I want to break the garage floor from the outside driveway. So I am thinking to have the garage door come down to the concrete and where it meets the concrete floor there should be 1" of rigid insulation separating the inside/outside of the garage? I uploaded an image to a website. Where should I place the EPS foam?

http://chicagocadcam.com/ChrisHahn/HVAC/GarageFloor.JPG

I'd line up the inside of the foam with the inside of the door, and install rebar in the slab to tie the inside & outside concrete together. Yes, the rebar will conduct heat & cold, but the total will be less than a non broken slab.

Directly under the plane that is labelled "Over-head door & track system". 2" of rigid foam wouldn't hurt, looking at your ICF foundation and 3" of underslab insulation. What is the thickness of the (insulated) garage door? You have to hold back the garage floors and not let them flow over the foundation at the openings - man doors and vehicle doors. After you strip off the garage floor forms, you stick the rigid foam to the fresh concrete face with foam board adhesive and them pour the outside driveway or sidewalk portion up to it.

I'm not as sold on tieing the outside slab and the inside slab together as Bob is. The outside slab sits on the foundation wall, so it's not going anywhere and you can make sure to compact the inside at the lip or add some extra heavy rebar to span the openings on the inside.

you can also taper the foam near the top so the concrete has a less than 2" gap at the floor.

If I understand right we are looking at a vertical break. How long does expose eps stand up to weather and vehicle traffic?

I had thought of something along these lines for my patio door and one car garage in the ICF basement. My arrangement is slightly different and my slab rests directly on the footing with 1" of 2# density EPS between the slab and footing concrete. I had planned on using white vinyl fence rails (~1-1/2" wide by 5-1/2"tall by whatever length needed) for my thermal break. I will probably have to run the vinyl fence rail through my table saw to cut it down to ~5" tall. I have a bunch of EPS scraps left over from my ICF walls and was going to rip those pieces down to the proper size and stuff them inside the fence rails and then seal off the ends with some spray foam. The placement of my vinyl thermal break would be roughly under the garage door at the inside edge of the ICF foam.

They make engineered products for what you are looking to do. Yes, it might be overkill but I thought it was worth mentioning:

SCHOCK thermal breaks for run-through concrete slabs


It is a load bearing thermal break so it will transfer loads if needed. It also has stainless steel rebar which helps with preventing thermal bridging of the rebar in the slab. The main purpose of these products is for cantilevered decks but it also has applications for slabs extending to the exterior that need to be thermally broken.

Lbear that is a bit overkill. Probably the best option though. I think i will do what i was thinking and what icf suggested but with the 2" and also taper it as bob mentioned. Thanks guys...

Surfsup - what we do is use high density poly (like a cutting board) 1/2 to 3/4" thick x by the depth of the concrete and install it under the door. Drill holes through it to allow the rebar to be continuous to the foundation wall.
The hd poly has not got a lot of r value but does give you a break, allows for the rebar, has high compressive strength and will stand up to vehicle traffic. If you want to be fancy take and run it over a round over bit on the router and then use round over tools on either side when you finish the concrete.

If you like you can also drop the outboard concrete by 1/2" to prevent water from running back into the garage.

Posted By Surfsup on 13 Sep 2013 07:34 PM
Lbear that is a bit overkill. Probably the best option though. I think i will do what i was thinking and what icf suggested but with the 2" and also taper it as bob mentioned. Thanks guys...

Schock was mainly designed for concrete building and high rises that have exterior patio/deck slabs. The product thermally breaks the slab from the outside and carries loads to the interior. That is something that cannot be done with a DIY foam approach. The product is engineered to take a cantilevered concrete deck and thermally break it, reduce the thermal bridging on the rebar (via stainless steel), add some R-Value, and most importantly carry the cantilevered load from the outside to the inside.

    




While a slab on grade design usually doesn't need the loads to be transferred, the Schock product can also work for that, but like you mentioned it is a bit overkill.

How long does expose eps stand up to weather and vehicle traffic?

I have 2" wide XPS in there and after a year and a half, it shows essentially no wear. My garage slab is about 1/4" higher than the driveway slab and the XPS sits about 1/4" below the driveway slab, so it is down in a "slot" which seems to protect it some. If I saw bad things happening to it, my plan was to get a few large tubes of "self-levelling" concrete repair caulk and let it settle in there to fill the gap with a tough, gray substance.

FBBP interesting. I'll look into that. Anything is better than nothing. Perhaps I can do a cutting board "cap" on top of the XPS rigid to protect the softer foam from foot/car traffic...?

It sounds like the original poster already has some ideas... but I thought I would share one anyway. In a pinch where you need to move forward with the build, but do not have the ideal materials or whatnot I have thought that sill plate gasket between the two slabs would be useful for this purpose. You will have essentially no R value, but the path of conduction is not quite so direct. That being said, I have no experimental data to verify how much benefit there really is.

The original plan for my garage was to use a thin layer of rigid foam, only 1/2 - 3/4", set down a bit between the two slabs and topped with grey expansion joint caulking to block UV deterioration and look a little nicer. I was planning on keeping it narrow to reduce wear, but I do like Bob I's idea of using thicker 2" EPS with a taper on top. The Question I have for this approach is, how much of a taper can you get away with before you will start breaking off the corner of the tapered concrete under the pressure of vehicle tires?

I have also learned a good technique is to not bother with a thermal break. The R value of concrete is such that if you position the tubing 2' from the door opening, the concrete itself acts as an insulator. The 2' spacing gives you a little extra heat loss but less complexity in the pour. I am not sure if this is true. As I understand it a 16" thick foundation has an R value of around 2.0 from what I've seen. So that is not much. 24" will be maybe 2.5-ish?

WOW! Maybe this works in Southern California, but hope no one in colder climates takes this advice. 8" of concrete is about an R-1; similar to single pane glass. Concrete is a very poor insulator, but conducts heat & cold very well. Ignoring thermal breaks in concrete would be a disaster in cold climates.

The R-value of a standard concrete slab is about 0.1 per inch. So 24 inches is only R2.4. That’s not much of a thermal break...

For slabs having hydronic radiant floor heating, we use additives to increase the thermal strength and to reduce the R-value to about 0.03 per inch for improved heat transfer efficiency.  So a good thermal break is even more important for a good hydronic radiant slab.

How does one achieve a thermal break with this slab design?

http://chicagocadcam.com/house/garage.jpg

I am zone5 (Chicago area). the rebar goes down into the foundation support. The slab is poured to the outside of the wall. The door will sit on the inside. Therefore this requires another setup, another visit, by the concrete company...?

I think I have said it before but I will say it again, I am no expert. I did my own radiant in the garage and did not put in a thermal break! I kick my self every winter for not doing it.

I drew on your diagram what I would do. I think the toughest part will be securing the insulation during the pour so it stays exactly where you need it to stay. Around the perimeter we just glued it to the foundation.

Chris

Use a drainge grate to separate the heated interior slab section from the unheated entry slab section.

I don't want a drain in the garage. I've heard lots of people say water can come up the drain and fill the garage due to pressure in the system.

For the drawing, I understand that but I am worried about the smaller triangular portion at the top that might crack with the weight of the car (the detail with the garage door area on left). What I think I will do is put in that XPS but not have it go all the way to the top. Perhaps stop an inch or 1.5" from the top and rather than tapered to a point, cut it at 45 to a 1" flat on top. While there will be more concrete to concrete, it will be significantly less - and I'll keep the tubing 18-24" away from the doorway. What do you guys think of this idea?

This also doesn't solve the issue with keeping the XPS board in place while pouring....