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Friday, September 10 2010 @ 11:26 BST

Sympathetic Window Design

Friday, September 01 2006 @ 02:03 BST
Contributed by: Admin
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How windows can be designed to be sympathetic to the style of the house - Author - Paul Jervis

What makes a good window design? Sounds a simple question and one that probably has many answers. Beauty is in the eye of the beholder and all that. But recurrent shapes throughout construction, art and even music suggests that there is more to it than just personal preference and that some shapes are more appealing to most people.

Researching for a British Plastics Federation document “A brief history of windows – Guide to Sympathetic Replacement Design” I learnt a lot about why some designs are more aesthetically pleasing to most people and how limits on glass technology governed window constructions.

To start with, what is window? It’s a hole in a wall to let in light and keep the weather out, or even to fire arrows out of. Early windows, before glass was available, used animal hides that had been scraped and then oiled to make them translucent and water proof to cover the hole in the wall. The same effect can be seen by grease on paper. Try it next time you get a chip supper. Some even went so far as to use a second hide on the inside of the wall thus providing an elementary double glazing whilst the gaseous odour from the hides filled the gap between the hides forming a primitive early form of gas-filling. OK, I made that last bit up.

The advent of glass made things better as it permitted more light to pass through. Window glass was used from the first century AD when the Romans developed a method of manufacturing glass, albeit with poor optics. Rare and expensive, this glass was used only in the most prestigious buildings and only in small pieces connected by strips of lead – the leaded light.

Not much progress in glass making followed for the next 1000 years – I suppose they were the Dark Ages in more ways than one – when new techniques were developed. These involved blowing glass into bubbles and either pierced and spun into a disc or spun to form a cylinder and then slit and laid out flat. The best bits of the resultant flattish glass were then cut out for use in windows. The former gave what we know today as the bullseye.

A few hundred years later, in the 17th century, the French developed a new method of pouring molten glass onto a special table. The glass was rolled flat and the surfaces ground flat with an abrasive. Later improvements in technique and mass production were made redundant by the invention of the float process in the 1950s and still in use today. Molten glass is poured across the surface of a bath of molten tin and the glass is drawn off in a continuous ribbon. Very large pieces of glass of high optical clarity can now be used while coatings improve thermal performance and toughening or laminating improves safety.

Each of these developments led to larger size panes being possible and so altered the styles of windows. The early small panes were used in the leaded lights and small casements we can still see today on old buildings. The ability to manufacturer larger sizes led to windows with astragals such as Georgian and Victorian style windows. Float glass today puts little in the way of limits on window design.

But one thing windows have retained over the years is their general shape. The vast majority of windows are either taller than they are wide or split into portions that are. True, some of the styles of windows installed by the replacement window industry since the 60s are not that pretty. The 2TF for instance. I don’t care if I never see a 2TF again.

There is a recognised aesthetic principle at work here which goes back into classical times, with a ratio of height to width of 1.618:1 called the phi ratio (which is the same as 1:0.618 which is cool), from the Fibonacci Numbers and the Golden Section. (Google Fibonacci and select from the 5.68m hits to learn more).

The box shows the ratio. Now look at windows that look most attractive to you and see how many of then are split into components of this sort of shape. From my window here, just about all the houses have windows that are around 1500mm wide 1200mm tall split into three, side hung, fixed, side hung. The odd ones that don’t look odd. Symmetry is also important in achieving the most pleasing effect.

Art Deco windows in the early 20th century, however, did not follow these general rules, using even circular windows (at this point I generally refer to switching from the phi ratio to the pi ratio, but I won’t). But Art Deco as a whole was a radical departure from the norm and didn’t last too long in architectural terms.

Modern windows can replicate most styles of existing windows so there is no reason for installing unsympathetic windows. There is a row of terraced houses near me which all had two double hung sash windows with stone mullions, lintels and sill originally. A couple of them still have the original timber windows. Most have had them replaced over the years and what a hodge podge of windows have been used. Many have removed the stone mullions and you can see cracks in the stone lintels of some of them as consequence. There are timber bow windows with bullseyes, top hung over fixed windows with a tiny top light; there are fixed lights with no openers. Then there are some that have been more sympathetic – top hung over fixed with a centre transom; PVC-U vertical sliders – and they look so much better. A whole history of replacement windows in one terrace showing the good the bad and the downright awful destroying the whole appearance of a Victorian terrace. Mind you, the village is more famous for producing the Moors Murderers and Dr Shipman so perhaps a few dodgy windows isn’t that bad.

PVC-U extrusion and fabrication techniques have advanced to the extent that most system suppliers have profiles that can closely mimic most styles. Colours and wood effects are also readily available. There really is no need anymore to fit windows which do the house no favours, and competing on style and appearance rather than price can only be a good thing for margins.

The Guide is downloadable (or soon will be) from the British Plastics Federation Windows Group (http://www.bpfwindowsgroup.com/ ) in pdf format for a small price yet to be confirmed but much less than a tenner. Those who have read it tell me it is a good read. I think so, too, but then I would being one of the two authors, wouldn’t I?

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