Ceiling insulation

[Thomo39]

Good morning.
I am looking to insulate my external garage.
The garage is a brick building about 3m x3.5m
The roof is a flat roof.
Joists at 600mm
The void is about 200mm
I was looking to lay some wool insulation but wondered if i need to leave a gap from the ceiling and a gap from the plasterboard?
Thanks

 

[John D v2.0]

What is the ceiling made of? You wouldn't want a gap between the ceiling and insulation and you'd need a vcl (like a poly sheet) at ceiling level. You'd need a void above the insulation, Also you will need ventilation above the insulation to outside.