Construction Details

Whilst repeating thermal bridges are accounted for in U-value calculations, a separate Psi-value calculation is required to assess non-repeating thermal bridges at all the external junctions within a building.

As accredited thermal modelers, we recognised that architects and designers tend to rely on the governments Accredited Construction Details (ACDs) as their main point of reference for the reduction of thermal bridging in domestic buildings. Whilst the ACDs have encouraged architects and designers to consider thermal bridging in greater detail, the details have their limitations and rely on a component specification, which is not as optimised and cost-efficient as possible. Our research also suggests that, in some form or other, construction detailing does not directly align with all the key principles outlined within the ACDs, which can result in a significant performance gap between design and construction

Using our knowledge in thermal modelling coupled with our experience in construction, we have produced two thermally modelled detail packages, based on timber frame construction, giving architects, designers and clients a viable alternative to resources such as the ACDs.

A key aim our detail packs, is to provide a comprehensive set of details, aligned to typical construction practices, utilising an optimised component specification, which marries performance with buildability and practicality.

Our detail packs come in six versions and include most of the common junction types listed in SAP. In terms of performance, the detail packs can provide up to a 50% improvement in thermal bridging performance when utilised on a typical dwelling (when compared against ACDs).

This resource is available to contractors, architects and designers who are keen to achieve an enhanced ‘fabric first’ solution through improved thermal bridging and U-value performance. The packs are particularly beneficial in reducing carbon emissions and the energy required for space heating, assisting with Part L and Section 6 (Energy) compliance under the Building Standards.

The detail packs are designed to reduce unwanted infiltration and heat loss in buildings. Each detail has a corresponding Psi-value calculated in accordance with BR497 (2nd Edition), which can be used in energy assessments, provided the key principles and component specification are followed.

An example of our in-house detail packs is available on request via enquiries@carbonfutures.co.uk.

Why calculate psi-values?

• Junction heat loss is 20-30% of total building heat losses, which is significant. These losses are often underestimated contributing towards the significant ‘performance gap’ in new dwellings.

• If your proposed construction detailing does not reflect any of the options included in the Accredited Construction Details and you do not want to be penalised for using ‘default’ values which are significantly worse than the actual performance of the junction.

• Optimising and calculating psi-values can lead to a significant improvement in the performance of individual junctions leading to a lower y-value per dwelling, which makes achieving compliance easier.

• Lower Psi-values can help to significantly reduce construction costs.

DISCLAIMER:

The detail packs illustrate the reduction of unwanted infiltration in buildings and provides a psi-value for each individual junction situation, which can be used in SAP Calculations, provided the principles outlined on the drawing and any identified component specification is followed. No liability will be accepted for any omissions or inconsistency should the drawings be used for construction.