Surveyors only do this for semi-detached houses because they assume that both semi-detached house partners know each other. At the very least, they create an incentive with the offered discount to catch up on this if it hasn’t happened yet ;)
This is offered to all neighbors who share the same property boundary. So also for two detached single-family houses next to each other. After all, every saved euro is welcome ;)
That’s why I asked... I also know that travel costs are sometimes shared... and there was nothing about semi-detached houses ;)