What is a lintel bearing?

A bearing is the amount of the lintel that rests on the masonry on either side of the opening. In the UK, the minimum standard bearing is 150mm. For wider openings (over 3m), this may need to be increased to 200mm or more depending on the structural load.

How do I calculate the length of a lintel?

The formula is: Clear Opening Width + (Bearing x 2). For a standard 1200mm wide window, you would add 150mm for each side, resulting in a total lintel length of 1500mm.

Do I need a cavity tray with a steel lintel?

Yes. For external cavity walls, a cavity tray (DPC) should be installed above the lintel to direct moisture that has entered the cavity outwards through weep vents. This prevents water from pooling on top of the lintel and causing damp inside the property.

What is thermal bridging in lintels?

Thermal bridging occurs when a material (like steel) allows heat to pass through it more easily than the rest of the wall. Modern lintels often feature built-in insulation or 'thermal breaks' to minimize heat loss and prevent condensation on the internal face of the lintel.

What is a lintel bearing?

A bearing is the amount of the lintel that rests on the masonry on either side of the opening. In the UK, the minimum standard bearing is 150mm. For wider openings (over 3m), this may need to be increased to 200mm or more depending on the structural load.

How do I calculate the length of a lintel?

The formula is: Clear Opening Width + (Bearing x 2). For a standard 1200mm wide window, you would add 150mm for each side, resulting in a total lintel length of 1500mm.

Do I need a cavity tray with a steel lintel?

Yes. For external cavity walls, a cavity tray (DPC) should be installed above the lintel to direct moisture that has entered the cavity outwards through weep vents. This prevents water from pooling on top of the lintel and causing damp inside the property.

What is thermal bridging in lintels?

Thermal bridging occurs when a material (like steel) allows heat to pass through it more easily than the rest of the wall. Modern lintels often feature built-in insulation or 'thermal breaks' to minimize heat loss and prevent condensation on the internal face of the lintel.

Lintel Calculator

Ensure your openings are safely supported.

Clear Opening Width (mm)

Distance between the brick/blockwork reveals.

Wall Construction

Lintel Specification

Bearing Tip: Ensure your lintel is bedded on a full course of block/brickwork using a strong 1:3 mortar mix. Never use 'shims' or offcuts of wood to level a lintel as they will rot and cause structural settlement.

Supporting the Span: UK Lintel Standards

Structural Safety

A lintel is a horizontal beam that spans the opening between two vertical supports (reveals), such as windows and doors. Choosing the right length and profile is critical for maintaining the structural integrity of the wall above.

Our **lintel calculator** ensures you meet the minimum 150mm bearing requirements, preventing point-load failures and ensuring compliance with UK Building Regulations.

Standard Load Types

Standard DutyTimber Floors

Heavy DutyConcrete Floors

Extra Heavy DutyLarge Openings

Weatherproofing

On external walls, the lintel must do more than just hold weight. It acts as a bridge for moisture. Installing a **cavity tray** and **weep vents** is non-negotiable for cavity wall lintels.

The tray should extend at least 150mm beyond the end of the lintel on both sides to ensure water is channeled away from the opening and down the face of the brickwork.

The 150mm Rule

The 'bearing' length is vital for spreading the load into the masonry. If the bearing is too small, the pressure can cause the bricks or blocks at the edge of the opening to crumble. Always ensure a minimum of 150mm bearing on each side.

Propping

When installing long lintels, they should be propped at the centre (using Acrow props) until the mortar has fully cured and the wall above is finished. This prevents the lintel from sagging under the initial weight of the wet masonry.

Pro Tip: Order Lengths

Lintels are typically sold in increments of **150mm** (e.g. 1500mm, 1650mm, 1800mm). If your calculated length is 1540mm, you must order the next size up (1650mm). Never cut a steel lintel on site as this removes the protective galvanised coating and leads to rust.

Lintels & Openings FAQ

Technical Disclaimer

This calculator provides dimensional estimates only. The specific load capacity of a lintel depends on the height of the wall above, the type of floor/roof it supports, and the specific manufacturer's performance table. Always consult your structural engineer or architect's specification.