ᐅ After the attic conversion, the KALLAX no longer fits into the niche – should it be shortened?

If you only shorten the shelf slightly, you can do it, but some rework will be necessary. Also ask yourself: How important is stability to you? It might be enough to position the shelf slightly at an angle within the niche to save space.

Domau0 schrieb:
The KALLAX shelf from IKEA is made of MDF with a melamine coating, which provides a stable structure, but mechanical modifications to the carcasses carry some risks.

I want to go into more detail: MDF becomes more brittle when cut because its fiber structure is interrupted. When sawing, a suitable saw with fine teeth should be used to avoid chipping and flaking of the melamine surface. Then, the cut edges should be thoroughly sealed, for example with edge banding or a double-sided veneer strip, to prevent moisture damage.

For the back panel, it is advisable to cut it together with the shelf, as otherwise this can cause uneven load distribution in the structure. After cutting, all screws and nails should be reset, possibly with additional metal brackets, to restore the original stability.

I wonder whether the other option—buying a custom-made shelf or redesigning the niche—is actually less labor-intensive. How often will the shelf be heavily loaded? Will it hold documents, heavy equipment, or just light decorations?

That could strongly influence the decision.