Insulating the roof - Which structure?

Hello,

our house was built in 1962 and we want to insulate the roof because we need to replace the roof tiles.

It is a rafter roof, where the rafters rest on a ring beam of the exterior walls. Around 1984, the eaves were raised and the roof was boarded up. On top of that come roofing felt, counter battens, battens, and the tiles. In the attic, the spaces between the rafters were filled with pumice stones? In the loft, the spaces are open.

I favor an external roof insulation, but I am not sure what we should use instead of the roofing felt, i.e., between the boards and insulation. We plan to integrate the loft as a sort of gallery into the attic apartment. To keep the roof beams visible, we want to forgo insulation between the rafters.

What material and construction would you recommend for the external roof insulation? What should I do with the existing pumice stone insulation, remove it partially or completely?

Hello Andy, an above-roof insulation is a very good idea. There are roof panels with 28.9 mm and a U-value of only 0.10. The m² costs sFr.68.00 and you can install these panels yourself.

I definitely recommend 14 cm thick

As material for an above-rafter insulation, I suggest using fiber insulation materials (mineral fiber, wood fiber). Rigid foam boards can significantly worsen sound insulation. Depending on the frequency of the sound acting on them, they act similarly to a speaker diaphragm and noticeably amplify certain frequencies. Regarding the rafter infill, the detail would need to be examined closely in order to recommend a construction. What is important in any case: this detail must ensure airtightness; otherwise, above-rafter insulation is of little use.