ᐅ Roof Insulation: Expanded Polystyrene (EPS) or Glass Wool

Just a quick question:
I plan to add insulation to the interior side of my roof in the uninsulated area.
I could use mineral wool (Isover) or expanded polystyrene (EPS).
Which option makes more sense? Also, how do the required thicknesses compare?
For example, mineral wool is 16 cm thick (0.032 W/m·K).
How thick would the EPS need to be to achieve the same insulation value?
I think EPS might be easier to work with.
Thanks in advance.............................................

Fahrenheit schrieb:

I plan to add insulation to the interior of my roof in the uninsulated area.

Is it the roof structure or the ceiling of the top floor? What is the purpose of the insulation? Are you planning to convert the attic?

Fahrenheit schrieb:

I could use mineral wool (Isover) or polystyrene. Which one makes more sense? And how do their required thicknesses compare?
I mean, what is the thickness ratio for the same insulation value? Isover is 16cm (6 inches) thick (0.032W).
How thick would the polystyrene need to be to achieve the same value?
I think polystyrene is easier to handle?

Try searching for “ubakus” online. You can calculate everything yourself there.

Otherwise, do you know about the correct construction methods for insulation? Mineral wool is actually much easier to work with. There are also other insulation materials that offer significantly better thermal performance. It all depends on your specific requirements. See my first question.

Thanks for asking.
It’s the roof, not the ceiling. The house has a pitched roof with an attic space that has been converted. The floor between the upper floor and the attic is insulated.
The attic roof itself is only boarded, then covered with roofing felt, followed by slate tiles.
On the inside, there is still space between the rafters to add additional insulation.
This worked fine for years, but due to the recent energy debates, I thought that adding insulation to the attic, which is currently not insulated on the outside, might still help somewhat.
I already visited a hardware store today. Styrofoam is more expensive with a similar thermal resistance. It is also flammable.
So, I will use mineral wool, which is also easy to cut to size.
Thanks for the tip (mineral wool); I thought it was only for facades. Apparently, it is more dimensionally stable, so it fits well between the rafters.
I will research prices and insulation values.
As mentioned above, hardly anyone gave it much thought for years, but with the current prices, people are starting to calculate more carefully.
Last year, my heating oil cost 0.75 per liter; this year it is 1.52 per liter. — That really grinds your teeth.
My wish for everyone: Hopefully, gas prices will go down again as well. (But I really doubt it..........................)

Fahrenheit schrieb:

The floor between the upper floor and the attic is insulated.

If you don't need to use the attic otherwise, simply lay two layers of mineral wool on the floor and you're done. That would be an alternative.

Thanks for the tip, but I’m using the basement as a storage room, so the mineral wool insulation would probably get damaged there.

The space between the rafters is available, which is why I believe the additional insulation will fit better there.

By the way, according to my research, mineral wool is more expensive. It’s fine for the facade, but for rafter insulation, precise fitting is not that important.

In my insulation planning, I had also considered the facade, but after recalculating and evaluating the payback periods, I’d rather burn my money in the Bermuda Islands.

Reading through the discussions here in the forum, I notice that during a (partly industry-driven!) hype, careful calculations are often neglected. The main focus is on investing new money, no matter what the return is.

Some people think they are contributing and saving the environment but don’t check what is happening in the rest of the world. It’s very positive from a human perspective – but?

Best wishes for more sunshine on the roofs of our photovoltaic and heat pump experts.

I installed my insulation between the rafters using polystyrene. I am very satisfied with this.

This is because I really dislike mineral wool. I cannot tolerate the tiny fibers and the itching they cause. That’s why I didn’t use it, except for the ceiling insulation, where it is installed without direct contact between the layers.

However, I didn’t use regular polystyrene from a hardware store, but special inter-rafter insulation from Schwenk. It was scored, so it could be slightly bent and fitted very precisely. It also had tongue and groove edges, making installation quick and easy. I installed a total of 15 cm (6 inches) plus drywall. Even during midsummer, the upper floor remains comfortable, and in winter, it stays nice and warm. So I can definitely recommend it.