ᐅ Insulating the sloped ceilings of the upper floor from the attic space

Hello,
I rent a very old house with an uninsulated roof structure.
The upper floor extends into the roof and has a sloped ceiling of 2.5m (8 feet) length on both sides of the house.
From the attic, I can see into the spaces between the rafters (100mm / 4 inches) up to the exterior wall.
Considering the rising energy costs, I’m thinking about what could be done with low cost and effort.
I’m not sure yet if the landlord will contribute.
In my opinion, installing a breathable membrane under the roofing is hardly possible given the described situation.

I could cut EPS (expanded polystyrene) boards and slide them in, or insert mineral wool batts.
The insulation would be placed directly under the tiles.
With mineral wool, I’m concerned about moisture issues, and with EPS, that the boards won’t fit properly against the rafters.
Are there any alternatives?
What would be the lesser of two evils?

I know that my thoughts are far from an ideal insulation and roof assembly.
The goal is to save some energy over the next five years.

Thanks for all suggestions.
Remo

Have you ever looked into loose-fill insulation or blown-in insulation? There might be solutions that don’t require a vapor barrier.

You are a tenant and need the landlord’s approval for something like this. You are responsible for any damage caused by improper workmanship—think mold—and your landlord can hold you liable.

Especially with thermal insulation in older buildings, a lot can go wrong, and often very badly. Stay away from it. Your landlord should hire a professional. If they do a poor job, at least it won’t be your problem.

Thank you WilderSueden, I took a look at the options available. It would certainly be practical to accomplish. However, I would then have material right up to the bricks. But as an alternative, it’s a good suggestion.
@MisterD. I’m writing that I don’t know if my landlord will contribute to the costs...so I plan to talk to him. (I have done so, and he will cover the costs...of course, not for replacing the roof or anything like that.)
To avoid mistakes, I’m informing myself (including here) and hope that professionals will give me good advice.

mykelog schrieb:

(I did that, he is covering the costs... of course not for re-roofing or similar work)
To avoid mistakes, I inform myself (among other places, here) and hope for experts who can give me good advice

Then avoid making the mistake of placing yourself as the client (and point of contact for compensation) between the landlord and contractor. Don’t just let him cover the costs, but let him take on the entire matter. Your involvement should be limited to assisting with obtaining quotes. He also benefits from deducting the labor costs of the tradespeople, which you wouldn’t be able to use as well.

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