Specifying lintels for the energy savvy

Steel lintels can have a crucial impact on a project, especially when it comes to addressing energy conservation. Richard Price, Technical Director at Catnic, provides a useful overview to help architects make a well-informed decision.

No matter what type, size, scale or design of building, its appearance and performance will only be as successful as its many components, parts and systems. When tackling energy efficiency it would be fair to say that without careful and correct specification, lintels have the potential to provide a path for energy loss through the wall.

However, this cold bridging effect can be mitigated through correct specification and the use of thermally modelled lintels that have been optimised for their energy performance. This will ensure they do not compromise the energy efficiency of the external envelope.

As architects will be well aware, heat loss at any structural junction is measured as a Psi value, in W/mK. Combining this with the u-value of each plane element provides the overall heat loss through the fabric of the building. It is important to opt for lintels that will combine the required structural performance with the desired level of energy efficiency. Therefore a lintel with the lowest Psi-value and correct structural performance will result in the optimum result.

There is a lintel design that incorporates a complete thermal break between the inner and outer leaf of a cavity wall. Thermally Broken Lintels can deliver the thermal performance of two separate lintels but with the same easy installation as a traditional steel cavity wall lintel. The result is a BRE certified energy transmittance Psi value of 0.02 to 0.05 W/mK with no compromise to structural performance.

Architects should look for lintels that can achieve the criteria of Appendix R, SAP 2012 and compliance with Part L of the Building Regulations. In addition, by selecting a lintel with a flat top, this will provide a consistent junction with the cavity wall insulation, removing the reliance on site workmanship and ensuring the actual performance of the junction meets the architect’s design expectations. Replacing traditional lintels with Thermally Broken Lintels can reduce heat loss through window head details by up to 96 per cent – then you can appreciate the significant and positive impact this can have on the overall efficiency of a building. For further information visit: www.catnic.com/TBL

Aside from thermal performance there are a variety of other issues that have to be taken into account as well.

A daunting task

Given that there are over 10,000 lintel variations to select from, sourcing the right product can seem like a daunting and time-consuming task. To ensure that the lintel selected is indeed fit for purpose, always ensure you have addressed:

·       The type of wall construction
·       Width of the structural opening
·       Load type to be supported

There will be a steel lintel option to suit any type of wall construction and load as well as the option for bespoke and special lintels to be manufactured to suit unique designs as well as non-standard widths.

Always ensure that the steel lintel is CE marked and the Declaration of Performance certificate is available. This is inline with BS EN845: Part 2-2013 to ensure compliance with the Construction Products Directive (CPD). Furthermore, steel lintels should be independently tested in accordance with the relevant parts of BS EN476 and the stated Methods of Determination for the Fire Resistance of Loadbearing Elements of Construction.

Corrosion should also be considered and architects can again look to BS EN845, which identifies materials and corrosion protection systems for steel lintels. It looks at the core steel material and any coatings applied to it at pre and/or post manufacture stage. As such, lintels will either have to be manufactured from galvanised mild steel with a minimum of 600gms/m² coating of zinc, from galvanised mild steel with an additional organic coating or manufactured from austenitic stainless steel.

Lintels are a crucial structural component. By investigating manufacture claims, and being clear on the factors that have to be considered, it is then possible to make precise and robust specifications that address thermal performance, structural integrity, corrosion and legislative compliance.