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Where do homes have "exterior drywall"?

I guess they meant demolish the interior finishes of exterior walls, spray foam the wall cavities.

That's certainly a way to retrofit an older building, but you still need a heat pump.

Ah, thanks. I get what they mean now. It doesn't sound like a good idea, but I get what they mean. :)

You really don’t. I’ve been in a house in Maine with spray foam in 20 degrees with no heat turned on and interior temp was around 65. It was pretty amazing actually.

A heat pump isn’t cost effective compared to Reno with spray foam. An average heat pump probably takes a decade minimum to pay off.

drywall on the interior of exterior-facing walls

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