Stay up to date. Follow us on LinkedIn

03301 901 200
info@enevo.co.uk
Close Search

PSI Values &
Part L Compliance

PSI Value and Part L Compliance

Understanding PSI values and why they matter

What are PSI values?


PSI values (or Ψ-values) measure how much heat passes through the junctions and connections of a building, such as where walls meet floors or roofs. They show the rate of heat loss per metre of junction, measured in watts per metre kelvin (W/mK). This figure is a key part of how a building performs thermally, as it highlights where extra energy may be lost—beyond what’s picked up by U-values for walls, roofs, or glazing.


In the UK, PSI values are required for SAP (Standard Assessment Procedure) calculations in residential projects, and are an important part of energy modelling for non-domestic buildings as well. They help identify thermal bridges, which are areas where heat can escape more easily, leading to higher energy bills, colder spots, and potential condensation or mould.


Why do PSI values matter for Part L?


Part L of the Building Regulations sets mandatory energy efficiency standards for both new and existing buildings. PSI values are central to this because they allow a more accurate assessment of heat loss. This means that designers and contractors can make better choices on construction details, minimising weak spots and ensuring the building is comfortable and efficient for occupants. Early focus on PSI values can prevent costly redesigns, delays, or non-compliance issues at completion.

Send us your project details and we’ll send a quote

Our PSI values and Part L compliance services

We calculate PSI values for all critical building junctions using approved software and recognised methodologies, ensuring accurate data for your SAP or SBEM assessments. Icon

PSI value calculations

We calculate PSI values for all critical building junctions using approved software and recognised methodologies, ensuring accurate data for your SAP or SBEM assessments.
We assess your building design to find areas where unwanted heat loss could occur, highlighting any thermal bridges that might affect energy efficiency or comfort. Icon

Thermal bridging analysis

We assess your building design to find areas where unwanted heat loss could occur, highlighting any thermal bridges that might affect energy efficiency or comfort.
Our team provides straightforward advice on how to meet Part L requirements, covering junction details, insulation, and construction methods for the best compliance outcome. Icon

Part L compliance guidance

Our team provides straightforward advice on how to meet Part L requirements, covering junction details, insulation, and construction methods for the best compliance outcome.
We advise on the best construction details and material choices that help minimise heat loss, offering solutions that are practical and cost-effective for your project. Icon

Construction detail and material support

We advise on the best construction details and material choices that help minimise heat loss, offering solutions that are practical and cost-effective for your project.
We produce clear, compliant reports and summary sheets, ready for submission to Building Control or Approved Inspectors, reducing the risk of delays or queries. Icon

Full reporting and certification

We produce clear, compliant reports and summary sheets, ready for submission to Building Control or Approved Inspectors, reducing the risk of delays or queries.
For more complex or non-standard projects, our engineers use advanced modelling tools to deliver detailed analysis and accurate PSI values, even for challenging junctions. Icon

Advanced thermal modelling

For more complex or non-standard projects, our engineers use advanced modelling tools to deliver detailed analysis and accurate PSI values, even for challenging junctions.
We stay involved from initial design through to completion, answering questions, making adjustments, and ensuring you remain compliant at every stage. Icon

Ongoing project support

We stay involved from initial design through to completion, answering questions, making adjustments, and ensuring you remain compliant at every stage.
We calculate PSI values for all critical building junctions using approved software and recognised methodologies, ensuring accurate data for your SAP or SBEM assessments. Icon

PSI value calculations

We calculate PSI values for all critical building junctions using approved software and recognised methodologies, ensuring accurate data for your SAP or SBEM assessments.
We assess your building design to find areas where unwanted heat loss could occur, highlighting any thermal bridges that might affect energy efficiency or comfort. Icon

Thermal bridging analysis

We assess your building design to find areas where unwanted heat loss could occur, highlighting any thermal bridges that might affect energy efficiency or comfort.
Our team provides straightforward advice on how to meet Part L requirements, covering junction details, insulation, and construction methods for the best compliance outcome. Icon

Part L compliance guidance

Our team provides straightforward advice on how to meet Part L requirements, covering junction details, insulation, and construction methods for the best compliance outcome.
We advise on the best construction details and material choices that help minimise heat loss, offering solutions that are practical and cost-effective for your project. Icon

Construction detail and material support

We advise on the best construction details and material choices that help minimise heat loss, offering solutions that are practical and cost-effective for your project.
We produce clear, compliant reports and summary sheets, ready for submission to Building Control or Approved Inspectors, reducing the risk of delays or queries. Icon

Full reporting and certification

We produce clear, compliant reports and summary sheets, ready for submission to Building Control or Approved Inspectors, reducing the risk of delays or queries.
For more complex or non-standard projects, our engineers use advanced modelling tools to deliver detailed analysis and accurate PSI values, even for challenging junctions. Icon

Advanced thermal modelling

For more complex or non-standard projects, our engineers use advanced modelling tools to deliver detailed analysis and accurate PSI values, even for challenging junctions.
We stay involved from initial design through to completion, answering questions, making adjustments, and ensuring you remain compliant at every stage. Icon

Ongoing project support

We stay involved from initial design through to completion, answering questions, making adjustments, and ensuring you remain compliant at every stage.

Our PSI Values & Part L Compliance process

01

Initial review
Send us your drawings or project details. We assess the junctions and note what information is needed.

02

Thermal modelling
Our engineers calculate PSI values using industry-approved software or published tables, depending on the detail and project type.

03

Advice and optimisation
We share clear feedback, pointing out any junctions that could cause issues and offering practical solutions to improve performance.

04

Reporting
We provide a full set of calculations, summary sheets, and guidance notes ready for submission with your SAP or SBEM assessment.

05

Support to completion
We stay available for queries, adjustments, or clarifications right through to project sign-off.
Why choose enevo for PSI values and Part L compliance? Image
Why choose enevo for PSI values and Part L compliance? Icon

PSI Values & Part L Compliance

Why choose enevo for PSI values and Part L compliance?

  • Deep expertise: Our engineers have years of experience in thermal modelling and Part L compliance across residential, commercial, and mixed-use projects.
  • Up-to-date and accurate: We use approved software and methods, keeping pace with current regulations.
  • Practical support: We give direct advice that helps avoid delays and unnecessary costs.
  • Trusted by leading clients: Our work is used in projects across the UK, from small residential schemes to major commercial developments.

How can we help you
with your project?

Testimonial IconTrusted, Time And Time Again

5 Star Rating

Harry gave me excellent advice and clear understanding on what BREEAM means as well about the specific accredited assessing required by professionals like Harry.

Angela Singh

5 Star Rating

Very efficient and professional service. Cant recommend enevo enough, glad I chose them for my project.

William Brannon

5 Star Rating

Very impressive on all aspects of energy calcs. Responsive and cost competitive. Highly recommended

Nick Spencer

5 Star Rating

enevo are always helpful, friendly and efficient in carrying out SAP calculations for our clients.

Lizzie Hicks

5 Star Rating

Dan at enevo has completed for us SBEM Calculations and EPC Certificates for 6 commercial units on an industrial estate. The cost of the works was very competitive and the service we received was second to none. With very limited time to get these works completed Dan worked round the clock (and into his annual leave!!) to ensure that our completion date was achieved with very little notice. Would highly recommend!

Mollie Belton

5 Star Rating

We have always found enevo to provide an excellent service in the preparation of SAP Calculations and Assessments as well as EPC Certificates for projects that they have worked on for us. They are also reasonably priced so we would certainly recommend them to anyone looking for this type of service.

Martin Booker

5 Star Rating

Used enevo from start to completion of our recent project of 2No. new builds. Services included SAP/EPC and property air testing. Great service, understanding of requirements and cost. Person friendly company and good with communication.

Mark Radcliffe

5 Star Rating

Very efficient, personal, professional service, with a quick report turnaround. Highly recommended if you're a self-builder trying to navigate the complexities of the latest regulations.

Edward Broadhead

5 Star Rating

Always efficient and prompt service, enevo are an asset to my company, having used their services on multiple developments I wouldn't hesitate to recommend them.

Mac Chappell

5 Star Rating

Great service with a fast turnaround. Communication was excellent throughout. Richard the engineer was polite and professional. Will certainly be using enevo again.

ECO PROPERTY DEVELOPMENTS LTD

Testimonial IconWhat We Think

30/01/2026

The Dutyholder Role defined
Read Insight

28/01/2026

Environmental monitoring & permit assessments
Read Insight

21/01/2026

Code for Sustainable Homes
Read Insight

08/12/2025

Energy & Sustainability Planning Statements: What They Are and Why They Matter
Read Insight

24/11/2025

BREEAM Services – navigating Version 7, credits, and sustainable strategy
Read Insight

We’re Ready To Help

Psi Value Calculations & Part L Compliance

We’re Ready To Help

Psi Value Calculations & Part L Compliance

Scroll To Top Arrow