Screed necessary? Unfinished but insulated attic

I had a raw basement floor for over 20 years and several raw garage floors, and I also know attic storage rooms with [Rauspund]. Why should you need screed there? - I consider any "insulating effect" to be negligible.

So can you imagine it like that?


I don't really know the insulation value of reinforced concrete (really 20mm?) and maybe 4-5 cm of screed... but I think that definitely a lot of heat is wasted upwards into the attic.

: Yes, exactly like that. Does that mean the attic heats up excessively? An opening (window) is not planned. How much is "a lot of heat"? Does this construction method affect the KfW rating?

Is it really only 20mm concrete slab or 20cm?

I found some information while googling "Betondecke Dämmwert"... among other things, there is a page that states a U-value of 1.1 for 20cm concrete thickness and 4-5cm screed... that would be roughly like double-glazed windows... but as I said, with 20cm + 5cm screed...

But as I said, others in the forum can surely provide more information on that...

there is among other things a page that states a U-value of 1.1 for 20cm concrete thickness and 4-5cm screed... that would be roughly like double glazing...

That should be about right. The screed is denser than concrete. It does not primarily "insulate," that is not its job, it is not designed for that. It does not make that much of a difference. It certainly cannot fix the fact that insulation was placed in the wrong spot here—although better than nothing, the ceiling would have been more appropriate. The screed "changes" this by such a microscopically small amount that it will not justify the difference. The mistake was made elsewhere and cannot be corrected by this (even mitigating it only so slightly that it would be pointless).

Before you think about screed, battens on the floor, insulation wool in between as described above, and OSB on top. Time required 2-3 days, costs under €1,000.