Concrete: Garage floor doweled into foundation?

[54FordPanel]

Hello. I am getting bids from concrete contractors on replacing my driveway, my front porch, and the floor of my regular old 2 car garage (as opposed to my shop floor, which if fine)
The parking garage is heaved/sunk and cracked. The front porch is sunk. Both are cracked and mud jacking wouldn't work on these slabs.

One of the contractors I got a bid from says he will dowel into the existing foundation to anchor the new garage floor and front porch. The others haven't mention doing that.

Is dowelling into the foundation the way to go? We have expansive soils here, and I'm worrying a rising/falling slab that is anchored into the foundation would compromise the foundation. The porch and garage floors are going to move somewhat, aren't they?
The house foundation is on caissons. I believe this guy knows what he's doing, and he said there are differing opinions on dowelling into the foundation.


What say ye concrete experts?

 

[bluesman2a]

Let me first start by saying that I'm no expert, and CERTAINLY not in an arena where frost/heaving is as big a deal as where you are, BUT I have poured a lot of concrete around my place.

All the slabs I have ever had poured, where they abut existing slab/foundation are pinned in like that. My only concern, as you pointed out, in your climate, would be the question of tying a "floating slab" into something with deeper roots?

 

[54FordPanel]

I don't think they are supposed to be "floating" by design, but I don't know.

But, for instance, the original porch and the original garage floor are obviously not dowelled into the foundation. Was that because the builder took a short cut, and this is the result? Or because the original builder didn't want the garage floor or porch putting strain on the foundation?

For instance, my basement floor: Could it be considered "floating", because it is a slab within foundation? As far as I know, the basement floor is poured after the foundation and isn't pinned to the foundation, because it isn't on caissons like the foundation, and there will be movement.

 

[t. jones]

I would not dowel an unheated concrete mass to a heated it will move and in time just bend the steel and or crack the concrete, causing a bigger mess than just a bit of movement. I have theese issues now with front porch steps and shop door apron.
Thanx Trevor

 

[kbs2244]

If the garage has a rim foundation that goes below the frost line you should let the floor “float.”
That is a very relative term.
An 1/8 inch is common, sometime ¼, but it will not hurt anything.
Most of time a cracked garage floor is due to bad under slab preparation that causes frost heave or overweight vehicles.

You are right about you basement floor.
It floats, but it doesn’t move much since it is below the frost line.

Any attached garage has a rim foundation tied into the home foundation to keep it from raising and falling relative to the home.
But the floor is a floating slab inside the rim.

 

[54FordPanel]

If the garage has a rim foundation that goes below the frost line you should let the floor “float.”
That is a very relative term.
An 1/8 inch is common, sometime ¼, but it will not hurt anything.
Most of time a cracked garage floor is due to bad under slab preparation that causes frost heave or overweight vehicles.

You are right about you basement floor.
It floats, but it doesn’t move much since it is below the frost line.

Any attached garage has a rim foundation tied into the home foundation to keep it from raising and falling relative to the home.
But the floor is a floating slab inside the rim.

Thanks for the input everybody. I'm sure the garage floor heaved and sank because of bad prep. It looks like it heaved in the middle and sank on the corners. And I believe this contractor when he says he will do the prep work (compacted road base) to fix the problem.
But I'm still confused as to whether or not it would be a good idea to tie into the houses foundation, even if the new floor gets the right prep work.
It seems to me the same forces will still be acting on the new garage floor, and it should "float" independent of the house foundation.
I think this contractor knows what he's talking about, but that his main concern is the garage floor, and that it doesn't heave or sink. I'm thinking it wouldn't be so great for the house foundation.
Especially the front porch. I would think a porch that moves a little is no big deal, but that a porch that is trying to move and is tied into the foundation would be a big deal.
Or am I overthinking this?

 

[Ezzie]

Around here house foundations are typically in excess of 4' below the surface and sitting on footers that are typically 6"-8" thick and 18"-24" wide (depending on soil type). A garage that is "attached" to a house must also have a perimeter foundation wall that is to a depth of at least 4' (below frost line) and be pinned to the house foundation. Most home builders pour the house and garage as one contiguous foundation pour. Porches are normally poured on top of these foundations and are not allowed to float. All floors (basement, garage, etc.) are allowed to float so sub-service prep. and compaction as well as drainage are the key factors in determining the life expectancy of the floor.

 

[ScaldedDog]

No, if you live in Littleton, CO, you're not overthinking it. As you know, the soil here expands for reasons other than frost heave.

I wouldn't pin it. I had a driveway placed a year ago, and they pinned it to the adjacent driveway. Now I have tiny cracks every two feet.

Who are you using as a contractor? I've run into a couple of good ones, and at least one complete knucklehead.

Mark

 

[ddawg16]

I think the dowel might be worth considering....it should not have an impact on expansion....there should be an expansion seam between the two slabs regardless if you dowl or not.

The dowel basically insures that slabs stay flush with each other....

But for it to properly work, the slab needs to be a lot thicker at that spot....I would think that a min of 8" would be necessary to prevent the dowels from causing cracking noted Scald....

In some of the places I go...they are using some serious slabs...typically a foot thick or more....they use dowels....these dowels are typically a smooth steel rod about 1.5" thick and about 24" long.....the holes are about 1/16" larger than the dowel and they coat the **** out of the dowel with grease...

 

[54FordPanel]

Well, as much as I know about this contractor, I think he's knows what he's talking about. He's not a fly by night guy. I believe he's one of us that strongly believes in doing it right.
After all, this isn't a case of him cutting corners; it's just the opposite.
For him, pining it to the foundation is alot more work than not pining it, and he wants to pin it. And his estimate is only maybe 5% more than the other bids I got that didn't mention pining it.

For instance, he wants to put caissons under my front porch supports, and the other contractors bids I got would just put the porch supports on the slab. That's going the extra mile, in my book.

I did a little back and forth email with him about this, and he said it's up to me. He would do the job without pining it if I wanted to, but in his experience, it's the way to go.
I'm still up in the air about it.