Radiant in slab new garage build

[Fred61]

I guess the one thing that would concern me is that the 2 inches over the insulation is only supported (attached) on one side. Concrete strength is poor when subjected to bend pressures. It's strength is in compression.

 

[Karl_northwind]

looks nice. unless you drop a corner of a mill or something on that edge, you won't have a problem. fiber is awesome stuff. you or your concrete contractor can get little wire "chairs" to set the 6x6 mesh on right before the pour.

 

[woodsmaster]

I skimmed threw this post and wanted to add my 2 cents.

1. I don't think you would save much, if any money going radiators verses in floor.
2. Special thermally enhanced concrete is not necessary in my opinion.
3. you should try to let the slab dry slowly weather or not you have heat in the floor.
4. as long as you have re-mesh in the floor so the concrete cant shift if it cracks its more than likely not going to leak weather it cracks or not. Don't ask how I know When I cut the cement I did't know the cuts needed to go continuously from one side to other so I have a couple of cracks. no worries.
5. with in floor heat, the building will stay warm for days even without a fire going.
6. It is going to take a day or two to raise the temperature significantly if you need quick heat often it may not be the best option.
7. They sell spacers to put under the remesh to keep it spaced properly in the floor. tie the tubing to the remesh and use the spacers and you don't have to worry about having it to deep or not deep enough and cutting into it when you cut the concrete.

I have in floor heat in my shop and love it. I would also like to add a modine type heater for times when I'd like to raise the temp fast. sometimes I'm away from home most of the day for weeks at a time sometimes and turn the heat back to save on wood.

 

[Buzz Saw]

I guess the one thing that would concern me is that the 2 inches over the insulation is only supported (attached) on one side. Concrete strength is poor when subjected to bend pressures. It's strength is in compression.

I've though about drilling a hole and putting some rebar through the form to support the 2" when I pour the approach.

 

[maple1]

I have a question. Trying to educate myself a bit - I am hoping to build myself a garage in the next couple years or so.

What would be the issue, if you poured the approach & floor all in the same pour? Just run the concrete out the doorway - an extension of the floor?

 

[Buzz Saw]

I have a question. Trying to educate myself a bit - I am hoping to build myself a garage in the next couple years or so.

What would be the issue, if you poured the approach & floor all in the same pour? Just run the concrete out the doorway - an extension of the floor?

Things to consider:

1.Cost - I understand in the end it's going to be the same cost, or slightly more, but In my case I'm limited by money on hand.

2. Thermal Break - No sure how reliably keep the foam board and expansion joint in place during the pour.

3. Not sure how big of an approach I want/need yet.

4. Timing - I need this project to move forward so I get some interior work done. We are going to temporarily live in this building while we rehab the house. House project starts real soon.

So nothing is wrong with pouring it all at once if you can overcome the issues/don't apply to you. If this was just an unheated storage/machine shed it would be poured all at once.

 

[gfirkus]

your approach needs to be separate. Don't use rebar from garage slab to approach either. Bad deal. The approach is a floating slab and will move up and down between seasons.

 

[Buzz Saw]

your approach needs to be separate. Don't use rebar from garage slab to approach either. Bad deal. The approach is a floating slab and will move up and down between seasons.

Never thought of the approach heaving. Good call.

 

[700renegade]

I'm pouring my building next week and have decided to put 2" foam directly under where the overhead door comes in contact with the floor. I'm going to leave about 1" concretrete on top and use the expansion joint (when I pour the approach)for the thermal break for the top 1" of concrete.

Buzz saw, what is your garage door going to seal against if that skinny strip of concrete cracks out of there ( which is possible since it's bearing on compressible foam ) ? Also, since your future exterior slab could frost heave do you really want it doing so right at the face of your door?

Personally I'd push that heated slab out at least a few inches past the door and live with the few BTU lost out there. You could always pull in your pex a touch at the OH doors so the slab temp is a bit lower there to start with.

Also, a trick I've used on commercial apron pours ( exterior slab on grade ) is to put them on foam board for the first 12 feet. start with a 4' strip of 2" thick, then lay a 4' strip of 1", then finish with a 4' strip of 1/2". This does a decent job of limiting frost penetration into the subgrade near the building face so It doesn't heave ( as much ). The point of tapering the foam is to gradually transition to the unprotected state. Anytime you introduce a different subgrade condition onto the slab you are asking for a crack to form. Also never make the mistake in clayey or silty soils of putting a big layer of gravel under the exterior slab, as it is an invitation to heaving. Concrete right on compacted native clay soil is superior to building a bathtub full of water under your slab.

 

[hondaracer2oo4]

Interesting points renegade. For one, the foam is stronger in compression psi than most compacted sub grades are I believe. Interesting point about the clay being better than a 6 inch lift of 3/4 gravel compacted. The consensus it seems is that the 6 inch of gravel is necessary for a capillary break to keep the moisture from wicking up through the slab or bringing the moisture and soaking the underside of the vapor barrier.

 

[Buzz Saw]

Buzz saw, what is your garage door going to seal against if that skinny strip of concrete cracks out of there ( which is possible since it's bearing on compressible foam ) ?

Also, since your future exterior slab could frost heave do you really want it doing so right at the face of your door.

Worse comes to worse I'll cut out that strip and install some square tubing to take it's place. Granted it could happen but I think it will be ok as long as I have an approach when I drive over it. In 2 inches of run I gain 2 inches of fall bring my concrete to 4" pretty quickly.

The future exterior slab will also have an expansion joint to give me a 1/2" buffer, so I'm not sure if a heaving slab would affect the door.

Also since I do have a decently sizable compacted stone lift I do intend on running a tile under the lift to drain water before I pour the approach.

Sounds good on paper.....Hope it works in real life........ This is my "you have me questioning things" face. [emoji52]

 

[700renegade]

I'm not sure if a heaving slab would affect the door.

Since we are thinking...... if it does heave, when you get a late winter driving rain against your OH door, and the water sheets down the door, where does the water go?
A. into the shed
B. Possibly worse - into the joint and soaks under the exterior slab, so that tomorrow the slab heaves a bit higher still.

I've seen my mother-in-laws garage door trim torn clean off the shed by her slab heaving 3". Brother-in-law was well meaning and perplexed "gee I put nearly two feet of sand under that slab, I can't believe this is happening!" I had to draw him a diagram of the bathtub full of water he unintentionally created.

I design streets and highways for a living and I don't think most people realize there is almost zero concern for the strength of the subgrade when designing a concrete pavement. What matters? Uniformity, Uniformity, Uniformity.......and after that, thickness. A perfectly uniform subgrade is critical to a slabs long term performance. There is only one reason we put a foot or more of gravel base under the concrete - it is ONLY so that the trucks and the paver have a spot to drive on that keeps them from leaving ruts before the concrete goes down. Why do you put gravel under your shed floor? It has nothing to do with the floor strength, but it sure is handy to level out so you can achieve the holy grail of uniformity.

Buzz Saw has no option but to float the slab. Hondaracer (with a frost wall) has an option to:
> Run the interior slab past the door 6" and put plenty of pitch away ( keep driving rain away from coming inside)
> bear the exterior slab on the outer 3" of the frost wall ( so it cannot settle )
> put foam under the outside slab ( limit frost penetration so it does not frost heave )

Note that all the discussion of 2" foam thermal breaks ( which I consider a tad excessive, just me.... ) makes detailing out a good solid transition to your apron more difficult. You only have an 8" wide wall to bear on.

 

[Buzz Saw]

Now the gears are really turning. I have till Thursday morning to make changes. I could move the 2x4 out 3" and cut the foam off and move it out.... But then I would have to dig out some of the stone holding my foam in place so I can compact it. What to do......[emoji20]

 

[Fred61]

Not only do you need to worry about driving rain. You need to worry about splash that will occur every time it rains because your door is on the drip side of the building as opposed to being on the gable end.

 

[Buzz Saw]

Not only do you need to worry about driving rain. You need to worry about splash that will occur every time it rains because your door is on the drip side of the building as opposed to being on the gable end.

With gutters how does this differ from the gable end?

 

[huffdawg]

I just cut the foam off and overlapped the floor foam and the wire mesh to the edge of the form. I don't think that triangle piece of foam is giving you much rvalue anyway

 

[Fred61]

With gutters how does this differ from the gable end?

I assumed I was seeing a metal roof. I don't know much about Ohio weather but in Vermont the snow sliding off the roof takes them down every winter.

 

[Karl_northwind]

I just cut the foam off and overlapped the floor foam and the wire mesh to the edge of the form. I don't think that triangle piece of foam is giving you much rvalue anyway

it's not about straight R value, it's about breaking the thermal contact. 1/4" of foam is way better insulator than 1/4" of concrete. it'll make a big difference. a piece of treated wood will do it as well.

 

[huffdawg]

it's not about straight R value, it's about breaking the thermal contact. 1/4" of foam is way better insulator than 1/4" of concrete. it'll make a big difference. a piece of treated wood will do it as well.

Ya good point.. I dont think I lose a whole lot of heat through mine though, its 6" thick and the tubing is held back 18" from the opening.. I prolly lose a lot more heat through the 10-6 x 10 2" insulated overhead door.. but you guys get a lot colder winters than us .

 

[711mhw]

7. They sell spacers to put under the remesh to keep it spaced properly in the floor. tie the tubing to the remesh and use the spacers and you don't have to worry about having it to deep or not deep enough and cutting into it when you cut the concrete.

 

[lotawood]

711mhw is that a re-pour over existing concrete? Is there insulation underneath?

 

[711mhw]

That was some weird insulation with a 1/2" of concrete on it. Used material from an industrial type flat roof. It was 2" of blue DOW with the 1/2" 'crete, I think used for insulation and "ballast" instead of loose stones. T&G all 4 sides and strong & cheap.
But no, not a re pour over existing.
I had some left over and made a stay in place forms for another slab, it provided the stregnth for a form, with 2" of insulation and a nice exposed aggregate type of durable finish for the portion that was above grade, all in one!

 

[711mhw]

Not the best pic, but it has a decent finish and is a good solution for exterior insulation on frost wall type const.
I cut the foam back to apply the treated 2x6 plate that also held the panels in place for the pour.

 

[711mhw]

Forgot the damn pic!

 

[woodsmaster]

I assumed I was seeing a metal roof. I don't know much about Ohio weather but in Vermont the snow sliding off the roof takes them down every winter.

Then they weren't installed right. the gutters have to be lower than the roof so the snow will slide over them. then you can put snow jacks on the roof also and that will keep most of the snow from sliding off and it will melt into the gutter.