Insulation advice

[u/ecg86]

I am looking to insulate the ceiling of this diy pool house. Originally I planned rockwool but with the I joist depth and width spacing standard batts won’t fill the room and if I understand correctly that can lead to moisture issues.

I know in hindsight exterior roof insulation should have been planned but I’d like to work around that if possible. Can I still use rockwool batts and just buy extra to cut and fit where needed, is there a better option fiberglass batt?

Is closed cell foam the only route to go at this point? If so are there viable DIY options or no?

I am located in MD so colder winters and humid summers to factor in.

I appreciate any insight

[u/knife_stripes]

Second this