account in the SAP calculation. Architectural Technology professionals strive to consistently design buildings which take energy efficiency into consideration. There is a need to be aware that while the thermal performance of building elements such as walls, floors and roofs have continued to improve over the years in response to changes in the Building Regulations, the heat loss at the junctions has actually increased, as the junction is considered to be relatively ' cold' in relation to the higher performing building element. Building Regulations The issue of thermal bridging is dealt with in approved technical booklet F1 in Northern Ireland ( Part L in England and Wales) which states that ' The building fabric should be constructed so that there are no reasonably avoidable thermal bridges in the insulating layers caused by gaps within the various elements, at the joints between elements, and at the edges of elements such as those around window and door openings.' The technical booklet refers to the Department for Communities and Local Government ( DCLG) publication, Accredited construction details for Part Lor alternatively, details can be individually modelled provided they give an equivalent level of performance when assessed in accordance with BRE IP 1/ 06 ( Ward, 2006). SAP Calculations Each construction detail within which a non- repeating thermal bridge occurs has an associated heat flow through that thermal bridge, which is represented by its linear thermal transmittance or ? ( psi) value. The ? value represents the extra heat flow through the linear thermal bridge over and above that through the adjoining thermal elements. The lower the ? value, the less heat is lost. Within SAP, there are four options to consider when looking at thermal bridging. In 2006 a set of accredited construction details were published, allowing a dwelling constructed to fully comply with these details to use a " y" value of 0.08 W/ mK in the SAP calculation. The " y" value is a factor to estimate the heat loss at the junctions of building elements. More recently in 2008, the Energy Saving Trust produced a set of Enhanced Construction Details. If a dwelling is constructed to fully comply with these details a " y" value of 0.04 W/ mK can be used in the SAP calculation. If any of the construction details are not at least accredited construction details, a default value of 0.15 W/ mK must be used. The alternative to using the accredited/ enhanced construction details is to calculate the heat loss of individual details using the procedure set out in BRE IP 1/ 06 ( Ward, 2006). This requires specific building details to be modelled using thermal modelling software which calculates the actual heat loss at a particular junction. This can be done for all non-repeating thermal bridges in the building construction. These are then multiplied by the length of the particular non- repeating thermal bridge and added together to determine the total heat loss for the building. The process of innovative detailing and use of thermal modelling can lead to a dramatic reduction in the total heat loss through the building fabric. To demonstrate the effects of thermal bridging the above images show a ground floor detail modelled using TRISCO software. Figure 1 shows the modelled EFFICIENCY ATJULY- AUGUST2010 15 Figure 2. Right: A typical wall/ floor junction where innovative detailing can improve thermal performance Figure 1. Those involved in building design are faced with the challenge of trying to increase energy efficiency at minimal cost to clients

detail giving a ? value of 0.16 W/ mK ( the default value stated in BRE IP 1/ 06 for a ground floor). The detail was then enhanced by looking at measures such as increasing the depth of the insulation in the cavity, using thermal blockwork on the inner leaf to ground floor level and introducing a drylining system. When recalculated, the ? value was shown to be 0.035 W/ mK which equates to a substantial improvement. Figure 2 illustrates the heat loss through the enhanced detail. If you compare the details you will notice that the enhanced detail has a higher internal surface temperature represented by the " warmer" colours. All other details for non- repeating thermal bridges can be modelled in a similar way, and as you can imagine there is considerable potential for improvement. As Architectural Technology professionals we should lead the way in improving the building fabric of our designs. Tackling this elemental aspect has to be an essential first step in the energy efficient design process before other renewable technologies are even considered. This has to go hand in hand with ensuring that contractors are aware of the dwelling specific details and understand the principles behind the designs. Although the topic of thermal bridging is not fully understood by everyone within the industry, with the new Part L due to come into force later this year it is an area that we all need to begin thinking about. I hope that this article has enabled people to further understand the potential dwelling specific detailing has in reducing heat loss in building elements. If anyone has any questions or would like to discuss further the possibilities of implementing thermal modelling on future projects please feel free to contact me using the following details. David Comiskey MCIAT Lecturer in Architectural Technology and Management, Room 06C39E, School of Architecture and Design, University of Ulster at Jordanstown, Newtownabbey, Co. Antrim, BT37 0QB Phone: + 44 ( 0) 28 9036 6476 Email: da. comiskey@ ulster. ac. uk EFFICIENCY 16 ATJULY- AUGUST2010 Innovative detailing and use of thermal modelling can lead to a dramatic reduction in the total heat loss Left: A typical wall/ floor junction where innovative detailing can improve thermal performance. As Architectural Technology professionals we should lead the way in improving the building fabric of our designs