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Double Glazing Timber Sash Windows

Double Glazing Sash Windows

Can wooden sash windows be double glazed?

Yes, into your existing frames we install replica replacement timber sashes with low-E double glazing.

For over 20 years we have been double glazing timber sash windows.   Our bespoke replica sashes are installed into your existing box sash window frames and will transform your period property.  We can match any glazing patterns, ensuring the original charm of your home remains unaltered. 

Sash Window Specialist - Double Glazing.

Our bespoke double glazed timber sashes for period homes.

Winchester Sash Window Specialist Double Glazed low e timber sashesWe manufacture & install authentic wooden replica sashes into existing timber frames, paint finished and double glazed with energy efficient (low E) glass.  Accoya wood ensures a product that lasts a lifetime. 

Authentic Replicas

We carefully reproduce a copy of the original sashes, paying close attention to horn, moulding & sectional details. By increasing the rebate depth we accommodate a sealed double glazed unit.  If your original sash frames are missing then we can work from old photos or copy neighbouring property.

Glazing bars can either be bonded with duplex bars or more expensively with individual Slimlite sealed units.

Reading Sash Window Specialist. Double Glazed Castellated Sash.

In some cases it is even possible for us to convert existing single glazed sashes to accept double glazed units. 

Regardless of the temperature outside a window with good insulation properties will help to improve the comfort of your home.

It is estimated that double glazing a period window can reduce the amount of heat transfer through a home’s windows by up to 40%. This ability to retain heat makes double glazing more energy efficient compared to single pane windows.  Reduced heat conduction through your window glass means less energy is required to heat and cool your home, cutting energy bills.

Sash Weather & Draft Seals.

Double Glazing benefits include:

  • An energy efficient home is a comfortable home
  • Double glazing reduces your homes carbon footprint.
  • Double Glazed Units should reduce heating bills by around 20%.

  • Reduced UV prevents furnishings from fading
  • Reduced condensation on glass
  • Air borne noise, dust and other pollutants that are suspended within draughts are also greatly reduced.
  • Low friction draught proofing strips aid smooth window operation and stop annoying rattles

Counterbalancing Heavier Glass

Sash Window Lead Counterbalance Weights

Additional weight is required to counterbalance the heavier double glazed timber sashes.  The original cast iron weights are replaced with lead weights; these make up a considerable part of the total service cost.

Sash Replacement Service includes:

  • Survey of the existing frames.
  • Our standard Draught Seal & Restore service.
  • Bespoke replica timber sashes.
  • Balancing the weighting mechanism, to ensure ease of operation.
  • Large selection of double glazed units.
  • A choice of paint or stained finishes.
  • A wide range of ironmongery in a choice of finishes.

Draught Seal / draft seal & sash window Recondition by Sash Window Specialist.


Double glazed & draught proofed timber sashes offer significant savings on heating and cooling costs in a typical home.


Single glazing contributes to energy loss by allowing heat to conduct directly through the glass.  Double glazing overcomes energy conduction by introducing an air space between two panes of glass.  Our double glazing units are also filled with an inert gas, such as Argon, which further extends the insulation performance. 

One of the panes used in our double glazed insulating units is low emissivity,  energy efficient glass.   Low e glass has a special insulating surface that reduces the amount of radiant heat transfer. 

How Does low-emissivity glass work?

low e glass for period casement and sash windows

Low-e glass has a special coating which is a poor radiator of heat and does not allow heat to be transferred through the glass. In winter, heating is reflected back indoors; in summer heat from the
sun is reflected away, keeping the room cooler. 

Draught Excluders

Draught-stripping your existing period sash windows can reduce the draughts by almost 90%, and is an essential step to improving energy efficiency in period windows.

Heat loss through single glazed windows is in excess of 25%.​


Wood is a natural insulator

The natural insulating properties of timber make this an extremely energy efficient building material.  Timber window frames are highly energy efficient as they do not conduct heat. 


Timber windows help to lower your carbon foot print. 

Wood is a sustainable building material, derived from a renewable source. Any home owner choosing green living should consider preserving or reinstating timber windows.    

In order to grow, one kilogramme of wood needs about 1.55 kilogrammes of carbon dioxide from the air, the carbon of which is stored in the tree. About half of timber is carbon. A rule of thumb is that 1 cubic metre of wood stores 1 tonne of CO2.


Historic Glass

Before choosing this service some consideration should be given to the benefits of your existing glazing.  Heritage window glass was hand made resulting in an uneven surface with flaws and distortions.  Historic glass adds to the windows character in a way that modern float glass can not match.  If your property has unique historic value or your existing sashes are still in good structural order then first consider if our Draught Seal & Overhaul Service might be sufficient . 


Heritage aproved draught seals

We have been using the same top quality British made draught seals for over 20 years.  Brush draught seals are the best option for long life in a sliding sash window.

Blending the latest advances in technology into period homes


Timber Selection

Bespoke wooden replica sashes area constructed from range of premium timbers. 

Redwood pine timber used for wooden sash windows, casement windows and doors. Douglas Fir premium softwood timber used for wooden sash windows, casement windows and doors. Oak hardwood timber used for wooden sash windows, casement windows and doors. Meranti hardwood timber used for wooden sash windows, casement windows and doors. Mahogany hardwood timber used for wooden sash windows, casement windows and doors. Jarrah hardwood timber used for wooden sash windows, casement windows and doors. Accoya modified softwood timber used for wooden sash windows, casement windows and doors. Choose Accoya for long life, durablity and eco friendly.

See our Guide to Timber Type

Accoya® Wood

80 years of research resulted in Accoya, a high performance wood that exceed those of the best tropical hardwoods. Using nontoxic processes fast growing pine is structurally altered to produce a stable, very durable product.  The manufactures guarantee against rot in its natural unpainted state for 30 years and they confidently claim at least a 60 year life cycle in painted windows.  Light weight and durable; Accoya is the perfect choice for double hung counterbalanced windows.

accoya wood for sash windows


Choice of Double Glazed Units

  • Argon filled for better energy efficiency
  • Acoustic DGU configuration.
  • ‘Low E’ energy efficient glass.
  • Etched or patterned glass.
  • Safety Glass.
  • Slimlite units or duplex bars.
  • 5 – 16 mm spacer bars depending on the sash thickness.

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Window Security & Hardware

Sash Window Renovation. | Double Glazed Timber SashDouble Glazed Wooden Sash Window. Double Glazed Sash Window.

Various catches effectively bring the sashes into a locked position, however the screws holding these in place are small and these catches should not be considered an effective security measure. We have a range of sash window security options available.  We also supply a wide range of sash window furniture, available in variety of finishes.