ᐅ Insulation for the top-floor ceiling – which material to choose?
Created on: 18 Jul 2022 16:02
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Elias_dee
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!
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!
E
Elias_dee19 Jul 2022 20:22WilderSueden schrieb:
Can you just remove that and install something else? After all, that’s the thermal envelope that needs to be properly calculated to comply with the energy saving regulations.You’re right. I’ll talk to my energy consultant tomorrow, but I’m 99% sure I can’t just take it out like that.Another idea: I have the general contractor install the polystyrene as agreed, but instead of OSB boards on top, I would add something myself afterward. Or can I, for example, put mineral wool over the polystyrene? Would that actually improve thermal insulation, or would it be redundant?
I find the expanded polystyrene (EPS) to be poor quality. If the concrete ceiling still releases moisture, it cannot pass through the EPS and will condense. Or is a vapor barrier installed in between?
Additionally, with EPS as a panel material, there is a risk that it will not lie flat on an uneven surface, reducing its insulation effectiveness.
Mineral wool on top is not better.
Mineral wool usually has a better thermal conductivity rating (WLG), providing better insulation at the same thickness. It is flexible, adapts to the substrate, and is vapor permeable. In other words, it is breathable according to the general contractor.
Additionally, with EPS as a panel material, there is a risk that it will not lie flat on an uneven surface, reducing its insulation effectiveness.
Mineral wool on top is not better.
Mineral wool usually has a better thermal conductivity rating (WLG), providing better insulation at the same thickness. It is flexible, adapts to the substrate, and is vapor permeable. In other words, it is breathable according to the general contractor.
A
Axolotl-neu19 Jul 2022 22:59Elias_dee schrieb:
That's true, you're right. I'll talk to my energy consultant tomorrow, but I'm 99% sure I can't just remove it like that. That's just the construction company's issue. The energy consultant has no problem with it.
Elias_dee schrieb:
Or can I, for example, put mineral wool insulation over polystyrene? Would that actually provide better thermal insulation, or is it just redundant? It's redundant and a waste of money.
I also consider the idea a waste of money and see it as a mistake to completely forgo walkability.
In my opinion, the polystyrene should be replaced with mineral wool, and OSB boards installed on top. Increasing effort here will not significantly improve thermal insulation, as other factors play a larger role in heat transfer. You can save the additional costs and rather invest them in air conditioning or similar, which would be much better spent.
Giving up walkability is something you will probably regret at some point. There are always situations where it is important or practical to be able to move around up there, whether for repairs, photovoltaic or satellite installations, or similar tasks. With exposed 320mm (12.6 inches) mineral wool, you simply won’t want to walk on it, especially since OSB also serves as a vapor barrier.
In my opinion, the polystyrene should be replaced with mineral wool, and OSB boards installed on top. Increasing effort here will not significantly improve thermal insulation, as other factors play a larger role in heat transfer. You can save the additional costs and rather invest them in air conditioning or similar, which would be much better spent.
Giving up walkability is something you will probably regret at some point. There are always situations where it is important or practical to be able to move around up there, whether for repairs, photovoltaic or satellite installations, or similar tasks. With exposed 320mm (12.6 inches) mineral wool, you simply won’t want to walk on it, especially since OSB also serves as a vapor barrier.
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