Bungalow with hipped roof, built in '62 - general questions before purchase

Hello everyone,

we have finally found a house that made it into the shortlist. Although I originally trained as an electrician, I have been out of the profession for at least 10 years. I can still do and know quite a bit, but of course, you can’t know everything about a house. I want to have as many things clarified as possible before I buy this property. For that, your opinion and knowledge are important to me. Of course, the house will be inspected once again by a building expert in the end.

Key data about the house as far as I know:
- Bungalow with hipped roof, built in 1962
- Entire roof from original build, uninsulated and not converted
- Masonry: pumice stone - air cavity 3cm - clinker (I think connected to the masonry with steel pins)
- Basement dry as far as first inspection shows. No musty smell, no visible moisture damage
- Electrical: original from build year
- Heating: oil condensing boiler from 2008 with hot water tank (Buderus), tank: 4700 liters
- Cast radiators, I think from build year
- Windows partly plastic, partly wood, single or double glazed

We would of course like to gradually improve the house to be as energy efficient as possible. I’ll write down what we’ve thought about. Maybe some of that doesn’t make any sense at all?!

Roof:
We’d like to fully convert the roof from the inside. A breathable membrane should also be installed. Since the battens need to be replaced and the tiles removed for that, I would also want to put new tiles on directly. I would have all that done by a specialist company (except for covering and ceiling). I would do the interior finishing again myself.

Walls:
Here I am totally at a loss as to what kind of energy efficiency can be achieved. The air cavity is only 3cm and is probably connected to the masonry with anchors. I was told that blown-in insulation brings little or no benefit. The steel pins would rather cause thermal bridges. As far as I know, the air cavity is not ventilated. What would be the best solution here? Tear off the facade and install ETICS? Or just leave it as it is?

Basement:
Is anything even possible here? The basement ceiling is too low for insulation. At some point, paint the basement floor.

Heating:
The house has no gas connection, but it is located in front of the house. I was told that heating with oil is not bad when the house is well insulated. With supporting methods such as solar thermal and a wood stove in the living room, oil heating can be almost as cheap as gas, as long as the oil price does not explode. Additionally, the system is already a condensing boiler from 2008. However, I don’t know much about heating systems. I only have Google knowledge.

Electrical:
Screw fuses without residual current devices, no question -> must be replaced.
Main connection box from build year
Electrical cabinet currently in the hallway. Planning to move it to the basement. That was my daily business 10 years ago... so no problem.

Windows:
A wild mix of original windows and "newer" plastic windows from the 80s. Due to insulation reasons, I would also go for triple-glazed plastic windows. Front door from build year.

So, do you maybe have some tips and advice here? Even though the price of the house is "okay" by today’s standards, I am worried it could become a bottomless pit. Of course, I want to do as much as possible without having the expertise to know what is really necessary and feasible. I am aware that such things are hard to answer without knowing the house. But maybe you can still help.

Thanks in advance.

Hello and good luck with your project! We read a lot of text here without photos etc. It definitely seems highly advisable to get a trusted person (civil engineer, architect, or similar) on site and perhaps, sensibly, to engage a construction supervisor on site. In my opinion, you will quickly make back the costs.