vapor barrier.
Or, should I just leave this uniform thickness and place the insulation under this?

 

[Firebrick43]

If you want the area where the lift goes thicker that's fine but isolate it from the slab. Concrete will crack where thickness changes, from both difference in shrinkage as it cures and the deeper area keeping things from sliding as it shrinks. Form the areas for the lift and pour them latter. Or leave them the same 4" thickness but ensure strength with good rear reinforcement in that area, using 4000 or even 4500 psi concrete, ensurin you don't exceed 5" slump(might need plasticizers to keep your concrete guy happy ) and wet curing for a week to develop full strength and prevent curling. It will be as strong or stronger than thicker concrete poured with average practices.

 

[road_king]

Also, I forgot to mention... I want a 2 post lift.
The plan is to leave a pit about 4" deeper, 3 foot wide by about 14' where the lift will be.
I am planning to leave the bottom of the pit with no insulation, just vapor barrier.
Or, should I just leave this uniform thickness and place the insulation under this?

Have you decided on make/model 2 post lift? I ask because with radiant you want to be sure pex runs are clear of posts base plate locations. That can vary based on model lift and how its installed.
As far as concrete thickness, generally speaking most lift manufactures recommend around 4.5" for new slab pour. Check with the lift manufacture about all of this.
Mohawk recommends min 4.5" , but I went with 6" for my 30 by 40 slab pour. Decided on Mohawk System I from the start of project and made sure all pex was no where near the lift posts locations.

You should insulate under all of the slab and up the sides.
You will love radiant heat and having a lift. Both are my fav parts of my garage.

 

[pv74]

For the lift... How about two 4' X 4' squares (the minimum that the Bendpack rep recommends for pads) with no insulation and some rebar in the bottom 2". This way I have 6" of concrete under my pads and no concerns about maxing out the load capacity of the foam. I could have the contractor sawcut or tool cuts around the pads.

My concern is if I dig pits deeper, I have no support underneath the edges of the foam that faces the lift posts.

 

[pv74]

I think I'm the only guy in Idaho who rented a plate compactor in the middle of the winter! Surface has been leveled twice and compacted three times. It's not perfect, but it's as flat as I can make it.

I'm now ready to lay down my vapor barrier and put down my foam! I am using Owens Corning Foamular 250. Pex tubing has arrived and the pex stapler should be here at the end of the week. Pex will be stapled to the foam and remesh will be laid over the top.


One question dealing with the garage door. I am thinking that I should terminate the foam at the door frame and have the concrete overlap to form a solid edge of several inches that goes under the door frame/garage door facing the exterior?

 

[Randy in Maine]

Where my 2 lift posts go, I just did not put insulation or pex in that 4x4 area. It gave me 2" of extra concrete there (8"vs 6"). I also did not put any thermal break at the garage doors. Not a big deal and they never freeze stuck.

 

[pv74]

Where my 2 lift posts go, I just did not put insulation or pex in that 4x4 area. It gave me 2" of extra concrete there (8"vs 6"). I also did not put any thermal break at the garage doors. Not a big deal and they never freeze stuck.

Sounds like a plan then.

I am doing a 4" pour. I intend to leave out the insulation for the lift posts and for 1 support post for a loft that I will put in. So, in those areas, it will be 6" of concrete. The lift manufacturer states that 4" is the minimum and the heaviest thing that I will ever lift is an F-150, which is fairly light as far as trucks go.


I'll leave the insulation out under the garage door to form a 6" thick lip..

 

[Randy in Maine]

Even if you don't put any pex under the lift it s not a big deal. It will still be nice and warm.

 

[pv74]

Where my 2 lift posts go, I just did not put insulation or pex in that 4x4 area. It gave me 2" of extra concrete there (8"vs 6"). I also did not put any thermal break at the garage doors. Not a big deal and they never freeze stuck.

Put the tubing down today...

I'm not going to run mesh over it for fear of sharp edges puncturing the tubing.
I'm just going to have fiberglass added to the concrete mix and call it good.


Used LoopCad for the layout...

 

[walrus]

You will want to be able to walk around that post next to the wall. Hard to tell from pic but it looks pretty tight. I have a similar setup and its kind of a pain. I have about 3 ft between wall and post.
I did a 6in slab with insulation every where and left a 3ft square area with no pex. I'd suggest you document where those areas are with tape measures and a camera. Print them out. My hard drive **** the bed and I lost my pics. I did have 1 or 2 and I could remember somewhat where they were. I ended up paying someone with a thermal imaging camera to pinpoint exactly where they were before lift install

 

[pv74]

I've read about a way to locate the tubing by spraying water on the floor with the system on. However, I don't want to go there Measurements of the 4'x4' squares are on center with the poles on the sides of the buildings. I am going to write them on the poles in sharpie. Good idea on printing out the pics and placing them with the shop documentation.

 

[850xpeps]

I've read about a way to locate the tubing by spraying water on the floor with the system on. However, I don't want to go there Measurements of the 4'x4' squares are on center with the poles on the sides of the buildings. I am going to write them on the poles in sharpie. Good idea on printing out the pics and placing them with the shop documentation.

Take photos with a tape measure lol you’ll always second guess. And drilling into the slab without knowing 100% is nerve racking.

Did you use a gun to pin the pipe down? It common practice here to tie it to the rebar.

 

[pv74]

Take photos with a tape measure lol you’ll always second guess. And drilling into the slab without knowing 100% is nerve racking.

Did you use a gun to pin the pipe down? It common practice here to tie it to the rebar.

I purchased a Malco Foam Board Stapler for the project. It worked extremely well and made the tube install go very quickly. I'll most likely sell it after the floor is poured as I'll probably never use it again.

 

[850xpeps]

I purchased a Malco Foam Board Stapler for the project. It worked extremely well and made the tube install go very quickly. I'll most likely sell it after the floor is poured as I'll probably never use it again.

I’ve watched a few videos of guys using them. Looks pretty easy.

 

[pv74]

Take photos with a tape measure lol you’ll always second guess. And drilling into the slab without knowing 100% is nerve racking.

Did you use a gun to pin the pipe down? It common practice here to tie it to the rebar.

I’ve watched a few videos of guys using them. Looks pretty easy.

Over 750 ft of tubing in a few hours and that was with double checking the plans from loopcad. Made a pex dispenser out of a 5 gallon bucket, an old piece of siding, some old square tubing that I had laying around and my 12 year old daughter. Just keep the pex under your foot when stapling down. The staples have a lot of holding power, but they will tear out.

 

[pv74]

Thanks for all of the advice in this thread. Tubes were under pressure test the entire time and nothing was broken. I was lucky and had a great concrete crew that took a lot of pride in their work and had poured over foam and radiant tubes many times. I'm very happy with how the pour went.

 

[yeldogt]

Nice job .....

 

[Kburk09]

Looks good. Thanks for the great info, planning a similar install this summer.

 

[EricVonHa]

Creating a thermal brake/break (both terms apply, ha!) is very important at the garage doors.

Best way to do this is to fasten a section of foam to the face of the pad. Cut a diagonal from the interior slab downward and away from the building on a 45 degree angle.

This section of horizontal foam separates the interior slab from any exterior driveway temperature. It prevents the leaching of the heat

 

[EricVonHa]

Also, if wire mesh is used above the foam, there is a company called "Mesh-Ups" that makes plastic tripods which hold the mesh up 1" to 3" thereby placing the tubing in the middle of the pad. This causes the heat to equally heat upward and downward at the same time. During the pour, it is possible to walk on the mesh because the Mesh-Ups are spring-like

 

[pv74]

Creating a thermal brake/break (both terms apply, ha!) is very important at the garage doors.

Best way to do this is to fasten a section of foam to the face of the pad. Cut a diagonal from the interior slab downward and away from the building on a 45 degree angle.

This section of horizontal foam separates the interior slab from any exterior driveway temperature. It prevents the leaching of the heat

Good idea for others to consider. I had very little advice on this aspect, so I chose to run the foam to the beginning of the garage door threshold. The concrete guy tooled a joint in at where the foam ended (He told me that it would most likely crack in that area). I have a 6" wide, 16' long and 6" deep strip of concrete in front of the tooled joint and the foam.


I did consider beveling the edges of the foam surrounding the slab, but was running out of time to get everything installed and tested. I had to get the slab poured before the really nasty weather sets in (we've been lucky so far).

 

[EricVonHa]

Looks like the apron area is still dirt in front of the garage pad. Still time to do the horizontal piece of foam at the door entry from the look of it?

 

[pv74]

Looks like the apron area is still dirt in front of the garage pad. Still time to do the horizontal piece of foam at the door entry from the look of it?

I think I'll go ahead and do that....It would be as simple as gluing a piece of foam to the front with construction adhesive and packing roadmix over it.

 

[EricVonHa]

I think I'll go ahead and do that....It would be as simple as gluing a piece of foam to the front with construction adhesive and packing roadmix over it.

Yeap, it is worth the effort.

I find myself walking around in my building from time to time with my infrared thermometer checking the various temperature differences here and there. The insulated Foundation is absolutely huge and the thermal break to the garage Bays makes a big difference. There is truly a line in the sand for the bay entry temp transition. The outside apron is roughly Ambient Air Temperature and the garage apron on the other side of the insulation is 6-10 degrees cooler than the heated floor (roughly 12" inside)

Can you imagine how much more heat would be leached away without a thermal break from outside to inside the garage bays? Been below freezing here since !

 

[hausfxr]

Nice job on the insulation and pex installation, and thanks for the progress photos and update. Too late for my two-cents on best methods, but I thought I'd chime in anyway in case someone else reads to the end of this thread.

I know people are still commonly using WWF in their slabs, but it’s not a good way to reinforce concrete. If you’ve ever demolished a slab with it, you’ll see exactly how hard it is to keep it near the middle no matter what tricks are employed. Good move to leave it out.

We’ve taken the position that rebar is far better for keeping a slab from cracking, and, even when architects specify WWF, we insist on leaving it out and using at least 3/8” rebar at min. 24" o.c., and universally they are grateful for our stubbornness – the engineers we work with have never specified WWF unless it’s a heavier gauge used in thicker slabs. With your space (and finish) being more utilitarian, your decision to put fiber reinforcement in it was probably smarter than the WWF. But fiber alone won't help your concrete after it cracks. And it's the pex you are protecting from stress at the cracks.