Steel lintel for cavity wall construction

Thermally Broken Lintels

A unique design, providing a complete thermal break between inner and outer leafs with NO brackets, resulting in outstanding thermal performance always 0.05 W/mK or less.


  • Patented design

    Catnic’s latest innovation is the biggest evolution in steel lintel design for a generation. An elegant, simplistic design derived from extensive research and rigorous development testing.

  • Complete thermal break

    Catnic thermal broken lintels are the only steel lintel solution on the market with no brackets, providing a complete thermal break between the inner and outer leaf's, delivering industry leading linear thermal transmittance psi values of 0.02 to 0.05 W/mK. Independently verified by the Building Research Establishment.

  • Part L compliant

    Achieving a remarkably low psi value ensures Catnic’s TBL range will always meet the performance criteria requirements of Appendix R found in SAP 10.2 providing easy compliance with Part L of the Building Regulations.

  • 90-205mm cavity options

    Options are available to suit cavities from 90 to 200mm, in standard, heavy and extra heavy duty performance categories

  • Safe working loads

    It’s patented design provides the thermal performance of separate lintels, whilst offering users the same stable installation benefits of a traditional cavity wall lintel and safe working loads in line with Catnic’s existing Cavity wall lintels

  • Limit surface condensation

    To limit the risk of surface condensation or mould growth the temperature factor for a detail used in the external wall of a dwelling must be greater than 0.75. Catnic Thermally Broken Lintels a have temperature factor of at least 0.95.

Thermal Performance

The Fabric Energy Efficiency Standard (FEES) forms the foundations of the Building Regulations Part L 2021.

This focuses on the thermal performance for walls, roof and floors of the building, which have been continually improved with the revisions to the regulations. Improving the thermal performance of the walls emphasises the increasing proportion of heat lost through thermal bridges in the building fabric such as lintels if these details are not improved. The heat lost through linear thermal bridges in called the Psi value and is measured in W/mK.

Replacing the traditional lintels with Catnic Thermally Broken Lintel the heat loss through the window head detail can be reduced by up to 96%.

Existing default psi values for lintels as listed in BRE IP 1/06 are shown below:

Junction detail in external wallsDefault Psi value (W/m.K)
Steel lintel with perforated base plate0.5
Other lintels0.3

On a typical 4 bedroom house with 1200 square feet, the heat loss through a standard lintel can account for about 6%* of the overall heat loss through the fabric of the house. Using a Catnic Thermally broken Lintel reduces this to 0.25% making it effectively insignificant.

*based on a default lintel psi value of 0.5 W/mK

0.02 to 0.05

Psi values (W/mK)

SAP 10.2 Appendix R

Part L of the Building Regulations has got progressively more complicated

To make it easier to comply an optional “standard recipe”, based on the Part L 2021 Notional dwelling, has been introduced. A summary is shown in the table below, full details can be found in Sap 10.2 Appendix R.

If you follow the standard recipe you will achieve the CO2 and fabric energy efficiency targets to comply with Part L.

The standard recipe requires a lintel psi value of 0.05 W/mK. All Catnic Thermally Broken Lintels will provide psi values of 0.05 W/mK or better.

Opening AreasSame as actual up to 25% of floor area
Ext. Wall (W/m2K)0.18
Party Walls (W/m2K)0
Floor (W/m2K)0/13
Roof (W/m2K)0.13
Windows (W/m2K)1.4
Air tightness5
Non repeating thermal bridgingStandard psi values from Appendix R of SAP
Ventilation TypeNatural (with extracts)
Gas Boiler89.5%

How does the Catnic thermally broken steel lintel achieve its performance?

The Catnic TBL comprises powder-coated galvanised steel components either side of an expanded polystyrene (EPS) insulation core. The steel components are bonded to the insulation using adhesive and, as there are no brackets, the steel is not continuous from one side of the lintel to the other. This is a unique design, with Catnic being the ONLY steel lintel manufacturer to offer a solution with NO brackets.

The low psi values offered by the Catnic TBL can allow other areas of the building fabric to be optimised. Where the aim is to achieve an even higher level of energy efficiency compared to building regulation compliance, specification of Catnic TBLs is essential.

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