Home>Discussions>EXTERIORS>Attach concrete patio to the foundation?
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thomasnt
Attach concrete patio to the foundation?

I am having a concrete contractor remove my existing concrete patio and pour a new one. My back yard is flat. The new 4 inch patio will butt up against the house foundation. I would like to know if the patio needs to be attached to the foundation using rebar? Will it slide away if it is not anchor to the foundation using rebar? If rebar is needed then what is the recommended rebar size?

A. Spruce
Re: Attach concrete patio to the foundation?

No need to attach the patio to the foundation, the only thing you'll likely succeed in doing is causing the patio to crack later on when it can't move the way it wants to.

goldhiller
Re: Attach concrete patio to the foundation?

More info would be helpful......such as geographical locale.

For instance, if you're in a freeze zone and have a house with a foundation that is below frost......you would not want the slab attached/knitted to the foundation. Or at least, I wouldn't. The slab could/will heave upward with the frost while the foundation wouldn't. Fracture/cracking would result.

We're in a freeze zone. Frost-line is generally considered to be 4'. What we do in the situation such as you propose is to set rods sticking out of the foundation...UNDER the slab and don't allow them to knit to the slab. Wrap 'em with tape, 30# or whatever.

We also don't allow the edge of the slab to knit to the foundation wall by placing a piece of thin expansion joint or similar between the slab edge and the foundation.

This "no-connection" allows the slab to heave upward during the winter months, while the pins provides a reliable resting/support when the frost comes back out in the spring. Without those support pins, the slab may settle lower than desired when the frost comes out.

These are the very basic/recommended.. considerations/practices for our locale. Different situations may require additional considerations/techniques. It all depends.

thomasnt
Re: Attach concrete patio to the foundation?

I live in Seattle WA. It can get cold in winter time but not as cold as in the East coast. The reason I ask because some contractors say that it is not needed and some say they will rebar to the foundation. So I don't know which is correct.

Thanks

canuk
Re: Attach concrete patio to the foundation?

I totally agree with goldhiller.

Frankly this is something I've never heard of or considered before coming to this forum.

It's hard to imagine the need to even do this since it's only a slab on grade.

Even if you have no issue with frost heave ..... expanding or active soil conditions would also create movement on the slab.

In my mind the slab should be independent and allowed to move on it's own without putting unnecessary stress on the foundation.

ed21
Re: Attach concrete patio to the foundation?

One thing you don't want is the slab settling toward the house & directing water back to the house.
Two things I've done are: on retrofits expansion bolt a galv angle to the block wall to keep a slab from settling. On new construction I've doweled slabs together with #4 smooth w/ one end greased at 32" o/c. This keeps the slab from settling, but allows for movement.
In your case I would lean toward the angle. The soil should be well compacted in any event.

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