30 November 2022

Methods for Surveying a Bay or Bow uPVC Window

Methods for Surveying a Bay or Bow uPVC Window

There is a difference between surveying a bay or bow window and surveying and fitting a flat UPVC Window.

Methods for Surveying a Bay That Isn’t Rectilinear

A pair of windows in a bay configuration are joined by a bay pole assembly at the bay’s splayed corner. Size requirements for a bay plan are calculated as follows:

A bay’s back span is its internal width, as measured from wall to wall within the structure. In order to find the edge of the frame, you may need to remove some interior plaster. While height is measured from the outside, all other measurements, such as brickwork sizes and plaster line locations, are taken from the inside.

Below is a diagram showing how 300 mm of space separates the bay’s inside from the imaginary string line. If you need absolute certainty, you can use a string line to take projection measurements. This is especially useful on bays with numerous inlets.

Internal facet widths are 649mm, 625mm, and 600mm, respectively, as shown in the above diagram, brackets, and central window, respectively. The UPVC bay pole assembly will fit in the space between the two frames, so the window production size should be the smaller of the two.

Using the above technique, the angle formed by the two windows can be determined using trigonometry. Our software can then use these dimensions to generate a bay plot similar to the one shown above, which can be sent via email for approval before production begins. 

How to survey a Bay Window – The Simple Way

The goal of the preceding steps is to determine the bay angle from which a deduction can be made regarding where to place the pole. However, as will be seen below, there is a simpler way by using an angle finder. A delivered angle finder from Screwfix costs around £30.00.

An angle finder will allow you to measure the angle on the inside of the bay window and the bay facet (window) internal widths to go with the angles. The bay can be determined from these coordinates. In order to expedite the manufacturing process, please email Spectrum Glazing with the window sizes and styles, and we will email you a sign off sheet.

Windows with a Square Bay

The square bays are the simplest to measure because an angle finder is unnecessary. Since the bay is already at a right angle, you only need to determine the internal dimensions of each facet. Next, we’ll screw in the two posts at right angles to each other. They’re 70mm on a side, which adds another 140mm to the overall width of the brick (see square post picture). Both the interior and exterior heights are taken into account.

The main distinction between bow and bay windows is the shape of the bow.

A bow window’s projection and angle are much smaller than those of a bay window. When determining the internal dimensions of a preexisting bow window, it is important to measure from brick to brick rather than frame to frame. The target of the throw is inside the picture.

If you want to turn a regular window into a bow window, you’ll need to calculate the external brickwork opening sizes, the number of facets your window will need, and the desired window projection. About 1/8 the width is optimal for this. Please direct all questions to sales@spectrumglazing.co.uk.

In many cases, bay windows are load bearing, so make sure to use Acrow props to bridge the gap between the floor and ceiling before attempting to remove the window.


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