Should the attic be heated in winter?

Hello everyone! :)

I am actually a silent reader and have learned a lot from this forum, especially in the financing section. Thank you very much for this!

At the beginning of the year, I bought my parents' house (mid-terrace house, built in 1999).

The attic is converted into living space (there are 2 radiators in there, it used to be my childhood room). Unfortunately, it is unknown what insulation was used because we no longer have any documents about it and my mother doesn’t remember anymore.

In the attic, there are two Velux roof windows. These are also from 1999.

You can access the attic via a Samba staircase and a normal room door. So, I don’t think that there is much insulation between the attic and the rest of the living space (it's all kept quite open anyway).

The attic is currently completely unused, it is also (still) not used as storage because we still have a basement.

Now I am asking myself: do I have to heat the attic in winter? And if yes, to what temperature? I am a bit worried about mold...
There is no controlled residential ventilation system either, so I have to ventilate manually (is once a week enough?)

Thank you very much in advance for your answers! :)

Best regards!

You don't have to. You could just ventilate regularly. but: The door to the floor could warp, too great a temperature difference, and too much cold could also fall down from up there. so keep the room at 12-15 degrees C.

It depends on where the insulation is located, is the roof open and the ceiling insulated or is the roof insulated?

Hello everyone,

thank you very much for your answers!

Regarding the insulation: I can't say that right now... I would have to ask my mother if she still remembers.

What would be the difference? Does one require heating and the other not?

Thank you in advance and best regards!

If the attic is within the insulated envelope (which I assume if it is used as living space and radiators are installed), it should not be left unheated.
If warm, moist indoor air flows into the attic through open doors or door gaps, the air cools down. It can then no longer hold as much moisture, causing the moisture to settle.
That is exactly when you get mold.
The warped door mentioned by Nordlys is likely also a consequence when water condenses on or inside the cold door.

You can certainly calculate the temperature required to prevent condensation using the dew point. However, I am not the right person for that.