ᐅ Insulating a cold roof with compressed fiberglass insulation, cost

Hello friends,
We have a bungalow with a slab measuring 13.5 by 10 meters (44 by 33 feet), and a hipped roof with a 30° pitch along the length and 45° on the short sides. So far, the roof is not insulated. The roof area is approximately 160 square meters (1,722 square feet), possibly a bit more. The ceiling between the floors is insulated. We use the attic not as living space but as a cellar substitute. It is accessible by a staircase, not a hatch, since the stairs are easier to use. A patio door separates the living area from the unheated attic well, providing good thermal separation. Unfortunately, this floor gets very cold in winter during frost — I’ve even had paint freeze — and very warm in summer. Now that we have some funds available, we have asked a carpenter to provide a quote for insulating the unheated attic floor (ceiling below the attic).

He is quoting us 8,500 gross for installing 200 mm (8 inches) of cavity insulation between the rafters, along with a vapor barrier and drywall lining, without plastering or painting.

Is this a fair price? Too expensive? Or even a good deal?
Karsten

The quote from our construction company was 30€ per square meter (sq ft) for the insulation between the rafters using mineral wool, including a PE foil. If your quote includes battens and drywall panels, it sounds realistic to me.

That would be just under 5800 including tax for us. But the drywall cladding is still missing. The knee wall also has to be built here....see pictures.

Actually, you should not insulate an unheated attic. Warm air from the living area condenses in the cold attic but cannot dry out because the surrounding walls are equipped with a vapor barrier.
And money aside, do you really have to spend a few thousand euros to prevent paint residues from freezing? You’d be better off putting a hot tub on the terrace.

By the way, I don’t find the price quoted to be either excessively expensive or cheap. The material should cost around €20/m² (about $20/m²), but the labor effort under these conditions is likely significant.

Thank you for assessing the price as, let’s say, reasonably fair. Regarding the technical aspects: I specifically asked the carpenter whether this is okay or a bad idea. He knows that no living space will be created there and that there will be no radiators. He said it’s a good idea, technically sound with a vapor barrier, and that the separation from the heated house through an insulated ceiling, patio door, and insulated stairwell is ensured. So, basically, I tend to trust a professional on this. Especially since the company that provided the quote is the same one that built our house. Karsten

We also installed double insulation right from the start during construction. Various experts, including a building surveyor, have confirmed that this is acceptable. However, I remain somewhat skeptical and am monitoring the situation in our home. The lowest temperature in the roof during the first winter was 8°C (46°F).