Wooden Box Sash Window
Timber Box Sash Window – Cords & Weights
Our traditional cords and weights sash windows combine heritage design with modern thermal performance, available in three box depths to suit both period and energy-efficient projects.
Product Overview
Designed for homeowners and architects seeking authentic detail with long-term reliability, our timber box sash windows use the classic cords and pulleys system, counterbalanced with lead weights for smooth, dependable operation. Each unit is precision-made from multi-layer engineered timber and supplied fully glazed, painted, and weather-sealed — ready for installation in listed buildings, conservation properties, and new-build projects alike.
Standard & Deep Box Options (150 mm and 165 mm)
Our traditional box sash windows are available in two main frame depths — 150 mm (standard) and 165 mm (deep) — both built around the classic cords and weights mechanism for precise counterbalance and smooth operation.
The 150 mm standard box achieves a tested 1.2 W/m²K centre-pane U-value, offering excellent performance for most period properties and new-builds. It accommodates standard 4/16/4 argon-filled double glazing or optional acoustic laminated units. Each window includes a hardwood cill, full perimeter weather-seals, and dry internal glazing beads for long-term serviceability.
The 165 mm deep box allows for triple glazing or acoustic double glazing up to 28 mm thick. Ideal for homes near busy streets or where higher insulation is required, this version delivers superior energy efficiency while retaining authentic sash proportions.
Both variants share refined sightlines, traditional meeting rails, and optional glazing bars to complement any architectural style.
Our Cords & Weights Sash Windows
Our cords and weights sash windows are built using time-honoured joinery methods enhanced by modern precision manufacturing. Each window is made-to-order with traditional box frames, smooth sash operation, and discreet weather seals that preserve the original look while improving insulation and longevity.
Key Features:
Authentic cords & pulleys system for traditional operation
Smooth sash movement with lead weights and pre-stretched cords
Standard 150 mm deep box with tested 1.2 W/m²K U-value
Deep 165 mm option for triple or acoustic glazing
Ultra-slim 134 mm profile for vacuum glazing (< 0.9 W/m²K expected)
Fully sealed, internally beaded glazing system
Weather-stripped meeting rails for improved thermal and acoustic comfort
Factory spray finish in any RAL colour (dual colour available)
Brass, satin, chrome, or black ironmongery options
FSC-certified timbers, sustainably sourced
134 mm Slim Box Sash Window (Vacuum & Thin Glazing)
Developed specifically for listed buildings, conservation areas, and projects requiring authentic slim glazing, our 134 mm box sash profile achieves exceptional performance without compromising period detail.
It preserves the slender proportions of original Georgian and Victorian sashes while delivering outstanding thermal performance and natural light transmission.
Key Technical Highlights
Slim applied glazing bars: available in ovolo, lamb’s-tongue, or square profiles — the narrowest applied bar is only 17 mm wide.
Dedicated to thin glazing: accepts 16 mm (4/8 Ar/4 Low-E) double glazing (internally beaded); duplex bars not available at this thickness.
Perfect for putty-line imitation and vacuum glass: frame geometry designed for these specialist applications.
Optional thicker sash version: increasing sash depth to 54 mm (rebated externally) enables glazing up to 24–25 mm thick, supporting acoustic or laminated glass.
Solid bar widths: 22 mm or 24 mm for authentic “putty-style” appearance.
When combined with LandVac vacuum glazing, this ultra-slim 134 mm system delivers anticipated U-values below 0.9 W/m²K, offering full Part L compliance for heritage properties.
Timber Options
Our sash windows are made from multi-layer engineered timber for strength, stability, and resistance to movement. Each timber type offers its own character and performance level to suit different projects and budgets.
Engineered European Redwood – standard softwood for stability and performance.
Meranti – dense and durable hardwood with a fine grain and consistent texture.
Sapele – strong, stable hardwood with rich colour and tight grain pattern.
Oak – premium hardwood option.
Accoya – ultimate dimensional stability and 50-year rot-free guarantee
All timbers are multi-layer engineered to resist twisting and warping.
Glass Options
We offer a choice of high-performance glazing to meet a range of design, energy, and acoustic requirements. Each unit is factory-sealed and tested for durability, ensuring long-term clarity, insulation, and protection for your home or project.
Standard Double Glazing (4 / 16 Argon / 4 Low E) – Part L compliant
Vacuum Glazing – ultra-slim 8.3 mm units with centre-pane U-value 0.4 W/m²K
Acoustic Glass – enhanced noise reduction
Obscure Glass – satin, reeded, or patterned styles for privacy
Decorative Glass – stained, bordered, or etched designs available on request
Ironmongery
We supply a range of durable, high-quality fittings that complement both traditional and contemporary interiors. Each component is tested for strength, ease of use, and long service life, giving you the flexibility to match finishes across your project.
Polished Brass, PVD Brass, Satin Brass, Antique Brass, Polished Chrome, Satin Chrome, Antique Pewter, Oil Rubbed Bronze, Matt Black
Additional PAS 24 security hardware available for new-build compliance.
We also work with leading architectural ironmongery suppliers if you’re looking for a more refined finish.
Downloads
Access detailed resources to help plan and specify your project.
Our technical drawings include typical sections and elevation details for both hidden and visible spring balance sash windows.
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