[Ian Robinson]

Based on my many years of engineering I'll only insulate the roof when I build my observatory , will use insulated roof sheets , I think insulating the walls of an observatory is a big mistake .... you want the walls to have minimal thermal mass and minimal thermal inertia and to not retard cooling of the interior in anyway.
Insulated roof sheets will stop a lot of the heat from radiating into the interior.



A small window mounted 1/2 horsepower a/cond mounted through a wall will do the trick .... when I build my ROR shed , that'll be my plan .... I've an old Kelvinator 1/2 horse that used to cool our main bedroom before I bought the big Fugitsu 2.4kW split unit and retired it.

Was more than adequate for our big bedroom , so will work a treat in a 4m x 3.2m shed.

You can also get portable a/con units on wheels , they be OK too.