Project Details
Service: PSI value calculations
Client: UK residential developer
Project: 20 new build homes across mixed detached and semi-detached housing scheme
Location: Aylesbury, Buckinghamshire HP21
Regulation Driver: Building Regulations Part L (energy efficiency and thermal bridging compliance)
ATSPACE Team: Building energy compliance consultants, thermal bridging specialists
The Headline Result
ATSPACE completed PSI value calculations for a residential development of 20 new build homes, achieving Part L compliance first time and supporting smooth Building Regulations approval.
The project required detailed assessment of thermal bridging at key junctions, including floor-to-wall connections, roof interfaces, and window reveals. Through accurate PSI value calculations and early design review, ATSPACE confirmed compliance without redesign or construction delay.
ATSPACE Delivered:
Full PSI value calculation set for all key junctions
Thermal bridging assessment for building fabric
Part L compliance verification across all dwelling types
Review of junction details and construction drawings
Identification of thermal performance risks
Building Control-ready compliance documentation
Project Overview
This project involved a 20-unit residential development consisting of a mix of detached and semi-detached new build homes. The scheme was designed to meet modern energy efficiency standards while maintaining cost-effective construction methods.
As part of Building Regulations compliance under Part L, the developer was required to demonstrate that thermal bridging at junctions had been properly assessed using PSI value calculations.
Thermal bridging occurs where different building elements meet, such as walls, floors, roofs and openings. These junctions can result in heat loss if not correctly detailed and assessed.
ATSPACE was appointed to carry out PSI value calculations across all relevant junctions to confirm that the design met compliance requirements and could proceed without delay.
Why The Service Matters
PSI value calculations measure heat loss at junctions between building elements. These junctions are critical because they can significantly impact overall energy performance even when insulation levels are adequate.
Under Part L of the Building Regulations, thermal bridging must be properly assessed and accounted for in energy calculations. PSI values are used to quantify this heat loss and ensure compliance.
This service is required for:
New build residential developments
Energy performance compliance submissions
Building Control approval documentation
Designs using modern insulation standards
PSI value calculations ensure that:
Thermal bridging is properly quantified
Heat loss at junctions is controlled
Energy efficiency targets are achieved
Building Regulations compliance is demonstrated
If PSI value calculations are not completed accurately, projects may face compliance failure, underperformance in energy modelling, or delays in Building Control approval.
The Problem
When ATSPACE was appointed, the project design was already well developed, but several thermal bridging risks had not been fully assessed.
Key issues included:
Unverified junction details between walls and floors
Limited thermal bridging data for window and door openings
Variations in construction detailing across dwelling types
Unclear assumptions around roof-to-wall junction performance
Pressure to maintain existing design without modification
There was also a requirement to secure Building Control approval within a fixed programme timeline, leaving no room for redesign or late-stage adjustments.
Without PSI value calculations, there was a risk that energy modelling would be inaccurate, potentially resulting in Part L non-compliance or delays in approval.
What ATSPACE Was Asked To Do
Carry out PSI value calculations for all relevant junctions
Assess thermal bridging performance across all dwelling types
Confirm Part L compliance requirements
Review construction details and junction drawings
Identify potential energy performance risks
Provide practical guidance without redesign
Deliver Building Control-ready compliance documentation
Our Approach
Step 1: Understanding The Compliance Requirement
ATSPACE confirmed the Part L requirements relating to thermal bridging and defined the methodology for PSI value calculations across all building junctions.
Step 2: Reviewing Junction Details
We reviewed architectural and construction drawings, focusing on key junctions including:
Wall-to-floor connections
Roof-to-wall interfaces
Window and door reveals
Intermediate floor junctions
This allowed us to identify potential heat loss risks early in the process.
Step 3: Practical Thermal Bridging Optimisation
Before finalising calculations, ATSPACE provided targeted recommendations, including:
Improving continuity of insulation at key junctions
Refining window reveal detailing assumptions
Optimising floor slab edge insulation performance
Aligning construction details across dwelling types
These improvements were incorporated into the calculation model without requiring design changes.
Step 4: Clear Compliance Reporting
ATSPACE completed PSI value calculations and issued a structured Part L compliance report. The documentation clearly demonstrated that all thermal bridging effects had been accounted for and that the development met regulatory requirements.
Real Issues We Faced And How We Solved Them
Issue A: Incomplete Junction Detailing
Some junctions lacked full construction detail information.
How ATSPACE Helped:
We worked with available design data and made compliant assumptions to complete PSI calculations accurately.
Issue B: Thermal Bridging Risk At Floor Edges
Floor-to-wall junctions showed potential heat loss concerns.
How ATSPACE Helped:
We refined PSI inputs and confirmed compliance through improved thermal assumptions.
Issue C: Variation Between Dwelling Types
Different house types had slightly different construction details.
How ATSPACE Helped:
We standardised PSI calculation approach across all units for consistency.
Issue D: Programme Pressure For Approval
The project required rapid submission for Building Control approval.
How ATSPACE Helped:
We prioritised fast turnaround of PSI calculations to avoid delays in the approval process.
Results
PSI value calculations completed for all junctions
Part L compliance achieved first time
No redesign required across dwelling types
Building Regulations approval supported successfully
Thermal bridging risks fully assessed and resolved
No delay to construction programme
Clear compliance documentation issued for submission
What This Project Proves
This project demonstrates that PSI value calculations are essential for achieving reliable Part L compliance in modern housing developments.
When carried out early and accurately, they help project teams:
Control thermal bridging risks effectively
Maintain consistency across multiple dwelling types
Avoid costly redesign of junction details
Secure Building Control approval without delay
PSI value calculations are a critical part of energy compliance and ensure that building performance is accurately represented in design submissions.
Mini FAQ
What Are PSI Value Calculations?
PSI value calculations measure heat loss at junctions between building elements such as walls, floors and roofs.
Why Are PSI Values Important For Part L Compliance?
They ensure that thermal bridging is properly accounted for in energy performance calculations.
Do All New Homes Need PSI Value Calculations?
Yes, most new build residential developments require PSI value calculations for Building Regulations compliance.
What Happens If Thermal Bridging Is Not Assessed?
Energy models may be inaccurate, leading to compliance failure or redesign requirements.
Can PSI Value Issues Be Fixed Without Redesign?
In many cases yes, through improved detailing assumptions and insulation continuity adjustments.
When Should PSI Calculations Be Completed?
They should be completed during the design stage before Building Control submission.
Call to Action
Need PSI value calculations for your residential project?
ATSPACE helps developers, architects and contractors achieve fast, reliable Part L compliance with clear thermal bridging analysis and no unnecessary delays. Send your project details and we will confirm requirements and next steps.
