ᐅ Additional Roof Insulation (Built in 1978)

Hello everyone,

We are currently renovating an attic floor under the roof. The house was built in 1978, so the existing insulation is rather minimal. Now the question is whether it is possible to improve the insulation without completely redoing everything (unfortunately, the budget doesn’t allow for that).

The roof currently looks like this:

The old panels are going to be removed and then replaced with either new panels or drywall (which would then naturally need wallpapering). For this, I plan to add extra battens to reduce the spacing, as it is still too wide. Possibly even replace the old battens, depending on the situation.
At the moment, the insulation consists of about 16cm (6 inches) of glass wool with an aluminum foil facing. Below the roof tiles on the rafters, there is a breathable roofing membrane (Delta foil).
Now the question is whether it makes sense to increase the insulation thickness a bit more. The battens running crosswise in the photo are 58mm (2.3 inches) deep, so I could install 50mm (2 inches) thick insulation (glass wool, mineral wool?) there. Does that make sense? What about a vapor barrier? Where should it be installed?
Any other suggestions?

Thanks in advance for your answers.

deewd schrieb:
Now the question is whether it is possible to increase the insulation a bit more. The battens running across in the picture are 58mm deep, so I would have added 50mm insulation (glass wool, rock wool?) there. Does that make sense?

With an existing 16cm (6.3 inches) layer of mineral wool, it makes sense to increase the insulation. If 58mm (2.3 inches) battens are already in place, you can use those as well. I would recommend using about 60mm (2.4 inches) insulation and pressing it firmly into place. For this thickness, it’s best to choose a thermal conductivity rating of about 0.032 W/(m·K), which only costs a little more. Glass wool or rock wool... glass wool is generally cheaper, while rock wool should provide slightly better protection against summer heat, but only minimally. Both are fine options.

deewd schrieb:
What about a vapor barrier? Where should I install it?

With 16cm (6.3 inches) of existing insulation and an aluminum foil facing on the interior side, you can generally skip an additional vapor retarder inside — though I wouldn’t recommend it, especially since the aluminum foil facing appears to be damaged. Ideally, remove or destroy the foil facing, add the new insulation, then install a vapor retarder film on the inside, and finally cover with drywall.

deewd schrieb:
Any other suggestions?

Even if the budget allowed, I would keep the old insulation in place and just reinforce it as described above.