Thanks for asking and for your kind words.
Curb height, is answered different ways on the internet, not always by people in authority or willing to mention their professional or trade licenses, and it is confusing. I understand enforcement, interpretation and local codes may be inconsistent.
Disabled people, and any of us could be, temporarily or permanently, are often limited or excluded by curbs, which others easily step over. I am not a lawyer, architect, or engineer, but I expect where the ADA and other regulations conflict, it will eventually be resolved in favor of the federal rule.
The total height in this photo from the top of the drain to the top of the waterproofed threshold at the bathroom door is about 2.” It just worked out that way. If you need 2" in your bathroom, you can adjust the run and rise of your slope, and level of your threshold. It is not a curb, but I understand it satisfies the requirement in some areas, as written or enforced.
My licensed plumber reported it as “Ordinary Plumbing” in an existing house, because there was a fixture there previously, and my city can’t afford to send an inspector whenever a home owner replaces tile and fixtures.
As a practical matter, the entire bathroom floor and all walls are waterproof with Schluter Kerdi fabric membrane, more than 2” up, and more than 76” up in the shower. The threshold and the base of the door jams are also waterproofed. Flood water rising from a blocked drain and reaching the top of the threshold, would exceed the amount contained by a 2” curb, or a much higher one, if it were around the shower only.
NYC Code, last time I checked, still describes the two-stage, lead-pan system, but a plumbing contractor for the often expanding NY Methodist Hospital, recently told me he does not allow his employees to install lead in showers. Lead is poison. Two stage shower drains are obsolete (lead or vinyl) and highly problematic.
Exposing workers to lead, may expose contractors to litigation from them. I suppose, since it is in the building code, that may protect contractors from litigation from home owners regarding mold, ceiling damage, etc. To protect home owners, I explain why lead pans are hazardous and ineffective. If they still ask for it, I walk away, but they rarely ask.
Good luck on your renovation.