The whole house fan solution is great though.

Edit. I think most people simply do not realize what temperature have internal and external walls in houses and how it interacts (or counteracts) AC. If you will go to read greenbuildings/passive houses forums, there are a bunch of discussions about thermal mass of the walls

Also, building codes should be considered the minimum.

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.

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.

That seems unbelievable! Is that a typo?

Actually, it's possible to inject foam insulation into walls without ripping them off. It goes in through small holes, or through utility boxes. Plenty of companies do that. I've even seen it advertised on TV in California.

But injectable foam insulation usually going into empty walls. I already have butted fiberglass in there. I don't think it's viable to make laparoscopic wall surgery to remove fiberglass . I did a quick google, and looks like you can do injectable foam over fiberglass. But I am not sure how much R it will add, but I am sure that for cost of of injectable foam + wall repair, I can get another hvac and run it for next 10 years...

I did consider recently to double walls on sunny side of the house with few layers of foil backed foam boards.

It’s cheating, a bit, to live in a place that drops 20-40 F at night … but even if we didn’t, the ability to turn every open window into an air conditioner is a great trick.