Inter Sacrum Saxumque Stare

There's generally going to be rooms dedicated to and build for warmth, the living quarters, both for nobles and their servants. This will be the central living tower, or parts of it called a Kemenate (literally 'room with a stove'), the great hall and work spaces around the kitchen. You can put the Kemenate on top of the hall to catch the big fires' and daily living's heat through the wooden floor, but you often can't put wooden stuff on top of the kitchens (that's a fire risk). If you have the money and space, you build a whole separate comfy place for living because you don't have to stay in the most defensible part of the castle all the time. These separate living buildings are also called Kemenate and are often build from wood, cob, brick etc.

People used to wear much more clothes indoors, including while sleeping, and those clothes were much thicker and sturdier than what we largely wear today. Every time you think of how cold those stone walls are, think about everyone wearing a linen shift + two-ish layers of wool on all body parts except hands and head + stockings and shoes + some kind of head-covering. In Ye Old Middle Ages, women are probably wearing a wimple, which is kind of like a modern Hijab in terms of coverage. People wear shifts, socks, and a head-covering to bed.

I think people used to radiators also really underestimate how much a large open fire/tiled stove heats up a room. Also, middle and northern Europe (as well as parts of Northern China) had and to this day have beds and benches build into tiled and cob stoves. Those fuck.

Beds are enclosed so you stay warm in them, either by curtains, in wall niches or with wood. There's also a type of bed that's inside a chest (like a coffin) so you can stuff your stuff inside during the day and put down the lid to use it as a bench. That's also another reason for people to always sleep in groups. Depending on the era, one of the jobs of a lady's maid or a retainer might literally be warming their master's bed. In early times and among servants, people also sleep in large groups in rooms together in general even outside a farming context, often with animals like pet dogs, too, which further warms everything up.

Walls are not bare, cold stone, but covered with a layer of plaster or cob, tiles or wooden panels, sometimes layered, and believe me, this makes such a difference. Source: I lived in a Ye Olde German Farmhouse with 70 cm thick stone walls and flag stone floor and all that converted to modern flats for a while.

On top of that you hang tapestries on the wall, which are not like modern printed cloth but basically wall rugs, sometimes several inches thick, and rugs or rushes (like a light cover of hay) on the floor on top of stone, tile, wooden panelling or a cob floor cover that goes over the heave flag stone. Pillows and blankets on all sitting surfaces, often on top of panelling (in the case of benches build into the stone). The roof of a room is also tiled, panelled or plastered. Upper stories will generally have wooden floors. Stories in a tower heat each other upwards, so the nicer rooms are further up.

The inner stone walls of a castle, even if stone and very thick, will heat up a few degrees in comparison to the outside walls if the castle is continually heated/lived in, and also trap heat inside, and this will make a difference. Inner walls might also be thinner and made of wood, cob or brick. You're defending against the outside, after all.

You put stuff in the windows. Holy shit. Screens of wood, horn, cloth or leather/hide, often treated for extra insulation. Why are these fantasy castles all so drafty.

This is a spot from an italian estate agency (we are governed by the right-wing party)

The woman says "Ridiculous..."

The old lady is not in her home. She is at work. She's meant to be what in Italian is called "la portinaia", aka a cross between a doorwoman and cleaner of a residential building. She's in her small "office" space, at the entrance of the building, from where she can survey the coming and goings of the inhabitants. It's a job that has mostly disappeared, but is culturally very clear to us as having the connotation of "potentially gossipy, one-million-percent judgmental woman who sees everything that goes on in the apartment complex, knows everyone and their secrets, and has Strong Opinions™️".