"The contractor has hung them all with rather large clearances between door's edge and floor  partially defeating the sound-insulation... When confronted, he pointed out, that Code mandates clearance between 5/8" and 7/8" in our case, where the central air system pushes cold air into every room, but has only one return per floor (in the middle). " There is absolutely no such mechanical code "requirement" that there needs to be a minimum door height above the floor for AC or forced air heating purposes. NONE. What you have been told is complete and utter NONSENSE. I am a nationally certified Residential and Commercial Mechanical Code Inspector and challenge anyone to provide a Code section from any Code that has ANY such a requirement. While a design to provide a balanced air output and return air within a forced air system IS required, the 'means' by which this should occur is written into NO CODE and depends upon the design and the circumstances. Particularly on older existing homes with centralized (not individual room) air returns like the original poster's...the house should simply not ever be 'tight' enough to restrict air changes per hour or to restrict air flow when interior doors are closed. Those who think doors need to be cut extra high above floors to maintain air flow are simply ill informed. There is nothing in any Mechanical Code that prevents even sealed door units and sealed thresholds from being installed. Nothing. In some situations, Mechanical Codes actually require sealed doors....(like between bedrooms and closets containing boilers, furnances and water heaters). Likewise...some rooms, like bathrooms and kitchens, garages and some types of basements and crawl spaces are prevented from having return air vents and ducts installed within them. ---------------- I don't believe your contractor is lying to you. He does not stand to benefit enough for his false claims. I DO beleive he just doesn't know what he is talking about, and thought he 'learned' something along the way that simply is not true. ----- Tell him to repair the doors he damaged at his own expense....and do not pay him until he does.

I will tell you what i did in the same situation you have, roof trusses on 24" centers. moved into the house the attic door had no insulation just trim holding a piece of drywall up. So i took down the trim. The hole was already framed to the ceiling. I took 1 x 4 boards framed them around the edge of the ceiling drywall. picture framed the 1 x 4 with the same trim as the door trim. Cut a 2' x 2' piece of birch plywood 1/2" thick to fit on top of the 1 x4's. Painted everything. Got some 3/4" wide self stick foam weatherstripping and put it on the top of the 1 x 4's. Had a 4 x 8' sheet of blue styrofoam and cut it to the same dimensions as the plywood. glued as many pieces as I could get out of the sheet to the plywood after the plywood was in the attic. Also cut a piece of R-25 fiberglass insulation to fit on top of the plywood and foam board. I figure it insulates well enough. Also installed 2 hooks and eyes to hold the plywood tight to the weatherstripping. I could have used foil faced board at R-7 per inch like I did at the previous house we owned. When I remodeled that house,when I gutted rooms I put 1/2" foil faced board on the interior of the exterior walls, so I had plenty of scrap. I had at least 8" of foil board on the 2 attic doors.

2009 IRC: SECTION R807 ATTIC ACCESS "R807.1 Attic access. Buildings with combustible ceiling or roof construction shall have an attic access opening to attic areas that exceed 30 square feet (2.8 m2) and have a vertical height of 30 inches (762 mm) or greater. The vertical height shall be measured from the top of the ceiling framing members to the underside of the roof framing members. The rough-framed opening shall not be less than 22 inches by 30 inches (559 mm by 762 mm) and shall be located in a hallway or other readily accessible location. When located in a wall, the opening shall be a minimum of 22 inches wide by 30 inches high. When the access is located in a ceiling, minimum unobstructed headroom in the attic space shall be 30 inches (762 mm) at some point above the access measured vertically from the bottom of ceiling framing members. See Section M1305.1.3 for access requirements where mechanical equipment is located in attics."

"1st question, since I have bought CBU for the walls but all the how-tos for kerdi have them using it on sheet rock. Im still leaning toward CBU, but figured it was worth asking. " Good instincts to use CBU. For several reasons I recommend you stick with stick with the CBU. Here's a Kerdi over CBU ditty, it might help if you've never used Kerdi before. 2) "2 The ceiling in the shower. Initially, i was going to tile the ceiling, but my wife thinks it would look like a cave...I had several people suggest to me PVC Beadboard. Any other thoughts? " If a beadboard ceiling will fit the style, you can go in that direction. If you want beadboard but want to avoid the sterile look of PVC, how about teak beadboard? Or a teak plank ceiling. Wood can go well with marble/travertine. Then you can always fake wood on the ceiling with wood-look tile. Or go for a lighter look with glass tile on the ceiling, though plain glass can look cold and modern. Of those I listed, I'd consider teak boards. Natural stone and a natural wood? Why not? 3) L/1100 is plenty good for travertine. But you have to consider deflection in two directions; deflection along the length of the joist (your L/1100), and the often overlooked across deflection fo the plywood that spans the joist bays, in your case, across the 19.2" space between the joists. I recommend you consider two layers of plywood (3/4" subfloor and then 1/2" underlayment if able. If not 1/2", then 3/8" minimum. Ditra (or equivalent) over that. Then tile. Large format travertine demands a protective floor beneath it. 4) Your last photo shows a 1/4" thick to 3/4" thick sloped bed of "sandmortar and membrane". I presume "sandmortar" is deck mud? Mud generally requires a 1-1/4" thickness at the drain. You can go thinner, some guys ust an admix and go 1", some push hard to 3/4" thick. . But going to 1/4" thick, it may not provide a durable base to the shower; cracks, etc. Deck mud just doesn't have any structural integrity when placed that thin. Have you considered QuickSlope or one if its derivatives to establish your slope. I mention QS because it pretty much feathers down to nothing. I think it's an 1/8" thick at the drain end, it's honeycomb structure gives the bed structural integrity. which fits your low-profile requirements. Going hybrid? It can be done. But I generally recommend staying within a company's product line and avoiding "hybrid showers" unless the hybrid version has been warranted, ie, Laticrete's Hydroban membrane with Schluter's Kerdi Drain. Enough for now. Got to go. I'll try to check in tomorrow...Oh, and I'm glad I didn't have to do that drywall. Fun fun fun!!