How the two differ in kind
Two checks on the same component, and the second is habitually skipped because the first is what the lintel is selected from.
LOAD CAPACITY is the span check: can the lintel carry its load across the opening without failing in bending or shear, and without deflecting more than the masonry above it will tolerate? Deflection matters as much as strength here, because the wall sitting on a lintel is brittle and cracks if the lintel sags — which is why lintel tables give a load capacity at a deflection limit rather than at failure.
BEARING LENGTH is the other end of the problem, literally. Everything the lintel carries arrives at its two ends and is transferred into the masonry beneath them, over a small area. The stress there can be very high — high enough to exceed what the masonry can carry — so a lintel that is entirely adequate in bending crushes the brickwork under its ends, and the symptom is spalling and cracking at the jambs rather than a sagging lintel. The check is the reaction divided by the bearing area against the masonry's compressive capacity, and the remedy where it fails is a longer bearing, a padstone to spread the load, or a stronger unit beneath.
The third thing, and the one that decides both, is what the lintel actually CARRIES. Masonry above an opening does not behave as a beam handing its whole weight down: it ARCHES. Provided there is enough wall above and enough masonry either side to resist the thrust, a roughly triangular area immediately above the lintel is carried by it while the rest of the wall spans around the opening — so the load is substantially less than the full height of wall above.
The exception is what catches people: a floor or roof bearing within that triangle puts its load onto the lintel as well, and a concentrated load such as a beam end within it does so decisively.
The factors that actually differ
Show
| Load capacity | Bearing length | |
|---|---|---|
| What it checks | The lintel spanning the opening — bending, shear and deflection. | The masonry under the ends — whether it can take the concentrated reaction. |
| Failure mode | The lintel sags or fails, and the wall above cracks as it deflects. | The masonry crushes and spalls at the jambs beneath the bearing. |
| Which is habitually skipped | Neither — this is what the lintel is selected from. | This one, because selecting the lintel feels like completing the job. |
| The remedy when it fails | A stronger or deeper lintel. | A longer bearing, a padstone to spread the load, or a stronger unit beneath. |
| Deflection | Governs as often as strength, because the masonry above is brittle and cracks as the lintel sags. | Not directly relevant. |
| What the load is | The arching triangle of masonry, plus anything bearing within it. | The same load, delivered as two reactions. |
| Arching | Reduces the load substantially — the wall spans around the opening rather than sitting on the lintel. | Reduces the reaction correspondingly. |
| When arching cannot be relied on | Insufficient masonry above, insufficient wall either side to resist the thrust, an opening close to a corner, or openings stacked above one another. | The same conditions. |
| Concentrated loads | A beam or joist bearing within the arching triangle adds its load directly. | And concentrates the reaction further at the bearings. |
| Both required | Yes, and passing one says nothing about the other. | Yes. |
Which one, and when
Choose load capacity when…
- Selecting a lintel for an opening — the starting point for every one.
- Where the span is long, so bending and deflection govern.
- Where something bears on the wall within the arching zone and adds load.
- Where the masonry above is a finish that will show any deflection, which tightens the limit.
Choose bearing length when…
- After selecting the lintel — this is the check that completes it.
- Where the reaction is high: a long span, a heavy load, or a concentrated load from above.
- Where the masonry beneath is weak — a lightweight block, an old soft brick, a narrow pier.
- Where the bearing is short because the opening is close to a corner or to another opening.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Why does masonry arch over an opening?
- Because brickwork and blockwork are bonded, so a wall is not a stack of independent units sitting on whatever is beneath them — it can span. Above an opening, the mortar bond and the interlocking of the units let the wall behave as a shallow arch, carrying its load out to the masonry either side and down the jambs rather than handing it all to the lintel. What the lintel carries is roughly the triangle of masonry immediately above it, which is a fraction of the full height of wall above the opening, and the rest goes round. The consequence is that a lintel designed for the entire wall above it is heavily over-designed — which is why lintel load tables are expressed in terms of the arching assumption, and why understanding when that assumption fails matters more than the arithmetic.
- When can arching not be relied on?
- Whenever the conditions it needs are absent, and there are four common cases. Insufficient masonry ABOVE the opening: the arch needs enough height of wall above it to form, so an opening near the top of a wall, with a roof or a floor immediately over, may have nothing to arch through. Insufficient masonry EITHER SIDE: the arch thrusts outward at its springings, so an opening close to a corner or to another opening has nothing to resist that thrust. Openings STACKED above one another, where the lower one's arching zone is interrupted by the upper one. And freshly built masonry, where the mortar has not gained strength. In any of those, the lintel is designed for the full load above rather than for the triangle.
- What actually fails when the bearing is too short?
- The masonry beneath, not the lintel. Everything the lintel carries arrives at its ends and is delivered into a small area of brickwork or blockwork, so the compressive stress there is far higher than anywhere else in the wall. Exceed the masonry's capacity and it crushes: the visible symptoms are spalling of the brick faces immediately under the lintel's bearing, cracking running down or stepping away from the jamb, and in a bad case the lintel end settling into the wall. It is worth recognising because the symptom looks like a structural problem with the wall rather than with the lintel, and because the remedy is at the bearing — a longer bearing length, a padstone spreading the load over more units, or a stronger unit beneath — rather than a bigger lintel.
- How long should the bearing be?
- Long enough that the reaction divided by the bearing area stays within what the masonry can carry, subject to a minimum that codes and lintel manufacturers state. The calculation is straightforward once the reaction is known: the reaction is half the total load for a uniformly loaded lintel, the bearing area is the bearing length multiplied by the lintel's bearing width, and the resulting stress is compared with the masonry's design compressive strength. What makes the minimum necessary is that a short bearing is also vulnerable to construction tolerance — a lintel set a little off centre loses bearing at one end — and to the edge of the masonry spalling. Where the calculated requirement exceeds what is available, a padstone spreads the load over a longer length of wall, which is the standard remedy.
- Why does deflection matter as much as strength?
- Because what sits on the lintel is brittle. A lintel could be strong enough not to fail while deflecting enough to crack the masonry above it, and cracked brickwork over a window is a defect even though nothing has failed structurally. That is why lintel load tables state a safe working load at a DEFLECTION limit rather than at a strength limit — the figure quoted is generally the load at which the deflection reaches an acceptable fraction of the span, which is well below the failure load. The limit is tighter where a brittle finish is applied over the opening, and it is why substituting a lintel selected on strength alone, or reusing one from a shorter span, produces cracking that appears within the first year as the wall settles onto it.
- What about a floor bearing over the opening?
- It changes the load substantially and it is the commonest reason the simple arching assumption does not apply. If joists or a floor structure bear on the wall within the arching triangle above the lintel, their load is delivered into that zone and comes down onto the lintel rather than arching around the opening — so the lintel carries the triangle of masonry plus that floor load. A beam end bearing within the triangle is worse, because it is a concentrated load at a point. Both raise the reaction and therefore the bearing stress as well as the bending. The practical rule when assessing an existing opening or designing a new one is to look at what is above it for the height of the arching zone before assuming anything about the load.
- Does a cavity wall change the calculation?
- It splits it, and how it splits depends on the lintel type. A cavity wall has two leaves, frequently of different materials carrying different loads — the outer leaf carrying itself and the inner leaf carrying itself plus any floor bearing on it. A combined cavity lintel carries both and is selected from a load table that distinguishes the inner-leaf and outer-leaf loads, because the split affects how the lintel is stressed as well as how much it carries. Separate lintels in each leaf are checked independently. The bearing check applies to each leaf on its own masonry, which matters because the inner leaf is often a lightweight block with a much lower compressive strength than the outer brick — so the inner bearing can govern even though it looks like the less exposed side.
- What is a padstone and when is one needed?
- A dense unit — a concrete padstone, a piece of engineering brick, or a steel plate — placed under a bearing to spread a concentrated reaction over a larger area of masonry. It is needed whenever the bearing check fails: the reaction is high, the available bearing length is short, or the masonry beneath is weak, which on a lightweight inner leaf is common. Its size follows from the same calculation — the area required to bring the stress within the masonry's capacity — and its own strength has to be adequate to spread the load rather than simply transmitting it. It is a routine and cheap component, and the reason it gets omitted is that nobody did the bearing check, which is why the two checks belong together rather than sequentially.