I own a 200 year old cottage. It has a LOT of mass. The walls are a meter of stone, and the mortar is lime. The thatched roof is about 1.5 meters of straw.

It's REALLY COLD. Keeping it warm takes a huge amount of energy. I've removed some of the modern Portland-cement based render and replaced with lime mortaer and that at least helped with damp (it breathes a bit) but it's still really cold.

Once you _do_ get it warm, though, it does take a while to cool down. Similarly, it can be quite warm outside and still take a couple days for the cottage to properly warm up - there's a lot of thermal inertia.

The extension to it, built last year, uses 70x200mm (about 3"x8" in inches) studs, and has 200mm thick Rockwool insulation throughout the walls and in the roof. The windows are triple glaze. I heat the extension with less energy than the cottage, and it's 3 times as big and 5-6 times as much volume, due to the higher ceilings.