Helping highly glazed extensions achieve Part L compliance
At Barlings KWA, we provide professional excess glazing calculations for house extensions and glazed building alterations across Lincolnshire and the UK.
If your extension includes large bifold doors, roof lanterns, sliding doors, or extensive glazing, Building Control may require a calculation to demonstrate compliance with Building Regulations Part L.
We help homeowners, builders, architects, and developers achieve compliance quickly and cost-effectively.
Our aim is to provide clear guidance and fast turnaround times so your project can progress without unnecessary delays.
Email: [email protected] or [email protected]
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What Are Excess Glazing Calculations?
Building Regulations Part L generally limits glazing in domestic extensions to:
25% of the extension floor area plus the area of any existing windows or doors being removed.
If your proposed glazing exceeds this allowance, an excess glazing calculation is usually required to show that the extension still performs thermally as well as a compliant design.
This is common with:
- bifold doors
- sliding patio doors
- roof lanterns
- corner glazing
Do I Need One?
You may need an excess glazing calculation if your extension includes:
- full-width bifold doors
- large rooflights or lanterns
- floor-to-ceiling glazing
- glass corner details
- modern “glass box” extensions
A typical example:
A 20m² extension would normally allow:
5m² glazing (25%)
If you are removing an existing 3m² patio door, your total allowance becomes:
8m² total glazing.
Anything above this may require a calculation.
What our clients say
We have recommended Barlings KWA to many of our clients for their air testing and energy assessment services. William and Kerry are extremely helpful and always deliver the work accurately and on time
Joe Campion
How We Demonstrate Compliance
At Barlings KWA Ltd, we carry out detailed calculations to compare your proposed extension against the notional Part L compliant standard.
This may include:
- area weighted U-value calculations
- SAP extension calculations
- thermal performance comparisons
- glazing ratio checks
- insulation upgrade recommendations
Where necessary, we advise on improvements such as:
- better wall insulation
- improved roof U-values
- upgraded glazing specifications
- lower U-value frames and glass
- reduced rooflight area
The aim is to help retain your preferred design while achieving approval.
Common Projects We Assess
We regularly assess:
- rear extensions with bi-folds
- glazed kitchen extensions
- orangery-style extensions
- lantern roof extensions
- side return extensions
- wrap-around extensions
- highly glazed garden rooms
We work closely with architects, developers and contractors to ensure compliance is achieved efficiently.
Why choose Barlings KWA Ltd?
- Experienced in Building Regulations compliance
- Reliable and professional service
- Clear reports suitable for Building Control
- Practical advice to help projects meet Part L requirements
- Local Lincolnshire based service
We understand the requirements of construction projects and aim to provide a reliable and efficient service throughout the process.
More client feedback
“Always happy to answer any queries we have; the service and information they provide is excellent.”
— Kirsty Uttley
“A fantastic, professional company to work with. Great communication and turnaround time.”
— Chris Henderson
What we need to quote
- Drawings for your proposed extension
- A brief specification
- Address of the project
Get a Quote for Excess Glazing Calculations
If you require excess glazing calculations, we would be happy to help.
Please contact us to discuss your project or request a quote.
Email: [email protected] or [email protected]