Specifying steel lintels

[edit] Introduction

Steel lintels are used widely used in many different building applications and it is important to specify the right steel lintel to match the construction method and building type in question.

This article summarises the comprehensive white paper ‘Specifying Steel Lintels’ written by Catnic. The white paper details the important criteria for identifying, specifying and installing steel lintels successfully. The full version can be downloaded here.

[edit] Meeting the standard

Steel lintels must be structurally sound and fit for purpose. Products may be accredited by the NHBC and must be CE marked in accordance with BS EN 845-2:2013+A1:2016.

[edit] Structurally sound

The steel lintel specified will need to carry the loads imposed on it by masonry, floor, roof loads and so on. The specifier can obtain safe working load (SWL) tables from the manufacturer to help specify the correct lintel for the span and loads imposed.

Consideration should be given to the safety limits built into the SWL and load ratios for any non-symmetrical loading, as is common for traditional cavity wall constructions.

[edit] Thermal solutions

The thermal performance of each component in the building envelope needs to be taken into account when specifying products and systems, in relation to energy saving legislation and sustainability standards. Ideally these should be approached in a holistic manner that does not treat components individually.

The thermal performance of building components need to be designed to work together to form an integrated and truly ‘Fabric First’ approach to energy efficiency, sustainability and legislative compliance.

Steel lintels support the structural span across the openings above doors and windows in cavity walls potentially creating a thermal bridge from the inside to the outside of the building. The psi values for the lintels, that specifiers need to calculate the potential U value for a building, can be sourced from the lintel manufacturer.

It is possible to achieve improved lintel psi values by using lintels without a base plate (removing the potential for additional thermal bridging) and thermally broken, or separate, lintels within cavity wall constructions.

[edit] Damp course specification

Some lintels have a built in damp proof course. For a steel lintel to act as a damp proof course it must be a minimum of 140mm deep and manufactured from austenitic stainless steel or galvanised steel with an additional 40 micron powder coating.

If the building to be constructed is located in exposure zones 1 or 2 in the UK (according to BS 8104:1992) and the specified lintels have a damp proof course built in, then there is no need to specify a separate damp proof course.

A separate damp proof course will need to be specified if:

• The building is located in exposure zones 3 and 4 in the UK
• The specified lintel does not have a built in damp proof course

[edit] Durability and corrosion resistance

To minimise the risk from corrosion, when specifying steel lintels the specifier should reference the following standards in relation to the chosen products:

• BS EN 10346:2015 – Continuously hot-dip coated steel products
• BSEN 845 – Standard of corrosion resistance
• BS EN 1996 (Eurocode 6) – Masonry structures

[edit] Fire safety

Specifiers should check that the chosen lintel has been independently assessed in accordance with BS EN1363-1:2012 or BS 476-21:1978.

[edit] Structural specification

Three key factors that should be considered when making a lintel choice are:

1. Structural load
2. Structural opening - A minimum 150mm should be added to each end
3. Construction method

A reliable lintel manufacturer can provide additional technical support in determining the structural loads.

When specifying lintels for cavity walls, the following measurements will be required:

• Width of outer leaf
• Cavity size
• Inner leaf

The most common lintel used for cavity walls are open back lintels. Open back lintels are suitable for standard duty through to extra heavy loading conditions, including direct roof and attic truss loading.

For timber framed buildings, lintels must be suitably propped during construction, the time and cost of which need to be included in the costing and construction schedule. Timber frame lintels use lintel restraint clips, which in conjunction with pinch battens, help to minimise rotation of the lintel and allow for differential movement between the timber structure and the brick facing.

For external solid walls, lintels are available in three formats:

• Single element – Single leaf brickwork
• Two part – Two separate leaves of brickwork, 215mm
• Box profile with toe – Solid brick / block walls 200-215mm

Three formats of lintel are also available for internal walls:

• Corrugated – light loads
• Channel - Standard duty
• Box – Sized for brick and block course heights. Plus heavier loads and wider openings

A variety of lintels are available for semi-circular arches, apex arches, bay windows and other curved openings. And bespoke lintels can be manufactured to order for specific architectural challenges.

[edit] Accessories

The lintel specification may need additional accessories to complete the specification. Accessories can be related to construction, water removal and protection and could include:

• Arch centres
• Weep vents
• Stop ends
• Soffit cladding

[edit] Installation

The following needs to be considered for an accurate and effective installation of the specified lintels once they arrive onsite:

• Knowledgeable contractors and trade professionals
• Damage incurred in transit
• Accurate wall dimensions
• Masonry overhang does not exceed 25mm
• Masonry above lintel has time to cure prior to floor loads
• Lintels must be level
• Nominal 150ml end bearing each end
• Fully embedded on bricklaying mortar
• No greater than half SWL carried by outer leaf – external cavity wall
• Point loads NOT applied directly to lintel flanges
• Drip on lintel projects forwards of frame
• Consider soffit cladding for extra protection against moisture

[edit] Conclusions

There are many variables involved in the specification, scheduling and accurate installation of steel lintels. For those specifying the lintels there is plenty of technical expertise to draw on from any trusted lintel manufacturer. For example Catnic’s lintel scheduling service, CLASS, which is free to use and accessible via email and telephone.

To download the full guide to ‘Specifying Steel Lintels, please visit our website here.

--Catnic 13:21, 31 Mar 2021 (BST)

[edit] Related articles on Designing Buildings Wiki

• Braced frame structures.
• Lintel.
• Steel.