Will my new loft insulation ruin the loft joists?

[Bug-bugga]

In an attempt to reduce heat losses, i am replacing old loft blankets with celotex panels. I cut panels to fit exactly between the joists and also used foil tape to seal all the gaps - both between the panels and where the panels are touching the joists. Next, i want to lay Tri-iso insulation on the top of joists and board it all with chipboard.

This should create very good heat insulation but i am worried about the celing joists. They will be completely inslulated from the air (i.e. not vertilated at all), may this in some way trigger a rot or something?

My loft itselt is very well ventilated and Tri-iso 10 should act as a water barrier so i don't expect any water to reach the joists from the loft side.

Can please someone tell me if i am doing right or wrong? I stopped the works after these worrying thoughts came to me, need to make sure i am on a right track before continuing.

Thank you