Insulating roof - am I missing something??

[the_rapture]

Hi all. We suffer from a lot of noise in our top floor bedroom. The walls are slopey - directly below the roof. The insulation there looks minimal to me. There appears to be enough space to add further insulation without losing the 50mm gap needed for air circulation. Can I just slide in more rock wool slabs on top?? Insulation specialists are quoting to remove plasterboard instead and add insulation inside. I can see light from inside the roof which could be for ventilation - will I block that with the slabs? Or is leaving 50mm above new insulation slabs enough? Thank you!

 

[OvertonPlumber]

Current insulation requirements are 130mm celotex between the rafters 25mm over the top.

 

[big-all]

you dont need 50mm air gap 20mm should be fine even with the odd area where no to say 10mm gap for air flow as long as the air can travel somewhere a cold space works by not having much condensation as its all cold so a low to good airflow will clear the moisture