ᐅ Insulating a wooden intermediate floor

Hello everyone,

We recently bought an old prefabricated house built in 1969. Since a lot of heat seems to be lost through the ceiling of the upper floor, we are planning to insulate it in the near future. The structure is timber frame. There is already 10cm (4 inches) thick glass wool insulation in the ceiling, but it has compressed significantly over the decades.

I have now received a quote for blown-in insulation: 12,000 EUR! The high cost is due to the ceiling being open toward the eaves, allowing heat to escape more or less freely into the roof overhang. According to the quote, the open areas must first be sealed, which can only be done by opening the roof.

I have been considering doing it myself, opening the ceiling from above and simply adding some mineral wool to save costs. I discussed this with an energy consultant, but he said that the sides definitely need to be sealed so that the insulation (regardless of the type) is not undermined by cold air. "Only if it is completely sealed all around does the insulation actually work." Is he right?

In my opinion, sealing from the inside is not possible because there is no access. I don’t feel confident working on the roof or the eaves. It seems that everything depends on whether sealing is really necessary.

What do you think?

Thanks in advance!
Best regards
KlausWendler