U-values and Thermal Bridging

U-values are a measure of the heat loss through the building envelope. In order to demonstrate compliance with Building Regulations it is necessary to prove the U-values of the various components used to construct the building envelope. It is also necessary to demonstrate that thermal bridges have been properly allowed for, which frequently requires recourse to advanced computer modelling techniques. Both linear and point thermal bridges can be analysed.

U-values and thermal bridging can either be calculated by hand or simulated using finite element analysis, and both 2-d and 3-d analyses can be undertaken. Sandberg are very experienced in both 2-d and 3-d analysis, on both small and large details. These analyses are undertaken in accordance with the requirements of British and European standards, and in line with guidance published by the BRE, CWCT, GGF and CAB:

• BS EN ISO 13789 Thermal performance of buildings - Transmission heat loss coefficient - Calculation method
• BS EN ISO 6946 Building components and building elements - Thermal resistance and thermal transmittance - Calculation method
• BS EN ISO 10211-1 Thermal bridges in building construction - Heat flows and surface temperatures - Part 1: General calculation methods
• BS EN ISO 10211-2 Thermal bridges in building construction - Calculation of heat flows and surface temperatures - Part 2: Linear thermal bridges
• BS EN ISO 10077-1 Thermal performance of windows, doors and shutters - Calculation of thermal transmittance - Part 1: Simplified method
• BS EN ISO 10077-2 Thermal performance of windows, doors and shutters - Calculation of thermal transmittance - Part 2: Numerical method for frames
• BS EN ISO 13370 Thermal performance of buildings - Heat transfer via the ground - Calculation methods
• BS EN 673 Glass in building - Determination of thermal transmittance (U-value) - Calculation method
• BRE BR 443 Conventions for U-value calculations
• BRE IP 5/98 Metal cladding: Assessing thermal performance
• BRE IP 17/01 Assessing the effects of thermal bridging at junctions and around openings
• BRE IP 10/02 Metal cladding: Assessing the thermal performance of built-up systems which use ‘Z’ spacers
• CWCT Standard for specifying and assessing for heat transfer (the U-value)
• CWCT Guide to good practice for assessing heat transfer and condensation risk for a curtain wall
• CWCT Guide to good practice for assessing glazing frame U-values
• GGF 2.2 Window and door system U-values: Provision of certified data
• CAB Guide for assessment of the thermal performance of aluminium curtain wall framing
• CAB A guide for assessment of the thermal performance of aluminium windows

and in accordance with any other standard or guide requiring either hand calculation or computer simulation.

Sandberg can advise on techniques to improve thermal performance, and can review designs to assess their likely benefits in reducing heat loss through the building envelope.