Is sound insulation according to DIN standard 4109 relevant for building permits?

Apart from the fact that the DIN is not correct, he must have had a reason for it! And I would be glad if railway tracks nearby comply with this DIN.

The regulatory overzealousness of the authorities is sometimes really exaggerated. If the builders want to season their own soup, that’s their business. Noise protection glazing will certainly be included. Probably it’s just some piece of certificate missing, for which you pay a lot of money again for nothing! (no equivalent value). If the construction company is supposed to guarantee building according to some DIN higgledy-piggledy, the company will charge a surcharge, for the stupid case that someone complains at some point. The customer pays tens of thousands of euros more, even though nothing is built differently. Consequently = money thrown out the window.

I have been a "silent reader" in this forum for a long time, but here is a man of the profession. In this (admittedly somewhat older) thread, outrageous statements are made that simply make my hair stand on end, which I cannot leave uncommented...

My question would now be whether this DIN 4109 actually applies here, since it actually only regulates sound insulation for apartment buildings, terraced and semi-detached houses, and single-family homes with granny flats.

DIN 4109 regulates sound insulation in building construction. Both between different residential units of an apartment building/terraced house, and, now here it comes, sound insulation against external noise.

as you already say, DIN4109 is only intended for apartment buildings, as it basically specifically concerns noise protection for neighbors.
the authority is then right if, before purchasing the property (e.g. in the development plan), it was already clearly regulated that DIN4109 applies to all houses.

No, no and again… no. DIN 4109 is a recognized rule of technology and introduced by building regulations, thus defining a minimum standard for sound insulation that must be compulsorily observed. However, the recognized rules of technology always lag behind scientific and technical developments, so that DIN 4109 (which describes the state of the art at the end of the 1980s) can nowadays really only be seen as an absolute, by no means to be fallen below minimum standard. According to a Federal Court of Justice ruling, the term sound insulation must not be used here!

We are aware of the noise disturbance and are also taking sound insulation measures, but we will probably find it difficult to achieve the values from DIN 4109.

I have to ask: Who is building this? A general contractor who cannot meet 4109 does not exist! The requirements are so low that with today’s state of building practice, not such a bad build can be made. And here it is... precisely because the requirements of DIN 4109 are already extremely low by today’s standards, there has been a Federal Court of Justice ruling for about 10 years, according to which compliance with 4109 is no longer an indisputable proof that construction services are proper and free of defects! For reasons of legal certainty alone, nowadays no developer will build a residential house near the tracks for you that does not at least meet the stricter characteristic values of Appendix 2 of DIN 4109. These can also be easily met without any additional effort with today’s state of building practice!

I constantly deal with such people who conjure up some DIN and then demand this, although this was not contractually agreed beforehand.

Complete nonsense. A state of the art does not have to be contractually agreed. Such must be complied with. If not -> defect.

DIN 4109 is undisputed and is to be regarded as a generally accepted rule of technology ... also in ordinary single-family house new construction.

The only reasonable answer in the entire thread.

Sorry, just my2cents...

So then we will get back in touch once again. Apologies first and foremost for being laypeople and asking questions. I thought that’s what forums are for, anyway.

We have now had a paid expert report created, which has shown that our soundproofing measures lead to significantly better values than required.

The report was submitted and the approval granted.

I am providing legal assistance to MayrCh here and agree with all points.

According to case law, the entrepreneur is presumed, unless a higher or lower standard has been agreed upon, to implicitly commit to observing the recognized rules of his trade (in accordance with the "generally accepted rules of technology" - see also § 641 a III 4 Building Code regarding the completion certificate!), as they may be set out in the rules of the craft, DIN standards, European standards, accident prevention regulations, building regulations, VDE regulations, etc. (BGHZ 139, 16).

The entrepreneur must prove any favorable deviating agreement in case of dispute (and inform the client sufficiently of any deviations in the execution, for example, and also prove this).

The relevant rules are those at the time of acceptance.

Reduction in value or suitability are no longer prerequisites for a defect (as was still the case in the old version of § 633 Building Code).

The Federal Court of Justice has stated sufficiently on the minimum sound insulation according to DIN 4109. At the BGH, you won’t win any prizes with that anymore.

We have now had to commission a paid expert report, which showed that our soundproofing measures lead to significantly better values than required. The report was submitted and the approval granted.

As above, since the DIN standard only appears minimalistic there and the "more" can therefore be achieved relatively easily.

Then everything is fine - and hopefully everything will be sufficiently quiet later.