In my opinion dev should add some things.
- If we put 2 houses for 5 ppls next to each other we can upgrade it too 12 ppl version,
- similar to 5 ppl house, when we put 2 houses for 12 ppl next to each other we can upgrade it to the biggest one
Of course there's a little bit of bugs ( like textures one ) but it happend to me only 1 time.

You mean you managed to place a bigger house on top of two smaller houses?

[It can be a solution like the walls or a classic upgrade with material cost