Insulate concrete ceiling upper floor

Hello everyone,

I want to tackle the insulation of the top floor ceiling myself.

Facts:
- Semi-detached house built in 1972, two-story with heated basement rooms
- Upper floor ceiling made of reinforced concrete - B225, thickness 16cm according to plan
- Roof pitch is 18 degrees and cannot be converted into living space.
- The foot purlins rest directly on the concrete ceiling
- The roof should not be insulated, but the floor instead.
- The attic space should be partially usable as storage and walkable.

See sketch top view attic 110 sqm area, about 40 sqm walkable


Questions:

1) Preparatory work:
What preparatory work do I have to do on the concrete before I start? Clean thoroughly?

2) Vapor barrier:
Do I also have to lay a vapor barrier foil on the reinforced concrete - B225 in the upper floor?

3) Insulation material:
I would like to lay double-layered and staggered (without cross joints) EPS 040 WI/DI/DZ 50mm polystyrene boards (W 500mm x L 1000mm) (approx. 7.30 EUR / m2) everywhere.
That means about 9-10 cm insulation. What U-value would I achieve with that? The material price comes to about 800 EUR including VAT.
Which inexpensive insulation boards would you recommend for my project? Has anyone had experience with polystyrene boards?

4) OSB boards (thickness - no idea - any recommendations)?
For the walkable part, I would additionally lay OSB-3 tongue and groove installation boards 12mm 205 cm x 62.5 cm (approx. 4.28 EUR / m2).
The price for the material comes to about 200 EUR including VAT.

5) How should I proceed regarding cables embedded in the concrete ceiling and at the foot purlin in terms of insulation?



6) How should/could I insulate the attic stairs?



7) Any special considerations that I might not have thought about yet?

Looking forward to your opinions/ideas/tips and tricks

Chippy

1) Preparations:
What preparations do I still need to do on the concrete before I start the work? Clean thoroughly?

Make it broom clean

2) Vapor barrier:
Do I also have to lay a vapor barrier with foil in the upper floor on the reinforced concrete - B225?

No

3) Insulation material:
I would lay double-layered and staggered (without crossed joints) EPS 040 WI/DI/DZ 50mm polystyrene boards (W 500mm x L 1000mm) (price approx. 7.30 EUR / m2) everywhere.
That means about 9-10cm insulation. What U-value would I achieve with that? Price-wise I come to about 800 EUR including VAT for the material.
Which cheap insulation boards would you recommend for my project? Has anyone already had experience with polystyrene boards?

Take a look at ubakus and calculate yourself. You can play around with it wonderfully there.

4) OSB boards (thickness - no idea - do you have recommendations)?
For the walkable part I would additionally lay OSB-3 subfloor boards 12mm 205 cm x 62.5 cm with tongue and groove (price approx. 4.28 EUR / m2).
Price-wise I come to about 200 EUR including VAT for the material.

I would throw on the cheapest material I can find

5) How should I proceed regarding insulation around cables embedded in the concrete ceiling and at the wall plate?

Make yourself a conduit or cut a channel into the insulation if lying on the basement ceiling

6) How should/could I insulate the storage stairs?

Buy a well-insulated new staircase

With poor insulation, you can also save yourself the effort,...

With poor insulation, you can also save yourself the effort,...

That is nonsense. Of course, 10cm of 040 insulation improves the heat transfer. Especially the first centimeters bring the highest percentage improvement. Just the feeling alone should improve since the ceiling radiates less cold.

Best regards

With such poor insulation, you can save yourself the effort,...

What a stupid statement.
U-value of a reinforced concrete ceiling around 4.x
U-value with 10cm EPS 40 around 0.37
I find that quite decent for very little money.

If possible, leave the attic unused and insulate it with 2x stone wool or similar (2x16 or 20cm). Then the attic is at a good new-build level.
Or buy good 2nd choice cheaply from the insulation king for pocket money instead of the intended EPS insulation.

Thanks already for the feedback.

Can you actually just lay the EPS loosely on a concrete floor without screed on top like that? What if the top floor slab consisted of concrete and a 3 cm screed? Is it allowed to lay the EPS on the screed as well?

What else could I cost-effectively optimize in the insulation? Should I maybe use the 10 cm styrofoam in double layers, i.e. 20 cm insulation? That would be double the cost for the insulation. i.e. 20 EUR / m2, i.e. about 2200 EUR for 110 sqm.

I was also thinking of stone wool WLG 035 120m, but this insulation material costs about 52 EUR / m2 for double layers, i.e. about 5500 EUR for 110 sqm.

From the insulation king, which product would you recommend to me?