I'm designing a new house and I've run into a couple of problems. First, some info on the house: it's a 1 1/2 story (is that what it's called when you put a second story under your roof space?). I originally designed my exterior walls to be 10 feet tall, so that I had a little room for varying ceiling heights on the first floor. However, my contractor strongly recommended against exceeding 9 feet with my exterior walls for cost reasons. I'd still like to have a 10-foot-tall ceiling in my den, but the master bedroom will be directly above it. My questions are these:
1. Why would 10-foot exterior walls be drastically less cost effective? Do they require fire stops, or extra bracing to keep them flat?
2. If I go with 9-foot exterior walls and put a 10-foot ceiling in one first-story room, I assume I'll have to raise the subfloor of the area directly above the raised ceiling and put in a couple of risers to access that area of the second floor. But can that be done (and should it be done)? If so, how would the second-story subfloor have to be constructed?
There are no great technical problems between 9 or 10 ' walls, he is probably just warning you that it is more expensive. Costlier(taller) studs, more sq footage of exterior sheathing and finish, insulation, interior wall finish, either taller upper kitchen cabinets or bigger furr downs if applicable, and possibly longer windows to keep the facade asthetically proportionate.
Without seeing the specific layout of the upstairs living area, it is hard to suggest much for your second question, but it is generally handled in two ways. The first is to use 2 x12's across the bumped up ceiling, making them floor joists,, and extending them outward so as to bring the entire floor of the upper living area to this height. This will require a longer staircase to accomodate a couple of extra risers, so it will affect the first floor plan as well. Another option is to have a landing at the top of the 9' high wall staircase, then a couple of risers perpendicular to the main stairs, to get you to the added floor height.