Concrete advice needed

I bought an old steel staircase for the outside entrance to the 2nd floor of the old building I'm remodelling. The price was 1/3-1/4 of what I would have paid for materials to build a wood one, it looks more original, and once I POR-15/bedliner it, it should last another 100-years.

Here's my question: it's heavy, just a guess, but probably 1000-lbs. It already has the uprights for it, so I will need to pour 6-footings for it. I'm planning on Sonotube, but how large & deep do I need to go for this much weight? Also, 3 of the footings needs to be almost against the side of the building, can I cut the Sonotube off on the side & butt it up against the foundation?

Some of the answers depend on where you are in the country and your frost situation.

Doh! I'm in east-central IL, so yes frost is an issue.

Realistically 42" should be more than deep enough. Me, I'd dig right along the foundation and drill some 1/2" holes into it for rebar, to tie the works together. If using piers, keep them low enough below grade so that they can be all tied together with at least a 6" pad, the size of the base of the stairs. Tie the pad into the piers with some rebar(or pipe)and tie the pad to the foundation. You only want to do do this once, so while it might be overkill, it will support it way longer than you'll ever need.

Local building codes will be a guideline in whatever you do. Frost line in that area may be 36".I would think that the height of your structure would dictate the size of the foundation more than the weight of the unit. Think sailboat and keel. Not an architect or engineer though one may show up with a degree and calculator in hand any minute now.........

The only reason to use sonotube would be if you intend for the concrete to extend high out of the ground. Even then, in a frost area, the area at the base of the sonotube will not make a sufficient footing for itself. The holes need to be bell shaped, so the base is wider than the tube.

Additionally, with a structure like this, the piers will probably be so close to each other that you will dig one hole into the other through the natural sloppiness of a backhoe by the time you get 36" deep and dig 6 of them.

If the metal legs are already near the correct length to sit approximately on grade, it would be a lot easier to pour a little slab on top of long turned down sides. It's known as a monolithic pour.

How were you going to dig? If by hand, build concrete and block piers. You can dry stack the blocks (12"), drop rebar into them, and fill them with concrete. If by backhoe, build a monolithic slab. If you have access to a large post drilling machine, the sonotubes are a good idea.

Ask Margie, seems like she's always working on another addition to her patio. before too long, the whole yard'll be concrete.

The ground slopes away from the building slightly, so I'll probably end up with the outer-3 slighly above grade, though I also need to remove some dirt from against the building, or the stairs will be a little tall.

How deep I need to dig was going to determine how I do it. I hadn't considered blocks, but that could work well.

Any advice as to what type of concrete I need?I'm thinking I'll contact the one local supplier & get their advice, but I like hearing other opinions/options.

Oh, and one other thought. I suppose I could do a slab, if I remove some dirt from the foundation. But the stairs will be straddling an existing A/C unit. I could remove it to install the slab/stairs, then remount it, but I'm just looking at the cheapest/easiest ways to do it right - and still trying to figure out what exactly "right" means in this situation.

Don't remove the AC- freon recharge, etc.

Can it bolt to the wall? Some all-thread through the wall might eliminate 3 of the footings.

Honestly, I really don't want to do anything that might compromise the brickwork, or cause more grief later. Also, the exterior brick walls are all hollow in the middle(I don't know if that is normal?), so I'm concerned that may be an issue.

FWIW, I don't believe the A/C units were ever charged. I know the furnaces have never been turned on. That will be fun to see what happens after they've sat installed but unused for 7-years...

Knowing the age of your building and the area of the country, it's likely that the walls are about 18" thick 2 (or more) layers thick with a void in the middle. You should have brick interior walls (which probably have cement plaster on them). Look hard at the exterior brick pattern. I'd guess that every few feet there is what is called a header bond course- you will recognize it because it will be an entire row of brick ends, rather than the sides of the bricks laid in the typical running (stretcher) bond like the rest of the wall. Could be flemish bond, or rat trap (here's a link to show the differences):

Brickwork

That means that the inside layer of brick and the outside layer of brick work together for the overall integrity of the wall. It's pretty strong, even with the voids.

A threaded rod through the wall with plates on the inside spreading the load around will usually not compromise the structure.

Unless your brick is really deteriorated.

Yes, that's exactly how it's built!

Here's another question for you, since you're so knowledgeable on these old buildings - would it be a good idea to(eventually) have the voids in the walls filled by one of those spray-foam insulation places, or will there be issues with trapped moisture and/or brick deterioration?

Definitely do not fill that void. You will trap moisture in that wall and probably ruin it. Look at the outside wall near the bottom and you will see voids in the mortar between bricks, that's where the water gets out of the cavity, and if you do anything that blocks those the water will stay in there and destroy the wall. The air gap actually improves the insulation value of the wall by creating a thermal break between the interior and exterior walls. If you really want to add insulation, you can use rigid on the interior, but it probably isn't neccesary, a thick brick wall insulates pretty well on it's own. Upgrading your windows is likely to have a much greater effect on your building's performance, especially if they are older single pane units.

The air gap is not a bad insulation, while the bricks add pretty good thermal mass.

What Josh said- DO NOT fill the voids with insulation, unless you are looking to accelerate the deterioration of your building exponentially.

The air gap isn't actually a thermal break, because there are plenty enough bricks tying the exterior to the interior to have LOTS of conductivity, but airspace is a good thing.

Insulation is essentially controlled airspace.

If you are cold, you are probably feeling the drafts around and through the windows.

Insulate the attic, the first floor floor, and get new windows.