Looking for some info/help with the best way to get a good thermal break at overhead doors.

The house will  have walkout basement with two overhead doors built in upstate ny (zone 6)  The slab will be 4" with wire mesh and radiant tube on top of 2"-4" of foam (have to figure out the point of deminishing return to figure out how much I'm going to use)  I was planning on using the icf up to the roof (couple of questions there too, but that's for another thread)

I've done quite a bit of searching, but can't find exactly the info I'm looking for (I did see the thread about using hose as a thermal break)

My concern is the outside threshold/apron will act like a giant heat sink, if it is in contact with the concrete where it sits on top of the icf, and draw heat out of the entire structure

I'm in Zone 5. I'm not sure you can do too much better than separating the heated and unheated slab with 2" of rigid foam directly where the overhead door comes down. In a more severe climate you might consider even more separation.

I think this is one those cases where you can wrapped up in chasing onesies and twosies of Btu losses at the risk of losing sight of the 1000s you are already saving. I put a thermal break between the slab and the sill right under the door just as ICFHybrid says. The sill touches, but is not connected to, the driveway slab so heat transfer from the wall through the sill to the drive slab is somewhat obstructed. My guess is that heat moving up from the ground below the garage wall and slab will offset a big part of the heat that radiates from the sill, so the actual heat loss from the garage isn't that great.

What you could do is pour the sill as one piece with the drive way slab and put foam between the sill and the concrete in the ICF below the sill. Or you could put foam vertically at the ends of the door way portion of the wall to create a thermal break from the wall proper and pour the foundation wall and sill as one piece. Here again though, I think you're chasing 1s and 2s of heat loss and it probably isn't worth the extra hassle.

Here's how I formed up the sill. The sill and floor slab were poured at the same time, hence the foam strip stayed in place with no problem.





After the pour. You can barely see the foam strip.

Since the slab is on grade, insert a minimum of 1" EPS in the slab where the door comes down, after the floor is poured, cut it lower then the surface of the slab and caulk the joint to seal it. Welcome to the cold areas, thermal breaks are needed or no matter how hard you try the first 6' in of that floor will always be ice cold in the winter or your in floor heating will be working overtime and be heating the exterior of the building...not too good for energy savings

I'm in upstate NY and we use a piece of composite decking vertically at the door. My radiant guy backs off the tubing near the door

Krom - you are right that it will draw heat out of the building but you need to consider a few more issues.

With a break right at the door, you significantly weaken the slab at a crucial point. The part in the door opening is on the stem wall and the part just inside is on fill and has the added vehicular weight. For sure it will shift at this point.

If you are sloping the floor to the door, any break will receive copious amount of (salt) water. This will enter the joint and cause problems over the years.

IMO you are wasting your money with mesh, especially if it is cheap rolled mesh from the box store. Use 3/8 or preferably 1/2" rebar @ 16" o/c b/w.

While you are loosing heat from a 5" slab, you are loosing more heat from the 6 to 8" core of the icf stem wall. Think of heat like water (well maybe maple syrup) It will run to the lower concentration and as concrete is very conductive, it runs quite quickly.

Possible solution. Use Smartwall's composite deck, which probably has grooves in the back, to give it a better seal and then run a couple of dovetail grooves in the from. This will help to seal out water. Drill the board 16" on center and run the rebar through to the stem wall. Yes, you will get some heat lose through the bar but that is what it is. If you want, price out some stainless for this section. Don't use epoxy coat.

Put a couple or 3 inch cap of eps (or window buck if your block supplier handles it) in the top of the core.

If you put the break right under the door, drop the finished level of the apron by 1/2 inch. This will prevent wind driven rain from backing up under the door and help inside water drain way quicker.

Posted By FBBP on 04 Nov 2013 10:37 AM
With a break right at the door, you significantly weaken the slab at a crucial point. The part in the door opening is on the stem wall and the part just inside is on fill and has the added vehicular weight. For sure it will shift at this point.

If you are sloping the floor to the door, any break will receive copious amount of (salt) water. This will enter the joint and cause problems over the years.

The slab could shift, yes, if the compaction isn't done sufficiently. However, the slab/sill interface in my garage hasn't shifted yet, and it's been five years. The concrete guy made sure the soil was compacted very well before we poured the slab. I also used fiber in the concrete, no rebar or mesh. No cracks anywhere, yet, except of course in the crack control cuts.

My joint foam got clobbered by the concrete sealer I put on the garage slab. I need to replace the foam, but it's one of those things that's easy to put off. I don't think water will be a problem. At least I haven't seen any evidence of ill effects of water over the joint.

dmaceld - If you isolate from both slab and stem wall, you need the rebar or the extension/apron is not attached to anything.

Fibre is always a good thing.

For the rest time will tell.

I swept out about 10 gallons of salty water this morning after parking the Envoy last night. Nice little storm over the weekend.

we use a piece of composite decking vertically at the door.

Like Trex? What's the thermal conductivity of that? I was gonna use it, but when I got to hefting it, it seemed kind of dense.....

For sure it will shift at this point.

About an hour or less with the bar of compaction labor. With rebar in the slab, how is it going anywhere?

My joint foam got clobbered by the concrete sealer I put on the garage slab

I figured if mine ever went bad, I'd dig it out down to a half inch or so and squeeze in some flexible concrete repair sealant and then rip some 1/2" High Molecular Weight Poly Sheet to set in there

Posted By ICFHybrid on 04 Nov 2013 03:26 PM

For sure it will shift at this point.

About an hour or less with the bar of compaction labor. With rebar in the slab, how is it going anywhere?

It won't with bar but it will with mesh or nothing.

There is always this option which provides a thermal break and at the same time transfers the loads:

Schock Thermal Breaks

Posted By FBBP on 04 Nov 2013 03:32 PM

It won't with bar but it will with mesh or nothing.

One concrete expert who I talked to before building my house said that tying an exterior slab, such as patio, porch, or driveway, into the foundation with rebar was not the best idea in a climate subject to frost heaving. You're better off the let the slab float free of the wall. Less breakage of the slab from fighting the rebar connection. He told me to be sure to let the slab float around the foundation columns under the posts of the porch roof support, and not it let rest on top of the foundation columns.

There is always this option which provides a thermal break and at the same time transfers the loads:

It's beautiful.

Is that stainless steel I see?

Posted By dmaceld on 04 Nov 2013 04:49 PM

Posted By FBBP on 04 Nov 2013 03:32 PM

It won't with bar but it will with mesh or nothing.

One concrete expert who I talked to before building my house said that tying an exterior slab, such as patio, porch, or driveway, into the foundation with rebar was not the best idea in a climate subject to frost heaving. You're better off the let the slab float free of the wall. Less breakage of the slab from fighting the rebar connection. He told me to be sure to let the slab float around the foundation columns under the posts of the porch roof support, and not it let rest on top of the foundation columns.

I would not disagree if it is a big slab like a patio or if it is anchored around something like deck posts. If you just have a 12" strip in front of the door or even a five foot apron, it needs to be anchored to something to prevent it from taking off on its own.

In my case with the garage door the 12" wide strip is right on top of the stub wall and anchored by the exposed portion of the webs.

I think my concrete expert friend would argue that even a short apron, like maybe 5' deep, should not be anchored. His argument is that a slab, regardless of size, is going to want to move up and down in a cold climate, and efforts to prevent that movement are largely futile and end up with busted concrete. Now, if the apron were to rise above the sill, or floor slab, then that would not be good. The best way to minimize that possibility is to place the apron or driveway end 1/2" to 1" below the sill elevation.

He did admit that his thinking runs contrary to conventional thinking and practice, but he also never has had to go back and repair or replace a cracked or busted slab!

Posted By ICFHybrid on 04 Nov 2013 06:04 PM

It's beautiful.

Is that stainless steel I see?

Yes, that is stainless steel. The reason why the engineers designed it that way is because stainless steel re-bar conducts 90% less thermal transfer than standard steel. It does look like a work of art. The picture is a cutaway which shows the inner workings of it. The real piece looks like this:



It's pretty amazing design and it has been around Europe for 20+ years and it is just beginning to penetrate the US market. Europeans tend to be on the cutting edge of green building.

It breaks the concrete slab and is mainly used for concrete balconies and cantilevered balconies but it can be used for other applications.




Special compression modules (HTE High Thermal Efficiency modules) are used in the bottom to transfer the compression loads. The HTE module is made of 17,000 psi high strength steel and poly propylene fiber reinforced concrete. The combination of high strength concrete, small section area and low thermally conductive materials again offer advanced thermal performance in comparison to carbon steel and stainless steel.

Posted By dmaceld on 04 Nov 2013 07:09 PM
In my case with the garage door the 12" wide strip is right on top of the stub wall and anchored by the exposed portion of the webs.

I think my concrete expert friend would argue that even a short apron, like maybe 5' deep, should not be anchored. His argument is that a slab, regardless of size, is going to want to move up and down in a cold climate, and efforts to prevent that movement are largely futile and end up with busted concrete. Now, if the apron were to rise above the sill, or floor slab, then that would not be good. The best way to minimize that possibility is to place the apron or driveway end 1/2" to 1" below the sill elevation.

He did admit that his thinking runs contrary to conventional thinking and practice, but he also never has had to go back and repair or replace a cracked or busted slab!

As mentioned there is more critical heat loss to the ICF core when the "slab is right on top of the stub wall" then if just the slab was not isolated. If I had to pick between the slab or the core which is continuous to the house, I would isolate the core.

Since most aprons are designed to slope away from the garage, how would you prevent it from migrating down the slope if it is not anchored? As it starts to move, water invades the gap and now you have sever frost heave due to wet soils under the apron slab.

Where are you such that concrete is doing all this moving? I don't even slope concrete 1/4" a foot to get runoff and that's hardly enough to encourage migration in the downhill direction. Moreover, concrete flatwork properly goes on compacted gravel so it drains and avoids the frost heave in the first place.

I guess if you felt there was any tendency to "slide", the easiest thing to do would be to dig some holes in the slab base to provide some "grip". Never heard of this as a common problem.