Outside fireplace footing

[mark beemer]

I am building an outside masonry fireplace. The width will be about 3' and length about 12'. The unit will be about 12' heigh built out of cinderblock and clay tile with a real rock veneer. I am planning on pouring a pad and footing for the fireplace. How wide would you suggest the footing around the perimeter of the pad and how deep? Our frost line in Kansas City is about 3' and the soil is very high in clay. I was planning to use 1/2" rod in the footing. Also, insight into the thickness of the pad would be greatly appreciated. I was planning to complete both footings and pad at one time.
Thanks
MB

[Rich]

Being that tall which equates to weight..etc..etc.. and with the clay soil you might want to look at doing some piers also. I don't think they would have to be all that deep - maybe another 4' down from the bottom of the footing (2 man post hole digger comes to mind). I would probably pour the whole depth of 3' across the whole thing - you'll save a bunch of time on forming etc. You could pour the caissons / piers at the same time also - 12'x3'x3' = 4cy plus piers - maybe 4.5 cy.

[RobBase]

According to the International Building Code which is in effect here in MD, (check your local building inspection dept for the code which is in force where you live) the footing for that fireplace would be min. 6" wider than the masonry in both directions making your footing 4' x 13'. Also it would be a solid pad footing as opposed to strip footings around the perimeter. The footing also has to be min. 12" thick with min. #4 rebar projecting up to tie into the masonry cells at the 4 corners and every 4' around the perimeter.

I can't remember their requirement for rebar in the footing, but #4's @ 12" o.c. each way should do.

For the clay, 6" below the frost line depth, thrown in 6" of crushed stone and run a plate tamper over it, then place your rebar and pour your footing.

[ALMIN]

Unilock sells a prefab fireplace. See page 7 of this link for the concrete pad they specify: http://www.unilock.com/downloads/documents/fireplaceInstallatioInstructions.pdf

[concretestan]

Does anyone have a set of engineered drawings for the footings on a outdoor fireplace? It needs to be stamped by an engineeer. Email me at stan@bnbbuilderswichita.com

[concretemasonry]

That is not that much of a monumental structure. If you have good firm clay the bearing pressure are not that high and could possibly better off with a spread instead of concentrating the load into individual caissons that will have much higher soil pressure under them and could settle differently.

You may not be required to get a signed design from the engineer, depending on your local requirement, but it could save you some money in the big picture or long run.

Dick