ᐅ Roof insulation for KfW 55 standard: what is the most cost-effective option?

Hello,

what is the most cost-effective roof insulation (above-rafter / between-rafter) for a KFW 55 house, if you exclude polystyrene and similar materials?

Best regards, Peter

The most cost-effective construction is probably with 20cm mineral wool. However, since insulating the roof is relatively inexpensive, it is often better insulated, with savings made elsewhere.

That means that continuous insulation above the rafters is definitely more cost-effective than insulation between the rafters. It then mainly depends on the thickness of the insulation and the material (glass wool / stone wool).

The most cost-effective option, I would argue, is insulation only between the rafters with a thickness of 20cm (8 inches). Whether this makes the most sense within the overall concept is another matter.