Restore or remove glued parquet flooring?

Hello "Neckarweg". A blanket answer to your inquiry is - although one might be inclined to do so - not possible if one wants to answer you seriously. You do mention the year the residential property was built and that the parquet floor was sanded once 15 years ago, but nothing else. So we do not know whether it is solid parquet or multi-layer parquet (formerly called engineered parquet). Your hints point towards "gluing," which will certainly mean a higher effort when renewing the floor. The answer to the question "Remove and Replace - or - Refinish/Renovate" should partly depend on whether the parquet floor is made of solid wood (then it is almost always worth renovating the surface) or an older multi-layer parquet. In the latter case, the risk is simply obvious that the wear layer (back then <4mm) may unintentionally be sanded down to the middle layer during the next sanding (meaning: total loss) or that the glue bond may have loosened between the middle layer and the top layer due to aging. For old multi-layer parquet, the tendency is therefore towards removal. ------ An old solid parquet has a life expectancy of at least 80 years. The formation of gaps between the strips or boards is common and is visually neutralized by filling during a parquet renovation. Since it cannot be ruled out that the adhesive used in solid wood loses its bonding strength due to aging over the years, the loose-sounding strips (which you mentioned) should be checked to locate and assess the break zone. A master parquet layer can certainly judge this (although the neutrality of the statement could naturally be subject to some economic considerations...). -------------------------- Your question: "How do I find out if the floor can even be sanded again?" is not easy to answer for multi-layer parquet but important; for solid strips or boards, this would not be an issue at all. Let's put it simply: If it is an old, already once renovated multi-layer/engineered parquet, the risk of damage to the parquet due to the upcoming/planned sanding is unmistakably present for both you and the executing craftsman! ----------------- Best regards: KlaRa

If the room height is already only 236 cm, how can I get a nice wooden floor without losing too much room height?

By choosing either 2-layer or 3-layer multi-layer parquet plank flooring.
Both are suitable for gluing and are available in different thicknesses.
3-layer is rather used for floating installation.
2-layer is always glued.
Pay attention to the wear layer, which should be at least 4mm (can be sanded more often). The total construction height varies but is available starting at 10mm. For example, Haro offers: approx. 5mm wear layer, total construction height 12mm.

Can a layperson successfully glue down a [...] wooden floor?

If you don’t have two left hands, certainly. It is important to strictly follow the manufacturers’ specifications (adhesive, notched trowel, subfloor preparation, etc.).

If planks, then in all living rooms, but separately

Yes, as a rule, the expansion joints in the screed are also the joints that the parquet should have.

or continuous, basically in one piece

In my opinion, that should not be the case unless the screed has no expansion joints. Then it works up to a certain area.
The user can certainly say more about this as an expert.

That’s all from me for now.

The answer to the question "Replace and new - or - Repair/Renovate" should partly depend on whether the parquet floor is made of solid wood

Just because mentioned loose spots, I personally believe that the floor may already have "loosened" in several places. This can be determined. My experience has shown that if the joints are sealed again, they tend to be pushed out again over time. Certainly hard to judge from a distance, which is why it is clearly better to consult a professional who can assess the situation on site by inspection.