New Home Begins

[tkappeler]

I think this is a good idea considering how much the OP has to raise the level of the garage slab. Better to spend a few bucks now and correct it if need be then blow it off and have the hideous expense of replacing a garage slab later.

Are you saying the garage slab will be tied to the foundation walls? Does your soil conditions permit that? Did the structural engineer say that is OK to do? The reason I ask is that if that were done here with our expansive (hot) soils; you would more than likely end up with major damage down the road. Yesterday my wife and I toured a neighbor's house built by the same clown who built our place. Their problems make ours look minor. Besides shoddy workmanship by the builder, our hot soils finished wrecking their house. From what I saw of it, at a bare minimum the finished basement has to be gutted and the concrete floor blown out and redone; but based on additional damage caused to the main floor and exterior by the heaving soils it would be better to scrape the house off and start over. Be careful tying slabs to the foundation is my only advice, especially since you have such a high water table.

As I said, the soil was unknown when the house was designed. But all is good with the soil when they started digging. The slab will be tied to the basement walls which sit on a traditional footing

 

[sdkubota]

The proceeding post brings up some good points. Where there is freeze/thaw cycles never tie a slab to a foundation. Reason being as soil freezes and thaws it can move as much as 3" or more. If you tie the slab to the foundation the concrete will break as the soil freezes and expands. The same can happen to a lesser degree by small settlements. If the slab was ties would create hollow conditions under the slab causing eventual failure. I alkways specify the slab remain floating next to any type of foundation and have a 5/8" expansion board placed between sections to ensure seperation and allow for expansion.

 

[dave1949]

As it happens, across the road from my property a guy is building in fits and starts. Last summer (2011) he leveled off a built-up pad to build on. This October he put in a footer and frost wall foundation, then had that filled with sand. Don't know how much compacting was done other than driving on it a lot with a skidsteer. Then they poured a slab inside the frost wall, flush with the top of wall. Since then, they have done nothing, which surprised me since local custom is to not leave a slab exposed over the winter. People usually at least put a closed-in shell over them if nothing else.

Out of curiosity I checked it today. The slab is almost 1/4" above the top of the frostwall now that we have had some ground frost penetrating. It can't be good for the waste lines that are under and coming up through the slab with no sleeves of any kind. They will probably survive 1/4", but 1" or more is possible by Spring. I couldn't see any cracks in the slab, but that could easily come later.

There is no expansion break between the frost wall and slab either, they just used the frost wall as a form to pour the slab in. At least, they back-filled around the frost wall to within about 6" of its top.

 

[sdkubota]

I have watched my patio rise up nearly 3" because of frost during severe winter temperatures.anything piercing the slab needs to be isolated from the movement. Expansive soils are a whole different nightmare.

 

[dave1949]

I have watched my patio rise up nearly 3" because of frost during severe winter temperatures.anything piercing the slab needs to be isolated from the movement. Expansive soils are a whole different nightmare.

Yep, just for giggles I am going to see how high the slab goes. It's been relatively mild so far, but no snow cover yet which makes a lot of difference here in frost penetration depth.

 

[sdkubota]

Yep, just for giggles I am going to see how high the slab goes. It's been relatively mild so far, but no snow cover yet which makes a lot of difference here in frost penetration depth.

We can have frost reach depths between 4 and 5 feet during cold winters with little snow. This year it is bone dry so there will be less frost.

 

[tkappeler]

These talks about frost heave for slabs will make me double check with the architect and structural engineer. Thanks for the feedback.

 

[Dr Dave]

We can have frost reach depths between 4 and 5 feet during cold winters with little snow. This year it is bone dry so there will be less frost.

I was told, the drier the soil, the deeper the frost line will be, is this correct? And would there be less near the surface as you said?

Dave

 

[sdkubota]

I was told, the drier the soil, the deeper the frost line will be, is this correct? And would there be less near the surface as you said?

Dave

Not really, totally dry soil will not freeze. I suppose wherever the cold finds moisture will be the first place to form ice. Problem is the lower the depth the warmer the soil. It would by my opinion that there is less frost during dry soil conditions. I have been wrong before....well I thought I was wrong but actually was right.

 

[dave1949]

I have always heard frost follows the moisture down, so wet soil = deeper frost. Deep (18" +) snow cover = less frost depth.

Tom, I don't think you have any worries about slab heaving since yours will be covered in a relatively short time and your location has much higher average temps than here. But, it never hurts to ask. I don't think they put any insulation under the slab across the road either. It's down a ways from our house, so I can't be too nosy :laughing:

It really wasn't intended as something you should worry about, we were talking slabs and the neighbor created a test case to observe.