Lintel design
A lintel carries the masonry and the loads above a window or door across the opening below. We specify and check lintels for new and altered openings so they carry the load with control of cracking, for clients throughout the UK.
Do I need an engineer to specify a lintel?
For a standard window or door opening in a cavity wall a builder can often select a catalogue lintel. Where loads are concentrated above the opening, the span is large, or the wall is altered structurally, Building Control will want the lintel checked, and we provide that calculation and specification.
Loads on a lintel and how they are gathered
A lintel spans a relatively short opening but has to deal with a specific pattern of load. Directly above the opening the masonry can arch, so only a triangle of brickwork bears on the lintel rather than the full height of wall, provided there is enough masonry either side and above for the arch to form. Any concentrated loads landing within that zone, a beam end, a joist bearing or a floor above, cannot be arched over and must be carried in full. We work out which loads arch and which do not, because assuming an arch that cannot form is a common cause of undersized lintels and cracked brickwork.
For most domestic work we specify galvanised steel lintels to BS EN 845-2 and BS 5977, chosen from the manufacturer's safe working load tables against the design load and clear span we have calculated. Where loads are heavier, spans longer or the detail unusual, we design a purpose-made steel or reinforced concrete lintel from first principles to the Eurocodes. Either way the specification states the exact reference or section, the bearing length and any propping needed while the mortar gains strength.
Cavity walls, thermal performance and durability
In a modern cavity wall the lintel does two structural jobs at once, carrying the inner and outer leaves, and one building physics job, keeping the cavity's damp and thermal separation intact. A combined steel lintel supports both leaves and forms the cavity tray, throwing water back out through weep holes, so the profile has to suit the cavity width and the wall build-up. We check the load share between the two leaves, since a heavy masonry outer leaf and a lighter blockwork inner leaf do not load the lintel equally.
Durability and thermal bridging matter as much as strength on a lintel. Galvanised or stainless steel is specified to suit the exposure, and we note where an insulated lintel is needed to limit the cold bridge at the head of the opening, which the Building Regulations energy requirements increasingly drive. On period and stone buildings we design to match the existing construction, whether that is a natural stone lintel, a concealed steel to preserve the elevation, or a reinforced concrete lintel behind a stone face.
Bearings, deflection and building it right
A lintel needs an adequate bearing at each end so the reaction spreads into the masonry without crushing it. Standard steel lintels usually need 150mm of end bearing on each side; heavier or longer units may need more, and where the supporting masonry is weak a padstone or engineering brick course is required to spread the load. We state the bearing length and any padstone in the specification so it is built in, not improvised.
Deflection is limited to protect the brickwork above and the window or door below, because a lintel that sags will crack the masonry and jam the frame. We keep deflection within span/360 or the manufacturer's stated limit, whichever is tighter. The output is a clear lintel schedule, opening by opening, giving the reference, bearing and propping requirements, ready for the builder to order and for Building Control to sign off, delivered anywhere in the UK or Europe.
What we check.
The points our calculations resolve for a project like this.
- Arching action assessed to separate arched masonry from loads that must be carried in full
- Concentrated loads from beams and floors landing within the load zone above the opening
- Load share between inner and outer leaves in a cavity wall
- Cavity tray, weep holes and insulated lintel to manage damp and thermal bridging
- End bearing length and padstones where the supporting masonry is weak
- Deflection limited to protect the brickwork and the window or door below
Issued drawings, redacted.
From enquiry to sign-off.
Enquiry
Send drawings or describe the problem. We confirm the scope, the deliverables and a target timescale.
Information
We agree the survey, drawings or data we need and any site access required.
Engineering
Design, calculation or assessment to the relevant Eurocodes and UK National Annex.
Issue
A clear, defensible report or set of calculations, with assumptions and limitations stated.
Common questions
Do I need an engineer to specify a lintel?
For a standard window or door opening in a cavity wall a builder can often select a catalogue lintel. Where loads are concentrated above the opening, the span is large, or the wall is altered structurally, Building Control will want the lintel checked, and we provide that calculation and specification.
How much does lintel design cost?
Our fee starts for a lintel calculation and specification, fixed before we start. Several openings, unusual spans or a purpose-made steel or concrete lintel will affect the fee, agreed with you up front.
What lintel do I need over a new opening?
It depends on the span, the wall construction and what sits above. We calculate the load, allow for any arching, and either specify a proprietary steel lintel from the load tables or design a purpose-made unit. The specification gives the exact reference and the bearing needed.
Can a lintel be hidden on a period property?
Yes. On stone or period elevations we can design a concealed steel lintel behind the face, a reinforced concrete lintel, or a natural stone lintel to match, so the structure works without changing the appearance.
How much end bearing does a lintel need?
Standard steel lintels typically need 150mm of bearing at each end, and more for longer or heavier units. Where the masonry beneath is weak we add a padstone or engineering brick course. We state the required bearing in the specification.
Related in structural design & elements.
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Send the drawings or describe the project. We confirm scope, deliverables and a realistic timescale.
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