Decision house purchase: Existing property or new construction?

Difficult altogether, especially in today's times. But where I must vehemently disagree:

my partner and I have been searching for a suitable property (single-family house) in our place of residence for quite some time.

That is very good, stick to it. Many searchers make the mistake of expanding the radius and/or softening the requirement profile.

I actually see it as one of the most fundamental mistakes to push your search into a corset and be completely inflexible. You can search for years and find nothing, but right next door, just outside your search radius or town border, is your dream property. Apart from the changed postal code and new home address in the navigation system, there might be no significant changes.

Is it even possible to carry out such a renovation on your own, or is an architect absolutely necessary to coordinate all the trades, who of course also wants to be paid? How does an average Joe approach such a project?

Average Joes often find many things that do not require a building permit and "save" themselves the architect along with the inventory assessment, just award contracts blindly and get surprised behind every approved covering. That is the best way to constantly pour money in. I wouldn’t take "an architect," especially not a "new builder" with "service phases 1 to 4." A practitioner with extensive experience in existing buildings, fully mandated, is a good investment here. But first, show more details.

Here is a current example from a user who is renovating everything:
Or here from another one:

Oh, there is also this extensively described example from

I find it to be one of the most fundamental mistakes to squeeze your search into a corset and be completely inflexible. You could search for years and find nothing, but right next door, just outside your search radius or town boundary, your dream property is waiting.

No, not a corset. It’s about not constantly widening the search radius analogous to the desperation level due to lack of success in hunting and/or becoming "willing to compromise" up to the scrap limit. Focus (and if you want "Tsjakka!") rules.

If you do everything from scratch, you also have the complete finishing costs. Roughly estimated at 1500-2000€/sqm. And that results in the total sum, depending on the specific scope and own contributions. But with 250k including incidental purchase costs, you can definitely take the existing property. For 450k you won’t get a new build including land and outdoor facilities, certainly not with a basement.

Probably not for 450k, but definitely for 500,000 euros (according to statements from a builder), but of course without a basement.

The average consumer often finds many things that do not require building permits and "saves" themselves the along with the inventory survey, simply assigns carelessly and lets themselves be newly surprised behind every accepted cladding. That is the best way to constantly pump in money. I would not take "an architect," especially not a "phase 1 to 4" new-construction architect. A practitioner with extensive experience in existing buildings fully mandated is a good investment here. But first show more details.

So that means, I’d best ask a building surveyor who is familiar with energy-efficient renovations and ask him for a cost estimate?

I still have a few questions regarding the construction description of House 1. Maybe you can draw conclusions from it regarding the condition and the quality of the materials used.

Foundations: gravel-stamped concrete B 80

Basement:
Exterior masonry: 30 cm limestone sandstone masonry with a 12 cm cavity
Interior walls: 24 cm or 11.5 cm thick limestone sandstone
Floors: base concrete 10 cm
Insulation: horizontal insulation 500 bitumen felt vertical insulation of exterior masonry "inertol coat"
Ceiling: reinforced concrete

Ground floor:
Exterior masonry: 30 cm hollow masonry, outside hollow brick, inside limestone sandstone
Interior walls: 11.5 cm limestone sandstone
Floor: wood on sleeper beams
Ceiling: reinforced concrete
Interior plaster: lime plaster

Attic:
Exterior masonry: as ground floor
Interior walls: as ground floor
Ceiling: collar beam layer with rafter boarding, between 1500 g/m² mineral wool as insulation
Plaster: as ground floor, roof slopes 2.5 cm thick lightweight boards + plaster
Insulation: between beams and rafters 1500 g/m² mineral wool boards
Roof: 51° purlin roof
Base: facing strip

Can you draw conclusions from this about the quality of the materials used and e.g. about the question whether, for example, blown-in insulation would be possible in this house?

For 450k probably not, but for 500,000 euros definitely (according to statements from a builder), but of course without .

Plot plus house plus incidental construction costs plus outdoor facilities? Builders like to pass on various costs to the client. Utility connections, construction preparation,... outdoor facilities, garden house, carport are always the responsibility of the client. 500k all-in is already quite tight.

So, I should best ask a building surveyor who is familiar with energy-efficient renovations and request a cost estimate from him?

I still have a few questions about the construction description of House 1. [...] Can you draw any conclusions from this about the quality of the materials used and, for example, whether blown-in insulation would be possible for the house?

We can only do that to a very limited extent, and certainly not that detailed based on text alone. It requires text, pictures, plans. Afterwards ...

So, I should best ask a building surveyor who is familiar with energy-efficient renovations and request a cost estimate from him?

... you go to the property accompanied by an expert. Once you have purchased one of the properties, you hire an architect for the planning – as mentioned, one with relevant experience. You proceed with them at least through service phase 5, preferably 8. So basically like my "A house construction roadmap, also for you: the HOAI phase model!", only of course without decisions (but maybe still with the resting phase) between modules A and B.

I am the person mentioned above who wants to carry out a complete renovation and has already gathered some information. According to my architect, a complete renovation costs about 2500 euros per sqm. In the end, you strip everything down to the foundation walls and rebuild everything new.

I can only speak for my project (linked above) – with the complete renovation of my property, I am cheaper off than buying a plot in a new development area and building a new house. But maybe that is also because I am getting the property at a low price.

In the end, you have to see what you can or want to afford. Planning a new build is always better because you can determine the layout from the start. But most new builds are simply too expensive. In our area, I can’t get a new build under 700,000 euros... and that’s for a plot of at most 300 sqm.