Its a drop in the bucket relatively speaking, more like insulation in terms of upfront cost to provide a benefit and reduce long term costs.

It's... really not if you tried to actually build it.

The building materials aren't what's causing housing to be unaffordable. It's single family zoning and land speculation. The best thing to do to lower housing costs is to drastically reduce single family zoning (some cities have like 90% land area zoned for detached single family houses only!) to allow for infill development of SFHs into denser housing, and to implement an unimproved land value tax to discourage profiteering on land.

Sure, but slapping a 20-30.000$ on top doesn't help at all.