Initial ideas for building a small house on a backlot

If out of ten two-person households with a 170 sqm building wish, the nine who cannot finance that (but can finance 50 sqm) all build a tiny house, you would need more area for building plots in Duisburg alone than the entire city of Tokyo is. Just as a little food for thought ... (I am usually rather peaceful, but I do like to poke into naive calculations).

That would only be true assuming that building plots are available in unlimited quantities. But they are not; their number remains the same regardless of what is built on them. Just as a little food for thought...

A tiny house is a trailer and not a building structure.

Now you are mixing up tiny house and mobile home.

You need more area for building plots in Duisburg alone than the entire city of Tokyo.

Not necessarily. You would simply have to allow building on 15*15 plots. Each with 5*10m up to 7*12m, or even tiny houses arranged like row houses. Special areas could even be designated for this, or existing areas could be densified. For example, in Hanover, 3 tiny houses (each 28sqm plus a small terrace and community garden) were built in a backyard – more are planned.

You are mixing up Tiny House and mobile home now.

No, I don’t think so. A tiny house is movable and definitely has at least 2 wheels underneath… call it a wooden shed on wheels or a glamour camping trailer with a max width of 2.50 meters. They are also permanently placed but still mobile. A mobile home is a solid 4 meters wide, transported with accompaniment and placed, often on foundations. Often the chassis remains underneath, but often not. The mobile home offers ample living space at 4 meters wide for primary residence, which can also be permanently connected with extensions. Believe me: I have the whole range in front of me right now. The one in #55 is a mobile home, not a tiny house ;)

… and yes, there are also tiny houses and specially designated settlements. However, it must also be said: the market relies on terms that are then interpreted flexibly, sometimes this or sometimes that. But I am not Google, nor am I in a position here to convince myself of something that works somewhere and therefore should work on this property… otherwise, you know how it is called here, where you can apply for lease land for "tiny houses" or those that call themselves that in Hannover or elsewhere.

It's simply nice to have a retreat sometimes.

I think it's really a matter of taste :) we have retreats in 60m2 and had them in 45m2 as well :D so we should be able to manage that in 80m2 too, even in 20/30 years. For us, accessibility is more decisive, meaning that everything is on one level.

30sqm living kitchen is very tight.

Actually, that's pretty perfect. We have 30m2 – about 18m2 kitchen + dining table and 12m2 couch, cabinets, and co. I wouldn't even know what to do with a 40m2 living kitchen :D and at least 2 cabinets in our kitchen currently hold file folders and guest bed linen. At least the file folders will go into the new office. Then we'll have a temporarily empty cabinet in the kitchen :D

What are real advantages/disadvantages for prefab construction/new build?