Keep the character. Refine the comfort.
Crafted for period homes, traditional timber sash windows, metal-framed windows, and conservation architecture. Made-to-measure slim sealed units with Goethe restoration glass and authentic sightlines.
Historic sashes feature 7–10mm rebate shoulders engineered to conceal 5.5mm or 7.0mm slim perimeter spacer bars behind traditional putty/bead lines. Housing 11–14mm slim sealed units in historic single-glazed rebates requires 15–18mm bed depth (achieved via sympathetic rebate deepening or bespoke heritage reproduction sashes).
From Original Frame to Insulating Unit
Understanding why heritage windows require precision engineering: balancing narrow rebate depths, edge sightlines, and authentic glass reflections.
Concealed Sightlines
Historic sash frames feature 7–10mm rebate shoulders designed to conceal putty lines. Slim 11–14mm units employ 5.5mm or 7mm sightlines that remain completely hidden behind authentic moulding profiles.
5.5mm, 7mm & 8.5mm Seals
Sightline is the vertical height of the perimeter seal inside the rebate. Slim 5.5mm and 7mm warm-edge spacers keep the seal hidden behind traditional timber putty lines.
Goethe Drawn Glass
Unlike uniform modern float glass, 4.5mm Goethe restoration glass displays the soft optical draw lines, gentle waves, and authentic depth of historic cylinder and sheet glass.
Low-E Cavities & Dense Gas
Combining a 4mm softcoat Low-E inner pane with an Argon, Krypton, or Xenon filled 4mm or 6mm cavity delivers thermal refinement while retaining the architectural silhouette.
Who We Support
Whether you are restoring a single Georgian home or drafting an institutional conservation schedule.
Period Homeowners
Need guidance on whether your draughty sashes can be upgraded without replacing frames? Use our Simple advice mode to request advice and explore options before committing to surveys.
Joiners & Window Makers
Manufacture traditional sash or casement windows? Input multi-window schedules, specify exact sightlines (5.5mm/7mm/8.5mm), export CSV schedules, and request batch fabricator quotes.
Conservation Architects
Preparing listed building consent (LBC) applications? Access technical rule sheets, independent pane treatment data, Article 4 guidance, and Goethe restoration glass citations.
Engineered for Every Historic Window Type
Traditional Box Sashes
5.5mm & 7mm sightlines concealed behind authentic timber rebate shoulders, maintaining original counterbalances.
Flush Timber Casements
Lightweight slim sealed units preserve delicate friction hinges and cockspur stays while eliminating draughts.
Crittall-Style Metal Windows
Ultra-slim 11mm units with 5.5mm sightlines designed specifically for shallow 6–8mm hot-rolled steel rebates.
Window Appearance Explorer
Compare the optical character of standard modern float, Goethe restoration glass, and privacy textures in historic window frames.
4.5mm Goethe Restoration Glass
Manufactured via historic drawn sheet (Fourcault/restoration) processes, Goethe glass replicates the gentle surface movement, optical distortions, and soft reflections of original 18th, 19th, and early 20th-century cylinder and drawn window panes. It is preferred by conservation officers for Grade II and sensitive conservation area works.
Heritage Sealed Unit Configurator
Configure slim sealed units for historic timber sashes and metal frames. Every specification derives from authoritative manufacturer rules and carries through to quotation.
1. Sealed Unit Glass Make-Up
2. Dimensions, Quantities & Shape
Exploded Sealed Unit Architecture
Specification Summary
Repair First, Upgrade with Evidence
Heritage glazing policy across Historic England, Historic Environment Scotland, and Cadw prioritises historic fabric retention. We help you choose the honest, proportionate approach.
Preserve Original Glass
If historic cylinder or crown glass remains intact, replacement is rarely justified. Specialist perimeter brush seals and cord rebalancing eliminate 90% of draughts while keeping original glass.
Where Lost or Permitted
Where original glass was already replaced by modern float, or planning authorities permit thermal upgrades, slim sealed units (11–14mm) provide authentic warmth without altering joinery lines.
Reversible Conservation
For Grade I and Grade II* listed buildings where existing single glazing cannot be touched, discrete internal secondary glazing offers the highest acoustic reduction and thermal insulation reversibly.
1,000 UK Conservation Areas Covered
From the Regency terraces of Bath and Brighton to the granite tenements of Edinburgh and the Cotswold conservation villages. Each local hub provides Article 4 direction context and statutory local planning authority contact guidance.
BS EN 1279 Dual Seal Standard
Every slim unit is fabricated in dedicated UK cleanrooms to BS EN 1279 standards. Our dual-seal system pairs a primary polyisobutylene (PIB) vapour barrier with a high-modulus secondary structural seal, ensuring noble gas retention in ultra-slim 4mm and 6mm cavities.
Direct Technical Appraisal
Need to discuss non-standard apertures, complex shapes, or heritage officer specifications? Speak directly with our technical glazing desk.