There are several ways to calculate the envelope areas of bay windows but there are also some very quick ways, which you may already be aware of.
Floor and Roof Areas
The floor area and roof area, which is generally a flat ceiling, are basically formed from a rectangle and two triangles. The shape of the bay window also needs to follow the wall so ignore the windowsill.
The quick way to calculate this is to treat it as one large rectangle and calculate it in one go.
The floor and roof area can be calculated as: 1.414 x 0.494 = 0.699m2
Perimeter and Wall Area
There are multiple ways that the wall area can be calculated for the bay windows and one of them uses less steps compared to the other methods. However, before this is looked at the length of the cheek of the bay window needs to be calculated.
Pythagorean Theorem is being used here because we have two given dimensions and the calculation of the length of the cheeks is shown below. This can also be measured on site using a laser measure.
The quick way to calculate the wall area is to look at the additional perimeter that the cheeks of the bay window add into the building, assuming that you have worked out the perimeter of the rest of that storey.
With the cheeks of the bay window having a length of 699mm and the width of the cheek being 494mm this means that the cheek adds an additional 205mm into the perimeter (699 – 494 = 205). With there being 2 cheeks this adds 410mm to the perimeter of the storey (205 x 2 = 410).
With bay windows typically being 2.1m tall this adds 0.861m2 to the wall area of the storey (2.1 x 0.41 = 0.861).
