The outer wall in my bedroom is freezing cold, especially at night. I've been wondering if I can insulate it myself without totally botching it since I don't have much experience with DIY. What options are there that aren't too complicated?
the easiest way is to glue a thick styrofoam board to the wall and then cover it with wallpaper - you just need adhesive, a cutter and a spirit level for that 🧤 alternatively you can also use mineral wool boards, they're a bit more eco-friendly but also a bit more tedious to work with. quickest though is probably to hang a thick wall fabric or thermal insulation film behind your curtain, it looks good and actually helps a lot against the cold - just needs to be fastened with small nails or tape.
If the wall gets particularly cold at night, it's usually down to missing insulation or thermal bridges - adding an extra layer really does help. Besides rigid foam or mineral wool, you can also go for self-adhesive insulation wallpaper rolls, which are even more beginner-friendly since you don't have to mix as much and you just stick them straight to the wall. The important thing is to wipe the wall down properly first (get the dust off!) and apply the boards from bottom to top so nothing shifts. Then put fiberglass tape over it and paint - looks like new afterwards and it'll hold up too.
The cold wall is annoying, but before you jump into full interior insulation - watch out, there's a catch that the others didn't mention: if you want to insulate from the inside, you absolutely have to plan for a vapor barrier, otherwise moisture builds up behind the insulation and you'll end up with mold. That's actually a really common mistake in DIY projects and then it gets expensive.
The easiest thing would be to not insulate the whole wall right away. Try it with a thermal reflective foil behind some thin styrofoam (like 20-30mm) - it works like a kind of thermos and you don't need much handyman skills for it. Adhesive, utility knife, spirit level like I mentioned, and you're done. That gives you a noticeable improvement without ending up with a moisture disaster later. Alternatively: just use some thick wallpaper or even special thermal fiber wallpaper - doesn't do much, but something, and it's really minimal effort.
If it's really extreme and you want to do it properly, I'd honestly put up a vapor barrier (polyethylene film) first, then the insulation boards. Then you can work on top with wallpaper without worry. But don't start with the thick mineral wool boards if you're doing this for the first time - they're trickier to work with and need a cleaner finish.
As a last resort, you can just stick a thermal mat or some thin insulation behind a shelf or dresser - since the wall's hidden anyway, you don't need to cover the whole thing and you'll save yourself a lot of work.
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