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Our Measuring Guides 

Window opening
Accoya Sliding Sash Timber Window

Measuring Guide

Note: All sizes quoted are overall size of window including sash box, frame and cill.

Please note that accurately sizing replacement windows can be a complex and challenging task. Especially in older properties that may not have been built in accordance with any building regulations or may have been affected by subsidence or building alterations in the past. However, following some basic rules will typically give sound results.


Note: If you are in any doubt or wish to confirm your sizes, please feel free to contact us or a professional surveyor or joiner.


This guide is to provide typical window installations yours may be different.


Firstly, decide on your building type, as window openings

have changed dramatically over the ages.

Modern - Windows fitted into the outer leaf of brickwork,

may have stone heads and cills or brickwork below.

Victorian/Georgian - Windows fitted from behind the outer leaf of brickwork,

usually have a deep stone cill, stone heads and arched brickwork.

Historic – Windows fitted in between the deep stone walls,

with stone heads and cills.

Next decide on the type of window you want to install – Traditional Cords & Weights or Spiral Balance Sash Windows.



Traditional Weights & Cords Sash Windows are constructed with a box section which houses the counterbalance weights. The box can be closed at the back or open.



The size of the box should be considered, and allowances made to glass sight lines. This type of window is typically fitted behind the outer leaf of brick work, to give as much glass area as possible.


However, these types of windows can be fitted into historic or modern buildings if the design allows.


Spiral Balance Sash Windows are constructed with a much smaller solid frame and can be suited to all building types and can be fitted behind or in between the outer leaf of brick with minimal loss of glass sight lines.


Take note of the top of the window opening. This can be straight through in modern and historical properties or set back in Georgian & Victorian homes.


When measuring your openings, it is important to know your maximum height available and where the sight lines of your window will be. If the brickwork is curved above, consideration should be given to the height of the curve and the Sash Box dimensions to ensure adequate cover.





It is imperative for the correct working of your new Sliding Sash Windows, that the sash boxes, either Traditional Cords & Weights or Spiral Balances are installed Plumb & Level.


*Guarantees will not be valid on windows that have not been install Plumb & Level.


Decide on where you want your window to sit, behind or in between the outer layer of brick work.


Use our Guides Below as a visual aid.


GUIDE        Traditional Cords                                                     Spiral Balances

                    & Weights 

Use our survey sheet to calculate and confirm your window sizes.


Note all sizes quoted are overall sizes of window including sash box, frame and cill.

Transom drop refers to the split of the sashes in height, commonly the sashes have an equal glass areas giving an appropriate centre split, however some sash windows have larger bottom sashes and smaller tops – please Specify bottom sash height if required.

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