Are people considering insulating with carpet as an alternative to foam? No one: “I was going to use foam, until I realized that, for just a little more money I could put carpet in the walls.”
I used closed cell foam in one room that I tore back to the studs. It’s easily the most comfortable room in the house, so I like the product, but comparing the price of non-substitute goods seems not useful. Compare foam to other insulation products.
No but they won't hesitate to spend money on (8 sq/ft) something that will war out and they can easily change but something that you basically get one chance at and it determines your environmental quality and comfort, they could care less.
I take it you never worked in construction or home building and gave quotes. You would understand how people don't even give the mechanical any consideration (waste of money) but will spend 10's of thousands on cosmetics. You could build their foundation out of lego but you better use marble and gold leaf in their bathrooms.
I have not, but on the customer side, I have tried to buy mechanical services from salespeople who can't intelligently explain the value of the different choices or answer fairly basic questions about anything other than cost and schedule.
I'm a mechanical engineer (non-practicing) and generally in a position to buy something well above the entry level "we do 50 of these jobs a month" so if someone could manage to make a cogent explanation, they stand to get the sale over the other two jokers who have probably explained how "the basic system is just fine; no one ever complains" or "hey, the whole job is less than 1 Bitcoin [or other irrelevant reference]". I have a plumber that I trust; he wasn't the cheapest. I have an electrician that I trust; he wasn't the cheapest. I have an insulation contractor; he was FAR from the cheapest but did an excellent job, so he'll get the return call as well. [He was the only one who didn't make obvious blunders in the bidding process; my favorite was the one who recommended I pay an extra $1000 for him to spray foam my rim joists; said it was the best money I could ever spend. I have a structural brick house with no rim joists, so I took him down to the basement to have him point out what he was proposing to do; hilarity ensued, of course]. I wish I could find a good HVAC contractor. I'm 0 for 2 so far there.
Fiberglass batts are 4x cheaper for the R value and can be DIY. Spray foam cannot be easily added to an existing home without a professional coming out. (except for the cans used for air sealing gaps.
It's essentially a waste of money except for limited applications, which is why you won't find any builders at any price point using spray foam as a primary source of insulation.
Spray foam is also a pain if you need to get into wall/ceiling cavities for HVAC/plumbing/electrical repairs/additions.
