How do you calculate lintel load?

Calculating the load imposed on lintels depends on a variety of factors, including the wall type in which the lintel is installed, and whether floor or roof loads need to be accounted for in addition to masonry loads. Lintels are primarily design to support uniformly distributed loads (UDLs) but on occasions point loads also need to be considered.

This blog post only provides an overview of how the loads on lintel are established and should not be used as a substitute for obtaining loading calculations either direct from the lintel manufacturer or from a qualified structural engineer.

When calculating the load imposed on a lintel, it is first necessary to assess the masonry in the wall above the lintel. Due to the way that loads act and are distributed, the masonry load is taken as the weight of masonry in a triangle shape above the lintel (where the lintel is the base of the triangle).

This is the ‘triangulated masonry load’ and is simplest when there are no openings within the zone above the lintel. If there are openings, then the load must be adjusted.

Where intermediate floors and roof constructions bear onto the masonry above a lintel, they impose additional loads. The magnitude of the load varies depending on whether the construction, particularly of floors, is timber or concrete.

Finally, it is necessary to consider the live or dynamic loads imposed by the building type and its use. Residential and commercial uses with different occupancies impose different loads that are transferred through the floor and into the walls.

Overall, the aim is to specify a lintel with a safe working load (SWL) for the loads imposed (including a safety factor). This ensures that the lintel will not deflect vertically by more than 0.003 x the clear span of the opening. Lintel manufacturers publish loading tables with SWLs for their products, established in accordance with BS EN 845-2.

In masonry cavity wall constructions, the distribution of load between the inner and outer leaf of masonry is not necessarily equal. In this application, it is therefore necessary to consider the load ratio.

Where the lintel is supporting only masonry, the load ratio is generally 1:1. Typically this increases to 3:1 (inner to outer leaf) for lintels carrying timber floor loads, and 5:1 where concrete floor used. In eaves applications, the load ratio is 19:1.

To provide cost effective solutions, a range of different lintels are available to suit the same wall construction but are designed to support significantly different loads. These are often grouped as light, standard duty, heavy and extra heavy duty. The load that the lintel must support will determine whether the lintel needs to light, standard, heavy or extra heavy duty. Light and standard duty lintels are normally used to support triangulated masonry loads along with timber floor or roof loads. Heavy and extra heavy-duty lintels are used to where it is necessary to support concrete floors and attic trusses or where the opening sizes are larger and longer lintels are required.

Like all manufacturers, Catnic provides loading tables for all its lintels, including SWLs to assist with specification. To help with choosing the right type of lintel for the right application, the Catnic product selector tool allows users to narrow the range of lintel options by filtering for the type of wall construction and the loading condition.

The tool makes it easy to access comprehensive technical details for each lintel type, including the SWL for each standard length. For any queries relating to lintel specification and load calculations, you can contact us to discuss the specifics of your project.