Houses near me (Alexandria, VA) have done similar projects, but usually they are basements that have about 80" clearance to the joists, and they want to go up to about 90" so it meets code for habitable space after ceilings and floors are installed (I think the code here requires 84" to finished ceiling).

I think the most common issue is that your sewer drain pipe may not be deep enough under the slab, and it may run under the area you want to excavate. I know my 4" cast iron pipe is just below the slab level, and I assume this lines up with the main in the street. I would need some type of evacuation system to raise sewage up if I lowered the drain pipe.

Footings for existing walls may be an issue if they extend quite a distance out from the walls. I saw one "This Old House" episode where they excavated the area between the footings to get more height, but left the original footings in place. That created a stepped floor that had full head room in the middle, but had a shelf around the perimeter walls. I never saw how they finished the walls, so I don't know how they dealt with it.

Removing a basement cement floor and underlying dirt is going to be expensive if they can't get equipment in and out through a wide walk-out door. With only stair access they will have to jackhammer the cement into relatively small chunks and carry it out in buckets. Dirt will have to come out the same way. This is very labor intensive. When they do the new floor pour they will have similar issues if there isn't a window that provides a good location for the chute into the basement.

Bruce

Often the easiest approach to this, if you have the room, is to pour a new foundation adjacent to the current house location then move the house onto it. I doubt it is often done just to create headroom, but in a situation where you want to move an old house further back from the road and have a failing rubblestone foundation, and need new sill plates anyway it can be quite successful.

Undermining your foundation footers seems like a really bad idea, plus if you go below the footer drains (if any) you are inviting water to enter.

It is fairly commonly done where I live, the lower part of the foundation where it's been dug out is usually Inside the older foundation so there is a ledge around the perimeter and the floor area is smaller than the original basement floor.

Our neighbors (3 different homes) have dug out their foundations and the results are wonderful. As pal said, usually the old foundation is left in place, but not always. None had cement, just dirt floors.

Thank you everyone!

We do have a cast iron drain pipe that is right under the current floor's surface. At one pt it's even above the surface w/ an opening to expunge a clog. I would hope that a pump would be able to be used to accommodate the flow being against gravity?

Unfortunately, the house is in a very dense area, so moving the house isn't feasible and removing all of the cement would have to go through the Basement door into the backyard. Not a wide entrance either but we do have several large windows that could support moving the cement down.

What is the best way to identify if there is an existing ledge on the inside of our parameter or if footings extend? I think there may be b/c there is 4-5'' between the parameter wall and the drywall +framing.

I do like the idea of having a ledge inside the original parameter. Definitely OK to sacrifice some sq footage in the dig out to ensure that the foundation footer has extra support. The house is 22' Wide X 55' long and the front and half the back has the utilities. So, if I left an extra 1' around the walls and tossed some I beams or something up in key locations-- Would that elevate any issues and costs associated w/ foundation work?

When you get into questions about footer support and how wide it has to be to keep the house stable, you really need to have direct onsite review by a very competent contractor. Its beyond the advice anyone can give you over the net.

If you find a good contractor I think they would probably jackhammer a small area of cement near one of the perimeter walls to inspect the depth and width of the footing, and then plan from there. If your house is built like mine (1940 vintage), jackhammering through the cement floor is not an exceptionally difficult job because its not that thick (5-6"?) and there is no rebar reinforcement.

I think your project is feasible, but not cheap. If you keep the perimeter foundation supported, and add steel columns where needed to support the middle of the spans (based on engineering estimates), it should be structurally stable. With the additional headroom you may also have space to use newer materials like these LVL beams to span larger distances. https://lpcorp.com/products/framing/lp-solidstart-lvl/

Bruce

Thank you! I think I have at better gauge on some options and things to consider. Next steps is to save Money and get some estimates etc!

Thanks Again,

Andrew

This is often done in our downtown neighbourhoods where space is at a premium.

I've done it--but only after an inspection and plans by a structural engineer. The design called for a two foot high concrete ledge around the basement including parallel and perpendicular rebar to ensure support. We installed new sanitary drains since they were close to the new deeper floor.

To deepen the basement right up to the existing foundation walls, new walls and footings have to be installed in stages. This is called underpinning. And even with so-called professionals can be a dangerous job where structural collapse is not even the worst outcome.