Depth of Concrete Piers for A Deck

marathonman

Hello -

I am new to this forum. I am building a small wood deck off the back of my house in suburban Chicago. According to my municipal Building Dept, if the the deck is attached to the house, the concrete piers need to be below the frost line - 42" in this area.

However, they told me if I choose not to attach the deck to the house, then the concrete piers need only be 24" deep.

Is this sound construction technique?

Regards,
marathonman

Willie T

For an answer to this question, you have to ask yourself why they call for the deep footings on the house in the first place. The reason is that the freezing and thawing of the ground causes anything within the freeze boundry or layer to shift, move and heave upward. This caues unlevel houses. It will cause an unlevel deck too.

That's about it. If attached to your house, you don't want it to move around, causing stress on the connection area, cracking siding, twisting the deck, etc. And if the deck moves, when your house does not, those things can happen.

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Willie T

marathonman

Willie T -

I would only use the 24" deep piers if the deck was not attached to the house. It would be like a floating deck system (eg Dek-Blocks), or a skid foundation for a shed, except it would have superior resistance to lateral forces.

Thanks,
marathonman

UpComingBuilder

You should put them in 48" (4') into the ground. Stable and it goes past the frost line which you need.

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