The English Heritage of Sash Windows

The sliding sash window has been around for over three centuries and astonishingly, the operating principle of weights has remained almost unchanged throughout that time. Sash windows are made in such a way that they can be easily dismantled for repair or for replacing broken sash cords, weights or even just for repainting.  Many timber windows have lasted for decades because they have been properly maintained and painted regularly. When you contrast sash windows to contemporary windows, there are obvious flaws with the modern alternative; you cannot dismantle or repair the window easily, components cannot be made by any carpenter, they haven’t stood the test of time and once they no longer have a guarantee they can be very expensive to repair or replace.Furthermore, they are constructed in such a way that you cannot reproduce the mouldings and detailed characteristics of traditional timber windows.

 The campaign!

Back in 2009 English Heritage decided to launch a campaign in order to help protect official conservation areas, and one of its targets is the replacement of wooden sash windows with PVC.

On the one hand, it is understandable that sash windows are in frames made out of high-quality, slow-grown softwood timbers from the 19th Century, not only are they precious and historical they are also rare with the wood being used from the Baltic forests. The sash window classically consists of two frames, or sashes, with anything between one to a dozen or more panes of individual glass. They slide within the window case, while stabilised by sash weights attached to cords and hidden within the case of the window.

On the other hand, modern plastic windows, typically opening from a pivot and are readily available to everyone and normally come with a minimum of 10 years guarantee – no mess, no fuss! Therefore does the dependence on money count for the majority of the decision?

What happens if your building is listed?

Windows are an important feature of any Listed Building and they represent a very significant part of the building’s history and architecture. They are the single element which upholds the original character and era of the building. Traditional, historic windows play such an important part of a Listed Building’s structure that they should always be pre-reserved and repaired rather than replaced by modern examples. 

With all the different types of problems that can occur with windows it is important to assess what you are dealing with historically before you start. Traditional windows themselves are combined structures of timber, glass and metal, each part of which can be repaired as and when needed. Whenever possible the original fixtures and fittings of historic windows (hinges, fasteners, pulleys, handles, weights, stays etc.) should be kept just in case you find you need to refurbish the property and re-use on the window.

Replacing the glass

 If you find yourself in a situation where you have to replace the glass it is important to get a skilled professional to do the job of getting rid of the old window pane as there may be pieces of the window still in the frame that you cannot see. The glass itself has irreplaceable qualities of unevenness due to the original process of manufacture, two types of glass were produced; cylinder glass  by opening out a large blown cylinder of glass, whilst crown glass was produced by spinning a large disc. The flaws in historic glass catch the light and show off defects which cannot be found in any modern glass.

If you find that you need to reglaze your sash windows, take care to adjust the steel sash weights for any change in the balance of weights caused by different thickness of glass. However, in general upper sashes should be slightly lighter than the weights, whilst lower sashes should be slightly heavier. Any glazing should be undertaken using a traditional linseed oil putty rather than modern compounds. Timber beading, which increases the apparent thickness of glazing bars, is particularly unwelcome so make sure you know what product will be being used, as some companies will just go ahead with the replacement and not think to tell you!

Repairing the frame

 If and when the time comes that you need to repair your sash windows then it is preferred that you make careful repairs to any timber, whilst maintaining the maximum amount of historic fabric that you can. Sashes can be easily removed from their frame by taking off the outside staff beading. Not only this, but new sections of framing can be added, sash cords an easily be replaced and the weights can be altered.

The appropriate finish for historic windows after the 17^th Century is generally paint, most often white, and certainly not a modern stain. If you want to make your building completely genuine, especially if you have a Grade I or II* Listed Building, you can ask for permission to use a traditional lead based paint which gives that traditional look we identify with sash windows.

The history

Windows originated in timber-framed houses as openings within the frame in order to let as much light in as possible. The diamond or square panes were originally unglazed and usually had an internal timber sliding or hinged shutter, the grooves for this being the only remaining clue to their former existence. By the 16th Century small diamond shaped panes of glass were being produced, that were then set into lead canes within the mullioned framework of the window. The 17^th century saw the mullion and transom type of window grow, the traditional oak leaded light glaze then became more of a vertical larger plane of glass.  Moving forward to the 18th Century, with the increase of materials and resources saw larger panes of glass being developed on a mass scale. It also introduced a more domestic type of window, in the form of the “Yorkshire sash”, seen as a horizontally sliding version of the normal sash window, which did not require the elaborate counterweight system of vertical sashes.