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Building components · Wall Leaves & Backing

Masonry Arch

Explains the arch as a form that carries masonry by its shape rather than by bending, which is what separates it from every kind of lintel.

Form:Unit or moduleRoles:StructureSupport

Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.

Overview

What a masonry arch is

A masonry arch spans an opening using the geometry of its own units. Each unit is wedged against its neighbours so that load travelling down the wall is turned into compression running around the curve and delivered into the masonry at either side. Because the thrust arrives at an angle rather than straight down, an arch pushes outward as well as downward.

That outward push is the defining consequence of the form. An arch is only as good as what resists its thrust, which is why the masonry beside an opening, the presence of a return wall or a buttress, and the continuity of the wall above all matter to whether an arch stands. It is also why an arch is not complete until both sides are built and supported.

Boundaries

How it differs from nearby elements

The distinctions that keep this entry from being a restatement of its neighbours.

  • It is not a lintel. A lintel is a procured member laid across an opening to carry the masonry above it, and it works in bending, delivering its load vertically onto the masonry at each end; an arch carries the same masonry by its curve, works in compression, and pushes outward at its supports as a result.
  • It is not the head of an opening in general. The head is the position at the top of any opening; an arch is one of the forms that position can take, alongside a flat lintel or a supported course of units on end.
  • It is not a single element in the way a beam is. It is an assembly of individual units that only acts as an arch once the ring is complete and supported at both ends, which is why it behaves differently while it is being built than it does in service.

Terminology

Common names and aliases

These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.

  • gauged brickwork head
  • arch ring
  • arched head

Dependencies

What it depends on

What has to be right elsewhere for this element to do its job.

  • What resists the outward thrust at each side, which is commonly the wall, a pier or a return rather than anything within the arch itself.
  • The masonry above and around it, since the load the arch carries and the restraint it receives both come from the wall it sits in.
  • Temporary support while it is built, because the units cannot act together until the ring is closed.
  • The joints between the units, since the thrust passes across every one of them and the geometry depends on them staying closed.

Considerations

Topics that genuinely apply here

Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.

Structural transfer

An arch converts vertical load into inclined thrust, so the question it raises is not only what it spans but what receives the push at either end.

Movement

Spreading at the supports is one of the ways arches are commonly affected, because a small outward movement changes the geometry the form relies on.

Buildability

The arch does not exist as a structure until it is complete, so what supports it during construction is part of how it comes into being rather than an incidental.

Durability

Water reaching an arch tends to concentrate at the joints between units, and deterioration of those joints affects the geometry as well as the appearance.

Materials

Commonly formed from

Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.

Materials LibraryClay facing brick →Brick arches are among the most commonly encountered forms over openings in masonry walls.Materials LibraryDressed stone blocks →Stone arches are met in traditional construction and wherever the opening is treated as a worked feature.Materials LibraryEngineering brick →Encountered where the arch is in a more exposed position or carries a heavier wall above it.

Materials

Commonly incorporates

Materials this element commonly contains as a distinct constituent part, rather than being made of.

Materials LibraryMasonry mortar →The joints between the units are where the thrust crosses from one unit to the next, so the jointing material is part of how the form acts.

Assemblies

Building systems this element is met in

The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.

Primary supportEdge and terminationSolid Wall →Spans an opening through the full thickness of the wall, so the thrust is delivered into the whole wall rather than into one leaf.Primary supportLoad-Bearing Masonry →Carries the loadbearing wall across an opening by geometry rather than by a spanning member.Primary supportEdge and terminationTwin-Leaf Cavity Wall →An arch may be present in one leaf while the other leaf is spanned differently, which makes the two sides of the opening behave unlike each other.Edge and terminationWindow Opening Interface →Forms the head of the opening that the window interface has to seal and weather against.Primary supportEdge and terminationFreestanding Wall →Openings in freestanding walls are frequently arched, and the thrust has only the wall on either side to resist it.

Related elements

Neighbouring components

Typed relationships to other elements. There is deliberately no generic “related” category: an edge that cannot be classified does not exist.

Clarifications

Commonly misunderstood

  • That an arch and a lintel are interchangeable ways of spanning an opening. They put load into the surrounding masonry in different directions, so replacing one with the other changes what the wall either side has to do.
  • That an arch with a straight underside is not an arch. A flat or cambered arch can still work by wedging its units against one another, and the flat line beneath says nothing about how load travels through it.

Conversations

Questions for qualified professionals

Questions worth asking someone with the project in front of them. This page cannot answer them.

  • What resists the outward thrust from this arch at each side?
  • Has the arch or the masonry beside it moved, and does the geometry still hold?
  • Was this opening formed as an arch, or as a lintel with an arch-shaped face over it?
  • If work is planned near this opening, what would removing or disturbing the masonry beside the arch do to it?

Go deeper

Related Build Design Hub guides

Planning guidance behind the decisions this element involves.

Preparation

Related planning checklists

Owner-side preparation before the conversation where this element comes up.

What this entry does not do

  • This entry describes a form of construction. It states no span, no rise, no unit count, no ring depth and no load capacity, and none can be inferred from it.
  • Whether a particular arch is stable, or what has caused it to move, is a structural assessment made on site and cannot be answered from a reference entry.

Wall Leaves & Backing

The distinct vertical layers that make up a wall — outer and inner leaves, the cavity between them, and the backing that supports what is fixed to the face.

Browse all wall leaves & backing entries →