House size

I've read the advice that an amateur owner-builder should build small.

I am trying to design a house that stays under the 1250 sq. ft. threshold, because the law would allow me (or someone who buys this land later) to add a new, larger house to the property, and count the small house as an "ADU" (Additional Dwelling Unit, to be rented out).

1250 sq. ft. is not unreasonable for us, even as a family of 5. 2400 sq. ft. is the average for new homes in the U.S, wow!

The house we're renting is 1287 sq. ft., and we're comfortable. I wish there was another 10 sq. ft. around the laundry, and an actual second bathroom with sink. But there's also a long hallway that wastes about 60 sq. ft. and the back bedroom is way larger than we need. This house is not well-insulated, but the one I build will be, with thick cordwood wall, probably 16" thick. The county measures external square footage, which discourages insulation (I could get R-35 with 24" walls, like they use in Manitoba) but I won't make the 1250 threshold, and I will be taxed more. (That way of measuring makes sense when you consider the effect of a house footprint on a neighborhood.)

So, 1250 is doable without giving up much.  Could we go smaller? Many, many people live in much less space.

We make good use of all the rooms in this house. One bedroom doubles as my study. Another as Julie's. Another is where Reid goes to play by himself. I don't like how we split up in to singles like that, and the fact that we spend most of each day indoors in front of screens. I hope that when we are living in a house in the beautiful woods, growing much of our own food, we will want to spend much more time outside. For now though, I need to use this computer just to figure out how we're going to get there.

I also know we can add outbuildings. Anything under 120 sq. ft. can go up without a permit, so I could add a couple of those as needed. Like a study where I can really get away from everyone to do work for money. Or a sauna!