I am looking for a useful way to compare living space per household member, where adults and children have different weight-factors; similar to the OECD- and OECD-modified scales for income.
There is quite a lot of data out there, but it is scattered. A recent compilation has been done by the British Commission for Architecture and the Built Environment,
Interesting question - I was not aware of the OECD methodology (for all those who need a little help like me: https://en.wikipedia.org/wiki/Equivalisation).
However, I am skeptical regarding a different weighting of space for different members of the household. What is your hypothesis about that? You can imagine situations where children actually need more space then adults (e.g. parents with one child: one sleeping room for parents, while the child has its own room, rest is shared), but it can also be different and probably gets even more difficult if you want to apply the same weighting across different countries and 'cultures of housing' and e.g. say something about living conditions.
The point on "cultures of housing" is a good one... This is a true challenge.
But this might also partially be true for income - I do not know any exact numbers, but there might be significant differences in the relative prices of babyfood, toys etc. across different countries.
I think as a starting Point one could at least assume, that the overall dwelling size will most probably increase with a decreasing rate. Quite similar to the income scale (1st adult factor 1, 2nd to n adult factor 0.5, each child factor 0.3)