ᐅ After filling it with books, the Kallax unit starts to bow—how can it be reinforced?

Hello everyone,

I have a Kallax shelving unit from IKEA at home, which I recently filled completely with books. I noticed that the long shelves are sagging, especially the large middle shelves. The unit stands freely, has no additional reinforcement, and I am wondering if and how I can stabilize the Kallax to prevent the shelves from sagging further or, in the worst case, breaking.

Does anyone have experience with effective ways to reinforce the Kallax, for example additional cross braces, dowels, supports underneath, or maybe special techniques that reduce the load on the material? I would appreciate practical tips, also regarding the load limits that should not be exceeded.

Thanks in advance for your help!

Klawolf schrieb:
Does anyone have experience with effective ways to stabilize the Kallax, such as additional cross braces, dowels, reinforcements from below, or perhaps special techniques to reduce stress on the material?

Simply screw wooden slats under the sagging shelves; this usually does the job. Alternatively, reinforce with metal brackets screwed in from underneath.

Hello Klawolf,

I’m familiar with this issue since the Kallax shelf can sag under full load due to the relatively thin particleboard and large shelf spans. Although the shelves have a melamine coating, that doesn’t hold up indefinitely under heavy weight.

One option is to add extra reinforcements to the back panel. Many people install a thin, sturdy wooden strip or a consistent cross brace along the rear. This adds stability and prevents sagging.

Additionally, you can fill the compartments selectively with book bundles that distribute the weight more evenly across multiple shelves. Sometimes reinforcing individual compartments with short end strips or brackets on the sides helps to spread the load better.

Basically, you should avoid exceeding the load capacity of a shelf since the material gives way quickly. If you want to check the maximum load capacity: according to IKEA, it’s about 13-15 kg (28-33 lbs) per shelf, depending on the model. Good luck with stabilizing your shelving!

Klawolf schrieb:
I am now wondering if and how I can stabilize the Kallax so that the shelves no longer sag or, in the worst case, break.

The issue with sagging is closely related to the construction of the Kallax shelves. They are made from relatively thin particleboard with a melamine coating, which contributes to stiffness but does not distribute heavy loads well over time.

To stabilize the shelf, I recommend the following steps:

1. First, check how much the shelves are sagging and how tightly the books are packed. Is it mostly individual shelves or does it happen across several compartments?

2. The most effective way to stabilize is to better distribute the load. In particular, avoid having rows of books spanning the entire shelf width without additional support.

3. If you have the skills, you can attach a reinforcing wooden strip (about 2–3cm (1 inch) wide and 1–2cm (0.5 inch) high, made of sturdy hardwood) underneath the shelf panel. Ideally, this strip should sit directly against the underside of the shelf and not cause visible deformation.

4. Metal brackets can also be fastened in the corners with round-head screws to counteract the torque caused by the load.

5. Alternatively, there are special shelf supports or reinforcements made of aluminum that can be clamped or screwed on. These are often a bit more expensive but offer a neat appearance and very good stability.

One more question for you: What are the exact dimensions of the shelves (width x depth) and approximately how heavy are the books? Are they heavy large-format books or standard paperback novels? This helps with the assessment.

benon schrieb:
Many people install a thin sturdy wooden strip or a uniform cross brace at the back.

That is also a good solution, especially if you do not want to attach the shelf unit directly to a wall.

Filippo schrieb:
One more question for you: What are the exact dimensions of the shelves (width x depth) and approximately how heavy are the books?

Hi, I’d like to join the question, as the reinforcement approach really depends on the size and load density.

For my solution, I added cross braces that were fixed not only at the bottom but also on the sides. The shelving unit is also placed close to the wall, which significantly increases stability.

benon schrieb:
You can also selectively fill the compartments only with book bundles to better distribute the weight over several shelves.

That’s the most important advice for me, because if individual shelves are overloaded, the whole unit quickly loses stability. A good trick is to store the heavy books at the bottom and lighter ones higher up – this way, the lower shelf bears less weight.