If you want to build over current basement, I'd contact a soils engineer first. He'll know what local conditions are. At best, you may be able to break up the slab, but leave in place, and place compacted soil over the slab. At worst, you may have to remove the slab and place compacted gravel.

I don't really understand any of that, but that's why experts are available to hire!

Ideally you should remove all previous construction down to and including the footings. If you have to dig deeper to accommodate the new foundation footings and slab, you're good. If you have to fill to accommodate the new foundation and slab, the fill should be compacted to meet the required bearing capacity of the soil to carry the weight of the proposed structure.

Not using the existing basement is a cost of building your new house. Like not reusing the appliances or anything else from your current house. whatever you choose include a vapor barrer.

We've built many infill homes, all on existing lots with previous homes.

Sometimes, we've used lots that were used twice before, going back to 19th C. farmyards. Nothing like smelling 150-year old cow manure disturbed by your backhoe!

Out with the old!

The good thing is you know what was on your lot before.

Trading a basement for a crawlspace is foolish.

Changing to a crawl space isn't going to save a significant amount of money and might even turn out to be more expensive with the necessary site work. Unless you are building in the middle of a swamp or have a high water table, new basements are clean and dry. Have a couple large egress windows and LED lighting and you will have lots of useful storage and mechanical space for low cost. I don't know anyone with a modern basement who would prefer to have a crawl space instead.

Youre being short sighted and the opposite of thrify. You will alrady need to dig deep enoigh that you will have plenty of height fir a *nice* basement. The fact that you jave a crappy basement now doesnt mean that a nice future basement cant be done. Its the cheapest possible square footage addition to a home outside stick framing the roof so it can be expanded as a potential 1/2 story living space. Do both, and a 1000 sf main floor becomes 2700 sf very quickly.

Thanks for the feedback which i am taking to heart i will post more later when i am at my computer

I wanted to take the time to give a few more facts and try to understand a coupe of comments (since I know nothing about this subject, obviously). Our house is from 1930 but we are told the basement was built prior to that and the homesteader (we are in rural Oklahoma) built and lived in the basement, then built all the outbuildings, and then the house was built on top in 1930. (The original settler was apparently quite short, hence the barely over six foot ceiling height in the basement). Basements are not typical for our area. Our architect said that the only people who build basements in this area now are people from the northeast who believe every house is supposed to have a basement. We have not yet discussed with our architect the idea of putting the house on the old house site so we'll be getting his input as well, of course.

As a general matter, footings don't have to go very deep here so crawl spaces are significantly cheaper (and preferred by us probably because it is what we are used to). However, as many of you have pointed out, the basement is already built (sort of) in this case. This house was probably originally about 800-900 sf with some very poorly-planned additions added, so the basement is quite small and not at all the shape or size of our new design (nor would we want to design around the existing basement stairs). Our thoughts of crawl space versus basement have based on personal preference, not cost factor (though costs matters of course). I've assumed this would result in a somewhat higher cost and consider it worth it but you all are making me wonder. Once we start talking to builders, I'll be interested in what they have to say.

Based on the feedback on this board, I'm trying to picture how it would work to put our new (three times the size and totally different shaped) house on top of an existing basement (which would never be used though I suppose the hot water heater could go down there).

@User, we are in fact designing a story and a half house that has a stick frame roof that would allow for a future full second story later if we want (unlikely).

@User, we have a large barn and plenty of outbuildings, so storage is a non-issue during construction.

@dan1888, yes, vapor barriers are a must for us!

You all have given us a lot to think about. I'm going to contact our architect this week and see what he says. He might be a hard no on putting the new house on the existing home site.

I'm grateful for the people on this board (though I'm not sure even I am thick-skinned enough to post our actual floor plans for feedback).

OK needs a basement just as a tornado shelter. I went through Moore. It took the grass off the lots.

Of course, concrete is the most destructive material on planet earth. From that perspective, every basement foregone is a benefit to mankind--or the more environmentally friendly species ready to follow us.

The crawl space makes more sense to me now, knowing this is for an Oklahoma house. Tell your architect to design you a storm shelter space in that crawl space with access from inside the house.

We have a safe room designed in the house.

Other posters aren't telling you to use the old basement! They are telling you to dig it all out and build the new house with a new basement.

"I'm not sure even I am thick-skinned enough to post our actual floor plans for feedback."

WARNING: Posting your entire floor plan opens you up to facts you may not want to know, but should. Be prepared for suggestions that will make for a better design. Keep a thick skin, open mind, sense of humor, and a glass of wine within arms reach. You may not enjoy it, but everyone else will and you will be better off in the long run if you heed well the advice.

Chispa, that makes more sense!! Thank you. I was confused.

Mark, you are of course correct in your warning. We'll see. I'm not sure I have enough wine for that.

I will be on my best behavior.