ᐅ Insulation for the top-floor ceiling – which material to choose?

Hello everyone,

We are building a turnkey house with a general contractor. The contractually agreed scope of work and offer include the following insulation for the top floor ceiling (with an unheated roof above):

“The top floor ceiling will be insulated with EPS 035 polystyrene boards, 240mm (9.5 inches) thick, including 15mm (0.6 inches) OSB boards with tongue and groove all around.”

Since protection against heat is very important to us and summers unfortunately are not getting milder (quite the opposite), we have now discussed options for better heat protection with him.

I should mention that walkability or later finishing of the attic is NOT important to us – there are no windows up there, nothing at all, plus we have a 25° (25°) pitched roof, so not even my wife can stand up there :-) So, we don’t need the attic to be walkable.

We were offered the following options and additional costs:

Option A: Wood fiber boards → these also offer excellent summer heat protection. Additional cost: 4,000 € net

Option B: Keep the polystyrene insulation. Instead of battens and foil on the rafters, use 60mm (2.4 inches) spruce wood panels (for summer heat protection). Additional cost: 3,100 € net

Can anyone tell me which option is better for heat protection and if the prices are reasonable?

Thank you very much!

Elias_dee schrieb:

Can someone tell me which is better for heat protection and if the prices are reasonable?

What material is the top floor ceiling made of?

Axolotl-neu schrieb:

What material is the top floor slab made of?

Uh, sorry. It is made of reinforced concrete.

Then remove it and collect the compensation. Afterwards, lay two layers of 120mm (5 inches), preferably two layers of 160mm (6 inches) mineral wool crosswise and leave them exposed.

Joedreck schrieb:

Then remove it and claim the compensation. Afterwards, lay out two layers of 120mm (5 inches), preferably two layers of 160mm (6 inches) stone wool insulation in a staggered pattern and leave it exposed.

Exactly, because with the reinforced concrete ceiling you already have plenty of protection against summer heat, the stone wool insulation is completely sufficient. And with the money saved, you can treat yourself to a nice garden.

Can you just remove that easily and install something else? After all, this is the thermal envelope that must be properly calculated to comply with the energy saving regulations (energy performance requirements).