How do banks actually handle renovation & refurbishment costs in financing? Are these included in the financing value-enhancing (1:1)?
Renovation usually mostly yes, refurbishment no. So a completely new bathroom or electrical system would be fine. Old laminate replaced by new parquet, at most partially. Painting the walls, not at all. The calculation problem is that you are buying and paying for a functioning old property. The new electrical installation adds value, but not completely, since you already paid for the old electrical installation when you bought the property.
In the existing building, one would like to get rid of the old textured wallpaper and have settlement cracks and other untreated damages smoothed out and painted over with painter’s fleece.
That doesn’t really increase the value of the property. It just makes it look nicer.
Or renew the sanitary fixtures, re-tile the shower, etc.
Partially creditable.
Upgrade the terrace on the property and redesign the garden.
Here too, any increase in value is limited.
Does the cost estimate of the measures go together with the purchase price into the loan amount of a mortgage loan?
You mean that the purchase price together with maintenance (which is what most measures are) represent the value of the house and can be financed by the bank? Of course that’s possible, but then it would be a loan-to-value ratio well over 100% and correspondingly expensive. Good creditworthiness would be required. However, if the creditworthiness is that good, there should actually be enough equity available. In the end, nothing else is done in the purchase you described than what is done daily in older houses and rental apartments. Maintenance and cosmetic repairs. Not really value-enhancing.