R303.3
R303.3
OK....code number?
I have not heard of the light and fan having to come on at the same time.
That is probably because the jurisdictions you work in do not enforce a requirement. The mechanical air circulation is a UBC, MBC, and IRC requirement for interior bathroom venting code for methane and moisture exhaust. There are options such as installing an operable interior skylight or operable window on an exterior wall. Like leading a horse to water, the ventilation and light switch does not need to be turned on when using a bathroom but it needs to be installed.
The sequence of cascaded switching or a single switch requirement fulfills both national and local code enforcement for safety and health reasons. Check out the above books, I do not have the latest. I am sure most residential home buyers won't be peeing in the dark and lighting a match to clear the methane out. The above code books are available to electricians and contractors on most any construction webstore on the internet. Contractor City is a good source.
On a side note, first hand experience of submitting many house design plans to various building departments has not once required the switch data on the drawings, but on final buyoff, the switching combination has been a requirement from seasoned building inspectors in at least six left coast states I have worked in. rbj