Expert: Ted Barnhill (Principal, Design45 LLC) - 6/2/2009

Question
Hi.   I'm going to pour a concrete 17X19 patio (4" thick) and would like to be able to add a roof at some time.  I live in New York so I was going to put in 15"X43" footings at the 4 corners so I could put posts on top later.  I am not sure how high to go with the footers... to the bottom of the slab or up to the top.  If I go to the top should I pour it all at once.  I am concerned about the footing constricting the slab and causing premature cracking.  How would you construct the footings for the future posts?

Answer
Dave,

You are correct that the slab may move during freeze/thaw cycles, while your column footings will not.  You'll need to provide control joints between the footings and the slab to prevent cracking of the slab.

There are several ways to achieve this, with varying simplicity and aesthetic appeal.  The footings can be pour level with the top of the slab, or higher should you choose, and trowel/brush finished at the time of the pour.  When the slab is poured to the footings, create the control joint with 1/2" expansion material (normally bituminous).

Alternatively, you may pour your footings below the level of the future slab, then create control joints in your slab with a construction joint (stop and start; 2 pours), or by sawcutting the slab.

Good luck, and enjoy your new patio structure.

-Ted Barnhill