Heat pump upstairs and infrared heating in the basement? Does that make sense?

The building has 2 full floors and a basement. The ground floor and upper floor are to be built with Y-Tong without additional insulation. A underfloor heating system with a heat pump is planned here. But now there is also the basement which is cast as a white tank and is completely underground. The question is how cold does such a basement get over winter at all when the floor above is already heated through the floor? Is underfloor heating necessary in the basement as well since the basement will be fully developed as a granny flat? Or could maybe an infrared heater already suffice in the basement? Since the concrete can absorb more heat, I could imagine that an infrared heater could work very efficiently here and be completely sufficient. On the other hand, an underfloor heating system here might not have to heat that much anymore? Does anyone perhaps have experience with this?

Infrared element is only useful as an additional heater (e.g., if the design in the bathroom was messed up), or for very, very rarely used rooms.

Either the basement is INSIDE the thermal envelope, then please equip it with properly designed underfloor heating. Basement outside the thermal envelope then does not get any heating at all. Exception: You want to temporarily raise the temperature in a basement room somewhat, but only a few times a year. Then you can use infrared again.

For a granny flat, I would install the underfloor heating as well. Infrared is okay, but I wouldn’t want it as the sole heating source.

But now there is also the basement which is being concreted as a white tank and is completely underground....being fully developed as a granny flat.

I just don’t understand how that’s supposed to work.

I don’t understand how this is supposed to work.

What exactly? A granny flat is being put in the basement. There is a vestibule with stairs down and behind that is the actual hallway. Two separate apartments. And one is simply in the basement.

Now there is still the basement which is being cast as a white bathtub and lies completely underground

Basement apartment in the basement, which lies completely underground ... doesn't the basement apartment have any windows??? That is the question everyone is asking here.