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Traditional Box Sash Windows are a modern double-glazed replacement for original period windows often found in Georgian, Victorian and Edwardian historic properties. Offering high security, thermal, weather and acoustic performance, our Traditional Box Sash Window is an ideal solution for both period and new build properties where quality, high-performance timber sash windows are required.
This window is internally beaded to meet PAS 24 security levels and has applied slim glazing bars to keep the aesthetics of the original window but with a much higher performance, typically achieving a whole window U value of 1.4 W/m²K and acoustic ratings of 29-38dB.
Constructed with slim frame and sash profiles, the Traditional Box Sash Window functions with a classic system of cords, weights, and pulleys. These windows are typically installed within a check reveal, allowing the box to remain largely concealed behind external brick or stonework, although it can also be fitted flush with the brick face, where the box remains visible and is often finished with an architrave.
TRC’s Traditional Box Sash Windows can be supplied fully finished with a 3-coat spray-applied microporous water-based paint system or can be supplied primed only for a topcoat to be applied on site by others.
All our windows come with a choice of sash lifts, fasteners, locks and pulley wheels with a wide range of option finishes including antique brass sash, polished chrome, satin nickel, polished brass, matt bronze and polished nickel.
Product Guidance
| Frame | 100 x 140 mm (lining width x frame depth), manufactured using mortise and tenon joints, glued and mechanically fixed |
| Sash | 39 x 45 mm top rail and stiles, 90 x 55 mm bottom rail, 45 x 55 mm meeting rail |
| Mullion/transom | 39 x 45 mm top rail and stiles, 90 x 55 mm bottom rail, 45 x 55 mm meeting rail |
| Sill projection | 35 mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm |
| Staff / parting beads | Timber |
| Wood moisture content | 12-19% |
| Glazing beads | Internally Glazed with timber beads |
| Air Permeability | 450 Pa (Class 3) - EN 12207: 2017 |
| Water Tightness | 200 Pa (Class 5A) - EN 12208:2002 |
| Wind Resistance | 1600 Pa (Class 4C) - EN 12210:2016 |
| Whole Window U-Value | Thermal performance is calculated by the standards of EN ISO 10077-1:2006 and achieves a U-value of 1.5 -1.4 W/m²K depending on the type of timber, unit thickness and type of cavity gas used. |
| Whole Window Acoustic rating Rw, dB | Acoustic rating is Laboratory tested to BS EN ISO 10140-2: 2010 (Airborne Sound Insulation). Window Acoustic ratings Rw 29-38 Db. |
| Anticipated Life Expectancy | 60 years with the regular maintenance |
Product Specifications
| Material | Frame+Sashes Engineered redwood, Bottom Cill in Solid Hardwood - Standard. Engineered hardwood, Accoya, European oak. |
| Finish | Three coat spray applied factory finish using water based micro-porous paint/ stain. |
| Colour | White - RAL 9016 - Standard. Any RAL - from RAL classic range. Stain - from TRC stain range. |
| Glazing | Double glazed, 4/16/4 Low-E top sash – 4toughened/16/4 toughened bottom sash - Standard, Ug-value: 1.1 W/m²K; g-value: 0.52; |
| Perimeter spacing bars | White warm edge perimeter spacer with white warm edge integral spacers - Standard. Silver and Black spacer optional. |
| Solid Bar | Ovolo 1, Ovolo 2, Lambs Tongue. |
| Trickle ventilation | Concealed through frame head trickle ventilator. EA 1700, 4400, 5000 mm² |
| Child restrictor | Angel lock standard. Traditional Sash Stop optional. |
| Operation | A traditional box sash window uses an Iron (occasionally Lead) weight, attached to a cord, passed over a pulley and fixed to the glazed sash frame. As the window is operated the weights travel upwards or downwards concealed inside the frame. |
| Timber Species | Manufactured in selected engineered laminated pine, hardwood or Accoya, sourced from sustainable and managed forestry (FSC or PFEC certified). |
| Moisture Content | 12% +/- 2% on delivery |
| Glass | Windows to be factory fitted with 24-44mm thick sealed double-glazing unit Tested to BS EN1279. Composition of glass units is to be (from outside): 4mm float – 16mm argon filled cavity /4mm float glass with Low-E coating. Perimeter spacer in white or black. |
| Glazing Bars | Applied bars are used to achieve the slim section of traditional glazing bars. These are applied with double sided glazing tape to both faces of the sealed unit and capped with clear silicone |
| Ironmongery | A lockable Fitch fastener and two finger pulls to the bottom sash with options in colour and finish. |
| Cill | Manufactured in Hardwood with options of Projections: 35 mm, 50mm, 60mm, 70mm, 80mm, 90mm, 100mm, 110mm. |
| Horns | Solid feature horns to top sashes are included as standard (See Drawing No H-001) |
| Ventilation | A controllable trickle ventilator can be fitted to the window dependant on width of frame (See Drawing No HERITAGE-140/06) EA 1700, 4400, 5000 mm². |
| Finish as Delivered | Window supplied factory finished, externally and internally with Teknos Water-based micro porous opaque to specified RAL colour, or stained finish. Aqua prime 1410, Aqua mid-5200, Aqua top 2600. |
| Restrictors | Restrictors which allow the opening of the sash to be restricted to 100mm is an option |
| Fixing | Installation to be carried out using best building practices and in conjunction with recommendations of TRC windows |
| Warranty | Manufacturing and Material Defects: 10-year guarantee. Finishes: The standard three-coat opaque finished joinery guaranteed for 10 years. The stain finishes guaranteed against blistering or flaking for six years. Seals: The seals on double-glazed units are guaranteed for 10 years (from the date of delivery). Ironmongery: Functional failure is guaranteed on ironmongery for two years. |
Technical Drawings
U-values as low as 1.4 W/m²K reduce heat loss
Around 60-year lifespan with simple maintenance
PAS 24:2016 certified for tested security protection
Full RAL colour range and traditional wood stain options
Timber from FSC-certified sustainable forests
10-year warranties on glazing, finishes, and manufacturing
Browse completed installations showcasing TRC’s craftsmanship across a range of properties.
Our heritage sash windows are made to match box sash windows that are a staple of Victorian homes. These premium sash windows, with the classic weight-and-pulley mechanism, are the perfect choice for replacement windows in listing buildings, while also suiting high-end architect-led new developments.
Solid glazing bars come as standard, so each window comprises a number of individual glass panels, giving these heritage sash windows genuine character.
We can also add safety features to make them more suitable for a family setting, with an angel lock as standard and traditional sash stop. Restrictors can be fitted to make the opening of the sash to 100mm to ensure the safety of those in your property.
All windows are finished with three coats of sprayed applied microporous water based paint, to ensure the smooth operation and optimum performance of the window.
For non-listed buildings, you may also wish to browse our collection of traditional timber sash windows and doors.
Drawing on over 30 years of specialist experience in heritage window restoration and manufacturing, our Traditional Box Sash windows can be crafted to recreate any heritage window design.
Having serviced some of the UK’s most prestigious historic buildings, our customisation options encompass authentic moulding profiles that replicate original architraves, glazing bars, and frame sections.
Choose from an extensive palette of RAL colours or traditional stain finishes, perfectly matching existing paintwork or restoration specifications. Period-appropriate ironmongery options include various Fitch fastener styles, finger pull designs, and traditional hardware finishes in brass, bronze, or painted options to complement the window’s era.
Our skilled team can reproduce intricate details such as specific horn profiles, varied cill projections from 35mm to 110mm, and authentic glazing bar configurations including margin lights and geometric patterns. We also work to prioritise improving thermal performance and acoustic performance alongside authentic period style.
Whether recreating Georgian twelve-over-twelve panes or refined Victorian styles, TRC’s proven expertise in conservation work ensures every element can be tailored to match original specifications.
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