What is a lintel, and what types are there?
The thing spanning the top of every opening in a wall, the five kinds you will meet in British houses, why the bearing at each end matters as much as the span, and why the top mark on a concrete lintel is not decoration.
- Difficulty
- intermediate
- Time
- 10 min
- Read
- 5 min
- Safety
- warning
Short answer
A lintel carries the wall above an opening across to the masonry each side. In British houses you will meet prestressed or reinforced concrete, pressed steel combined lintels in cavity walls, timber in older and internal work, brick arches and soldier courses in traditional walls, and stone. Each end has to bear on sound masonry over a designed length. Reinforced and prestressed concrete lintels are marked because they only work one way up.
Every window and door in a masonry wall has several tonnes of building above it, and something is holding that up. Knowing what is up there changes how you approach hanging a curtain pole, diagnosing a crack from the corner of a window, or understanding why a builder's quote includes a steel you cannot see.
Safety
Step by step
- Understand what a lintel is resisting.The masonry above an opening arches to some extent and does not all bear on the lintel, but the lintel still has to carry a triangle of wall plus any floor or roof load landing on it. It bends, so its bottom face is in tension.
- Recognise a prestressed concrete lintel.A plain rectangular concrete section, very common internally and in inner leaves. Prestressing wires run near the bottom face and are tensioned before the concrete sets, so the section is squeezed and resists bending. These are marked TOP for a reason.
- Recognise a pressed steel cavity lintel.The galvanised steel box or angle section used across both leaves of a cavity wall, usually with an integral sloping top that acts as the cavity tray. Nearly every cavity-walled house built since the 1970s has these over its windows.
- Recognise a brick arch or soldier course.A flat, segmental or cambered arch of brick, or a row of bricks standing on end. An arch carries load by compression to abutments each side. A soldier course usually cannot, and is normally supported on a steel angle hidden behind it — which is why soldier courses sag when that angle corrodes.
- Recognise timber and stone.Timber lintels are common in pre-war and internal work, and are usually sound unless they have been wet. Stone lintels are structural in traditional stone buildings, and often decorative in front of something else in later ones.
- Look at the bearing, not the span.A lintel has to sit on sound masonry at each end over a designed length, and the masonry beneath has to be able to carry the concentrated load. Most lintel problems are bearing problems: a bearing cut back for a later alteration, or crushed masonry under the end.
- Know why steel lintels corrode.A steel lintel sits in a wet part of the wall. If the cavity drainage is not working, or the galvanising has been damaged, it corrodes; rust expands and lifts the brickwork above, which is why a horizontal crack along a bed joint over a window is a warning sign rather than a cosmetic one.
Tips
- Tapping tells you a lot. Concrete gives a dull dead sound, steel gives a ring, and timber sounds hollow and softer. Drilling a tiny test hole and looking at the dust tells you the rest.
- Older houses very often have no lintel at all in an internal wall, with the opening formed by a timber or by the bond of the brickwork itself. That is not automatically a defect, but it does mean you cannot assume something is there to fix into.
- If you are hanging anything heavy above a window, fixing either side into the reveal is nearly always better than fixing into whatever is spanning it.
Common mistakes
- Fitting a prestressed concrete lintel upside down — The prestressing wires sit near one face by design. Inverted, that face is in compression and does nothing useful, and the tension face has no reinforcement at all. It becomes a plain concrete beam, which is a very weak thing.
- Cutting back a lintel bearing to fit something in — The bearing is what transfers the load to the wall. Reducing it concentrates the load and can crush the masonry under the end, and the failure does not announce itself until it is well advanced.
- Filling a horizontal crack over a window and redecorating — A crack along a bed joint over an opening is a classic symptom of a corroding steel lintel expanding. Filling it hides an active structural process.
If it doesn't work
A horizontal crack in a bed joint directly above a window, sometimes with rust staining
Cause: A corroding steel lintel or a corroding support angle behind a soldier course — Fix: Stop and get a structural engineer or a surveyor. Do not fill it, do not load the wall above it, and deal with whatever is letting water reach the steel.
Diagonal cracks running up from the top corners of a window
Cause: Deflection of the lintel, or movement at one of its bearings — Fix: Record the width and date, and look for the same pattern at other openings. Cracking from opening corners is one of the standard patterns a surveyor reads, and photographs across time are what makes the diagnosis.
Bricks in a soldier course have slipped or dropped
Cause: Loss of support from the angle behind it — Fix: Keep clear of the area beneath and get it looked at. Dropped masonry over an opening is a fall hazard as well as a structural signal.
Questions people ask
How do I find out what my lintel is without damaging it?
Look, tap and use a small test hole in a mortar joint rather than the lintel. GuideHQ's guide on drilling into a lintel covers identifying concrete from steel by the dust and the sound, and it is worth reading before making any hole.
Do internal doorways have lintels?
In a masonry partition, yes — usually a concrete or timber lintel. In a stud partition there is a timber head across the opening instead, supported by studs each side, which does the same job in a different material.
Can a lintel be replaced?
Yes, and it is routine work for a builder or engineer, done by needling and propping the wall above, removing the old lintel and installing the new one on proper bearings. It is not DIY, and it is notifiable structural work.
Why does my window have no visible lintel outside?
Often because a steel cavity lintel is hidden behind a brick soldier course or a rendered face. The lack of a visible lintel does not mean there is none, and it also does not guarantee there is one.