Congrats to you too Grand-Ogre!
The bathroom/break area and the upstairs room will be climate controlled throughout the year. My HVAC guy strongly suggested insulating the floor of the room over the mezzanine for better temperature control, something I really hadn’t given much thought to. It was inexpensive so I did the whole floor. The sound deadening quality is definitely an added bonus.
Our temperatures here in North Texas can fluctuate big time. The winters are mostly very mild but occasionally we get below 40 degree weather for short durations with lows actually in the high teens not being uncommon. The problem we have is with the wind making it feel colder than it really is. Sustained winds at 20 mph with gusts up to 35 (and higher) are not uncommon. Thankfully these weather conditions are normally short lived which is another problem – no one can acclimate to the cold. Summer is by far the longest season for us as it seems we only have a hint of spring, fall, and winter. I’m weird. I like it hot, always have. If I can have some shade and a breeze I’m good. The shop with its 16 foot eves and spray on insulation provides the shade, a strategically placed shop fan provides the breeze.
The area under the mezzanine is 20x24. I should be able to move a vehicle under it with wheel dollies. It will also serve as an area for other projects similar to your 20x30 area. I’m going to design a quick way to hang canvas tarps around the perimeter of the mezzanine to temporarily partition off the area from the shop. Then I will be able to open the bath/break area for AC and heat if necessary.
I agree, bringing a room from -15 degrees or 110 degrees to a comfortable temperature is tuff and expensive.