Where can I get PSI values calculated?

A variety of sources exist from which to obtain PSI value calculations for use in assessing building regulation compliance. Choosing the right source depends on the nature of the junction details in the building design. If details reflect common practice or are standardised in some way, then it’s possible to get them from sources that are less suitable for creating detailing unique to a specific project.

PSI values entered into compliance calculations must be accurate to minimise the possibility of performance gaps occurring. The most useful solution is to obtain PSI value calculations from a source where it is easy to have something recalculated if the specification changes. Flexibility to make additional calculations is, therefore, something to look for when looking for specialist thermal modelling software.

Read on to discover where to get PSI value calculations for an accurate heat flow simulation to comply with building regulations.


Using pre-calculated PSI values

When linear thermal bridging was first introduced into the Building Regulations in 2006, an accompanying set of Accredited Construction Details (ACDs) was published. This document supported people in designing and constructing details to achieve the stated energy performance. It covered a large range of scenarios for masonry, timber and steel-framed construction elements.

Over time, other libraries of heat loss details have been published. Some have come from industry bodies and trade associations to support better thermal performance or a wider variety of construction methods than ACDs cover. 

Individual product manufacturers, such as companies versed in insulating buildings, have released detailed libraries to support the use of their products.

Accurate linear thermal transmittance to comply with building regulations


In the last fifteen years and more, ACDs have been withdrawn, as it is not possible to accurately present heat loss in buildings without considering all of the thermal elements.

Pre-calculated values make construction PSI values more accessible. They usually reflect the most common construction types and product specifications. To ensure building regulation compliance, linear thermal bridge design must match the selected predetermined detail or assumed PSI value. 

The total junction PSI value measures how much heat loss occurs in non-repeating thermal bridges, which U-values cannot achieve. U-value calculations are used to measure heat loss in building components.

PSI values in heat loss calculations indicate temperature differences in the thermal bridging component. Thermal bridges are two thermal elements that meet, causing greater heat loss. While U-values discover heat loss between thermal elements, they don’t consider all the different building elements. Solely using U-values to pass a SAP assessment isn’t viable; they don’t accurately reflect overall heat loss.


Improving access to project-specific PSI values

Despite the contribution PSI values make in compliance – usually helping to reduce U-values, passing the SAP assessment, and saving money – they are viewed as a burden. This is rooted in having to spend time and money employing a separate competent person to calculate a PSI value detail to the necessary standard. 

The importance of an accurate PSI value calculation


The value of project-specific details cannot be overstated. Even small differences between a pre-calculated output value detail and actual designs for building junctions can result in a change to the separate PSI value that is achieved.

This can be the difference between compliance and non-compliance. Or between condensation occurring or not because of the surface temperature factor that is achieved.

Project-specific and bespoke PSI value calculations are preferable to a simple U-value calculation, especially where unique products or construction techniques are being employed. A PSI calculation needs to be viewed as accessible, cost-effective, flexible, and user-friendly.

This combination of qualities led BRS Technology to develop AutoPSI, an innovative online tool that allows particular junction details and linear thermal bridges to be modelled according to an approved thermal bridging scheme. With our online PSI value calculator software, you can model details quickly and easily using a drag-and-drop interface.

Project-specific PSI values are calculated instantly with heat loss software, meaning users can experiment with different configurations to obtain the result that works best for their project.

AutoPSI: Innovative PSI Calculation Technology

AutoPSI was founded in 2019 to make calculating PSI values simple for a construction design team, architects, retrofit coordinators, and more.

A building calculator is necessary to acquire accurate PSI values that will enable you to pass regulations and BR497 compliance. Our online PSI value calculation software streamlines building thermal modelling while considering thermal bridging to prevent heat loss. 

Our heat loss calculator makes your PSI value calculation customisable. With our innovative online thermal modelling calculator, you can easily exchange data components and improve energy performance.

Many clients have obtained accurate PSI values with our PSI value software. With our streamlined construction design software for thermal modelling, SAP assessments are certain to be successful.

Sign up for a demo of AutoPSI’s fully online tool if you’re wondering where to get PSI value calculations and streamline your SAP calculations.

To find out more, visit the AutoPSI website.

Check out our LinkedIn for more information.