Insulate cold roof with clamp felt, price

Hello friends, We have a bungalow with a 13.5 by 10 meter floor slab, a hipped roof with a 30-degree pitch lengthwise, and 45 degrees on the cross sides. The roof is currently not insulated. There are about 160 sqm of roof surfaces, possibly slightly more. The floor between the stories is insulated. The attic is not used for living but as a cellar replacement; we have accessed it by stairs, not by an attic hatch, because stairs are more comfortable to use. A terrace door thermally separates the living area and the cold attic well. Unfortunately, such an attic floor is very cold in winter when it freezes; I have even had paint freeze on it, and very warm in summer. Since we have come into some money, we have had a carpenter give us an offer for insulating the cold attic floor. He wants €8,500 gross for 200 mm insulation wool between the rafters, vapor barrier, and plasterboard cladding without filling and painting. Is that okay? Or too expensive? Or even cheap? Karsten

The offer from our construction company was 30€ per sqm for the insulation between the rafters with mineral wool including PE foil. If your offer includes battens and gypsum boards, it sounds realistic from my point of view.

That would be just under 5800 including tax with us. But the drywall cladding is still missing. He also has to build the knee wall with us....see pictures.

Actually, you shouldn’t insulate an unheated attic. Warm air from the living space condenses in the cold attic but cannot dry out because the surrounding walls have been fitted with a vapor barrier. And money aside, do you really have to spend a few thousand euros so that leftover paint doesn’t freeze? Better put a hot tub on the terrace.

By the way, I don’t find the quoted price either excessively expensive or cheap. Material should be somewhere around ~20€/m², but the labor effort under these conditions is probably not negligible.

Thank you for the assessment of the price as, let's say, normally fair. Regarding the technical aspect. I specifically asked the carpenter whether this is okay or a stupid idea. And he knows that no living space is to be created there and that there will be no radiators. He said that it is a good idea, technically flawless with a vapor barrier, and the separation from the heated house by means of an insulated ceiling and terrace door and insulated staircase is given. So, actually, I tend to trust a professional on this. Especially since the company that made the offer is the same one that built our house. Karsten

We also insulated twice, already during the construction. Various experts have also confirmed to me that it would be okay, including an expert. But I am still a bit skeptical and am monitoring it with us. The lowest temperature in the first winter was 8° in the roof.