You need constant ventilation to get rid of moisture. Without ventilation moisture will condense on your equipment during the night due to cooling. Having ventilation, insulation doesn't make sense. You better invest in Sun shielding like a zinc coated reflective roof to reflect the Sun radiation during the day. Also in wall materials which cool down quickly in the evening like wood. Metal part will attract moisture, wood much less.
In hot summer, my shed (zinc coated roof , wooden walls) doesn't get more then 5 or 6 degrees Fahrenheit hotter then the environment and is full of vent holes.
+1. And the vapor barrier is a particularly bad idea, especially in a dry climate. You _want_ moisture to be able to move back and forth.The key to this all is ventilation.
My house has the west sun problem, big time. Brick siding retains and reradiates daytime heat, for hours. My wife doesn't understand why we need to run the air con well into the cool night.
My observatory walls are a plastic garden shed, reinforced by a conventional 2X4 frame. The aluminum flat panel roof has a full length high quality ridge vent at the top. There's some insulation between it and the observatory. The area behind the eaves is deliberately left completely open. Thermal heating pulls air out the roof vent, in through the eaves. The observatory stays quite close to the air temperature (you can do little better), the roof reflects the sun, protects the equipment from it. I open it fully at dusk. I never have to use a dew heater. The equipment got more dew on it when I was using it outside.
Watch out for cross venting. It's all too easy to have air flowing horizontally between them, leaving the area below the roof itself a dead zone. Especially if you power something. Previous owner of house made that mistake, managed to get mold in the attic in a dry climate. I vastly improved the minimal high roof vents, and added missing eaves vents. Closed off the big horizontal vent with motor, which was pulling a vacuum in the attic drawing in humid air in from the house. A recent reroof let me replace all the high roof vents with a _lot_ of ridge venting.
Air wants to do the right thing. You just have to guide it properly. Shoving it around, or impeding its flow, _often_ causes more problem than it solves. Powered roof vents feel good and make somebody money, using thermal energy properly is better. You have to insulate a house, to save energy, since you don't want it at outside air temperature. If an observatory is at outside air temperature, that's pretty good. I'm close.
Edited by bobzeq25, 23 January 2020 - 12:17 PM.