Help & advice

We’ve put together some help and advice articles as well as some answers to the most frequently asked questions. Please check back when you can – this section will grow and we add more advice.

How to measure a window for secondary glazing

Measuring up for secondary glazing couldn’t be simpler. All you need is a good quality tape measure and the following guide. Please note, you should always measure in millimetres, and always record the width first then the height (this is the standard method used throughout the window industry. Also, always draw window as viewed from the outside, even though you’ll be measuring and fitting from the inside. Again, this is industry standard and it helps avoid any confusion.

1. Measure the width, wall to wall

Make sure you measure the width of your window aperture (A) in at least two places – usually the top and the bottom. Window reveals are rarely perfectly square, especially on older properties. Take the smaller of the two (or more) measurements, and then deduct 10mm. This is the fitting tolerance, and it allows 5mm either side of your window for any bumps or irregularities in the wall. Write this final measurement down.

2. Measure the height

Follow exactly the same process as before, this time measuring the height (B) in at least two places. Measure down to the top of your existing window cill, and this is where the secondary will fit. Deduct 10mm for your fitting tolerance, and write the final measurement down.

3. Measure the distance to any transoms or mullions

If there are any vertical or horizontal divides in your existing window, you’ll almost certainly want to match these in your new secondary glazing. Therefore measure the distance from one side to the centre of the bar (C) and deduct 5mm (because you’ve already deducted 10mm from the overall window size, so you’ll need to take account of this). Make sure you measure in two or three places, to account for discrepancies.

measuring guide

How to measure for secondary glazing

4. Draw you window design (viewed from outside!)

Once you’ve taken all the measurements, make a simple drawing of your window as viewed from the outside. There are certain simple conventions used to highlight opening panes – triangles for hinged windows, arrows for sliders etc – have a look at our styles page to see what these are. Use F for fixed and LO for lift-out.

drawing a window

How to draw your window

If you have any questions, simply contact us and we’ll help you out. And remember, always double-check your measurements before ordering!