Components
What is a transom?
A transom is a horizontal tube running across the width of a scaffold, from the inner row of standards to the outer row. Transoms support the scaffold boards and hold the two rows of standards apart at a fixed distance.
Use this diagram+
Free to use on your own site, in training material or in a course handout, as long as the credit link stays on it. Paste this where you want the diagram to appear.
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<img src="https://scaffoldoptix.co.uk/glossary/transom/diagram.svg" alt="transom — scaffold diagram from ScaffoldOptix" width="880" height="620" loading="lazy">
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<a href="https://scaffoldoptix.co.uk/glossary/transom">What is a transom?</a> — diagram by
<a href="https://scaffoldoptix.co.uk">ScaffoldOptix</a>
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</figure>Transoms run the short way — into the building rather than along it — and they are what the platform actually rests on. Their spacing is set by what the boards can span without deflecting, so a platform that feels bouncy underfoot usually has transoms too far apart rather than anything wrong with the boards.
A distinction worth knowing: main transoms connect the standards themselves and are part of the structure, while intermediate transoms are added between them purely to support boards. Both carry the platform; only one holds the scaffold's width.
Because transoms tie the inner and outer rows together, they also fix the width of the working platform — which is why the number of boards a scaffold can take is a decision made when the transoms go in, not later.
What goes wrong on site
- Transom spacing set to suit the tubes on the wagon rather than the span the boards can take, which is what produces a springy platform.
- Removing an intermediate transom to get a tie or a brace in, and not replacing it — the boards above it lose their support and nobody notices until someone stands there.
- Treating main and intermediate transoms as interchangeable when striking part of a scaffold.