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2022 Update
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Building Regs Part L

Part L of the Building Regulations sets minimum thermal performance standards for windows, doors, and glazing in England and Wales.
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Part L Compliant
U-Value ≤ 1.4 W/m²K
FENSA Certified

What the regulations mean for your glazing project.

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We're not a national call centre. We're local glaziers who take pride in every job.

Window U-Value ≤ 1.4

Replacement windows must achieve a maximum U-value of 1.4 W/m²K. All Pane Relief sealed units comfortably exceed this requirement.

FENSA or Building Control

Window installations must be signed off either through a FENSA-registered installer or by local authority Building Control. Pane Relief is FENSA registered.

WER Band C Minimum

As an alternative to U-value compliance, windows can meet Part L through achieving a minimum Window Energy Rating of Band C or above.

Competent Person Scheme

Self-certification through schemes like FENSA means no separate Building Control application is needed — saving time and money.

Expert Knowledge

Understanding Part L for Glazing

Part L of the Building Regulations (Conservation of Fuel and Power) governs the energy efficiency requirements for buildings in England and Wales. For glazing, Part L sets minimum thermal performance standards that all replacement windows and doors must meet.

The 2022 update to Part L introduced stricter requirements. Replacement windows must now achieve a U-value of 1.4 W/m²K or better, down from the previous 1.6 W/m²K limit. This means older double glazed units may no longer meet current regulations if they need replacing.

How Pane Relief units comply:

Our standard double glazed sealed units with Low-E glass and argon gas fill achieve U-values of approximately 1.1 W/m²K — well within Part L requirements. Triple glazed units achieve even lower U-values of around 0.7-0.8 W/m²K, providing substantial headroom above minimum compliance.

When you order from Pane Relief, every unit comes with documentation confirming its U-value, making it straightforward for your installer to demonstrate Part L compliance to Building Control or through FENSA self-certification.

The June 2022 update reduced the maximum U-value from 1.6 to 1.4 W/m²K. If your current sealed units were compliant under old rules, replacement units must meet the new, stricter standard.

Common questions about Building Regulations and glazing.

Frequently Asked Questions

Everything you need to know about our double glazing repair and replacement services across the South West.

  • If you're replacing the sealed unit only (not the frame), Building Regulations typically don't apply — the frame itself is the regulated element. However, if you're replacing the entire window (frame and glass), Part L applies and you'll need FENSA certification or Building Control sign-off.

  • Replacement windows in England and Wales must achieve a U-value of 1.4 W/m²K or better (whole window, not just the glass). Alternatively, a Window Energy Rating of Band C or above is accepted.

  • Listed buildings and buildings in conservation areas may be exempt from certain Part L requirements where compliance would unacceptably alter the building's character. Consult your local planning authority for guidance specific to your property.

  • No. Scotland has its own Building Standards with Document L (Technical Handbook Section 6). Requirements differ — see our Document L Scotland page for details.

Part L Compliant Sealed Units

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