Bridging Heat Loss in Steel Frame Building Envelope

As winter approaches, heating systems round the country come out of summer hibernation and begin their hard work once again. As they work to maintain internal temperatures, balancing heat generation against heat loss, the vast majority of systems lead to the emission of carbon dioxide into the atmosphere.

A well insulated and airtight building envelope reduces heat demand and CO2 emissions. If designed or constructed poorly, interface details can be the weak link in the insulating envelope. They provide the potential for heat loss through discontinuities in the insulation layer, conduction across materials bridging the insulation layer and thermal bypasses.

This presents a particular challenge for steel construction, with its high thermal conductivity. Where steel penetrates the insulation layer, there is the potential for increased heat loss. When designing a building to have operational CO2 emissions low enough to pass the new Part L of the Building Regulations (which came into force from 1st Oct), there are three ways that the thermal bridging performance of construction details can be accounted for.

1. Basic design to minimise thermal bridging using guidance from BRE IP 1/06;
2. Calculation of thermal performance using approved software;
3. As point 2 but signed off by an accredited body to become an Accredited Construction Detail.

Option 1 will give poor performance values that will then be reduced by 50% (according to Part L Regulations) and will make complying with Part L very challenging, requiring difficult and expensive upgrades elsewhere in the building design.

Option 2 will allow use of actual performance values, with a 25% reduction. This is the minimum recommended level of proof to minimise heat flow through thermal bridges.

Option 3 is likely to be required for buildings where performance significantly beyond Part L compliance is sought, for example higher levels of the Code for Sustainable Homes.

SCI are well placed to help the industry calculate the performance of its current systems and work towards new Accredited Construction Details.

For further information, please contact:

Roland Chuter, Senior Engineer, SCI Sustainability
Tel: +44 (0)1344 636532
Email: r.chuter@steel-sci.com