With the upcoming changes to Part L of the Building Regulations, it’s important to be aware of thermal bridging and Psi-Values. Thermal bridging is estimated to account for up to 30% of a dwelling’s heat loss and therefore contributes significantly to heat loss, energy use and Part L1A compliance.
Thermal bridges occur where two adjoining materials exist within a construction (e.g. mortar and blocks) or where two constructions come together (e.g. a wall/floor junction). Currently, U-values, which account for the heat loss across surface area, are a widely understood part of Part L1A; but, with changes due later this year, more understanding of Psi-Values is needed. A Psi-Value accounts for heat loss across the length of a junction.
Why is it important?
All SAP and SBEM assessments must contain a thermal bridging component. Calculating Psi-Values can increase the chance of achieving a pass during these assessments. If they are not calculated manually, a default value is automatically assumed which can be worse than the actual value, therefore affecting whether your building is deemed as compliant or not.
Calculating Psi-Values provides greater accuracy than an assumed value and it can create greater energy savings for your project, which is especially important if you are aiming for higher levels of sustainability.
Preparing for the Future Homes Standard
The recent Future Homes Standard announcement revealed that there will be a 31% uplift on current standards by 2022. This is likely to lead to greater pressure on all elements of the SAP assessment to achieve compliance. There will be more emphasis on Psi-Values because the use of government-approved Accredited Construction Details (ACDs) is being removed.
How can Psi-Values be calculated?
Thermal modelling software can be used to calculate Psi-Values. Here at C80 Solutions we have an experienced team of thermal modellers using industry-leading software.