Thermal House

As we strive to lower U-values in building envelopes for improved energy efficiency, addressing heat losses through thermal bridges becomes increasingly significant. In some cases, heat losses due to non-repeating thermal bridges can account for up to 25-30% of the total heat loss from the building's fabric alone.

One effective solution to mitigate the negative impact of non-repeating thermal bridges is the use of H+H aircrete. Unlike denser materials, H+H aircrete offers superior thermal resistance, making it an ideal choice for building components at junctions. By incorporating H+H aircrete into these critical areas, it becomes possible to reduce the thermal bridge effect without resorting to costly enhanced detailing measures.

Building Regulation Compliance

For compliance with building regulations it is imperative to account for the additional heat losses associated with thermal bridges in the Standard Assessment Procedure (SAP) energy assessment calculations. These measurements rely on a parameter known as the Ψ-value (psi, pronounced "sigh"). The Ψ-value is a property specific to the thermal bridge junction and represents the rate of heat flow per unit length of the thermal bridge.

H+H UK has made available a comprehensive set of individual Ψ-values free of charge to provide the most up to date and accurate data where our blocks are being used. These calculations conform to both BR497 (2016) and IP 1/06 and may be used by energy assessors in their SAP calculations.

We have recently released the second issue of our calculated Ψ-values which has been expanded to include an additional 600 junctions, bringing the total to over 3,300 individual Ψ-values. These cover our Solar, Standard, High Strength and Super Strength Blocks and variations cover their use in partial or full fill in cavity walls, in beam and block floors, separating walls or as Foundation Blocks below DPC. 

The latest version now includes:

  • 500mm roof insulation at ceiling level 
  • 100mm and 150mm roof insulation (0.022W/mK) between rafters 
  • Keystone / IG Hi-therm+ thermal break lintel

Ψ-values given for Cavalok closers in 100mm cavities are now based on the use of a fully insulated closer and have improved over the first issue which, although not retained in the updated document, are still valid for partially voided closers (such as I100HORCBX).

Other than the 100mm Cavalok cavity closer, there are no other changes to the calculated Ψ-values given in the first issue.

You may find further information and download the latest version of the H+H Calculated Ψ-values document here: