The Zero Stress Guide to Double Glazing


What You Need To Know Before You Buy Double Glazing Windows

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Double glazing design issues

  • Sight lines
  • Gaskets
  • Neighbours

There are a number of issues worth considering regarding the design of your replacement windows.

Sight lines

Most modern replacement windows have smaller areas of glass wherever there are openings (sashes) fitted. Where the frames are fixed the glass area will be larger. This creates an unequal ‘sight line’ which is quite normal and acceptable to most people.

However on a lot of older properties it was more common to have an equal sight line making it impossible to tell from the outside which windows opened and which did not. Fitting ‘dummy sashes’ or ‘dummy openers’ into the frames created this equal sight line.

Equal sight line style

PVCu Bay window - Equal sight line style.

Some consumers prefer an unequal sight line to avoid the overall bulkier appearance that is a feature of an equal sight line – which, incidentally, adds to the cost. However, an equal sight line is recommended for properties with Georgian and leaded light window designs so that rectangles/squares can be matched in size.

Another option is vertical equal sight lines, in which fixed windows are always positioned above fixed windows and opening windows are always above opening windows. Suppliers can give more information on this.


Most companies have traditionally fitted black gaskets as, in the past, it was not always possible to get a matching white nor to offer a colour-fast guarantee. Advances in technology have changed this situation and increasing numbers of companies now offer both options.

White gaskets can often appear grubby and show up dust and dirt and this may be an important consideration is you live close to a major road.

An alternative to white gaskets is the ‘low profile’ black gasket which is very slim and less obtrusive. However, it is recommended that you choose white gaskets on white PVCu panelled doors.


Unless you live in splendid isolation in a rural location any changes you make to your home will have an effect on the overall appearance of your street.

For example, if two semi-detached houses have replacement windows both will be enhanced if the same style is used on each. Conversely, adopting different styles can spoil the appearance of both – and possibly devalue them, too.

French Doors

PVCu French Doors in a Georgian Style

VCu door sash

White PVCu door sash fitted into a PVCu woodgrain style frame



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