Prime Sash Windows
London, United Kingdom
Prime Sash Windows is a London-based specialist in bespoke timber sash windows, casement windows and doors, with over a decade of experience manufacturing and installing handcrafted timber windows for homeowners, architects and developers across London and the surrounding region. FENSA registered, PAS24 security certified, and a member of The Joinery Network and Made in Britain, the company builds every window by hand in its own workshop near London using premium hardwood, Accoya and oak, and installs them using FENSA-certified installers. Their proprietary Passive Glass technology achieves U-values as low as 0.8 W/m²K, making them a technically serious choice for architects navigating Part L compliance on heritage and conservation projects.
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Prime Sash Windows specialises in the manufacture and installation of traditional timber sash windows built exactly as they should be: from premium hardwood, balanced on lead weights rather than spring balances, finished with multiple coats of microporous paint, and glazed with slimline double glazing that achieves energy performance far beyond what conventional double glazing delivers.
The company's approach is defined by a refusal to compromise between traditional appearance and modern performance. Their lead weights are made from 100 percent recycled material, preserving the authentic feel and smooth operation of a genuine sash window while meeting contemporary environmental standards. Their Passive Glass technology achieves U-values as low as 0.8 W/m²K, compared to around 1.4 W/m²K for standard double glazing, a fifty percent improvement that makes a meaningful difference to building energy performance and a genuine solution for architects working on heritage projects where Part L compliance is required without compromising conservation requirements.
Every window is designed, built, tested and certified in the United Kingdom, not imported or assembled from parts made elsewhere, and comes with an insurance-backed warranty. The company's online 3D configurator allows homeowners, architects and developers to design and price bespoke sash windows, casements and doors in real time, generating a full PDF specification and estimate without any back-and-forth email exchanges or waiting for a basic quote. A free site survey is available within 25 miles of London.
Production takes eight to twelve weeks from order confirmation, with installation carried out by the company's own FENSA-certified team.
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Bespoke timber sash window manufacture and installation.
Casement window manufacture and installation.
Timber door manufacture and installation.
Heritage and listed building window replacement and restoration.
Energy efficient glazing with Passive Glass technology achieving 0.8 U-value.
Online 3D design and pricing configurator.
Free site survey within 25 miles of London.
Supply-only options available.
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FENSA registered installer.
PAS24 security certified.
Member of The Joinery Network.
Made in Britain certified.
Passive Glass technology achieving U-value of 0.8 W/m²K.
Part L compliance ready for heritage and conservation projects.
Insurance-backed warranty on all installations.
Part of Skylon Group.
