Steel Cavity Lintels (often called box cavity lintels or Catnic-style lintels) are thermally insulated, galvanized steel beams engineered to bridge and support both the inner blockwork leaf and outer brickwork leaf of a standard cavity wall above door and window openings.

They are primarily used for:

• Simultaneous Support for Both Wall Leaves: Spanning door, window, and bi-fold openings in external cavity walls, safely transferring the weight of both the inner block leaf and outer brick leaf down to the supporting jambs.

• Thermal Insulation & Preventing Cold Bridging: Featuring an expanded polystyrene (EPS) insulation core filled inside the central box section to maintain thermal continuity, preventing heat loss and damp condensation around window and door heads.

• Built-in DPC & Moisture Deflection: Designed with a slanted profile or integral drip lip that collects penetrating rainwater within the cavity and directs it safely outward through weep vents in the outer brickwork.

• High Load Bearing Capabilities: Carrying substantial structural loads from suspended timber floor joists, concrete floor slabs, and roof trusses directly above structural wall openings.

Available for collection from our Rugby branch or local delivery using our own fleet.

Delivery is kerbside and the final offloading position is always subject to safe access and the driver’s discretion.

Please tell us before delivery about:

• Narrow roads or restricted entrances
• Parked vehicles or limited turning space
• Overhead cables, trees or other obstructions
• Soft, sloping or unsuitable ground
• Any other access concerns

Enter your postcode on the product page to check your delivery area. We’ll confirm the delivery date after your order is placed.

How do I choose the correct size steel cavity lintel?

Measure the clear structural opening (width of the door or window frame) and add 300mm to allow for a minimum 150mm end bearing on the solid masonry on both sides. You must also match the lintel’s cavity width dimension (e.g., 50mm - 75mm, 90mm - 105mm, or 110mm - 125mm) to your wall's cavity gap.

Do steel cavity lintels require a separate damp-proof course (DPC)?

While most modern steel cavity lintels feature a built-in drip lip and water shed design, UK Building Regulations generally recommend laying a continuous flexible cavity tray DPC above the lintel (along with weep vents spaced at maximum 450mm centres) to safely drain penetrating rain water clear of the cavity gap.

Do steel cavity lintels need temporary propping during installation?

For spans exceeding 1.2m, place vertical timber props beneath the centre of the lintel until the wet mortar has cured and the masonry laid above has reached full strength. This prevents initial deflection or movement under the weight of green brickwork.

Can a steel cavity lintel be cut to length on site?

No. Manufacturers strongly advise against cutting steel cavity lintels on site. Trimming or cutting removes the protective galvanised coating, exposes raw steel to moisture, and reduces the structural load capacity certified by the manufacturer. Always order pre-sized lengths.

The right steel lintel depends entirely on your wall construction—specifically whether you are building a standard double-leaf cavity wall or a single-skin masonry wall.

• Choose a Cavity Steel Lintel if you are building a standard external cavity wall (an inner blockwork leaf, an outer brick leaf, and an insulated gap). Cavity lintels bridge both wall leaves in a single, thermally insulated unit to carry both masonry loads simultaneously.

• Choose an L-Steel Lintel (Angle Lintel) if you only need to support a single outer leaf of masonry, such as the brick facade of a timber-frame home, a single-skin garage, or an external brick skin. The vertical leg tucks behind the brickwork while the horizontal shelf supports the masonry.

• Choose a T-Steel Lintel (Inverted T) if you need to support a single-skin solid masonry wall centrally. The bottom flanges support brick or blockwork on both sides of a central upright web, making them ideal for fair-faced brick openings and solid internal walls.

The choice between a concrete and steel lintel depends on whether you are building an internal single-leaf wall or an external cavity wall, as well as your budget, load requirements, and site handling preferences.

• Choose a Concrete Lintel if you need a cost-effective solution for internal walls or single-leaf masonry. Prestressed concrete lintels are significantly cheaper than steel, offer high fire resistance without extra treatment, and will never rust or corrode. They match the density of blockwork walls perfectly, though they are heavy to handle manually.

• Choose a Steel Lintel if you are building an external cavity wall or need to support high structural loads. Galvanized steel cavity lintels (like box or catnic lintels) bridge both leaves of a cavity wall in a single, lightweight unit, reducing thermal bridging and simplifying installation. They are also ideal for wide openings where low profile height is required.