Structure and support · Frames & Load-Bearing Walls
Load-Bearing Masonry Wall System
This entry maps the vertical load path through a masonry wall and the restraint that keeps that wall standing, so an owner can see why forming an opening or taking a wall out is a whole-structure question rather than a local one.
Educational reference entry. How this system behaves depends on climate, jurisdiction, loading, substrate, the adjacent systems it meets, how the building is used, the manufacturer's instructions and qualified professional design.
Overview
What load-bearing masonry is
Load-bearing masonry is the oldest arrangement still in everyday use, and its defining feature is that enclosure and structure are the same thing. Units bedded in mortar accumulate the load of each floor and of the roof and pass it down through their own section to the foundation, so the plan of the walls and the plan of the structure are one drawing rather than two.
What makes it an assembly rather than a stack of units is that the wall is slender relative to its height and cannot stand alone against horizontal force. The floors that bear on it also hold it, and the walls returning at an angle to it keep it in line. An opening interrupts both duties at once, which is why the support over an opening and the wall around it are considered together.
The boundary against lateral-stability-system is visible in a building rather than in wording. Strip the floors out of a masonry house and the walls still carry whatever sits on their heads; they simply have nothing holding them upright against wind. This entry owns the downward path, and the horizontal path from floor plate to wall to ground belongs there.
It is equally not solid-masonry-wall-system, which describes the same physical wall purely as a weather and drying build-up and states no load path at all. If the question is where the roof load goes, this is the entry; if the question is how the wall wets and dries, it is not.
Terminology
Common names and aliases
These names describe the same assembly. The encyclopedia keeps one entry per system so that a trade term or a regional name never becomes a second, thinner page.
- structural masonry
- masonry bearing wall structure
- load-bearing brick and block construction
Purpose
What this system is intended to do
The job the assembly exists to perform, conceptually. An intention is not a guarantee that any particular build achieves it.
- Carry the accumulated vertical load of floors and roof through the wall itself and into the foundation beneath it.
- Keep that load path continuous from head to base, so nothing above is left bearing on something that has been taken away.
- Accept restraint from floors and returning walls so the wall holds its line under horizontal force.
- Collect and spread load around and over openings without concentrating it where the masonry cannot receive it.
- Allow the wall to change length at planned positions rather than at cracks of its own choosing.
Composition
The roles this system is made of
What each part does in the assembly and what it depends on — never a product, a thickness, a fixing or a determination that anything is adequate for the role.
Order is not meaningful in this system. These roles interact as parts of one whole rather than stacking up in a sequence, so the list below is not a build-up and nothing should be read into the order it appears in.
- Primary supportLoad-bearing leaf
The masonry itself, made up of units laid in a bond that overlaps the joints below so load spreads sideways as it descends. Its strength is its section, so anything that removes material from it - a chase, a recess, a flue - removes part of the load path.
- Jointing and sealingBed joints and perpends
Compression travels from bed joint to bed joint, so it is the horizontal beds that hand each unit's load to the one below across its bearing surface. The vertical perpends close the wall, complete the bond and help it weather, and in a good deal of blockwork they are deliberately left unfilled.
- Primary supportFloor and roof bearings
The positions where joists, beams, plates or slabs land on the wall and transfer their reaction into it. A bearing is a concentration point, and what sits immediately beneath it in the masonry decides whether the concentration is acceptable.
- Primary supportLintels, arches and spreader pieces
The elements that carry masonry and floor load across an opening and deliver it to the piers each side. They change the shape of the load path rather than removing load, and the piers they feed become the narrowest part of the route to ground.
- AttachmentLateral restraint and returning walls
Walls at an angle to the main wall, and straps or connections between the wall and each floor and roof, that stop the wall buckling or overturning. These are structural even though they read on a plan as room divisions and on site as ironmongery.
- Edge and terminationMovement joints
Planned separations through the masonry that let the wall change length. Their positions relate to the length of the run, the openings that already weaken it and the family of unit used, and a joint bridged by a tie or a bonded return is not a joint.
- SubstrateFoundation and base interface
The zone where the wall meets what supports it, including the damp-proof course that separates the two. It is where the masonry sits closest to ground moisture and splashing, and also the point at which the whole load path arrives, so the structural and moisture questions overlap here.
- AttachmentWall-to-wall and wall-to-floor ties
The connections that make separate elements act together, including ties between leaves, ties between new and existing masonry, and connections into floor structures. Where they are missing, elements that look joined behave as if they are not.
Interaction
How the parts work together
The reason this is a system rather than a list of parts: what depends on what, and what stops working when one part is changed.
The bed joint is not glue, it is the surface that lets one unit hand its load to the one below evenly. Where a bed is hollow, unfilled or over-hard relative to the units around it, load concentrates on the arrises of units instead of on their beds, and the wall reports the problem as cracking that follows the joint pattern rather than the unit.
A bearing is a transfer point whose behaviour depends entirely on what sits above it. Load arriving from a joist end or a beam end is concentrated, and the masonry immediately beneath has to be able to receive it or a spreader has to intervene. The same wall that accepts a distributed floor without complaint may not accept an equal total load delivered through a single point.
Restraint runs in the opposite direction to load. The floors do not only push down on the wall, they hold it in position. Cut a floor away to form a void, or take out a returning wall to open a plan, and the wall loses what was keeping it in line even though nothing about its vertical load has changed. Plan changes and floor changes are structural at the same moment.
Openings couple all of this together. A lintel carries the masonry directly over it, but what it collects has to travel down the piers on either side, and those piers are then the narrowest part of the route to the foundation. Widening an opening lengthens what is being carried and shortens what is carrying it in the same operation.
Movement joints work only because the rest of the wall is restrained. The wall changes length while floors, returns and foundation hold it, and a joint placed where the wall wants to move takes that as a planned gap. Bridge it with a tie or bond a return across it, and the movement still occurs and appears instead as a crack at the weakest position available.
Materials
Material families commonly met in each role
Commonly encountered, not recommended. Whether a material suits a given project depends on the whole assembly, the exposure, the manufacturer's documentation and qualified professional review.
Primary support
These unit families are commonly encountered in load-bearing masonry, and they differ in how they carry, how they move and how they weather. Whether any particular unit belongs in a given wall is a matter for the manufacturer's documentation and the structural designer.
Jointing and sealing
Mortar is commonly encountered as the bedding medium in this system. Its relationship to the units around it - which should be the sacrificial element and which should not - is a design judgement rather than a property of the mortar in isolation.
Attachment
Ties are commonly encountered where two leaves or a new and an existing wall have to act together. Type, material and arrangement are determined by the designer and the manufacturer's documentation for the specific condition, not by the wall alone.
Edge and termination
These are commonly encountered where masonry stops at an opening or at the top of a wall. Each of them changes the load path or the water path at that point, so the choice is made alongside the structural and weathering design rather than after it.
Control layer
A damp-proof course is commonly encountered at the base of load-bearing masonry and at other positions where water would otherwise track through. Nothing here implies that any single layer keeps a wall dry; resistance to moisture rising through a base is a property of the whole detailed assembly.
Junctions
Where this system meets others
Interfaces are where most assemblies actually fail, so they are set out explicitly rather than left inside the prose. What resolves a junction is a detail designed for the specific building — not a rule of thumb.
Wall base onto the foundation
The entire load path arrives at this line, and so does most of the water. The foundation has to receive the load the wall delivers, and the separation between wet ground and absorbent masonry has to remain continuous where floors, thresholds and external levels all meet the same zone.
Read about Strip Foundation →Joist ends bearing into the wall
Joist ends load the wall and restrain it, and they also sit inside it where they are hardest to inspect. The bearing detail therefore settles a structural question and a durability question together, and altering a floor alters the restraint the wall was relying on.
Read about Timber Joisted Upper Floor →Wall plate and roof spread
A pitched roof does not only press down on the wall; unless it is tied, it pushes the wall heads apart. The wall plate distributes the roof load along the wall and the tying arrangement resolves the outward push, which is why roof alterations reach the wall below.
Read about Roof Carcass →Restraint and the horizontal path
The wall supplies vertical resistance and receives horizontal restraint, and this junction is where the two entries meet. Anything that changes the floor plates, the returns or the connections between them changes the restraint condition without touching the load path.
Read about Lateral Stability →The same wall read as an external build-up
Where a load-bearing wall forms part of the external envelope, the inner leaf is usually the structural element and the outer leaf is not. The two entries describe the same construction from different directions, and confusing which leaf is carrying is a common source of error.
Read about Twin-Leaf Cavity Wall →Continuity of the barrier through the base
The barrier at the wall base has to join whatever protects the floor and whatever protects any adjoining structure. A discontinuity is invisible once the finishes are on, and the consequences appear at plaster and skirting level rather than at the position of the fault.
Read about Damp-Proof Continuity →
Considerations
Topics worth discussing
Which topics genuinely apply to this system and what to raise about them. Measured values, classes and ratings come from a qualified professional's design for the specific building, not from a reference page.
- Movement
- Masonry changes length with temperature and moisture, and clay-based and cement-based units do not move in the same direction. Where a run is long, where openings already weaken it, or where different unit families meet, the positions at which movement is permitted are a design decision.
- Moisture
- The wall wets and dries in both directions, and its base is the zone closest to ground moisture and to splashing off the surface outside. Whether that base behaves as designed depends on continuity through the whole detail rather than on any layer, and on what has been added later - raised ground, render, a solid floor - that bridges it.
- Durability
- Mortar is generally intended to be the part of the wall that weathers and is renewed. Where a repointing mortar is harder than the units around it, decay transfers into the units instead of the joints, and damage that would have been maintenance becomes replacement.
- Buildability
- Chases, recesses, flues and service routes all take material out of a wall whose strength is its section. Which of them are acceptable, and where, is settled with the structural designer before the wall is built rather than negotiated once the trades are on site.
- Interfaces
- Every floor and roof landing on the wall is both a load and a restraint, so an alteration to a floor is an alteration to the wall. Junctions with returning walls, chimney breasts and shared walls carry the same double duty and are altered with the same caution.
- Documentation
- Older masonry buildings rarely carry a record of what was altered and when. Establishing which walls are carrying, what has already been removed and what is currently propping what is a survey exercise, and assumptions made from appearance are unreliable.
Design
Questions the design has to answer
The decisions this assembly turns on. They are questions rather than answers, because the answer depends on the building.
- Which walls carry load, which provide restraint, and which are doing both at the same time?
- Where does the load from the roof and from each floor actually arrive on the wall, and what is directly beneath that point?
- Is the wall being asked to take a concentrated reaction where it previously took a distributed one?
- What holds this wall in line, and does the proposal alter that floor, that return or that connection?
- Where is the wall expected to change length, and is there a planned joint there or only a crack waiting to happen?
- Does the separation at the base remain continuous where floors, external levels and finishes all arrive at it?
- What has already been altered in this building, and does any of it sit on the load path being relied upon?
Boundaries
Commonly misunderstood points
Distinctions that are easy to blur, and the places where a familiar term means something narrower than it sounds.
- A thick wall is not automatically load-bearing, and a thin one is not automatically a partition; only the load path settles it.
- Replacing a wall with a beam does not remove the load, it changes where the load arrives and concentrates it at the beam ends.
- Cracking that follows the mortar joints is describing a different condition from cracking that runs straight through the units.
- Repointing is not a cosmetic choice, because the joint is doing structural work and moisture work at the same time.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Can you confirm which of these walls are load-bearing, and describe how you established that?
- What is restraining this wall at present, and what will restrain it during and after the works?
- How will load over a new opening be collected, and where does it reach the foundation?
- Is the existing foundation being asked to carry a different load, or the same load differently distributed?
- What temporary support is required, who designs it, and at what point can it be removed?
- Have previous alterations been identified, and do any of them affect what is being proposed here?
- Where are movement joints intended to fall, and does anything bridge them in the proposed detail?
What this page does not do
- Nothing here establishes whether a particular wall may be opened, altered or removed; that is a determination for a structural engineer on the specific building.
- This entry states no span, load capacity, bearing pressure or dimension of any kind, and none should be inferred from the descriptions given.
- Shared and party structures carry legal obligations in many jurisdictions, and those obligations sit outside the scope of this reference.
- Evidence of movement in a masonry building should be assessed before any alteration is designed, not diagnosed from a description.
Related systems
How this system relates to others
Every link states what the relationship actually is, rather than leaving a bare list of related pages to be read as a suggestion.
Alternatives
Different systems answering the same need. Listing them together is not a comparison and does not suggest one is better — which, if either, suits a project is a design decision.
Meets these systems
Systems this one physically meets. The junction is usually where the design problem lives, so these are worth reading together.
Commonly built alongside
Systems routinely present in the same building without necessarily touching this one.
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this assembly involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this system comes up.
Inspiration
Related Ideas Library pages
Design directions where this system commonly appears.
Primary Structural Frames and Load-Bearing Wall Systems
Complete primary load paths from roof to foundation in masonry, timber, steel and concrete, together with the stability system without which none of them stands up.
Browse all frames & load-bearing walls entries →