Please do not use gypcrete, the stuff is a nightmare for flooring contractors. I have researched this situation extensively and its not a good idea. Its just asking for trouble. Your building "inspector" needs some refresher courses in floor covering.
: PLEASE MAKE SURE what ever floor covering you choose is compatible with the gypcrete. Contact the manufacturer before you pour the gypcrete. As a flooring contractor I hate the stuff and my price automatically goes up when dealing with it. Its a major PITA. You can not accurately test the gypcrete for moisture vapor emissions. Most hard surfaces call for MVE tests. Most floor coverings can not be glued to gypcrete and keep the warranty intact. Its like trying to glue a floor covering to sand. We end up putting an expensive sealer on it that the adhesive companies won't warranty and have the customer sign off on it. If you are going to install carpet, plan extra budget for installation because every single tack strip will have to be screwed in with a screw gun until it hits the concrete. Ceramic tile will be a nightmare and will most likely fail in this application. Backer board must be screwed in with long screws to reach the concrete
: Having the gypcrete capping portland based concrete creates a whole slew of other problems as well. (as if that was not enough) If ANY water vapor comes through the slab and hits the gypcrete the chemical composition of the portland and gypsum together creates a crystal called etringite. Basically it blows the gypsum crystals up to 810 times their original size. Think the floor will stay put with that under it????? You'll be peeling it off the ceiling!
: If it were my house I'd go with the concrete. If you were my customer, I'd refuse to do it. Its a flooring failure waiting to happen.
: FYI, here's the waiver I put in for my last customer asking me to install a floor in this situation. She ran like the wind. Some poor uneducated installer with no experience in this situation most likely is eating this floor right now for breakfast lunch and dinner.
: WAIVER: Customer assumes all risks associated with pre existing conditions to gypcrete subfloor installed over slab including but not limited to ettingite crystal growth (calcium sulfo aluminate) gypcrete or slab de-bonding, breaking up, expanding, cracking, pulverizing, heaving, or otherwise changing original position, hydrostatic pressure & mold growth. Customer is aware that floor can fail if the above conditions arise and holds Best Laid Floors harmless in that event.
: Penny wise , pound foolish. The gypcrete floor's a whole lot cheaper, but fixing the problems it can create will be 5 times the price of a real concrete cap. What kind of "tile" are you installing? How high do you need to bring up the floor? Can you use a "sleeper system"? Can you use a portland based self leveling cement? Anything is better than gypcrete in this situation.