My dad built a house like this for his parents when my grandfather's health started to decline. It was a 2 BR, 1 Ba house with one walk-in closet, and a small LR with one wall kitchen.

It was probably a little larger than 20x20, but not much,
(maybe 22 x 22 or so). It was helped by the presence of a screen porch and a garage with storage.

My grandparents and great Aunt lived there, followed by my cousin, his wife and his daughter, and it seems to have worked out for everybody.

There's a 15' x 20' cottage on the street where I grew up. It was a garden shed for a larger home and then split off into it's own parcel sometime in the early 50's (as was the separate carriage house, barn, and "summer house" which were all larger, some substantially so). It's interior is studio style, with just a living space and only a private bath. Nothing but a small coat closet.

The gentleman that lived there was the neighborhood handy man and had a van and enclosed trailer for his tools and extra storage. He didn't need to dress up for his work and had minimal amounts of clothing. Also, he hardly ever did any more cooking than using the outdoor bar-b-que to grill a steak. It seemed to meet his needs well. Until he got a girlfriend. They moved within 6 months of that happening.

That was in the mid 60's, and it's been a rental ever since and the neighborhood has really gone down, but my 90 year old mom just won't move. I was in the neighborhood recently after bringing my mom home from some medical tests, and it's still occupied. My mom says that it's the brother of the guy who bought the barn house from the original estate. It seems that he is mentally disabled enough to need to have a bit of supervision, but independent enough to want his own place, so win/win for both.

Not to be sexist, but I can't imagine a woman being happy in such a small home unless she has a job where she wears a uniform and doesn't have any hobbies and never wants to have guests over. There simply isn't any storage for anything or space for any extra people at all. Heck, today, it might be more the man who has a "public facing" job where he has to be fashionably dressed, and so even a man might find the space too limited. Gone are the days when one blue suit, one gray suit, and a linen blazer for summer was all that was needed in a man's wardrobe.

I think tiny homes could be a wonderful option for people in mild climates (who can use the outdoors as living space much of the year).

Verify that is size is doable in your municipality. In some areas, there is a legal minimum size.

We currently live in about 860 sqft old country house, which isn't what you are talking about in the 400sqft range but feels it for a family of 4. We are currently building on the same farm but plan to keep the farmhouse for in laws and also plan to build a small space with garage for aging parents. I'm in favor of them and you can make small spaces work if you have the desire.
Jen

Our town has a 1500 sq ft minimum.

For a tiny home, this one was especially well appointed....lovely for any size home.

Here is a link that might be useful: Tiny home

You can live in a very small space if you live alone. Add a spouse and 2 children and you would need to wear hockey pads.

Up to a certain age children bounce off of you; when you start bouncing off of them you need more space. I know this well because it happened to me and to most of my clients.

I started a 20 x 20 house in Vermont and added 6 ft to one side before the roof was on.

So, even if you decide to build small, design for a future addition and use materials than can be easily removed and reused. No one can predict the future.

I'd love a small house, just not such a "tiny" house. :)

I'm really hoping that Mr. Bird and I can afford to build a second home of about 600 square feet somewhere near the grandkids for several months of the year. I'd be very happy with a small bedroom, bath, kitchen/living area, and a small office area for work.

My mom has a home just over 1000 sq. ft. and I can't imagine going much smaller. She does not have a garage (just a little storage shed) and we have 5 months of winter!

As mentioned earlier, maybe if you 'lived' outside most of the year...

I think that if you want to live in a really small space, it might make more sense to get an apartment in the city, and then you could use coffee shops and parks as extended living areas when needed.

I think a big part of it depends upon your climate, too.
I have friends who have a house on a bay, and the house itself is very small with captains beds that close off from a main room, a small kitchen and very small 3/4 bath. But the house is doubled in size by a screen porch that exends out over a dune and is surrounded by trees. It can be used for most of three seasons as the primary living space and slept in a good part of the summer.

If the house is in a place where you are trapped inside by excessive heat or cold, it could be a different story.