Following the Future Homes Standard Consultation, we now know what will be included in the next versions of Part L. The 31% uplift on current standards, which will come into effect in 2022, will mean there will likely be greater pressures on all elements of the SAP assessment to achieve compliance. More specifically, regarding the Psi-Values, we also know that the use of government ACDs will be removed, and the default values used for overall compliance are worse. Overall, this means more emphasis is placed on calculated Psi-Values.

With new regulations in place, there will be more emphasis on PSI values, as accredited construction details will be a thing of the past. So what are PSI Values? These are an expression of heat over a metre length of a building junction, so for example, the heat loss occurring between the wall and floor or around windows. U-Values are different, as they refer to heat loss of a surface area. Thermal bridging can occur at the edge of a material, as thermal performance is not as great compared to the centre of a material. This creates a highway for heat loss to occur.

The basic difference between U-Values and Psi Values is that U-Values will establish all areas where heat loss can usually happen, from places including the windows, floors, and even the roof, to name a few. Psi Values check the heat loss from the junctions and the junctions alone. U-values cover the heat loss from a surface area when the Psi Values cover heat loss from a linear length. That differentiates the two, as there is often (understandably) some confusion.

Working out the Psi Values of your build is an extremely specialist job. You will need to ensure that you can show evidence of an approved thermal bridging scheme on your build. To do this, you need to know what your Psi Value is. As stated, if you don’t have these figures calculated, a default figure will be generated for your build. This is more often than not the ‘the worst case’ figure for your type of construction. And over estimates what the actual heat loss is.

We are fortunate to have some highly experienced engineers and energy assessors who carry out PSI values with specialist software, which can calculate in 2D and 3D, which allows us to assess, identify and remediate the thermal bridging detail. Get in touch today to find out more…

PSI Values are ways to measure heat loss on your building junctions and help create the best possible SAP results for your build. When the continuity of insulation is interrupted by timber studwork or different types of material, a thermal bridge occurs. The uplift to Part L building regulations will mean you will fail your SAP assessment if you do not use calculated psi values.

So this is what we can offer you:

• Same day quotation and booking

• Certified Expert Energy Engineers

• Consultation – recommendations and implementation

• SAP Calculation – PSI value input

• One Stop Shop in Compliance: Pick from our full range of Services to complement your PSI Values

• Part L Building Regulation Sign off

Paul Whiffin ATSPACE Managing Director