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Recticel PIR Insulation
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Frequently Asked Questions
What is a U-value and how does this Recticel U Value Calculator work?
A U-value measures how much heat passes through a building element (like a wall or roof). Lower U-values mean better insulation. This calculator uses the BS EN ISO 6946 formula: U = 1 / (Rsi + Σ(d/λ) + Rse), where d is thickness, λ is thermal conductivity, and Rsi/Rse are surface resistances.
Which Rsi/Rse defaults are used for UK walls, roofs, and floors?
We use UK standard values: Walls (Rsi=0.13, Rse=0.04), Roofs (Rsi=0.10, Rse=0.04), and Floors (Rsi=0.17, Rse=0.04) in m²K/W. These values are automatically applied based on your assembly type selection.
What λ should I use for Recticel PIR insulation?
Recticel PIR insulation typically has thermal conductivity (λ) values between 0.022-0.026 W/m·K. Check your specific product datasheet for the exact value, as it can vary by product line and thickness.
How accurate is this vs on-site assessments/manufacturer tools?
This calculator provides theoretical values for design purposes. Actual performance can vary due to construction quality, thermal bridging, and material variations. Always verify with manufacturer tools and consider professional assessment for critical applications.
Can I export my calculation and share a permanent link?
Yes! Use the "Get Shareable Link" button to create a permanent URL that restores your calculation. You can also export your data as CSV for further analysis or record-keeping.
Does a lower U-value guarantee UK regs compliance?
While lower U-values generally improve compliance, Building Regulations have additional requirements for thermal bridging, air tightness, and whole-building performance. This calculator is for guidance only - always consult with a qualified professional for regulatory compliance.
Important Disclaimer
This calculator provides theoretical U-values for design guidance only. Actual thermal performance may vary due to construction quality, thermal bridging, material variations, and other factors. Professional assessment and manufacturer verification are recommended for regulatory compliance and critical applications. No liability is accepted for decisions based on these calculations.