Insulation on 1st floor Hollowcore slab. Yay or Nay?

glashanator

Putting in Radiators upstairs.

Have 150mm hollowcore slabs. slabs are wrapped at ends which continues airtightness from ground floor to 1st floor.

In my eyes, the hollowcore slab is inside the AT envelope of the house.And so like all internal walls should heat up to the temp of the house eventually, and become a thermal store.

So here's the rub.......

The common conception b4 screeding upstairs is to lay 50mm insulation on the slab, then screed over it.
This makes perfect sense to me if it was " UFH " as you'd want to reflect any heat you put into it away from the slab and into the room.
But with rads this is surely different......... There is no heat loss to worry about thru the slab cos as said b4, the slab should be the heat of house internally.
Surely the screed and slab should both be the same temperature if together...... and is there even an argument to say the insulation in this case may actually be hindering the thermal store built up over time from the slab, and into the room.

Maybe I am missing something here, whats your opinions on this and has anyone else had these thoughts or went ahead without insulation on 1st floor.....

I'm not against the floor being insulated and can do so still..... just not convinced its super important in this part of the house.

Thanks

4Sticks

If no ufh no need for insulation