What should be considered when installing a new roof?

Hello, I want to have my roof re-roofed and insulated. a) What should I pay attention to in the cost estimate? b) Which insulation is standard today (is WL40 sufficient or is WL35 recommended)? c) How thick should this thermal insulation be (100-140mm)? Thank you very much for your help

The insulation thickness is inversely proportional to quality. In new buildings, usually 18cm to 22cm of insulation with wlg 035 is installed; if it is to be insulated with a smaller thickness, a higher quality material must be used. What is feasible for you should be checked by someone on site. Often, old, sparingly dimensioned rafters cannot support the additional loads that are added by an expansion according to today's standards. A structural engineer should be involved there. Furthermore, the exact required insulation can be calculated. It is also important to properly plan the individual layers so that there are no thermal bridges, moisture damage, or mold growth. During installation, care must be taken to ensure that the insulation is sealed airtight on the room side and is not damaged.

Speaking of insulation: I installed the full rafter insulation (16 cm) in our attic, which is now to be converted, by just placing it between the rafters two years ago and now want to continue working (another 5 cm crosswise first and then airtight foil).

Could the insulation have lost certain insulating properties due to the missing foil over two years?

Subjectively, I cannot feel any loss of insulation.

so long :-?

If you want to be absolutely precise, you check the airtight sealing of the insulation with a Blower Door Test. This also detects any other leaks in your house. It doesn’t cost the earth, but it can save you a lot of trouble with mold growth and drafts!

So we were offered a Rockwool thermal insulation with WL 035 and 12 cm. Is that sufficient for a roof renovation? According to Dachheini, that should be very good.

to the last nameless: 12 cm in 035 is a joke, no offense meant, but the state of the art is different now, as are the legal regulations. Everything else is already mentioned further above.