Professional service and excellent product. OBSW were able to specify windows that other companies said were impossible.Edward Christie
Double glazed timber sash windows • London
Double Glazed Timber Sash Windows
Warmer, quieter sash windows without losing the character of your home.
Bespoke solid-hardwood sash windows with Box Sash-manufactured glazing, designed around period proportions and installed by our own specialist team.
- Argon-filled, flush-sealed double glazing
- Solid hardwood frames, made to measure
- Traditional bars, horns and mouldings
- 50-year frame and 10-year glazing guarantees
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1979Established specialist manufacturer & installer
50-yearTimber-frame guarantee
10-yearGlazing guarantee
25,000 sq ftPurpose-built UK joinery
Made + installedBy Box Sash
Customer experience
Reassurance from completed projects.
Good joinery is only part of the job. Customers also judge the survey, communication, fitting and how their home is treated during installation.
the fitting was done efficiently and neatly, and the windows are well-constructed and draught-free.Tony Roth
The windows are stunning- excellent quality and the installation was so smooth and straight forward. We were thoroughly impressed.Jill Benjoya Miller
Why Box Sash
A sash-window specialist, not a generic replacement-window installer.
Established in 1979, Box Sash manufactures and installs bespoke timber windows. The frame, glazing and architectural details are considered as one product, with one team responsible from specification to installation.
01
Made in our own UK joinery
Around 25,000 sq ft of purpose-built joinery gives us control over timber, proportions, mouldings, finish and quality.
02
We manufacture the glazing too
Our own glazing manufacture means the glass and timber frame can be specified together instead of treated as separate products.
03
Designed for period architecture
Sightlines, glazing bars, horns and mouldings can be tailored so improved performance does not create a modern-looking compromise.
Modern performance, traditional appearance
Double glazing should improve the room, not change the façade.
The best upgrade is one you feel more than you see. We design the whole sash window around the building, retaining traditional proportions while introducing modern glazing, draught control and security where appropriate.
That makes the specification especially suited to period homes where architectural character matters as much as comfort.
- ✓Flush-sealed, Argon-filled double-glazed units
- ✓Acoustic glass options where noise is part of the brief
- ✓Toughened, laminated, obscured, textured and decorative glass options
- ✓Property-specific advice where conservation considerations apply
Built as one complete window
Every component is considered together.
Rather than forcing a standard double-glazing system into an old opening, we can tailor the timber, glass and visible details around the property.
Glazing
Double glazing, acoustic options and specialist safety or privacy glass can be selected to suit the room and property.
Proportions
Meeting rails, glazing bars and sightlines are designed to retain a traditional sash-window appearance.
Timber details
Solid-hardwood frames, traditional mouldings and timber horns can be matched to the architectural character.
Finish & hardware
Paint colours and ironmongery can be specified to complement existing interiors and exterior detailing.
Craftsmanship & detail
Traditional detailing, seen up close.
Built for the long term
Strong guarantees, stated clearly.
50
Year frame guarantee
Our timber window frames carry a 50-year guarantee.
10
Year glazing guarantee
Our glazing units carry a 10-year guarantee.
Guarantees are associated with the Independent Warranty Association. Terms and conditions apply.
How it works
From first message to finished installation.
A clear route from first enquiry to a window designed for the actual property.
Tell us about the property
Start your online quote with a few simple choices about what you need and roughly how much the project involves.
We discuss the project
We review what you need, ask the useful questions and agree whether a property survey is the right next step.
We specify & manufacture
The timber, glazing, details, finish and hardware are agreed before manufacture in our UK joinery.
We install
Our installation team fits the finished windows around the agreed specification and project requirements.
Common questions
Useful answers before you enquire.
Period properties are rarely identical. Where the right answer depends on the building, we would rather assess the property than make a blanket promise online.
Can timber sash windows be double glazed without looking modern?
Yes. The window can be designed around traditional proportions, glazing bars, horns and mouldings so the appearance remains appropriate to the property while modern glazing improves comfort.
What type of double glazing do you use?
Our product information includes flush-sealed, Argon-filled double-glazed units. We also manufacture our own glazing units and can tailor the glass specification to the project.
Will double glazing help with draughts and heat loss?
Modern glazing and draught sealing are intended to improve comfort and insulation compared with a poorly performing window. We do not use a blanket percentage-saving claim because the result depends on the property and complete specification.
Can you help reduce outside noise?
Acoustic glass can be specified where noise is part of the brief. The appropriate option depends on the property, opening and type of noise involved, so we avoid promising a fixed dB reduction.
What guarantees are included?
Timber window frames carry a 50-year guarantee and glazing units carry a 10-year guarantee. Terms and conditions apply.
Can double glazing be used in conservation or period properties?
Often it can, but the acceptable frame dimensions and glazing specification can depend on the property and local requirements. We recommend a property-specific survey rather than assuming one specification fits every building.
Free online quote · No obligation
Ready to improve the comfort without losing the character?
Tell us about the property and the windows you are considering. Start online with a few quick choices. We review the details before confirming the right quotation route for your property.