[pjerem]

You are talking about a new construction project. On this you are right. Been there, done that.

However most people in the world already live in an existing building. Insulating an existing building is not what I would call cheap, especially if you are still paying a mortgage.

[bluGill]

There is for sure less you can do for existing construction, but it isn't nothing. There are still a lot of attics in cold places with R10-R20 insulation that can cheaply be brought closer to R40-R60. (About a month ago I bought my attic to R40 for $4k, remove all old insulation, air seal, and then new )

Most existing houses get a significant remodel once in a while as well. If you are doing that you should bring the changed areas to better code. Much siding only lasts for 25 years, so just put insulation under it while doing the regular replacement can make a big difference as well for not much more since you have to pay for a lot of labor.