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Why Bespoke PSI Calculations Can Improve Compliance and Reduce Costs

Using bespoke PSI calculations is the only way to ensure precision, compliance, and cost-efficiency—and AutoPSI makes this process faster and more accessible than ever.

The Problem with Default Ψ-Values in SAP Table K1

As the construction industry moves toward higher energy efficiency standards, thermal bridging has become a critical factor in heat loss calculations. Under SAP 10.2, assessors can no longer rely on outdated default Ψ-values from SAP Table K1 without risking inaccuracies in compliance reports.

Many SAP assessors, architects, and developers still rely on default Ψ-values from SAP Table K1. While this approach offers a quick way to estimate thermal bridging, it comes with significant drawbacks:

1. Generic Ψ-Values Ignore Actual Construction Details

  • SAP Table K1 applies one-size-fits-all values, failing to consider specific materials, insulation thicknesses, or junction configurations.
  • The same Ψ-value is applied regardless of real U-values, leading to misleading heat loss estimates.

2. Outdated Standards Lead to Inaccuracies

  • Many default Ψ-values were established using 2002 building regulations, long before modern insulation techniques and enhanced building fabric performance.
  • SAP 10.2 now discourages reliance on outdated figures, pushing assessors toward bespoke calculations.

3. Overestimating or Underestimating Heat Loss

  • Using generic values can inflate the thermal bridging factor (y-value), making buildings seem less energy efficient than they truly are.
  • Overcompensation may lead to unnecessary insulation costs, while underestimation risks non-compliance with Part L.

Why Bespoke PSI Calculations Matter in SAP 10.2

Bespoke PSI calculations provide accurate heat loss values, ensuring better energy performance and compliance. Compared to Table K1 defaults, a project-specific Ψ-value calculation offers clear advantages:

✅ Precision in SAP Calculations – Every PSI value reflects actual construction details, improving heat loss accuracy.


✅ Guaranteed SAP 10.2 Compliance – New standards encourage the use of junction-specific PSI values instead of default look-up tables.


✅ Optimised Design Flexibility – Architects and energy assessors can refine insulation strategies, minimising thermal bridging risks.


✅ Cost Savings – By avoiding unnecessary over-insulation, developers can reduce project costs without compromising energy performance.

💡 AutoPSI helps you calculate bespoke PSI values effortlessly—so you don’t have to rely on outdated estimates.

How AutoPSI Delivers Faster, Smarter PSI Calculations

Traditionally, calculating bespoke PSI values required complex thermal modelling software and specialist expertise. This time-consuming and expensive process discouraged many assessors from pursuing accurate PSI calculations.

AutoPSI Eliminates These Barriers by Offering:

🚀 Automated PSI Calculations – No need for manual thermal modelling—AutoPSI does the work for you.


⚡ Fast, Compliant Results – Get accurate junction-specific Ψ-values that comply with SAP 10.2.


🔍 User-Friendly Interface – Designed for architects, SAP assessors, and developers with minimal training required.


💰 Cost-Effective Compliance – Achieve better SAP ratings without unnecessary insulation costs.

📢 Still using Table K1 default Ψ-values? It’s time to upgrade to a data-driven approach.