How can PSI value calculation tools influence the early stages of building design?

A digital heat loss tool, such as one designed to make PSI value calculations more accessible, can quickly and easily provide valuable insights about thermal elements at the early design stage. More analysis carried out at this point in the process can generate useful insights to help reduce thermal bridging and build energy-efficient properties. 

Bespoke PSI value calculations are used to shape the design, give greater certainty, reduce risk on a project, and help avoid unwanted changes at the specification stage.

In the outline design and planning stage, the focus of the building project is on general setting out rather than making detailed decisions. Spending time and money on detailed specifications is risky if something can change. However, using digital heat flow simulation tools to assess options and help refine proposals can save time and money across the life of the project.

Learn more about the importance of early-stage PSI value calculations in building design to improve energy efficiency. 

What can cause initial design decisions to be changed?

Virtually all construction projects, whatever their size, follow the same fundamental process. Design options are outlined to meet the given brief, and planning permission is sought on the agreed version. 

Detailed design and specification work is then carried out on the approved proposal, ready for building regulations approval and construction. This involves assessments — like the SAP (Standard Assessment Procedure) — to ensure thermal performance complies with Part L of the Building Regulations 2021.

There is an obvious benefit to this process, as there is little point in doing detailed work on a proposal that a client doesn’t want to pursue, or which a local authority has not granted planning permission for. 

The Importance of Detailed PSI Value Calculations in Early-Stage Building Design

It’s not uncommon to uncover unexpected heat loss issues once a detailed design has started. For example, as U-values are calculated for the building envelope, it might come to light that there’s not enough space to accommodate the required continuous insulation layer. This is the case when national building regulations change and make PSI value and thermal performance more important, such as when Part L 2021 was introduced.

Finding solutions to these issues can compromise the original design or risk not achieving the desired building performance. It might be necessary to accommodate extra insulation within the building envelope to reduce heat loss, potentially reducing room areas or lowering ceiling heights. Or, the building footprint might need to be changed, requiring a new planning application and permission which will cause delays and affect budgets.

Assessing proposals and gathering data to support design decisions

One way to avoid the extra time and cost that this entails at the detailed design stage is to spend time assessing the outline or planning proposal. 

By checking for potential compliance issues and addressing them early, substantial design changes can be avoided. The results could support a planning application if justification is needed for the particular design direction chosen.

How could this work in practice?

AutoPSI is an online thermal bridge modelling tool, developed by BRS Technology to make PSI value calculations quicker and the detailing of predetermined junction designs reliable. 

Our PSI value calculation software features a drag-and-drop interface that allows construction junction details to be customised and modelled. All resulting PSI values and surface temperature factors are calculated by relevant standards and BR497 conventions.

PSI value calculation and modelling junction details are often left until the last minute or ignored. This makes compliance harder to achieve and is likely to result in an energy performance gap between as-designed and as-built.

How AutoPSI’s bespoke PSI values simplify building design and planning 

A digital tool like AutoPSI makes it much easier to quickly check the likely performance of a key junction or difficult thermal bridge detail. If there’s a risk that the performance could compromise regulatory compliance at the detailed design stage, steps can be taken earlier to create solutions to prevent heat loss.

Try our AutoPSI Thermal Modelling Tool

Understanding PSI values

Accurate PSI values in heat loss calculations help create low-energy buildings. PSI values are a critical component, written in metre kelvin (w/mK) and measure heat loss during linear thermal transmittance. 

PSI values improve energy performance by considering non-repeating thermal bridges. Thermal bridges form when two thermal elements meet and cause heat loss. This is largely why PSI values are preferred over U-values; U-values discover heat loss between thermal elements but don’t consider linear thermal bridging. 

The importance of a PSI value analysis for adjoining building elements

A total junction PSI value considers non-repeating thermal bridges for an overall heat loss value, while a U-value calculation only considers a thermal element. 

A non-repeating thermal bridge, like the space between an external wall and the ground floor, is discovered in a building envelope analysis.

The building fabric in geometric thermal bridges causes higher thermal conductivity than thermal elements. U-value calculations overestimate heat loss in a thermal bridging component, while PSI values are essential for accuracy and compliance.

AutoPSI: Specialist Thermal Modelling Software 

AutoPSI understands the importance of exact PSI values, as you can no longer rely on predetermined PSI values after the removal of Accredited Construction Details. Our online PSI value calculator software streamlines thermal modelling during the early design stage. 

We simplify your PSI values with a fully online heat loss calculator. If you avoid default PSI values from the beginning, you’ll get an accurate output value. PSI values consider different building elements and thermal resistance, making it easier to create an energy-efficient building design and pass SAP assessments early. 

Want to learn more about how you can benefit from PSI value calculations in your early building design stages? Sign up for a demo of AutoPSI’s heat loss software to streamline building design and SAP calculations.