Cellar Roof in Victorian Cellar

[johnsnower]

Im looking to insulate the ceiling of the loft between the joists. The room is 4 x 4m has some airbricks in the walls (2 external with air bricks) and one has a window in which i leave slightly open for airflow.

 

So the question is how best to insulate?

 

Im guessing its PIR, if so any idea on depth?

Do i push it right to the floorboards?

Can i plastboard it out when done or best leave the joists open to breathe/airflow?

 

Thanks

[markc]

Hi, confused with the title and question. Are you looking to insulate a loft or do something with a cellar?

[johnsnower]

Hi sorry, its a cellar but the ceiling of the cellar.

[johnsnower]

Jpeg attached maybe that makes it clearer?

[markc]

Have to be very careful here, the previous owner of my house had put insulation between cellar and kitchen and it caused damp and rot in the floor and joists, I had to rip everything out and now heat the cellar and have no insulation at cellar ceiling. Result is a nice dry cellar and warm kitchen floor.