Technical5 min read
Roof blocks: how to choose the right depth
The depth of a roof block is set by the joist span and the design load, not by site preference.
In a joist-and-block floor the block carries no structural load; its job is to fill between the joists and form permanent formwork for the topping. Its depth therefore ties directly to the effective depth of the slab, and so to the span the floor can cover.
As a rule a 20 cm block suits ordinary residential spans, while a 25 cm block is chosen for longer spans or heavier loads. That decision should come out of the structural calculations: changing it on site without revisiting them is a common and expensive mistake.
