Traditional timber sash windows

At Green Home Glazing we have architectural, environmental, design and construction expertise and we are here to assist you with choosing the right solution for your home project.

This is why we have prepared this Guide on traditional timber sash windows:

  • to answer your most common questions,
  • to inform you on what adds value and what works best, and
  • help you understand the best options for your budget and requirements.


  • How much do timber sash windows cost?
  • How long do sash windows last?
  • Do original sash windows add value?

We are suppliers and installers of timber door and window products and we work directly with manufacturers to source the best products to match your requirements and do so at the best price possible.

Are upvc sash windows cheaper to buy compared to the timber sash window cost? Of course they are.

Is installing upvc sash windows a false economy that will likely lose you money?

Of course it is.

There are many myths about all this and it is true that plastic frames have pretty much the same energy efficiency to any type of similar wooden sash windows. However, research finds that plastic needs to be replaced every 35 years compared to 60 years for wood.

Therefore you benefit over the product lifetime as timber sash windows are more economic in the long run. This might also be instant in regards to the value of your property:

“Estate agents suggest that using poor facsimiles of historic features can actually reduce the value of a property. A survey of UK estate agents carried out by English Heritage in 2009 showed that replacement doors and windows, particularly PVC-u units, were considered the biggest threat to property values in conservation areas. Of the estate agents surveyed, 82% agreed that original features added financial value to homes and 78% thought that they helped houses sell more quickly.

 This is a significant issue for homeowners, particularly those in conservation areas, because houses in these areas sell, on average, for 23% more than houses elsewhere. This has been shown by research carried out on behalf of English Heritage by the London School of Economics (Ahlfeldt, Holman and Wendland, 2012).” Historic England


  • Who invented timber sash windows?
  • What is the best wood to make windows out of?
  • Can you match the style of my existing windows?

The invention of the timber sash window (or box sash windows) is sometimes credited, without conclusive evidence, to Robert Hooke, an English scientist and architect, a polymath, sometimes called the “England’s Leonardo”.

Unlike witch windows that open diagonally, sash windows have two main panels that slide vertically up and down to provide the level of ventilation necessary. In order to facilitate this vertical movement a sash weight or counter-weight is concealed within the window frame.

Each panel is split into a number of panes with typically an arrangement of six panes per panel which creates the traditional Georgian arrangement of “six over six” for period sash windows.

Victorian windows are characterised by a smaller number of panes (typically “two over two” or “three over three”). Edwardian windows would later take advantage of developments in glass technology with larger glazed panels at the bottom of the wooden window and a variety of panes at the top.

At Green Home Glazing we will match the design and style of your existing windows.

Our specialist surveyors will measure the existing structural window openings, we will record the appearance of the timber frames and the window panels, and we will prepare detailed drawings for you to approve before we manufacture your new windows.

Your new windows will be manufactured by timber sourced sustainably (FSC® certificate), from a variety of high quality species (Pine, Oak, Mahogany, Larch, Accoya), in a wide choice of colours for varnishes and paints, made with hardware mechanisms of stainless steel, coated with zinc and aluminium.




  • How much will I save by replacing my windows?
  • Are wood windows energy efficient?
  • Double glazed sash windows or triple glazed sash windows?

According to the GreenSpec Guide, a typical house loses 10% of its heat through windows. As part of a refurbishment scheme the replacement of existing windows with new high performance windows should be seriously considered.

The Centre for Alternative Technology recommends timber-framed windows unequivocally. Hardwood (FSC-certified) or durable softwood frames come from a renewable source, use comparatively little energy in manufacture, last decades (with regular maintenance) and can be repaired easily.

The Energy Saving Trust states that the benefits of energy efficient windows include:

A more comfortable home – Energy efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.

Peace and quiet – Not only do they keep the heat in, energy efficient windows insulate your home against external noise.

Reduced condensation – Energy efficient glazing reduces condensation build up on the inside of windows.

By installing double glazing to windows in an entirely single-glazed property, you could save the following each year:

Triple glazing consists of three panes of glass, with two being gas-filled, and a typical u-value of 0.8W/m2K. According to Self-Build, modern double glazing can achieve 1.6 W/m2K (anything less than 1.0 W/m2K is very good, and Passivhaus’ requirement is 0.8 W/m2K).

The lower the u-value the better the insulation property of the window and the more efficient the double glazed sash windows are. Which means that triple glazing will achieve even greater savings for you compared to double glazing of lower u-value.


  • Can you put new windows in a Grade 1, 2*, 2 Listed building?
  • Do you need planning permission to replace windows in a conservation area?
  • Are upvc windows allowed in a conservation area?

At Green Home Glazing you will get expert architectural advice by our director is a Chartered Architect with the Royal Institute of British Architects (RIBA)  and has extensive residential experience with Listed Buildings and properties in Conservation Areas across London (see GOAStudio London residential architecture).

Also, read the residential guide to homeowners George wrote for Which? Magazine.

Any alterations of doors and windows to Listed Buildings will require prior Listed Building Consent (Grade I, II* and II) and Full Planning approval; the conservation team of your local authority will review the submitted proposals and will take a view on the right type of window, glazing and details for the building.

Historic England advises that “where a window that diminishes the significance of the building, such as a PVCu window or an ‘off the peg’ timber window of an inappropriate pattern, is to be replaced the new window should be designed to be in keeping with the period and architectural style of the building.

 It may be possible to base the design on windows that survive elsewhere in the building or it may be necessary to look for examples in other buildings of the same period and style close by. The local planning authority may also be able to offer advice. In some cases this may involve reinstating the structural masonry opening to the correct proportions.”

A similar approval process is necessary if your property is in a Conservation Area; typically in Conservation Areas the Council removed Permitted Development Rights to properties which means that any alterations to the size, location and type of doors and windows requires planning approval for both single family dwellings and flats.

Green Home Glazing has the expertise to advise and apply on your behalf for all the approvals you will need, including Listed Building Consent, planning, Building Regulations and Freeholder approvals.



  • Are wooden windows better than upvc?
  • What are the environmental advantages and disadvantages of timber sash windows?
  • Should I go for softwood or hardwood for my sash windows?

There are intrinsic and undeniable environmental advantages of using timber in construction, including in the manufacturing of traditional timber sash windows, when choosing wood from sustainably managed forests.

Wood is naturally renewable, low carbon, and using wood helps take carbon from the atmosphere making it the most sustainable mainstream building product. Over 90% of timber used in UK construction comes from Europe, where more trees are grown than harvested (source: TTF Statistical Review 2016).

The GreenSpec assessment of the relative environmental impact of timber framed windows is as follows:


  • The heat energy (operational energy) lost through a window frame during its lifetime is likely to be greater than the energy used to manufacturer it (embodied energy)
  • It is important to select a frame material with the least thermal conductivity. Wood is the least conductive followed by PVC and metal.

Wood, durability and environmental impact

The choosing of wood, its treatment and maintenance are crucial in reducing a window frame’s environmental impact:

  • Specify FSC sourced timber
  • Transport adds embodied energy. Try and source UK timber whenever possible.
  • For both hard and softwoods ensure that the specification explicitly excludes the use of sapwood.
  • Painting wood adds significantly to its environmental impact. Either specify a naturally durable species that doesn’t need treating or select a treatment with low impact. If frames are untreated, ensure that the client understands that initial colouring will change.
  • If the wood is to be treated/painted, ensure that this is done in the factory prior to arrival on site. Factory painted frames double the period before the need to repaint.


  • The design of the sections will have an effect on performance. Design to maximise rapid drainage, maintain dry glazing channels and locate weather seals away from wet areas.
  • Keep window panes as large as practically possible. Even with wooden frames, the metal spacers between the glass panes act as cold bridges. Large panes have less perimeter length than lots of smaller panes.

On site

  • Be careful to avoid damage to frames on site. Ensure that they are not used as formwork in wall openings.




  • How do I block outside noise in my bedroom?
  • How can I reduce noise when living on a busy street?
  • What are the best windows for noise reduction?

Aircraft noise. Road traffic noise. Anti-social noise. Rail or tube noise. Sound looks for the path of least resistance and will always find a way in the fabric of the building and the most vulnerable areas are through and around the window and door openings of your home.

At Green Home Glazing we will help you select the best timber sash window product for noise reduction and through our Full Installation Service we will seal the area surrounding your windows to ensure there are no empty spaces or openings where sound can travel by.

Typically a standard double glazed unit with two 4mm panes of glass and an air cavity will reduce noise by around 25dB.

Note that a noise reduction factor of 10dB equates to a 50% reduction in the volume of a noise, which is a substantial reduction that is enough to create a much quieter home environment and make any external noise much less noticeable.


  • Are timber sash windows safe for my children?
  • Are sash windows easy to break into?
  • How can I make my sash window more secure?

Our traditional sliding sash windows use dual screws, sash locks and or sash stops rather than the key locks that are found on modern uPVC windows and this is why they are intrinsically more robust and more secure than any upvc framed windows.

According to the Crime Prevention Website, if well maintained and properly locked, a traditional sliding box sash window will provide a good level of security.

Our traditional timber sash windows can come with dual screws, sash stops and frame to frame sash locks to give you added security. In order to enhance security our double and triple glazed window units come with the following glazing options:

Toughened – to increase strength and safety

Laminated – to provide additional security compared to toughened glass

Obscure – to improve privacy to windows

In regards to safety, our sliding sash windows consist of two main wooden panels that slide vertically up and down; unlike casement (French) windows, this ensures that a barrier to prevent from falling is an integral part of the window design.

In addition to the locks, when used properly, allow for ventilation openings that remain less than 100mm wide at all times to ensure that children do not have access to the outside of the window.


Why Us

Our offer – We offer triple glazing for the price of double glazing as standard for all quotes across Greater London.

Our full service – Uniquely we offer a full service that includes architectural advice, obtaining all approvals on your behalf, as well as supply and fitting of window and door products.

Our architectural, environmental, and design expertise – By our Architect Director (RIBA Chartered member and registered with ARB), George Omalianakis | GOAStudio London residential architecture limited.

Our construction expertise – By our Builder Director (Federation of Master Builders member), Kia Karamian | Dream Building limited.

Our manufacturers – We work directly with vetted manufacturers which allows us to control the quality, design and cost of the window and door products we will provide for your home.



  • Multi-layer (laminated) hardwood or softwood without Knots
  • 4-stage process for factory finish including wide range of RAL and stain colours
  • Spiral or traditional weights balanced
  • Decorative horns to top sash
  • Standard triple glazing or alternatively double glazing (thermofloat + argon gas Low “E”)
  • U-value 1.1 w/ m2 for unit glass
  • Internally beaded for security
  • Silicone sealed for ultimate weathering protection
  • Fully drained and vented Trickle Vent PCV 4000mm2

Links to our other product range

Traditional timber sash windows
Timber Casement Windows
Sliding Patio Bifold Doors
Aluminium Doors & Windows
Steel Windows & Doors








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