Choosing a lintel starts with four questions: what is the wall made from, how wide is the structural opening, what loads sit above it, and how much sound masonry is available at each end?
This guide explains how those factors affect the choice between cavity-wall, solid-wall, concrete, box and timber-frame lintels. It also covers what to measure before ordering, where costly mistakes occur, and when the decision should be passed to a structural engineer, designer, manufacturer or Building Control.
The essential warning is simple: never select a lintel purely from the visible width of the window or door.
What does a lintel actually support?
A lintel spans an opening and transfers the loads above it into the wall on either side.
Those loads may include:
- brickwork or blockwork
- an upper-storey wall
- floor joists
- roof trusses or rafters
- beams and other concentrated loads
Two openings with the same width can therefore require completely different lintels. A first-floor window beneath a short section of lightweight masonry presents a different loading condition from a ground-floor doorway supporting another storey and floor joists.
Lintel length matters, but it is only one part of the specification.
Start with the wall construction
UK buildings contain several generations of wall construction.
Older properties may have solid brick or stone walls, sometimes with brick arches, timber lintels or early steelwork concealed behind plaster and render. Twentieth-century housing commonly uses masonry cavity walls. Modern development also includes timber-frame construction, where the external brickwork and structural timber frame perform different roles.
The wall type determines which lintel configurations are appropriate.
Steel cavity-wall lintels
Steel cavity lintels are commonly used where an inner and outer masonry leaf are separated by a cavity. A single profiled lintel may support both leaves.
The selected product must suit:
- the cavity width
- the inner-leaf thickness
- the outer-leaf thickness
- the insulation arrangement
- the design load
This has become increasingly important as insulation requirements have produced wider wall cavities. A lintel designed for one cavity range should not be substituted automatically for another simply because its overall length appears correct.
Solid-wall and box lintels
Solid masonry walls may require a box lintel, solid-wall lintel or another profile designed for the full wall thickness.
Box lintels are also used in some internal masonry walls. An internal wall should not automatically be treated as lightly loaded. It may support another wall, a floor or part of the roof structure.
Concrete lintels
Precast and prestressed concrete lintels are widely used in blockwork, internal walls and other masonry applications.
They can be economical for relatively straightforward openings, but they still vary by:
- width
- depth
- reinforcement
- orientation
- load capacity
Longer concrete lintels can also be heavy. Access, lifting and temporary support should be considered before delivery, not once the lintel arrives on site.
Timber-frame and single-leaf lintels
In timber-frame construction, the external masonry leaf may need support across the opening while the structural timber frame is dealt with separately.
That usually requires a lintel designed for the timber-frame cavity arrangement. A conventional masonry cavity lintel should not be assumed suitable.
Single-leaf and angle lintels may be used where only one leaf of masonry requires support, but they are not universal alternatives to cavity or solid-wall lintels.
Opening width is not lintel length
The relevant measurement is the clear structural opening between the supporting masonry, not simply the visible width of the window or door frame.
The lintel must extend beyond that opening to provide adequate bearing at both ends.
Catnic states that lintels generally require a nominal minimum end bearing of 150mm at each end. Under that common arrangement:
1,200mm structural opening
- 150mm bearing on the left
- 150mm bearing on the right
= 1,500mm lintel
However, 150mm is not a universal rule for every lintel. The exact manufacturer’s technical information must take precedence, particularly for specialist products, unusual spans or different materials. Catnic’s guidance on lintel support and end bearing explains the general requirement and associated installation considerations.
The bearing must also sit on suitable masonry. Adding the correct bearing length does not solve cracked bricks, incomplete blocks or inadequate support below the lintel.
Check what bears onto the wall
Before selecting a load category, establish what the lintel will actually carry.
Relevant questions include:
- Do floor joists run into the wall or parallel with it?
- Do roof trusses, rafters or purlins bear onto the wall?
- Is there another opening directly above?
- Is a beam or other point load nearby?
- How much masonry sits above the opening?
- Are the inner and outer leaves carrying different loads?
Manufacturer load tables may classify lintels as standard, medium, heavy or extra-heavy duty. Those descriptions apply within a particular product range. They are not universal categories that can be compared by name alone.
Approved Document A covers structural loading and the construction of walls, floors, roofs and other building elements in England. It is a useful regulatory reference, but it does not remove the need for project-specific calculations where the loading or structure falls outside straightforward guidance. See the government’s Approved Document A.
Thermal bridging and damp protection
A lintel in an external wall also affects heat loss and moisture control.
Steel is highly conductive. A poorly insulated lintel detail can create a thermal bridge above a window or door, increasing local heat loss and lowering internal surface temperatures.
The complete construction may need to account for:
- insulation within or around the lintel
- continuity with cavity insulation
- cavity trays or damp-proof courses
- stop ends
- weep vents
- exposure to wind-driven rain
An insulated lintel should not automatically be assumed to provide every part of the damp-protection detail. The requirements depend on the selected product, wall construction and exposure conditions.
Replacing an existing lintel needs investigation
Replacing an old lintel is not necessarily a like-for-like exercise.
An older building may contain a timber lintel, shallow brick arch, corroded steel section or another arrangement hidden behind the finishes. The original lintel may also have been undersized or installed with inadequate bearing.
Cracking above an opening does not prove that the lintel itself has failed. Possible causes include:
- corrosion expanding within the wall
- movement elsewhere in the structure
- inadequate bearing
- deteriorated masonry
- altered floor or roof loads
- earlier structural alterations
Before removing masonry, confirm what currently supports the wall and how it will be temporarily propped. Temporary support is itself a structural consideration.
For further practical detail on door openings, wall types, lintel length and wider spans, Wade Building Supplies has published a detailed guide to door lintels. The guide also covers cavity, solid-wall, internal and timber-frame applications, as well as the distinction between lintel length and load duty.
Common measuring and ordering mistakes
Most lintel-ordering problems begin with incomplete information.
Common mistakes include:
- measuring the frame instead of the structural opening
- forgetting to add the required end bearings
- confusing cavity width with total wall thickness
- failing to identify both masonry leaves
- selecting by length without checking load capacity
- overlooking floors, roofs or nearby beams
- assuming the existing lintel was correctly specified
- ignoring product weight and access
- ordering before confirming thermal and damp details
- modifying a proprietary lintel to make it fit
A steel or concrete lintel should not be cut, drilled, welded or otherwise altered unless the manufacturer has expressly confirmed that the modification is permitted.
Practical pre-order checklist
Before requesting a quotation or placing an order, record:
- Clear structural opening width.
- Required bearing at each end.
- Inner-leaf material and thickness.
- Outer-leaf material and thickness.
- Cavity width and insulation arrangement.
- Total wall thickness.
- Height and material of masonry above.
- Floor or roof members bearing onto the wall.
- Nearby beams or concentrated loads.
- Internal and external finish requirements.
- Thermal and damp-protection details.
- Product weight and access for handling.
- Relevant drawings or structural calculations.
Photographs are useful for existing openings, but they should support accurate measurements rather than replace them.
When professional input is required
A structural engineer should normally be consulted where:
- a loadbearing wall is being substantially altered
- an opening is being widened
- the loading cannot be established confidently
- a beam or other point load is close to the opening
- the existing construction is unclear
- damaged masonry affects the bearing
- a standard manufacturer selection cannot be made safely
An architect or designer may specify the wall, insulation and moisture details. Manufacturers can interpret their own product data when given complete information. Building Control may request calculations or supporting documentation.
A checklist can organise the information, but it cannot assess an unknown structure. Select the lintel from the wall construction, structural opening, end bearing and actual loading conditions, never from the visible window or door width alone.
