Load-Bearing Masonry

Load-bearing masonry walls carry floors and roofs as well as enclosing the building. They are solid brick, stone or blockwork, sometimes cavity walls where the inner leaf carries the load, with arches, lintels and piers over and between openings. Most pre-war houses, terraces, warehouses and institutional buildings in Australia, Britain and the United States are load-bearing masonry, as are many low-rise apartment blocks of later eras. The façade aspects of masonry (ties, pointing, spalling) are covered on the masonry and brickwork page; this page covers how masonry carries load and how that fails.

Masonry is strong in compression and weak in tension and bending. It depends on being held in line by the floors and roof it supports, on arches and lintels spanning openings, and on not being weakened by holes and removed walls. Most structural failures in masonry buildings come from alterations or loss of restraint rather than from the masonry itself.

What shortens life:

• Alterations: walls removed, openings widened, chimney breasts taken out.
• Loss of restraint: floors and roofs not tied to walls, or ties removed.
• Water washing out mortar and rotting embedded timbers.
• Foundation movement.
• Hard cement repairs and impermeable coatings.

Alterations

Load-bearing walls removed to open up rooms, openings widened, chimney breasts removed and walls chased for services remove support or concentrate load. Steel beams inserted without adequate bearings, padstones or engineering crush the masonry at their ends.

Bowing and lack of restraint

Walls that are not tied to the floors and roof they support can bow outward, especially tall gable walls and walls where floor joists run parallel and so do not bear on them. Removal of internal walls that braced external ones has the same effect.

Separation of rubble-cored walls

Stone walls with rubble cores separate as the core mortar washes out; the outer faces bulge and can collapse.

Lintel and arch failure

Timber lintels behind arches and timber bond courses in old walls rot; steel lintels corrode; arches spread when their abutments move or when nearby openings remove their support. Masonry above drops and cracks.

Overload

New loads such as storage, roof plant, added storeys and heavier roof coverings can exceed the capacity of slender or weakened walls, which crush, crack vertically or bow.

Settlement

Foundation movement cracks masonry walls diagonally through openings; see the foundations page.

Earthquake vulnerability

Unreinforced masonry is the most vulnerable common construction in earthquakes: walls fall outward, parapets and chimneys collapse, and floors pull out of their bearings. Seismic regions require or encourage retrofit.

On site

• Walls bowing outward or out of plumb, especially gables and tall walls.
• Cracks below beam ends; crushed or cracked masonry at bearings.
• Cracks and dropped brickwork over openings; arches cracked at the crown or separating at the springing.
• Bulging stone faces; loose stones.
• Rooms opened up by removing walls or chimney breasts, with new beams.
• Vertical cracking in piers between openings.

In the records

• Building approvals and engineering for alterations.
• Previous structural reports.
• Restraint or strapping works.
• Seismic evaluations in seismic regions.

• Doors and windows in upper storeys that bind or have been planed repeatedly, often the first sign of a wall moving out of plumb.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A structural engineer experienced with masonry and, for heritage buildings, conservation.

• Plumb and bulge survey of walls, with monitoring where movement is suspected.
• Restraint check: how floors, roofs and walls are connected, by opening up at representative points.
• Alteration review: identify removed walls and breasts and check what supports the load, with approvals.
• Bearing inspection at beam ends and lintels.
• Wall construction: solid, cavity or rubble-cored, by endoscope or opening.
• Load review against current use.
• Seismic evaluation in seismic regions.

The report should state stability, the cause of movement, safety measures and repairs.

Movement is judged over time: fixed survey targets on bowing walls, read several times over a year, show whether a bow is historic and stable or still growing, which decides between monitoring and immediate restraint.

• Restraint: straps tying floors and roofs to walls, tie rods with pattress plates across buildings, and helical ties into walls.
• Bearings: padstones and spreader beams under beam ends.
• Lintel replacement and arch repair.
• Crack stitching with helical bars after the cause is addressed.
• Grouting of rubble cores and pinning of stone faces.
• Rebuilding of badly bowed or failed sections.
• Seismic retrofit: anchoring walls to floors, bracing parapets, adding frames or walls.
• Retrospective engineering and approval for past alterations.

• Temporary propping and shoring while permanent repairs are designed, so that a bowing wall or failed lintel cannot collapse in the meantime.
• Lime-based repairs in traditional masonry so repairs move and breathe with the original, avoiding the damage hard cement causes.

Investigation is a lump sum. Restraint and stitching are priced per tie or per metre. Lintel replacement per opening with propping. Rebuilding by area. Seismic retrofit is a lump-sum project. Propping is an immediate cost.

Repairs to stop movement are condition items; ordinance retrofits are deadlines; safety items are immediate.

Propping and shoring can run for months while designs and approvals are prepared, and their hire is a recurring cost until the permanent repair is complete. Work to party walls adds surveyors' fees and agreement with neighbours. Heritage approval can extend programmes and require specialist materials and trades.

• Australia. AS 3700 and AS 4773 govern masonry; AS 1170.4 sets earthquake actions; alterations to load-bearing walls need building approval; heritage controls often apply.
• United Kingdom. BS EN 1996 governs masonry; Approved Document A covers structure and restraint; alterations need building regulations approval and often party wall notices; heritage buildings need listed building consent.
• United States. TMS 402 governs masonry design; the International Existing Building Code Appendix A1 covers seismic strengthening of unreinforced masonry; several California cities require unreinforced masonry and soft-storey retrofits.

In all three jurisdictions, past alterations without approval can create disclosure, insurance and certification issues at sale or refinancing, and may require retrospective approval or rectification before a building can be certified. Strata and leasehold buildings treat load-bearing walls as common or landlord structure even where they sit within a unit, so owners cannot alter them without consent.

• Building approvals and engineering for alterations.
• Previous structural reports.
• Restraint and strengthening records.
• Seismic evaluations and retrofit orders.
• Heritage listing.

• Records of chimney breast or wall removals, with what now supports the load.
• Monitoring data for bowing walls.
• Party wall awards for work to shared walls.
• Strata or landlord consents for alterations within units.