Cost estimate attic expansion

Hello everyone,

we want to renovate the attic in my wife's parental house soon. It is supposed to become a complete apartment. Now my question is, approximately what costs will we have to expect.

What needs to be done?

[*]Roof insulation (Will be done by ourselves with insulation between rafters - afterwards covered with drywall or wood)
[*]Window sills and windows (Renew double windows and kitchen window, install 3 skylights)
[*]Screed is already done, parquet in all rooms except kitchen and bathroom
[*]Electrical wiring is laid, sockets will be installed by an acquaintance
[*]Heating connections are available, radiators must be installed (5 radiators, 1 towel radiator)
[*]Possibly, the entire heating system must be renewed.
[*]11 drywall walls (3x 4.60m, 2x 2.90m, 2x 1.69m, 1x 2.40m, 1x 1.43m, 1x 2.10m)
[*]Doors (5x room doors)
[*]Complete bathroom (bathtub, shower, washbasin, toilet)
[*]Complete kitchen

The total area of the floor is about 140 sqm.
My estimate is €50,000, but other opinions suggest around €100,000.

I know an exact estimate is difficult here, but a rough guideline would already help me.


Dark gray, thick lines = exterior walls
Light gray thick lines = windows / skylights
Dark gray, thin lines = drywall walls
Gray boxes = wooden pillars, chimney, etc.
Double window in the large rear room is missing on the floor plan



As can be seen in the lower left, the roof is partially leaking. What needs to be considered here before insulation?

Additional info: except for skylights and bathroom, everything will be done by ourselves

I'll start. Velux windows per piece 1000,- installed with tax. Paid, not estimated price.

I would not be too tight here even if you want to do a lot yourselves. Realistically, it is 140k, if you can manage 25k of that through [Eigenleistung] you are doing quite well. Financially, these are not large amounts.

If all of this is to be done by yourself, then 50k is more than enough. Plus kitchen and furniture. A drywall partition is quite cheap. On the manufacturer sites, you can calculate the quantities yourself. You can then buy these somewhere. Find a local building materials store and explain what you plan to do. Then ask them to list some prices for you.

Otherwise, my main building materials supplier is the Internet. I think I also have to invite the postman to the housewarming party. Because no one has brought as much building material as he has.

Hm, and if he has lost his 50k after heating and bathroom, then does he come to you for the remaining 50k?