Thanks, I thought the joists would be a problem. I think if we flip the fixtures (swapping tub/linen closet with toilet/vanity) I can get the new drain stack to drop through a closet on the first floor. I'll see what the GC and plumber say about it. Anything to prevent a waste stack from becoming a stylish addition to the kitchen, right?

Purchasing decisions have to be weighed between benefits and costs. Most of us have to make compromises on location, size or condition of the property, (or in this case a large, unsightly addition). We simply can't afford to have it all. How much did they discount the price and what will it cost to have it fixed? How long has it sat on the market? How low can you get the owners to go? Do you have income growth potential that has yet to be fulfilled? Getting something for a great price in a great neighborhood with the intent to be there 20 years when our income will grow substantially over that time is sometimes a very wise decision. If this is at the top of your budget and you are in a life stage where income has leveled off, you can't afford to fix it and need to go forward looking for a compromise on location or size vs a costly future investment.

26ft is a very low number. Are you sure about that? Are you building on slab? What is your plan between floors - typical is 18 or 24 inches. With a slab, it really should be 24 inches - for HVAC ductwork primarily. So 12 ft 1st floor, 2 ft between floors, 9 ft second floor is 23ft. That would make for a pretty flat roof. I am used to somewhere around 38ft as a limit - and bumping up against it if memory serves - on a 2 story house. But where you call the "top" varies as is where you call the base. Are there houses in your county with 12 ft ceilings on 1st floor? As far as "shame" you out of something, I don't think being deliberate about a decision is a bad idea. I do think you don't see many 2 story houses with 12 ft ceilings - I have never seen one that I can recall - for a reason. And mind you, I had 11 in 1/2 my first floor. It was designed so the master suite had a few steps to get there separate from the main staircase. And the master suite was above the 11 ft area. We have 9 ft upstairs. You mentioned 8 ft doors. We have 7 ft. Try to imagine your door casing and crown molding. They would have to fit in that 12 inches and not looked crammed. In my area, most grand houses have a decent size crown. Not sure that would look right. I agree that the big transition to 6'8" doors is a bit much also. Curious where you are building because I like to learn about regional trends and I also have my guess and want to see if I am right.

Having to have a contractor work a schedule around people living in a home will cost you as much in time and extra work as it would to move into a rental. The quickest and cheapest scenario is to turn the services off and rip apart everything that needs to be ripped apart. And leave most the services off for the duration. You cannot have any HVAC running while a job of this involvement happens. Water and electricity are intermittent, depending on construction needs. Water can be off for weeks at a time. Electrical usually has a breaker or two up to power the job equipment, but nothing else. Unless you’re adding a sub panel for the upper floor? Then you’ll have to up your service, and that’s usually done first, so the sub panel supplies the job power. But with the leaks that happen from no roof, the site power is usually shut off at the end of the day. There is no way that the existing home doesn’t sustain damage from a job like this. Sometimes quite a large amount of damage. Just one good rain, and you’ll have damaged drywall and flooring everywhere. All of that has to get ripped up and removed to dry out. It’s part of the risk you take to do this, so you might want to contact your insurance company about a builder’s risk policy. Just packing up a few things won’t do it. You need to pack everything up like you’re moving. You want nothing left behind. Vacant. You should explore an addition rather than a second floor. That, you can live through. With minimal damage to the original home.