Clear span: what it costs, and what it buys you

Clear span is the distance a structure crosses with nothing standing in between. It is the figure that matters when a building has to stay clear inside, and it is worth being precise about, because it is often confused with the building's overall width. A 70-metre-wide building with a row of columns down the middle has a 35-metre clear span, and for most of the uses that drive this decision, that is a different building entirely.

The cost is real and it is not linear. As the span grows, the frame carries more of its own weight over a longer distance, sections get deeper, connections get heavier, and at some point the foundations have to change too. Doubling the span costs considerably more than double. This is why the right question is never "what is the largest span you can build" but "what is the smallest span that lets this building do its job".

Sometimes that smallest span is still very large, and then there is nothing to argue about. An aircraft movement envelope does not negotiate: the aeroplane needs the width it needs, and a column inside it is not a compromise, it is a wall. A sports floor is marked out to a standard that does not care about your structural grid. A warehouse aisle layout can sometimes be planned around columns and sometimes cannot, depending on the racking and the turning circle of the equipment that has to work between them.

Where clients lose money is the opposite case — asking for a long span out of caution, for a building whose use would tolerate an internal line of columns perfectly well. General storage, light manufacturing with a fixed machine layout, and workshops are frequently in this category. A column line placed where a partition was going anyway costs almost nothing and can take a large amount out of the steel tonnage.

Masas has delivered a 64-metre clear span on a sports hall and a 60-metre clear span on a hangar in Qatar. Both are column-free spans in the strict sense above. Those figures are useful as evidence that the long-span case is within reach, and they are not an argument that your building needs one.

The practical approach is to decide the interior first — the racking, the equipment, the movement, the markings — and let the structural grid follow it. A frame designed around a real layout is almost always lighter than one designed around a round number.