We have a bungalow 13.5 by 10 meters, hipped roof with a slope of 30 degrees along the length and 45 degrees across the sides. The roof is not insulated yet. The area of the roof is about 160 square meters. The ceiling of the floor is insulated. The attic is not used for living, but simply as a place for storage. We have made it accessible by stairs, not through a hatch in the floor, because the stairs are more convenient to reach. The patio door insulates the living area from the cold floor. Unfortunately, such a floor is very cold in the winter. Since we have money, the carpenter offered to insulate the cold floor.
He wants 8500,- gross for 200 mm of pressed felt between the rafters, vapor barrier and tongue and groove board cladding without puttying or painting.
Is that normal? Or is it too expensive? Or even cheap?
This whole story makes no sense for two reasons:
1) The attic is so cold because you're depriving it of the heat of your living room through the insulated ceiling of the upper floor; it won't suddenly warm up on its own because you throw in a few square feet of insulation wool. Frost protection: none. Only thermal protection is improved.
2) You want to wrap your attic in foil. Of course, this is possible, but there is a risk once it gets damp up there. Usually the water dries out because the attic is well ventilated. This possibility falls away when the roof is wrapped.
Your "expert" obviously agrees that moisture can get in there, otherwise he could have done without the (extra) vapor barrier and left the insulation exposed.
As for the price, it also depends on what you get for it.
At its simplest, he screws the battens behind the jamb so the insulation doesn't fall down, glues the vapor barrier visibly to the tongue and just stretches it over the jamb and rafters in the area of the accessible surface. Then screw one layer of drywall right on top, done. And I just now read that the price does not include stuffing.
For that amount of work (which would be enough for an attic) I would consider the price a bit steep.
However, if he got behind the jamb, installed OSB all around the floor as a joiner, primed well, then primed the vapor barrier around the jamb, taped on the rafters to seal the nails, attached another batten to straighten out the structure, glued 2 layers of drywall on top and finally put everything together, including the corner guard rails and such, it would certainly look very different.
We also double insulated, already directly during construction. Various experts also confirmed that it would be fine, including an expert. But I am still skeptical and watching it in our house. The lowest temperature the first winter was 8° on the roof.
Our contractor suggested $30 per sq ft for infrastructure insulation with mineral wool and polyethylene sheeting. If your estimate is battens and drywall, it sounds realistic from my perspective.
You really shouldn't insulate an unheated attic. The warm air from the living space condenses in the cold attic, but cannot dry out because the surrounding walls have vapor barrier.
The price seems fair, though.
My opinion of the project is also rather negative. There are two reasons for this:
1) Despite the patio door and vapor barrier underneath, moisture will slowly creep in. Every time you open the door.
2) As far as your whole philosophy goes, this project is like the proverbial sparrow hunt with guns.
If you need a more permanent (or at least warmer winter) environment for certain things, it's a very good idea to make a small insulated thermal box.