Thermal bridging and accredited construction details

We are now in the midst of the UK heating season and, despite a warm winter so far, domestic heating systems around the country are still working hard to ensure that internal environments are comfortable. 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 (CO2) 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 fully, or partly, there is the potential for increased heat loss. When designing a building to have operational CO2 emissions low enough to pass Part L of the Building Regulations, extra heat loss due to the thermal bridging performance of construction details must be explicitly accounted for.

Wall-floor detail with hot-rolled steel frame and light-steel infill walling.
Wall-floor detail with hot-rolled steel frame and light-steel infill walling.

Analysis of the thermal performance of details is usually undertaken by building a 2D or 3D computer-model and applying finite element analysis to this model. This calculates the heat flow across the detail being studied that is in excess to the normal heat loss through the planar elements.

Over the past 18 months SCI has been active in the field of thermal bridging analysis, working on projects for clients such as Lafarge and BCSA/Tata. SCI has helped them to understand the regulatory framework in this area, as well as evaluating the performance of current products, and recommending new details.

SCI is currently coordinating a large European Commission-funded project, Thermal Bridging Atlas of Steel Construction for Improved Energy Efficiency of Buildings. This project was won in a competitive bid to the Research Fund for Coal and Steel, and SCI is working with partners from France, Germany, Finland and the UK to compare construction technologies and modelling techniques for the thermal performance of details.

Finite element thermal analysis of the above detail.

Finite element thermal analysis of the above detail. (Click image to view larger)

Over the next three years, this project will clarify the modelling methodology in this area, with a focus on steel construction technologies. It will then outline the principles of building thermally efficient details and build a database of generic details and their performance values to allow the steel construction industry to better understand its performance and potential.

It is expected that the topic of thermal bridging of construction details will be brought to the fore over the next few years. This is due to improvements to insulation of the planar construction elements beginning to give diminishing returns. It is hoped that this will be covered by the forthcoming revisions to Part L of the Building Regulations in 2013 and 2016 but, even without explicit requirements in this area, it will be necessary to minimise thermal bridging in order to achieve the highest possible levels of thermal insulation and thereby pass Building Regulations.

SCI is committed to research and development in this area with projects extending over the next few years and has the tools and expertise to help industry achieve excellence in the thermal performance of steel construction details.

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For further information please contact Roly Chuter, SCI (01344 636525; E-mail:
r.chuter@steel-sci.com).