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Cracking Around Bay Windows – Common Property Defects # 3

Thursday, 30th July 2015 | by: Steve Hobbs

Cracking as a result of movement is one of the more worrying defects faced by homeowners and recently we have inspected a number of period properties where cracking has appeared in and around bay windows.

In 1894 building regulations were revised so as to allow windows to stand proud from external walls. Previous regulations required windows to be flush with the wall. House-builders in the late Victorian and Edwardian eras took advantage of the new regulations and presented their windows in bays, which allow more light into the building. Bay windows proved popular, and continued to be incorporated in a large number of houses built in the 1920s, 1930s and beyond.

Where cracking appears around bay windows it is, as in all cases of cracking, a sign of some form of movement. Movement in buildings is common – indeed, all buildings undergo some movement, and in the majority of cases this movement will not adversely affect the building’s performance. Cracking often manifests along lines of natural weakness, such as door and window openings and, in the case of bay windows, at the junction between separate elements of construction.

The causes of movement are numerous. Many, such as thermal movement and initial settlement, are unlikely to be progressive and may require only minor remedial work, such mortar repair to ensure water-tightness. Other causes of movement, such as subsidence due to overloaded foundations, or severe changes in sub-soil moisture levels, will often require more extensive repair.

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The small crack at the left side of this double-height bay occurred when the windows were replaced, due to the upper level of the bay being improperly supported whilst the old ground-floor windows were removed.

Bay window foundations are generally shallower than those of the main structure, as the load they are required to distribute (that of the bay) is not as heavy as the rest of the house. Indeed, many early examples were built on little if any foundations at all.  Consequently bay windows tend to settle at a different rate to the main structure (called differential settlement) and are more prone to changes in climate and subsoil conditions.  Where cracking occurs, it will often present at the junction of the bay and the external wall.

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The crack appearing on the right side of this bay window is due to slight rotational movement, as the bay, which is on shallower foundations than those of the main house, settles at a different rate from the rest of the structure.

Where cracking is extensive and movement is progressive it will be necessary to identify and remedy the cause of the movement. Changes in subsoil conditions, such as increased moisture levels due to leaking drains, or decreased moisture levels due to trees and foliage, may be remedied by fixing drains, removing foliage and pollarding trees. This, in itself, may be sufficient to stop further movement. Where damage is severe and the foundations have failed entirely underpinning will be necessary.

Diagnosis of the specific cause of cracking can often be challenging, due to the large number of potential causes.  However if you are concerned about cracks in your property our team of Chartered Surveyors are on hand to help. We can provide a bespoke report detailing the cause of the issue and the most appropriate remedial work. If you would like further information on the services we can provide please call us a call 020 7183 2578 or send us an email.