>Do you have any actual numbers for what is up to code insulation in California? California is a very temperate climate. I wouldn't exactly expect their code to

>Do you have any actual numbers for what is up to code insulation in California? California is a very temperate climate. I wouldn't exactly expect their code to have the highest insulation requirements. R-15 for 2x4 or R-21 for 2x6. Not highest numbers in USA I guess and after you buy house that already "exists", it's expensive to change it. >I am keenly aware of how much thermal mass walls hold. My apartment is 3 external walls that are constructed pretty much only of a few inches of concrete, bare. The result is that after a full day of summer sun, even though it drops to 64 degrees outside at night, my air conditioner cannot keep it 76 degrees or lower inside. It's crazy. It's worse in the winter when I can feel the walls sucking heat out of my apartment. Whole house fan is the way to go. If you can't install one, I think a couple of strategically placed window fans over night to create some air flow through the house might work better than AC I did some research on preventing walls from getting too hot (my room wall on the outside hits 170F i think). Narrowed it to - Transparent paint with some particles that reflect sun/reduce heat gain - Awning - Shade sail - Trellis and grow some vine to cover the wall.