Glorious Sash Windows
 The sliding sash window has been with us for over three centuries and the operating principle has remained almost unchanged throughout that time. Aesthetically too, the sliding sash offers definable architectural features that add significantly to the overall property design.
Variety of transom depths alter sight lines from both inside and out, whilst the shape, size and density of glazing bars adds a further design element. Technically, the control of the movement is much more manageable than hinged opening casements, although the amount of opening control has relied on sash friction and perfect weight control.
Many people fail to realise that sash windows are made in such a way that they can be easily dismantled for repair and believe that the only option is replacement. The component structure allows the sliding sashes to be renovated, allowing a window several sash repair instalments before the frame needs attention. Too often the plastic replacement route is taken without adequate inspection by a renovation specialist.
Some timber windows have lasted for centuries because they have been properly maintained and painted regularly. By comparison, plastic PVC-u windows cannot be dismantle and repaired so easily and the component parts are not so easily produced. If a plastic window has been made to size and the manufacturer has gone out of business, there is little to be done other that another complete replacement.
PVC-u sash windows have not been ‘time-tested’. They usually come with double-glazed sealed units and are generally only guaranteed for 10 years and are expensive to replace if they fail. Still further, they are constructed in such a way that they cannot reproduce the mouldings and detailed characteristics of traditional timber windows and, almost without a single exception; they are completely unsuitable for use in any historic context. By upgrading the quality of timber in modern sash manufacturing it is possible to achieve a life expectancy of around 60 years at least, and well beyond if a good maintenance regime has been adhered to.
Building Control
Fenestration is probably the most sensitive element of the Conservation Area planning procedure – windows are rightly a major architectural focal point and the unsympathetic replacement can ruin a beautiful building. Control over the development of new buildings and the alteration of historic buildings in the UK has evolved over the past 50 years as a reactive and preventative system of control. It is preventative in that most development requires permission from the local planning authority by law, and the application procedure leads to unacceptable applications either being refused or being modified and improved. It is no different in the case of windows, whether it involves repair, replacement or a new build project. It is important to work with experts and specialist window manufacturers, those who are known and recognised by planning authorities who have the confidence and knowledge to approve an application specifying a known and reputable brand.
 With Conservation and historic products the styling detail must be based on historically researched designs. The subtle shallow lines of the moulded sections create the delicate slender effect of traditional profiles and should be virtually indistinguishable from originals.
The traditional single glazed box sash is for use where double-glazing is not suitable and they are designed for replacement of original windows in existing buildings and listed properties, always subject to planning permission. It is important to select from a range that offers a choice of profiles, such as Georgian, from around 1750+; Victorian, from early to late 1800s and Victorian Fine Lambs Tongue, from around the mid-1800s, and that the manufacturer can offer a bespoke profile service when needed.
By the nature of single glazed historic sash windows, compliance with Part L Building Regulations is not applicable, but in all other applications it is important that products comply to meet modern thermal requirements while still manufacturing traditional sightlines. The potential use of a secondary glazing system within the window aperture is a formula that can enhance thermal efficiency.
Today’s premium sash window products embrace much technology as well as traditional craftsmanship. Double-glazed, gas filled panels are reliable and crystal clear. ‘K’ glass and laminate combinations protect against UV damage and enhance security, tension sprung balances are silent and maintenance free and opening limiters and double security locks all add to the beauty of stylish frames, moulding and running horns.
Sash windows often come under attack from the traditional problems of warping and sticking but this is really a myth and quite definitely a thing of the past. And it is normally no fault of the window or its design, but one of mistreatment, neglect or poor maintenance. They have operated in windows for hundreds of years and their failure can normally be blamed on simple problems such as sticking caused by painting shut or build up of paint layers, and commonly when a poor repair has been made to re-cording. But on the whole, the criticism of modern sashes can only be aimed at those of poor design and manufactured from cheap materials. The history of quality applies equally today – you must expect to pay for quality.
Professional Builder – February 2005
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