Indicative onlyThese tools provide indicative calculations only. No warranty is given as to the accuracy, completeness or fitness for purpose of any output. Using this site does not create a professional relationship or duty of care between brickdims and the user. Results must not be used as a substitute for professional advice, site-specific assessment, or formal compliance sign-off. Building regulations are subject to change, so always verify against the current editions of the relevant Approved Documents and consult a building control officer where required. brickdims accepts no liability for any loss, damage or non-compliance arising from reliance on these tools, to the fullest extent permitted by law. If any part of these terms is found unenforceable, the remaining terms continue to apply. These terms are governed by the laws of England and Wales. By using this site you accept these terms.
Glazing percentage calculatorBETA
Calculate glazing percentage and solid-to-void ratio. Input wall dimensions and opening types.
Results from brickdims.com tools are indicative only. Using this site does not create a professional relationship or duty of care. Not a substitute for professional advice or formal compliance sign-off.
Wall & building type
Openings
Area per opening: 1.4 m², total: 1.44 m²
Results
Glazing percentage
6%
of this elevation
Wall area
24 m²
Glazing area
1.4 m²
Opening breakdown
Opening
Size
Area
Of wall
Window
1 × 1,200 mm × 1,200 mm
1.4 m²
6%
Wall diagram (not to scale)
Window
Positions are evenly distributed for illustration. Doors shown 100mm from wall base.
FAQs
How is glazing percentage calculated?
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Divide the glazed area by the area it is measured against and multiply by 100. Check which base applies: Part L extension rules use floor area, while façade studies usually use wall area.
How much glazing can a house extension have?
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Approved Document L Volume 1 limits windows, rooflights and glazed doors in an extension to 25% of the extension's floor area, plus the area of any windows or doors the extension removes or covers. Going over needs a calculation showing the extension performs no worse overall.
What glazing limits apply to non-domestic extensions?
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Approved Document L Volume 2 gives reference values of 40% of wall area for offices, shops and assembly buildings, 30% for residential buildings and 15% for industrial and storage, with rooflights at 20% of roof area.
What is solid-to-void ratio?
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It is the proportion of solid wall to openings in a façade. A wall with 30% glazing has a solid-to-void ratio of 70:30.