Padstones Explained: Why They Matter, How They're Sized

Padstones are the unglamorous concrete blocks under each end of a steel beam. They cost R600–R2,000 each, take ten minutes to install, and prevent thousands of pounds of damage when sized properly.

What padstones do

Steel beams concentrate large end-loads on a small bearing area. Without a padstone, that load crushes the supporting masonry — sometimes immediately, sometimes over months. Padstones spread the load across enough masonry to keep stresses below the brick or block's compressive strength.

Typical sizes

For typical residential loads:

• Light load (small beam, single storey): 100×100×100mm
• Medium load (typical extension beam): 215×100×140mm (one brick course)
• Heavy load (multi-storey or wide span): 215×215×140mm or larger

Padstones are usually pre-cast concrete or solid dense blocks. Engineering bricks are sometimes acceptable for lighter loads.

Sizing principles

Engineer calculates:

• End reaction of the beam (kN)
• Bearing area required to keep stress below masonry strength (typically 2–7 N/mm² depending on block type)
• Padstone dimensions to provide that area plus dispersion through padstone depth

What goes wrong without them

• Crushed brickwork under the bearing
• Beam dropping over time
• Cracks radiating from the bearing into adjacent masonry
• Door frames distorting
• Catastrophic failure in extreme cases

Local Authority Building Control

Padstones must appear on calculations and drawings. Inspectors check for them at site. Beams installed without padstones will fail inspection.

Variations

• Spreader beams: small steel sections instead of concrete padstones, useful where depth is restricted
• Cast-in-situ padstones: mass concrete poured into formwork, used for very heavy loads
• Multi-course padstones: for extreme loads, padstones extend two or three courses deep

MCFAR specifies padstones on every beam design.

Frequently Asked Questions