My Beam Isn’t Wide Enough to Support the Cavity Wall Above — What Now?

A structural steel beam carries the loads from the wall above through its web and flanges — but its physical width is determined by the design section, not by the width of the wall it is supporting. It is common for a beam to be narrower than the full cavity wall width, leaving the outer leaf without adequate bearing.

The solution is a shelf plate.

What Is a Shelf Plate?

A shelf plate (also called a bearing plate or soffit plate) is a mild steel flat plate welded to the underside of the beam flange so that it projects outward, providing a continuous bearing surface for the outer leaf brickwork.

The plate runs the full length of the beam including the bearing zones at each end, and at the bearings it is grouted into the masonry bed joints to provide a positive connection.

Two Different Arrangements

The plate geometry depends on the wall arrangement:

Single beam supporting a cavity wall: The plate projects from the inner beam flange outward toward the outer leaf. It supports the outer leaf masonry at the beam sofffit and transfers the outer leaf loads into the beam.

Beam acting as a lintel in an external cavity wall: A slightly different arrangement where the shelf plate integrates with the external skin and is detailed to suit the weathering and cavity drainage requirements of the external wall. The plate is typically at or below damp-proof course level.

Welding the Plate

The plate does not need a continuous weld along its full length:

– For cavity wall support plates (detail a): spot welds at the fabricator’s discretion
– For external lintel arrangements (detail b): 100 mm long × 6 mm hit-and-miss fillet welds

The plate must not be wider than the full wall width including the cavity.

Confirming the Detail

Shelf plate requirements are confirmed between the architectural consultant and the contractor before fabrication. If it was not clear at the time of the original PorthouseDean scope, contact us with the wall layout and we can confirm whether a shelf plate is needed and what dimensions to specify. Get in touch.