Features of Thermally Broken Lintels

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Utilising steel strength combined with the thermal insulating properties of a high-density, fire retardant core, 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, delivering industry leading linear thermal transmittance Psi values of 0.02 to 0.05 W/mK and safe working loads in line with Catnic’s existing Cavity wall lintels.

Achieving a remarkably low Psi value ensures Catnic’s TBL range will always meet the performance criteria requirements of Appendix Q found in SAP 2012 providing easy compliance with Part L of the Building Regulations.

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. The 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 2013.

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 walls Default Psi value (W/m.K)
Steel lintel with perforated base plate 0.5
Other lintels 0.3

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

SAP 2012 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 2013 Notional dwelling, has been introduced. A summary is shown in the table below, full details can be found in Sap 2012 Appendix Q.

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 Areas Same 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 tightness 5
Non repeating thermal bridging Standard psi values from Appendix R of SAP
Ventilation Type Natural (with extracts)
Gas Boiler 89.5%

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