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Measuring Bay Windows, PVCU Windows, Double Glazing | U-fit Double Glazing

If you’re looking at having bay windows installed within your home then you will need to make some measurements to ensure that you have the right size UPVC windows delivered to your home. The process of measuring your bay window is a little different to how you would normally measure UPVC windows.

The hard way to survey a non square bay Bay Window Angle

A bay pole assembly connects two windows together at the angled part of the bay.

Bay Window Angle ”

The size required to produce a bay lay out are as follows;

  • The back span this is the internal width of the bay measured from inside frame to inside frame you may have to chop back the plaster on the inside to find the frame edge. Note that it is surveyed inside not outside excepting the height which is measured from outside.Ie outside brickwork sizes
  • The projection from the imaginary string line above in the drawing above it says 300mm to the inside of the bay
  • The internal facet widths show as 649mm in the above you will note that it says 625mm in brackets and 600mm for the centre window this smaller size would be the window manufacturing size as the upvc bay pole assembly will sit in the gap in between the two frames.

This method allows the calculation of the angle where the two window meet using trigonometry (remember that) our software will take the sizes and produce a bay plot as above we can email you this for you to sign off before we manufacture you can’t order bay windows online just yet.

The easier way to survey a bay window

Bay Window AnglesThe above is all about finding the bay angle so we can make a deduction to fit the pole in is there an easier way ? yes by using an angle finder as shown here

They cost £13.00 delivered. It will allow you to measure the angle on the inside of the bay window we then require the bay facet (window) internal widths to go with the angles from this we then calculate the bay. Please email us your sizes and window styles and we send a sign off sheet before we manufacture.

Square bay windows are easier!

Square Bay Window Inset
You will not need an angle finder to measure a square bay will you now! As its set at 90 degrees measure the inside sizes of each facet we will add on for the two 90 degree posts which are 70mm square to bring the external brick size up by 140mm see square post picture.  Height is again measured from outside

Square Bay windows

Bow windows how do they differ?
A bow has a very shallow angle and the projection is a lot less than a bay window for an existing bow measure the internal size brick to brick not frame to frame the throw is to the inside of the frame.

If you wish to convert a flat window into a bow window we need the external brick work opening sizes and how many facets you require and what projection you would like this normally works well at about 1/8 the width
Please email any query to technical@u-fit.co.uk

Note when removing an existing bay window you must use Acrow props to fit between the floor and the ceiling as many bays are load bearing.

Bay jacking posts what are they?
When a bay or bow is load bearing ie it has a bay window above it to comply with the building regulations it must be Bay Window Jacksfitted with load bearing bay pole jacks these fit through the external welded cill and can be adjusted wound up or down to compress the bay pole on to a top plate supplied on to the head of the aperture these cost £9 each and have a load bearing capacity of 2500kg each so a 3 on a 3 sided bay will load bear 7500kg.  They come in ones for square bays and non square bays.

U-Fit U-Fit Unit 1, Boston Pl, Coventry,

Tel: 02476 686682
Fax: 024 7663 8779

24 Hour Freephone: 0800 389 0595


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