Insulating a suspended floor over cellar

[Robbie1980]

Hi,
Looking for some advice on how to insulate the underneath of the floorboards.
As per the pics, there is a coal shute which comes under the downstairs toilet. Cold air comes into the cellar which is regulated but still leave a good air flow. All the cold air though goes underneath the downstairs toilet flooring and makes the room freezing and drafty.

I know I need to insulate the water and heating pipes, but what should I use between the joists and how should I secure it? Rockwool? Board? Which types? How much thickness?

Any advice welcome,
Thanks
Rob

 

[Wayners]

Not my area but I'll give an opinion.

This is one way

Or 50mm kingspan with a foam gun if needed with wood to hold it in place.
The kingspan will make it air tight and the foil coating will be a moisture barrier