Is anything actually required in a home bathroom, or is it all optional?

This question gets two wrong answers, and they point in opposite directions. One is that accessibility standards are the law and everything must comply. The other is that because they are not the law in a house, nothing is regulated at all. Both are wrong, and the difference between them is worth understanding before signing anything.

Accessibility standards, and where they stop

Standards of that kind are generally written for buildings the public uses, on the assumption that the users are an unknown population. A private house is usually not such a building, so they do not apply to it as law, and nobody will inspect a home bathroom against them. That does not make them worthless: they remain the most carefully considered set of dimensions available for this kind of work, and the sensible use of them is as a starting point to be adjusted for the one or two people who will actually use the room, which is the argument in the article on standards in a home.

Plumbing and building codes, which do apply

Anti-scald protection on a shower valve, waterproofing behind tile, drainage falls, ventilation, and electrical work near water are governed by the code your jurisdiction has adopted, and they are not optional whoever is doing the work or why. A level-entry shower in particular involves the floor structure and the waterproofing, which is exactly the territory codes care most about: recessing a subfloor between joists is structural work, and the membrane over it is the thing standing between a bathroom and the ceiling below. Where each of those falls in the order of a build is set out in the installation sequence.

Rented and shared buildings are different

A tenancy agreement, a freeholder, a condominium board or a housing association can each have its own permission process for altering a bathroom, and altering a common wall or a shared stack is frequently a separate approval again. People who assume a flat is treated like a house find this out late, usually after a contractor has been booked. Ask early, in writing, and ask specifically about the floor: a level-entry shower in an upper-floor flat touches the structure between two households, and that is the alteration most likely to need permission.

Funding conditions are their own set of rules

Where work is being paid for in whole or in part by a scheme, the scheme usually attaches its own specification, its own approved list of contractors and its own inspection, and starting the work before its assessment has happened can disqualify the whole claim. Those conditions can be stricter than the building code, and they are contractual rather than legal, which means they are negotiable in a way a code is not. What genuinely exists, and what does not, is discussed in the article on free installations.

What a contractor should be telling you

Which parts of the work are notifiable or inspectable where you live, who arranges that, and what documentation you receive at the end. A quotation silent on all three is not cheaper, it is incomplete, and the missing piece usually surfaces years later when the property is sold and a solicitor asks for a certificate nobody obtained. Ask for the answer in writing on the quotation rather than as a reassurance on a doorstep.

What to verify yourself, and how

Which code edition is in force, which amendments your jurisdiction has made, and what applies to your building type are questions with local answers held by the local authority. Nothing on this page substitutes for the rule in force where you live. The one general point that survives every jurisdiction: the requirements attach to the construction work, not to the accessibility of the result.