Loading Shelves Without Sag

A sagging shelf is not usually a sign of a badly made unit. It is a sign of a long span carrying a heavy, evenly-spread load.

Span is the main variable

Deflection rises sharply with unsupported length. The same shelf that is solid at half a metre may visibly bow at a metre. Units with a centre support or narrower bays are far stiffer for the same material.

Books are heavier than they look

A full metre of hardbacks is a serious load. Spread heavy items across several shelves rather than filling one row completely.

Which way up

Many shelves are stiffer one way round because of a lip or a thicker front edge. Follow the instructions rather than assuming it is symmetrical.

Sag is not always reversible

Particle board that has been bowed for a year will not straighten. If you see the beginnings of a curve, redistribute the load then rather than later.