I have a two-story 77 year-old house in Albany NY with a full basement. I'd like to drop the basement floor so that I can finish it as a 'habitable area'. I want to do the underpinning myself since the cost is so high.

Who is the best type of professional to draw up the underpinning plan, a structual engineer? Will I need a soil study?

Not a job for an amateur.

Dangerous and very easy to do wrong and really have big problems. - It takes experience.

When you say DIY, you may have a hard time finding someone who would gamble the professional liability on it. - It will take a selling job on your abilities to do it as drawn and signed.

You would definitely need a structural engineer and he may require a soils examination to see what he has to work with.

Underpinning is only one of several issues with converting a basement to habitable space. After that, you will still have to deal with an exit, sufficient natural light and ventilation, vapor retarders, insulation and a bunch of other details. It would more than likely be cheaper or as cheap to build new above-ground space of the equivalent size, and when you're done, you'll have something that's worth the money you spend and then some, and you won't have constant worries about moisture problems and mold. If you can do underpinning yourself, and we don't know that you can, you can certainly build a foundation yourself with about a quarter of the effort and none of the risk. That way, you'll have a space that is properly designed (if you use a good architect) and trouble-free for decades, and it stands a chance of bringing you more than your money back if you sell.