Hello Finch,
I first join the others and also have a strong tendency to say: "Buy it."
The main reason is that when selling within the family, you could assume that you not only get an attractive / fair price but above all are not being deceived regarding condition, technical / legal / neighborhood problems, etc.
However, as long as you don’t provide us with photos and plans, we can only comment on this with rough (and apparently consistently positive) assumptions.
One thing upfront: In a comprehensive renovation of a semi-detached house, the character of both halves must remain similar afterward. This criterion is interpreted extremely differently by building authorities. Sometimes not even a sarking insulation (let alone dormers) is allowed, sometimes the one half ends up visually having nothing in common with the other.
Regarding living space:
It was already mentioned that you might gain some space with dormers, maybe also with a small extension. But even with 100 sqm, in my opinion, you can live well with 4 people if you adapt the layout accordingly. You have to give up the fashionable concept of "open living," which, in my perception and after Corona, is on the decline anyway. It is important that every family member has retreat spaces. To illustrate: 2 children’s rooms with 10 sqm each are much more valuable than just one with 20 sqm. This also applies to other rooms (home office, etc.).
Here in the forum you will certainly get valuable tips for the best possible use of space after you upload a first draft of your intended floor plan.
I’ll summarize what construction issues I have encountered with houses from the 1930s – and will organize this according to “fixability”:
WELL fixable within a core renovation:
1) unsuitable floor plan
2) lines (electricity, water) not running in installation corridors
3) asbestos was barely used in the 30s but often found in later conversions.
4) damp basement (often built directly against the earth without waterproofing)
5) roof in poor condition
6) poor energy performance
7) roots of old trees grown into masonry or sewage pipes
8) badly documented house, especially (but not only) due to subsequent changes
POORLY / NOT fixable:
a) weak sound insulation to neighbor, probably 24 cm partition wall (possibly even thinner). Facing walls help a bit (especially if the neighbor cooperates and installs them too), but against continuous components like beams there is little you can do.
b) wooden beam ceilings with their typical problems (poor noise protection from upstairs to downstairs, vibrations, sometimes creaking)
And finally something positive: Such a house has a soul. This can never be achieved with a new building.
Great post. Thanks for that.
Dormers are already on both sides upstairs, so the potential is exhausted.
I would very, very reluctantly consider an extension. The semi-detached houses stand five times side by side like this (originally built for mining employees here), some have extensions – unfortunately, I find that looks like trying too hard and failing. Very patchy in places.
I would try to preserve as much as possible of the building’s origin. And since it is Grandma’s house, where Dad grew up, it is also somewhat a matter of the heart not to change TOO much of the original.
Regarding your individual points:
1) hopefully solvable with steel beams
2) we hope to create some kind of installation shaft next to the chimney flue
3) the building is still in its original condition, so there SHOULD be no asbestos
4) Unfortunately, I also suspect there is no waterproofing and that may still become a problem...
5) new
6) We want to get the maximum possible in a cost-conscious way – basement ceiling, roof with sarking insulation, windows...
Regarding the heating, we’re still at a loss. A functioning oil heating system, not that old, is installed. Of course, that has no future...
The idea is first to reduce consumption as much as possible through renovation measures. Then to rely less on oil by adding heating systems (domestic hot water heat pump, photovoltaics). But as I said, I really have little knowledge about heating.
7) Should not be the case
8) Documents are currently being gathered, and we would also have to inquire at the building authority. To our knowledge, there should have been no subsequent changes...