How do you regulate underfloor heating in a newly built first occupancy property?

I would say first wait and drink tea, you won't have to adjust much. The room thermostats are just emergency brakes. That means the control is done via the outdoor sensor for the whole house, and when it gets warmer outside, the heating won't go so high anyway that it becomes too warm, etc.

I would also set something about the desired temperature and wait for a while. Underfloor heating is very sluggish, so adjusting it up and down in the short term doesn't help much. In a multi-family house, you can only hope that the heating curve/settings are done properly, not on "more is better," then you might really need the individual room controllers. In a well-adjusted single-family house, they are really relatively superfluous. From on the go

I would set all the controls to 20 degrees and keep the doors closed for now. If you feel that the bedroom is generally too warm, set it to 17 or 18 degrees. In the bathroom or living room, if you want it a bit cozier, set it higher there. So set it one day, and the next day subjectively feel for yourself if it fits. Etc.

Regards

Hello. We already have an outdoor temperature sensor. So it is weather-controlled. However, I have an east-south facing apartment on the upper floor. And of course it is "warmer" than the apartment in the north or the one in the west. So the outdoor sensor switches on quite early to prevent anyone from having a cold apartment. Or does it make no difference to me how I have to regulate? Thanks

If the RTR in your room then measures 25 degrees due to solar radiation, while you have set a target value of 22 degrees, the valve will be completely closed anyway. To put it technically: The purpose of a control system is that it responds to variable disturbances (different solar energy input), unlike a simple switch.

I also live in a multi-family house with underfloor heating, supplied by a gas heating system. There is one controller per room. I have really brought every room to the desired temperature. And for 5 years I have hardly used the room controllers anymore. When it is very cold in winter, I sometimes set the living room a little higher. The room also gets a lot of sunlight and the underfloor heating does not heat when the sun has already warmed the room.

Compared to the apartment I lived in before, heating costs have decreased by about 1/3. And I am generous with the temperatures:
Office = 20 °
Living room = 21°
Bedroom = 17°
Bathroom = 24°

And that all year round. Even when I am not at home for several days. Or when I ventilate twice a day, etc.

Generous? That would be way too cold for me. Except in the bathroom, I need at least 2 degrees more per room.