I have a basement area that I want to make into a office/den, the house is over 40 yrs old. The concrete floor was poured so ineven I would like to know if it would be practicable to break up the old floor, which is out by about 5" from one side to the other, and dig down a little ways to get more head room, say about 3-5" and pour a new even floor with insulation under it with a vapor barrier? Need more room in my house and lot is too small for addition.
Would the costs be too great to do this, the area would be about 250 to 300 SQ FT and envolve cutting out old fllor in places and breaking up and removing, releveling the crushed stone already there and pour new floor. Any ideas of a ball park cost factor. in the Boston area. Thank you very much for any help anyone would have, Bill

It's tough to give a cost, because it is so labor-intensive. Contractors with experience in such work are best able to estimate the labor required.

How deep you can dig depends on the depth of your footings. If you imagine a plane extending down from the bottom corner of the footing at a 45-degree angle...you should not dig below that plane. That goes for your wall footings as well as any column footings that you may have.

Some mechanical equipment may be installed on the existing floor, and either you will have to leave that part of the floor in place, or you will have to disconnect the equipment and extend the piping, ductwork if any, and wiring to the new depth.

You may also expose your sewer discharge piping if it runs below the floor, unless it runs on a wall and you can see where it exits the basement.

Work like this is done frquently, so it's not impossible, nor is it a bad idea. What else can I tell you? Besides "good luck"?

Oh, if you're going to occupy your basement, you'll need to insulate the walls also. Often that is done by erecting framed walls essentially right against the basement walls, and insulating those.

I want to thank you very much Richard for your, reply, I know the labor is very hard to figure out, I would do breaking up and removing old floor but I can't do this type of work any longer due to open heart surgery and an heart attack.
Ricard, I must tell you something about what you said about the footings, THERE ARE NO FOOTINGS under the 10" concrete foundation walls, they are set on over 1' of crushed stone on a pour sand sub soil, and they have not moved for over 45 years now. Don't know how the builder got away with this but he did, have had it checked by an structural engineer and he said it was ok, has it has not moved in over 20 yrs when he checked.
Is what I'm trying do even feasible and economically sound?? It is the no footings I am mainly worried about and the cost???? Thank you very much for taking the time to answer my post, Bill
PS: ANY ideas anyone?
PSS: Only envolves cutting about 35'of concrete floor, breaking up and removing, and leveling and pouring new floor, no wireing, no mechical, no plumbing, nothing else involved, thanks again.

Stop worrying about your lack of footings. If I did the calculations of the pressure the concrete walls place on the soil, I'll bet the 10-inch bottom is sufficient. Now, the thing is, you don't want to undermine the bottom of your foundation walls. You have to respect that same 45-degree plane from the bottom edge, or else you have to underpin your foundation walls, and you don't want to do that for a few inches. Usually when people do that, it's to gain a few feet.

Wildbill38 -

Richard is right about the lack of footings. There are many basement system that do not use or require footings. The footings on most basements are meany to provide a well defined, level, dry surface to place the wall on. The vertical loads are low.

One thing to be concerned about is that when you remove the slab, you are removing a portion of the structure that prevents the walls/footings from sliding inward. Most codes require 3 1/2" of concrete be pourd abutting the bottom of the basement walls.

You should do the work in sections to preserve some lateral support for the bottom of the walls. I woulf think the best method would be to pour a curb wall inside your existing wall, bracing it until your slab can be poured.

It can be a dangerous DIY project, but many contractors are very familiar with it.

First I want to say, this was my first visit to this site that I found thru Google, and I want to thank both Richard and concretemasonry for there messages, they both were helpful. It is very nice to see people here that know what they are talking about.
I also want to tell them, that I have changed my blue prints around a little bit and there will be only a small 12' or so, section of exterior wall that will be involved, and the main wall that will be involve is an interior wall betwee basement and a garge, so it is no fill on eith side. I would like to do the job myself but account of heart condition can't but at least now I can sub it out and know what to watch for. Again thank you guys very much and would love to hear anymore suggestions from you or anyone with more helpful info, thanks, Bill