>There is probably a lot more that could be done to make houses more energy efficient, but it all depends on what the owner wants to spend, state and local building codes, etc.

For most of the houses, probably nothing will be done in advance. Maybe post festum.

Why? If you want to rent, you build it cheap. Insulation doesn't sell the space, it's other amenities that will attract the tenants. And it's not you who'll pay the monthly bills once it's leased.

If you want to sell, you build it cheap. Insulation doesn't sell the space, it's other amenities that will attract the buyers. And it's not you who'll pay the monthly bills once it's sold.

Now if you're building it for yourself, you're a minuscule minority, and statistically not too important.