[ClumsyPilot]

> retrofitting it is expensive and carries a huge risk

Because construction industry is shockingly incompetent and corrupt.

Lived in a few newbuilds, they are full of fuckups - walls aren't straight, the hole for a fire sprinkler is not where the sprinkler is, so in case of fire it won't actually work. The hot water plumbing was not up to spec and has discharged a swimming pool of boiling water into someone's apartment, they are lucky no-one died.

They will not get something as complex and humidity control right.

[Gibbon1]

I'll add I'm suspicious of insulation since all the modern stuff is foamed petroleum. I feel that's both a fire hazard[1] and has the potential to be classified as toxic waste. See lead paint and asbestos.

[1] https://en.wikipedia.org/wiki/Grenfell_Tower_fire

[defrost]

Know your products, I've built houses from scratch and added insulation to existing houses, extensions, sheds, and always used glasswool:

https://www.bradfordinsulation.com.au/information-centre/how...

https://insulation.com.au/product/pink-batts-insulation/

It's recycled glass.

[bafe]

I can't speak for other countries, but here (Switzerland) insulation is primarily mineral wool or else it must be fireproof