Garage is sinking!

Hello all, new to the forum. When my garage was built, the amateurs poured a slab of concrete over some crushed stone with no footers or even rebar, just a slab of concrete. They built my 2 car garage on it. Well, now the slab has cracked down the middle and is sinking on both sides. The only option I have come up with is this:

Score around the inside perimeter, cut and remove the floor inside. Then, with the concrete remaining along the sides that is holding up my garage I will drill holes and run a system of re-bar through them and pour new concrete inside. Also, I will dig in the corners down a few feet to install some supporting footers. Will this work? Thanks in advance.

I hate to say it but I think you need a professional on this one. I hate it but I think when it comes to foundations especially you should almost always go with the pro's.

I'd have to agree with the above. I'm also in NY and I can tell you that without any kind of foundation or support (footers) below the frost line up here it's only a matter of time before your floor is cracked.

All that, PLUS they seemed to have forgot to throw in the rebar? I'd be calling a lawyer or dusting off the shotgun....

I'm not a foundation man. It sounds like your plan would work- Digg some footers (4' code) add some rebar and you'd have a regular basketball court up in there. But like I said, I aint no concrete man, and I would defintly run this one by some pros in the area.

Either way, it looks like it's gonna cost you unless you can get ahold of the guys that did this to you.

Wow; what a problem. But there are a half dozen good solutions anyway. Much good advice has already been given by those who've already commented. You are in Rochester N.Y.. So that means you are subject to both deep frost, multiple freeze thaw cycles, and snow loads. You need to consult local building code, or N.Y.S. building code to determine at what depth below the ground the footings are required to be placed; i.e.probably somewhere between 36 to 48 inches below grade. This is what originally should have been done, and this is what should be done now as your cure, so that "heaving ground", due to frost, will not create the same settlement problems in the future. (Also, without doing this job according to code could hinder you from gaining other permints in the future, or from gaininging a C.O. on the premises if you ever decide to sell.). Doing the job is not at all difficult; i.e. only requiring time, materials, a plan to do it right,(according to code), and to work safley, as you are working around in improperly built structure. If the wooden part of your structure was built properly, then you could procede as follows; break out the existing garage floor a section at a time, supporting the outside garage walls as you go. Then, in preparation for excavation under these outside walls, support the garage under the sillplate at eight foot intervals with 6 or 8 ft long beams running through the brick foundation, and being perpendicular to the garage walls. Once these are in place, level the entire sill plate by adjusting and supporting the ends of the inserted beams as your way of leveling out the entire structure.. Starting in one corner, excavate down and build the footings, and then then build foundation walls up to the bottom of the already leveled sillplate, (The proper dimensions for both your footings and foundation walls will be spelled out in a readily obtainable N.Y.S. Building code book, available either from your loacal town,county or state building dept. offices.).(when complete in one section, then excavate and build the footings and foundation walls in the next section, do the next, and the next, and the next, etc, until completion. Before you set the sillplate on the finished foundation walls you might consider putting a secondary, treated sillplate in place with your termite shield. Now, as for the garage floor, before replacing it, you'll probably want to prepare the subgrade by compacting it with a vibratory compactor,(this will reduce the future possibility of cracking due to settlement of the ground beneath.). Finally, with your grading finished, place a visqueen or plastic liner on the surface prior to pouring your concrete floor. (The plastic sheets acts as a barrier between the concrete and the earthen subgrade so that water is not lost from the concrete before it has a chance to properly cure.)... regards; der swede

A concrete slab, even with rebar, depends upon the ground underneath for support. Lose the support and the slab will crack and rebar will snap (happened with my house after the Loma Prieta earthquake when the sandstone underneath liquified. The problem may be a lack of adequate compaction or you may have water seepage involved.

If you have the room to do so you might considering getting a house mover to lift up and set the garage to one side of the foundation and then it will then be much cheaper to remove the concrete, do a soil test bore, and get the necessary expert advice on how best to proceed with the design and creation of a new slab.

With a house there are multiple solutions but they presuppose that there is significant value in the structure and that is worth the expense of trenching and jacking and other costs involved with rebuilding the support for the building. Your garage does not seem to be this type of high value structure.

At this point you do not have enough information to make any decision but need to get quotes from various contractors which will also provide you with a lot more knowledge about viable options and probable costs.

Ask your building department if they accept this: ESB: Frost-Protected Shallow Foundations May be helpful...
Be safe, Gary

To be honest I think the most cost effective solution may be to just demo it. At least you would end up with a new garage that is built properly and SAFE.:beer::beer:

yeah it looks like you have a major problem but from my experience don't listen to me [and I have been in it for over 30 years]...or the subs... or the suppliers...check around for a good structural engineer that deals with residential construction [talk with some local builders]...shop around because there price go from a-z....they can come out and access the problem and tell them you want the cheapest solution to the problem...sometimes it's not as bad as you think...but whatever they come up with...get at least 3 bids to do it per the structural plan....i have never had it fail me..

Thanks for all the helpful advice everyone. The snow has melted, and I have begun excavation for my footers in each corner. My plan is to install 7 footers first, with the floor holding up the garage while I install these. Next, once the footers cure, I will break out the garage floor so the garage will be sitting on my footers.

For the footers, I'm using 12" sonotube forms and my question is this: Will a 12" diameter be enough surface area sitting on top of the virgin soil to hold up the garage and not sink once I break out the interior floor?