When building for low energy use, PSI values truly matter. We provide accurate thermal bridging calculations that help your project perform better and easily meet Building Regulations Part L, completely avoiding the penalties of default assumptions.
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If you are familiar with U-values—which demonstrate the rate of heat loss through flat surfaces like walls or roofs—PSI values are the vital missing link. They measure the heat that escapes where these flat surfaces join together.
Put simply, U-values cover heat loss across a continuous surface, while PSI (Ψ) values measure the linear heat loss through edges and corners (such as where a floor meets a wall, or a window frame joins a wall). These areas are known as thermal bridges and are often responsible for a massive percentage of a building's overall heat loss.
Thermal bridges might look small on a blueprint, but neglecting them during the design phase can severely damage your building's performance and compliance.
Heat escapes much faster through weak joints, leading to chronically higher heating bills and poor energy efficiency, especially in colder climates like Manchester.
Uninsulated junctions create "cold patches" that draw moisture from the air, inevitably leading to damp, aggressive mould growth, and structural decay.
Severe thermal bridges create cold downdrafts near exterior walls and windows, making rooms feel unevenly heated and chilly during a typical UK winter.
Without custom PSI calculations, assessors must use default "worst-case" penalty figures in SAP, often causing otherwise good designs to fail Building Regulations.
When it comes to energy efficiency in modern buildings, U-values simply don’t paint the full picture. A thermal bridge occurs when there is a break in the building's continuous insulation layer, creating a direct path for heat to aggressively leak out.
Whether you're developing high-end apartments in London or executing a deep retrofit in Liverpool, accurate PSI modeling is critical in three major areas:
To pass strict SAP targets, you must prove your junctions are efficient. Default assumptions are highly penalizing. Custom PSI modeling provides the accurate numbers needed to pass Part L seamlessly.
When adding internal wall insulation to existing structures, new thermal bridges are inadvertently created at party walls and floors. PSI analysis ensures these retrofits won't induce hidden mould.
Many developers spend thousands on extra solar PV panels or expensive triple glazing trying to force a failing SAP score to pass. Frequently, the cheapest and most effective solution is simply commissioning custom PSI value calculations to eliminate default penalties and dramatically lower the Y-value.
Working out a PSI value replaces guesswork with meticulous physics. Our accredited technicians use the following methodology to model your project:
We provide accurate, actionable thermal modeling for projects across the UK.
We abandon rough estimates and default penalties. We calculate bespoke, highly accurate PSI values tailored to the exact geometry and materials of your specific build.
By optimizing your thermal bridges on paper, we routinely save developers thousands of pounds on redundant insulation and renewable tech required to force a SAP pass.
Because we handle SAP calculations, EPCs, and PSI values simultaneously, our approach is highly cohesive, exceptionally fast, and notably more affordable.
Everything you need to know about navigating thermal bridging analysis.
Don’t risk your Building Control sign-off or rely on penalized default assumptions. Get in touch with Armeec today for expert, accurate thermal modeling.