I am thinking about replacing my existing triple 2×10 carrying beam in my basement w/ steel to remove some of the lolly’s. What is the easiest way to determine the size of the existing column footings? I went to the local building dept to look at the plans used to build the house but there is not much info to use. I would like to re-use one of the column locations however with the new design for the steel beam, the footing size needs to be 2′-6″ squared. I think the existing is 2′ squared.
Rich
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Mechanic's stethoscope and a ball-peen hammer.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
If you are looking for magic x-ray glasses, they just sold out last week.
The only way to know is to open up the floor and find the footing and measure it.
Likely that if it was spec'd at 2x2 they would not add another 6" just for fun.
You could drill thru the slab and perhaps determine approx where the edge of the footing is and then you would know how big the footing is at the top, but that would not tell you if they poured the footing with vertical side walls or if they got sloppy and concrete is everywhere or bulging out at the top which would not provide support.
If I were the building inspector, I would want to see the footing and verify that it is the right size.
Actually footings frequently end up larger than designed.
It costs less to put the gravel down, and dig out the volume for the footing, and pour it monolithically with the slab, than to form the footings, strip them, and do a separate pour for the slab.
The inspector is worried about whether it is on a solid soil base, and meets the minimum size. If it ends up 2 foot thick and 3-foot by 3-foot square, and the plans call for 1.5-foot thick, and 2-foot by 2-foot, the Inspector and Engineer are both happy.
Re. footing sizes.
Maybe in your area but in the hundreds and hundreds of homes I have been involved in in the Delaware Valley, there is almost 0 chance of a footing being 6" larger in each direction than what was on the plans.
Contractors typically form 4" and dig 4" or form 6" and dig 2" for footings and the pier footings are almost always 12" deep so they need to go down another 4". Since most of the contractors hand dig the piers, they are not in the habit of overdigging.
In fact, when I worked with a new concrete guy when I was real busy, I would often check pier sizes to make sure they were not cheating. (They did not last long if I caught them)
I went to the local building dept to look at the plans
Well, than, it likely does not matter what "we" think, your local AHJ (Authority Hving Jurisdiction) gets to make the rules.
Which may mean you do what ever the engineer who wet-stamps the drawings you have to submit says
Given how these things work, even when the existing footings are in the right spot, there is always some question on whether or no they will carry the new load. (Finding out that the lallys holing up 2.5 floors of house are 2-sack 24 x 24 x 6" pads on existing clay can be disheartening.)
I'd be inclined to start eyeballing where to make some test "windows" in the slab, and do not forget to eyeball over near where the ends of the new steel beam is to go, too--it can need more bearing surface than you presently have.