Cracking that appears above a window or a door, or that runs diagonally up from the top corner of an opening, is one of the most misdiagnosed defects in housing. It looks like the building is moving. Usually the building is fine and one specific component over one specific hole has stopped doing its job.
What a lintel is doing
An opening in a load-bearing wall interrupts the load path. The lintel carries the masonry above the opening and delivers that load into the wall either side, through its bearings. Everything that goes wrong with lintels is a variation on one of three themes: the lintel has deteriorated, it was never strong enough, or the bearings are inadequate.
The types, and how each one fails
- Timber lintels - standard in older housing, often concealed behind render or plaster. They fail by rot where damp has reached them, and by long-term deflection. Very common in Victorian and earlier property, and frequently discovered only when something else is opened up.
- Stone heads and stone lintels - characteristic of Yorkshire's stone stock. They crack in the middle, which alarms people considerably, and a cracked stone head is not automatically a failed one - but it has lost its ability to span and the load is finding another path.
- Brick arches and soldier courses - they work in compression and depend on the abutments either side. Movement at the abutment drops the arch, and cracking radiates from the corners of the opening.
- Concrete lintels, including the boot lintels common in the 1960s and 1970s - they fail by deflection, and where reinforcement is shallow and has corroded, by spalling of the concrete cover.
- Pressed steel lintels, standard in cavity construction from the 1970s onwards - they fail by corrosion, almost always because a cavity tray above them is defective or missing and water is sitting on the steel.
Why bearing length matters more than people expect
A lintel that is strong enough can still fail if it does not sit far enough onto the masonry either side, because the load concentrates onto a very small area of wall. That crushes the masonry beneath the bearing, the lintel drops, and the cracking appears - not because the lintel broke, but because what it was sitting on gave way.
This is the single most common defect we find in DIY and undesigned alterations. Somebody has widened an opening, put in a beam or lintel that is adequate in span, and given it 50mm of bearing on a soft brick. It is also why a padstone - a hard, load-spreading block under the bearing - is specified so often in the calculations we produce, and why leaving it out is not a saving.
What is normal
Fine cracking at the top corners of openings is extremely common and frequently thermal - openings are stress concentrations, and buildings crack at stress concentrations. Under the BRE Digest 251 classification, hairline to a few millimetres here sits in the negligible to slight range.
Cracked stone heads on older Yorkshire property are near-universal and mostly historic. The question is whether the load has redistributed safely, not whether the stone is cracked.
What is potentially serious
- Masonry above an opening that is visibly sagging, dropped, or stepped down relative to the courses either side
- A crack that is wider at the top than the bottom, or that widens as it rises from the corner of an opening
- Rust staining, or a visible steel lintel that has expanded and lifted the brickwork above it
- A window or door frame that has begun to bind, distort or crack its glazing - the frame taking load it was never meant to carry
- Cracking above an opening that was widened at some point, particularly where there is no paperwork for the work
- Damp or rot anywhere near a concealed timber lintel
- Anything that has appeared or grown within the last year
What you can check yourself this week
- Sight along the brick courses above the opening from one side. A dropped or sagging course is obvious at a shallow angle and invisible face-on.
- Open and close the window or door. If it has started to bind at the top, the frame may be carrying load.
- Look for rust staining below the head of the opening, which points at a corroding steel lintel.
- Ask whether the opening has been altered. A wider opening than the original is the single biggest clue.
- Photograph with a scale and a date, and repeat in three months.
When to call an engineer
A threshold: get it inspected if the masonry above an opening has visibly dropped, if the frame is binding or distorting, if there is rust staining, if the opening was widened without documented design, or if the cracking is growing. Fine, static corner cracking on an unaltered opening does not need an engineer.
It is also worth an inspection before you replace windows. Fitters are not lintel specialists, and taking a frame out of an opening where the lintel has failed occasionally reveals that the frame was doing more than it should have been.
How it gets fixed
Undramatically, in most cases. The opening is propped, the failed lintel is cut out and a new one inserted with proper bearings and padstones, and the masonry above is made good or rebuilt. Where a stone head is cracked but the load has found a stable path, sometimes the right answer is to record it and leave it. Where an opening was widened without design, the remedy is to give it the support it should have had.
We produce the calculations and the details, and we do not carry out the work or take commission from anyone who does. A structural survey and report is a fixed £580 + VAT, report inside 10 working days of the inspection, guaranteed; a straightforward lintel design is a smaller job and is quoted separately.
Frequently asked questions
Is a crack above my window serious?
Usually not. Fine cracking at the top corners of openings is very common and often thermal, because openings concentrate stress. It becomes a question when the masonry above has visibly dropped, when the crack widens as it rises, when the frame starts binding, or when the crack is growing.
My stone lintel is cracked in the middle. Does it need replacing?
Not necessarily. Cracked stone heads are near-universal on older Yorkshire property and most are historic, with the load having redistributed into a stable arch through the masonry above. What an engineer establishes is whether that redistribution is sound, not whether the stone is cracked.
Why do steel lintels rust?
Almost always because water is sitting on them. A defective, badly lapped or missing cavity tray above the lintel lets water reach the steel, and the corrosion product expands, lifting the brickwork above. Fixing the lintel without fixing the water is a repair with a return date.
What is a padstone and do I really need one?
A padstone is a hard, load-spreading block set under the bearing of a beam or lintel, so the concentrated load does not crush the masonry beneath it. Yes, where the calculations specify one. Failures at bearings are more common than failures in the middle of a beam, and leaving out a padstone is not a saving.
Can I replace a lintel myself?
Replacing a lintel means temporarily supporting the wall above while the existing one is removed, which is genuinely the dangerous part of the job. It also normally needs a designed replacement and, if the opening is being altered, Building Control involvement. Get the design done and use somebody who props properly.