Lintels Explained: Steel, Concrete & Stone

A lintel is the structural member spanning a door or window opening, carrying the weight of the wall, and sometimes floor or roof loads, above it down to the jambs on either side. Choosing the wrong type, size or bearing length is one of the most common causes of cracking and settlement around openings. This guide covers the three materials you will encounter on UK domestic and light-commercial work: steel cavity lintels, prestressed concrete lintels, and natural stone.

Steel Cavity Lintels

Steel cavity lintels are the usual choice on UK cavity-wall construction; Catnic, one of the main makers, has been producing them for more than 50 years.¹ They are pressed from galvanised steel and combine an inner leaf leg with an outer leaf leg in a single profile, bridging both leaves at once. The outer leg is shorter and set lower so it can support the face brickwork while the inner leg supports the blockwork inner leaf, the two legs are connected through the cavity, eliminating the need for separate single-leaf lintels.

Manufacturers make profiles in bands of cavity width, starting at 50–65 mm; Catnic’s thermally broken range, for example, covers cavities from 90 to 205 mm.¹ Many come with an insulation core that runs continuously along the lintel.¹ Lintels are made in three load categories:¹

• Standard duty (SD), typical domestic loads
• Heavy duty (HD), higher loads, for example where floors bear on the wall above the opening
• Extra heavy duty (XHD), the heaviest loads

The duty describes the load a lintel can carry, not its length: Catnic’s standard-duty CG50/100, for example, is made in lengths of 3 m and more.¹ Choose from the manufacturer’s load table for the actual loading, not by span alone.

Most are formed from steel strip that has been hot-dip galvanised before forming, to BS EN 10346, with a zinc coating of 275 g/m² (Z275) or 600 g/m² (Z600), and some makers add a polyester powder coat on top.² BS EN ISO 1461 is the separate standard for hot-dip galvanising steel articles after fabrication.³ Lintels are CE marked against the harmonised product standard BS EN 845-2, Specification for ancillary components for masonry. Lintels.²

Spans and Bearing

The total length of a steel lintel equals the clear span plus two bearing lengths. The nominal minimum end bearing is 150 mm at both ends, so the lintel length is the clear span plus 300 mm.⁴ Approved Document A’s guidance for masonry walls assumes the same 150 mm, which may be reduced to 100 mm where the clear span is 1.2 m or less.⁵ Longer spans and heavier loads can need more, and the figure that governs is the one in the manufacturer’s load table for the profile you are ordering, not a rule of thumb. BS EN 845-2 is the product specification the lintel itself is made to; it does not set the bearing you build in. The clear span is measured between the faces of the supporting masonry, not the rough opening.

Prestressed Concrete Lintels

Prestressed concrete (PSC) lintels are precast units with high-tensile steel wires tensioned before the concrete sets.⁶ They suit single-leaf masonry (inner leaf only or solid wall construction), garage door openings, and internal partition walls.⁷ A standard domestic PSC lintel is 100 mm wide × 65 mm deep (the height of one brick) or 100 × 140 mm (two bricks and a mortar joint); wider units up to 215 mm are available for solid brickwork.⁸

Makers use high-strength concrete: Stressline, for example, designs its lintels with a concrete strength of 50 or 60 N/mm².⁶ Prestressed strands are protected by the concrete cover, so in aggressive exposure conditions (coastal or chemically contaminated environments) check the maker’s guidance or have the lintel specified for that exposure.

PSC lintels are heavier than steel: a 1.2 m, 100 × 65 mm unit weighs about 18 kg, against about 7 kg for a standard-duty steel cavity lintel of the same length, which matters for manual handling on scaffold.¹⁷ They do not rust, and because each one carries a single leaf, a pair can be used with an insulated cavity closure between them, the arrangement Approved Document L suggests for limiting thermal bridging at openings.⁹

Natural Stone Lintels

Stone lintels are a repair and heritage material rather than a primary structural choice on new build. They appear in pre-1920 solid stone or solid brick construction and must be matched to the local stone type (limestone, sandstone, granite) for aesthetic and structural compatibility. Natural stone lintels act in pure bending, there is no prestress, so their safe span is governed by the bending strength of the stone, which is low and varies widely between stone types, and even between beds from the same quarry.

For repair work under a Conservation Area or Listed Building consent, new stone is often cut to match the original. Reclaimed stone lintels are common at salvage yards and may show previous weathering or surface decay; always inspect for bed-face lamination before reuse.

Comparison Table

Prices are supply-only from a builders’ merchant, excluding VAT, 2026, and rise with length: a standard-duty steel lintel runs from about £50 at 1.2 m to about £150 at 2.4 m. Fitting is extra: setting a lintel while new walling goes up is a small part of the bricklaying, but inserting one into an existing wall, with temporary propping, cutting out and making good, is commonly quoted at roughly £300–£800 per opening in labour.

The steel weights are for Catnic’s 50–65 mm cavity profiles at 1.2 m: its heavy-duty CH50/100 weighs 10.5 kg/m.¹ Its extra-heavy-duty CX50/100 weighs 16.0 kg/m.¹ Stressline’s load tables run to clear spans of 1.8 m for its 100 × 65 mm lintel and 3.9 m for its 100 × 140 mm lintel, with the safe load falling as the span grows.⁷

Bearing and Padstones

Bearing length and the condition of the masonry beneath the bearing are as important as the lintel itself. Where loads are high or the masonry is weak (e.g. aerated-concrete blocks of 3.6 N/mm²), a padstone, a dense-concrete block or engineering brick, may be required to spread the point load.¹⁰ Padstone sizing should be calculated by the structural engineer; for a heavily loaded lintel, a dense-concrete padstone either side is a common starting point.

Building Regulations

Lintel selection falls under Approved Document A (Structure).⁵ For domestic extensions and alterations, a structural engineer or a lintel supplier’s span table is normally sufficient evidence. Where the lintel carries more than a single storey of masonry, or where a new opening is formed in a loadbearing wall of an existing building, a structural engineer’s calculation should be commissioned and submitted with the Building Regulations application.

Thermal performance is covered by Approved Document L, which asks for the building fabric to be constructed so that thermal bridging is reasonably limited.⁹ For new dwellings it suggests independent inner and outer lintels with an insulated cavity closure between them or, where one lintel carries both leaves, a base plate that is not continuous and an insulated core.⁹ Many proprietary cavity lintels come with an insulation core as standard, and thermally broken versions are available; confirm this when ordering.¹

Practical Notes

• Order by clear span + 300 mm (two × 150 mm bearings) as the default, and check the manufacturer’s table for the profile before ordering, since a longer span or a heavier load can call for a deeper bearing.
• Set the window or door frame so that the drip on the front of the lintel projects forward of the drip on the frame.¹ Above the lintel, provide a cavity tray with stop ends and at least two weep holes, unless the maker confirms the lintel profile can act as the tray for your exposure.²
• Check the product’s load table before ordering: it gives a safe working load for the lintel, usually assuming the load is spread evenly and shared between the two leaves in a stated way.² Where floor joists, a beam or another concentrated load bear on the wall above, check the heavier-duty tables or get an engineer’s confirmation.
• Stainless-steel lintels are available for particularly aggressive environments, such as some coastal sites, or where a longer life is wanted; the lintel maker or engineer will say when the exposure calls for them.¹