Transom tubes should be sufficiently long to span the width of the scaffold (ledger to ledger) and project beyond the couplers. The requirement for a 25mm projection of the tube through the couplers has been removed from current NASC TG20:21 guidance so long as the tube projects past the coupler on both connections to the ledgers.
Transoms should not be allowed to protrude from the outer face of the scaffold to such a length that they would case an obstruction or unnecessary hazard. For Example, when lifting or lowering materials or at low levels where access maybe required.
Board bearing transom do not normally require butting against a building so to allow for a service gap for access by trades using the scaffolds, however there are circumstances when transoms should butt the building or structure to limit movement as described in TG20:21 Operational Guide section 6.23 Rakers and section 7.9 Tying principles.
Where transoms are used to support cantilever boards to inside platforms, they should be long enough to provide full support to the board (usually long enough to allow for a putlog single coupler to be used to secure an inside board if tube is used).
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