There are a lot of existing houses which have some rooms smaller than current laws allow, and they often make a lot of sense.

I can have my two kids share 100sqft room (10x10) but two 50sqft (5x10) rooms in the same space would make everyone happier and they're young enough that they don't need a big room.

A 5' wide room is _really_ pushing the limits of what a space can be used for -- you can't even place furniture on both walls and that's less than 2' from the side of a twin bed to the wall. I mean sure, you can use it, but it's _extremely_ limiting.

Yes, a 5' (1.5m) wide room is more a corridor than a room.

Only to give you a data point, in my country (Italy) norms require (since the '70's):

1) at least 9 sqm for a bedroom (for 1 person, 12 sqm for a double), rooms below 9 sqm in size can only be "studios" or "storage" or similar (at least officially)

2) at least 28 sqm total size to have the dignity of "flat" for 1 person or 38 sqm for 2 people (i.e. anything below 28 sqm cannot be registered as living space unit and while you can of course have two people living in a 28 sqm it is not "legal" , more generally, to be "legal", you need 28 sqm for the first person and additional 10 sqm for each other person resident in the house)

3) 2.70 m height for any room where people may stay for long periods of time (i.e. exception made for corridors, closets and bathrooms that must anyway be 2.40 m)

4) at least one bathroom of at least 4 sqm for each unit

5) a window or similar that must be at least 1/8th of the surface of the room (again excluded corridors, closets, bathrooms) for light and ventilation

A 10x10 room can’t be split into 5x10 rooms.. need some space for the wall in between.

Then you have two doors, and the space those doors need. Two windows for emergency exits.

Sure. But even if you handle the windows, doors, and have 3.5" for the wall (2x3 partition wall with half inch sheetrock) it's still i prohibited.

They are unnecessarily restrictive in my opinion. Why can't developers build 100 sqft bedrooms with shared bathroom/kitchen areas? Or more communal living areas? I can assure you that if you built something like that anywhere between SF and San Jose, there is a price at which those places would have full occupancy, and it's almost certainly over $800/mo, probably even $1k/mo.

I agree that height restrictions are a much bigger contributor to the lack of housing, but preventing dorm-style living seems to have little utility aside from preventing poorer people from living in your area.

> Why can't developers build 100 sqft bedrooms with shared bathroom/kitchen areas?

They have in the past. They were tenements, projects etc. Most have been torn down and a vow made to never do this again.

Look at places like Hong Kong and other big Asian cities today, to see what high density living looks like. It can be good but often isn't.

Most historic small roomed dwellings were not dismal "never again" tenements. Until zoned into illegality in the mid 20th century, tiny room SRO hotels and boardinghouses for middle and upper class people were common:

https://publishing.cdlib.org/ucpressebooks/view?docId=ft6j49...

Many people don't want to cook or clean. Many people don't want or need a living room or a private bathroom. This does not necessarily imply that these people must live in horrid squalor.

I grew up in a tract of suburban houses which typically had two 9x10 bedrooms plus a larger bedroom. Two twin beds could be stacked in one of those rooms. These totally-not-exploited people shared the rest of the 1300 sq. ft. house. So I think that small bedrooms in one place do not equate to small bedrooms in another place.

I respect the folks who try out tiny houses. It’s hard for me to picture them having a happy time or if they do maybe when they accurately document their experiences I will have a better idea of what I really need, which might still be a 2500 sq. ft. McMansion, but maybe not.

My 'apartment' when I was at university was 100 sq ft with 3 apartments sharing a bathroom and kitchen area. Sure I wouldn't have wanted to live there forever, but for the 2.5 years I was there it offered everything i needed, and it was 5 minute walk from campus and a ~20 minute walk to downtown. I also had the choice of a real 500+ sq ft apartment 30 minutes by bus from the campus, but I never even seriously considered swapping.

I agree 150 square feet is a bit high for a minimum. Where does that apply? In NYC, the minimum is 80 square feet.

Edit: according to this article, the regulations used by 90 percent of US communities allow 70 sq ft. https://www.hunker.com/13711464/building-code-requirements-f...