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single story foundation excavation to 2 story?

goalieump's picture

I recently saw an online article where a homeowner/contractor added onto his house, but unfortunately, he had to excavate out from under one exterior wall's footing, pour a larger footing under the existing one, allowing him to make that wall part of a 2 story addition.

Question for the experts:  Is this a fairly common/difficult process?  My house is small, but I am pondering an addition, building onto one side where I'm sure the footing only supports just a single story.  I could build a separate structure, pouring a foundation then bridging the two structures, but I'm not sure that the cost would warrant the extra work.

Any thoughts on this would be greatly appreciated.


In my experience it's usually (post #207031, reply #1 of 12)

In my experience it's usually not necessary unless the foundation needed a lot of work anyway. Generally you need to add piers at point loads, but that all depends on the type of foundation you have and what you're adding. Hire an engineer. 

foundation (post #207031, reply #2 of 12)

First, you should not assume that your existing foundation will not support a second story.  You should check with a qualified engineer or at minimun check with your local building authority.  You are worring about a problem that you may not have. No one here can give you any worthwhile advice because they can't see your house from here.

I'm reasonably sure my (post #207031, reply #3 of 12)

I'm reasonably sure my house's foundation would not support a 2nd story.  I've checked the width of the foundation wall, and since the exterior walls are 2x4 construction as well, I don't think the footing was built to take a 2nd story.

Mainly, my question was aimed at thoughts on the practice of retrofitting a footing for a 2nd story, not just specifically my house.

Unless you've dug down you (post #207031, reply #4 of 12)

Unless you've dug down you don't know what the width of the footing is.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Plenty of 2 story homes are (post #207031, reply #5 of 12)

Plenty of 2 story homes are made with 2x4 1st floors.

YAY!  I love WYSISYG editing!  And Spellcheck!


Get an opinion from an engineer. (post #207031, reply #6 of 12)

The width and depth of the footing as well as the soil conditions affect the determination of whether the exisitng footing is adequate.   You don't want to make a mistake, which could be very expensive.

To address your original (post #207031, reply #7 of 12)

To address your original question: Is it difficult or usual to add onto a footing? I'd suspect that it isn't uncommon but why do it? If you have to dig down to the footer anyway, why not just add another one for the new wall? You will have to build three other new walls anyway, why not the fourth? The footer isn't the only thing suspect either... your foundation wall may be the weak link. So adding a new one (adjacent to the existing) solves the problem. The additional cost of this is really minor compared to all the rest of the project. 

Keeping the addition structurally seperate from the existing is adventageous in that it is then all new construction. Remodeling is always more money per square foot then new. And doing new lessens the hassle factor of living in a torn up house that's being remodeled. (If that is your intent.)

 My POV is northeast NJ.  (post #207031, reply #8 of 12)

 My POV is northeast NJ.  Here nobody checks (including the inspector) if footing is the right size.  Usual practice, single or 2story one family houses, was to pour one kind of footing, not engineer it to the house being built.  Footing inspection would be for unusual or suspected additions, etc, which you should do yourself anyway.

Footing, foundation and walls are separate structures, and you can't assume the size or conditon of one by looking at another.  If your foundation is concrete structure, your footing is likely to be adequate for 2nd story addition.  You can dig down (hire couple of cheap helpers) in a day to check.  Although outside inspection is no guarantee, you can at least check for the thickness and the soil condition under the footing.  You have to be absolutely sure there is no electric, gas, oil, plumbing, sprinkler, etc under where you are digging, and as you near the footing, watch out for foundation drain pipe.  Separate the soil, gravel, etc as you dig and return/compact in order.  You don't want that hole to become a weak link in drainage.

Your inspection office may have some information on how your house was built, or usual practice for footing in your area.  At the end, the liability is yours, though.

xlol   How many footings are  (post #207031, reply #9 of 12)

xlol   How many footings are  build oversized?!  Not an effin one!    Under digging alternating 4' sections of existing footing and pouring a new footing is something highschool kids could do with minimal supervision.  Once that is set up under dig the next half of the foundation and you're ready to go to a second story.  Absolutely no normal footings poured 40 years ago are up to our standards today for a 2 story addition!   Save you money on an engineer to check the footing size and just build it right - concrete is cheap.


If I could edit my location it would say I'm now in Reno :-)

I'm with k1c.  Though it no (post #207031, reply #10 of 12)

I'm with k1c.  Though it no doubt varies with locale and soil conditions, in many parts of the country there is very little difference between a minimal 1-story footing and a 2-story one, and contractors are apt to do a "one size fits all" overbuilt job, rather than spend the bucks on an engineer to calculate the footing size.  It's faster and cheaper.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

I have yet to see an (post #207031, reply #12 of 12)

I have yet to see an oversized footer in anything I've ever worked on!  lol   I take that back - I did see an idiot who used 16" footers on solid rock - that's just stupid.

If you are going to use existing footers you have to have the soil tested for it's bearing ability and I'm sure there are many situations where an existing footer is just fine - but even in those situations reusing what's there is just not going to happen in many areas where the building department is nit picky.  There is no way to tell how the footer is pinned to the wall, the rebar is normally not up to code, but $500 to have it tested is a good way to throw away $500 since it's a no-brainer that it won't be up to code.   So very few builders from the past build to todays codes (they didn't have to!) that I'd win the bet 9 times out of 10 that. 

If I could edit my location it would say I'm now in Reno :-)

Ya need to get a permit or (post #207031, reply #11 of 12)

Ya need to get a permit or not?

If no, no need for any foundation 'improvements'. 

If yes, with the big buck you pay for a permits,  just put 'existing foundation' on the plans and they will redline your plans if you need to go bigger.