Summary

Every opening in a load-bearing wall — door, window, or archway — requires a lintel to carry the load above it. Getting the lintel wrong is one of the most common structural defects in UK residential construction. Lintels that are too small deflect and crack the masonry above them; lintels without a cavity tray allow water to track into the inner leaf.

The UK lintel market is dominated by a handful of manufacturers who provide free load tables and technical support — there is no need to guess, and no excuse for guessing. Catnic (now part of Corus/Tata Steel), IG Lintels, Birtley, Longreach, and Ancon all publish comprehensive load tables. Most builders' merchants stock standard sizes from at least two manufacturers.

The structural requirement is straightforward: the lintel must span the opening plus minimum 150mm bearing each end, must carry the triangular load of masonry above plus any dead/imposed loads from floors and roofs within the 45-degree load-shedding triangle, and must not deflect more than span/360.

Key Facts

  • Minimum bearing — 150mm at each end for lintels up to 1.2m span; 150–200mm for longer spans. Check manufacturer's tables
  • Load types — Masonry dead load (triangle above opening), plus any floors/roofs bearing within the triangle
  • Cavity tray — Mandatory above all lintels in cavity wall construction per Approved Document C and BS 8215. Must include stop ends and weep holes
  • Weep holes — At 450mm maximum centres in the first perpend joint above the DPC/cavity tray
  • Pre-stressed concrete — Used for heavier loading, longer spans. Minimum L-shaped for cavity wall
  • Pressed steel cavity lintel — Most common for residential work. 100mm, 150mm, 200mm inner leaf depths; various outer leaf profiles
  • Steel catnic lintel — Open-back pressed steel, typically 3mm galvanised zinc coating minimum, increasingly hot-dip galvanised for longer life
  • Span rating — Always use the manufacturer's load table — do not interpolate or guess
  • Standard span range — 600mm to 4800mm in 150mm increments for most pressed steel products
  • Galvanising — Minimum G275 (275g/m² zinc) for internal use; hot-dip galvanised (HDG) preferred for coastal/aggressive environments
  • Installation temperature — Not relevant for steel, but concrete lintels should not be installed in freezing conditions without protection
  • Fire resistance — Most steel lintels have a minimum 30 minutes fire resistance when plastered over. Check manufacturer data for specific applications

Quick Reference Table

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Lintel Type Application Advantages Limitations
Pressed steel cavity (Catnic-type) Cavity wall, residential Lightweight, integral DPC feature, wide range Galvanising can corrode in aggressive environments
Pre-stressed concrete Heavy loading, long span Strength, fire resistance Heavy, needs crane for long spans
RSJ (universal beam) Large openings, structural Very high capacity Requires bearing pads, padstones, and SE
Timber Internal, light non-structural Easy to work Not suitable for external or heavy loading
Boot lintel (pre-stressed concrete) Cavity wall, heavy loading Integral DPC channel Heavier than steel, less common
Thin joint masonry lintel Aircrete block construction Matches thin-joint blockwork Specialist product, limited range
Typical Pressed Steel Lintel Types Inner Leaf Depth Typical Load Range
Catnic CN or IG L1/HB70 100mm (1 block) Light to medium residential
Catnic CG or IG L2/SB140 140mm Medium loading, wider spans
Catnic WG or IG L3/HS 200mm Heavy loading, long spans
Special lintels (SL) As specified Structural engineer specified

Detailed Guidance

Selecting the Right Lintel

Step 1: Determine the opening width. Measure the clear opening between jambs. Add 300mm minimum for bearing (150mm each end).

Step 2: Determine the wall type. Standard UK cavity wall = 102.5mm outer leaf + 100mm cavity + 100mm inner blockwork leaf = 302.5mm overall. Party wall or solid wall is different.

Step 3: Determine the load. For most domestic openings in load-bearing masonry, you are looking at:

  • Low load: opening in a single-storey extension or under a flat/pitch roof with no floor above
  • Medium load: opening in a two-storey house with one floor above
  • High load: opening carrying two or more floors, heavy roof loading, or a significant structural feature

Step 4: Use the manufacturer's load tables. Both Catnic and IG Lintels publish free downloadable load tables. Enter span and load category → read off lintel reference number. It's that simple — do not guess.

Step 5: Check availability. Standard lintels up to 2400mm span are typically ex-stock at builders' merchants. Longer spans (up to 4800mm) may require special order with lead times of 2–5 working days.

Cavity Trays

Every lintel in a cavity wall must have a cavity tray DPC immediately above it to prevent water tracking across the cavity into the inner leaf. This is mandatory — not optional.

Pre-formed cavity trays: Most cavity lintel products have an integral cavity tray or are designed to accept a pre-formed polythene tray. Pitched pre-formed trays (Cavitray type, or similar) are placed over the lintel before the outer leaf is continued.

Stop ends: The cavity tray must have upstands or stop ends at each end, turned up 25mm minimum, to prevent water running off the ends of the tray sideways into the cavity.

Weep holes: Leave the perpend (vertical) joints un-mortared at maximum 450mm centres immediately above the cavity tray to allow collected water to escape. At least two weep holes per lintel, minimum one in each 900mm section.

Common failures:

  • Cavity tray omitted entirely (especially on extensions and conversions)
  • Stop ends not installed
  • Tray pitched in the wrong direction (must slope to outer face)
  • Weep holes mortared up by the bricklayer

Installing Over an Existing Opening (Lintel Replacement)

Replacing a failed or undersized lintel in an occupied building requires careful temporary propping:

  1. Install temporary props and needles above the opening inside (and outside if the wall is in doubt). Props must bear on a solid floor or pad — never on suspended timber floors without spreader boards
  2. Allow temporary props to take the load before disturbing the existing lintel
  3. Cut and remove the old lintel — typically with an SDS drill along the bearing ends and a cold chisel to break the bond
  4. Clean out bearing pockets and check condition of masonry
  5. Prepare new lintel — apply DPC paste or bed on lime mortar to bearing surfaces
  6. Lift lintel into position and bed level on mortar. For heavy lintels (pre-stressed concrete over 1.5m span), use props or a block and tackle
  7. Place cavity tray immediately above
  8. Continue bricklaying — maintain temporary props until the new lintel mortar has cured (minimum 48 hours, ideally 7 days before removing all props)
  9. Remove temporary props

Building Control: Lintel replacement in a load-bearing wall is structural work that may require Building Control notification depending on the extent of work. If you are replacing like-for-like as part of a larger notifiable project (extension, alteration), the lintel will be included in the Building Control scope. For standalone lintel replacement, consult with your local Building Control office.

Long-Span and Structural Lintels

For openings over 1.8m span in load-bearing walls, or where there are significant loads (floors, roof loads) within the 45-degree triangle above the opening, a structural engineer should check or specify the lintel. Above approximately 2.4m clear span in a domestic property, pressed steel lintels reach their practical limit and universal steel beams (RSJs) become the norm.

RSJ installation requires:

  • Padstones (engineering brick or concrete pad) at each bearing
  • Minimum 150mm bearing length (often 200mm for RSJs)
  • Temporary propping as above
  • Building Control notification and structural engineer's calculations

Frequently Asked Questions

What is the minimum lintel length for a given opening?

Lintel length = clear opening width + 2 × bearing. Minimum bearing is 150mm each end, so minimum lintel length = opening + 300mm. For example, a 900mm door opening requires a minimum 1200mm lintel. Many manufacturers size their catalogue in 150mm increments — go to the next available size up.

Does a non-load-bearing wall need a lintel?

Technically no — a partition wall carries no structural load, so an opening can be formed without a lintel. However, if the wall is carrying ceiling plasterboard, there will be a small load, and a timber or lightweight steel lintel is good practice to prevent cracking. In a masonry partition, a simple angle iron or galvanised steel flat may suffice.

Can I use a timber lintel externally?

No. Timber lintels are suitable for internal use over light openings only. External applications require a preservative-treated timber at minimum, but steel or concrete is strongly preferred for any structural application. Historic properties may have original timber lintels — these should be assessed for condition before reuse.

How do I know if an existing lintel is failing?

Signs of lintel failure include: stepped diagonal cracks radiating from the corners of a window or door opening, the window or door frame sticking or distorting, visible deflection (sagging) of the masonry above the opening, or rust staining emerging from the joint line immediately above the opening. Any of these warrants investigation — photograph and monitor initially, then call a structural engineer if there is active movement.

Regulations & Standards