While Annex E calculations for tapered roofs have improved clarity for the insulation designers, they are less easy to understand for specifiers, contractors and some suppliers and that can be its own issue. It is critical to ensure the building design and specified U-values can be achieved on site, otherwise the finished building will suffer a shortfall in performance (the Performance Gap). This means underperforming elements can be offset by improved thermal performance elsewhere in the build. The noted methods offer this flexibility through a compensatory approach in relation to the buildings elemental U-values. The required U-value performance is determined by SAP (Standard Assessment Procedure) calculations for domestic properties and SBEM (Simplified Building Energy Model) calculations for commercial buildings. U-value targets for floors, walls and roofs are just one part of the overall picture, and that picture is flexible, allowing freedom in design and specification subject to meeting a set of minimum criteria. The annex containing this guidance has become synonymous with the calculations issued to demonstrate the U-values they are now known as Annex E calculations.Īcross England, Wales and Scotland the Building Regulations relating to energy use and thermal performance take a holistic view of the whole building. The calculation of U-values is defined by an international standard “BS EN ISO 6946” and in 1997 it included for the first time guidance on how tapered insulation should be calculated.

James Wilkinson, Design Office Manager for Gradient, explains. A GUIDE TO ANNEX E CALCULATION FOR THERMALLY EFFICIENT ROOF APPLICATIONS.ĭesigning a roof requiring tapered insulation is beset with challenges, with consequences for the contractor and specifier.

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