Cracking stemming from structural movement is a significant concern for homeowners. Overtime inspections of period properties have revealed a notable trend: the emergence of cracking in and around bay windows.
The year 1894 marked a pivotal moment in building regulations, as revisions permitted windows to protrude from external walls. Prior regulations mandated windows to be flush with the wall, but the new guidelines allowed for greater architectural flexibility. Seizing this opportunity, housebuilders during the late Victorian and Edwardian periods embraced bay windows, capitalising on the increased light penetration they offered. This architectural innovation quickly gained popularity and remained a prominent feature in many houses constructed during the 1920s, 1930s, and beyond.
The appearance of cracks around bay windows is usually symptomatic of underlying structural movement, a phenomenon inherent in all buildings. Although structural movement is inevitable, it often does not pose a serious risk to a building’s stability. Cracks typically form along lines of inherent weakness, including door and window openings, and notably at the junctions between different construction components, as observed in bay windows.
The causes of building movement are diverse and can range from common occurrences like thermal expansion and initial settling to more concerning issues like subsidence or variations in sub-soil moisture levels. While minor instances of movement, such as thermal expansion or slight settling, may only require minor interventions like mortar repairs to maintain watertightness, more severe issues like foundation overload or drastic changes in soil moisture may mandate extensive repair work.
Bay window foundations are less robust than those of the main structure, as they support a lighter load. Some early bay windows were constructed with minimal or no foundations at all. As a result, bay windows tend to settle at a different rate than the main structure, experiencing “differential settlement” and increased sensitivity to changes in climate and subsoil conditions. This frequently manifests in cracks forming at the junction between the bay and the external wall.
When faced with extensive cracking and continuous movement, it becomes paramount to identify and resolve the root cause of the structural instability. Changes in subsoil conditions, such as increased moisture levels from faulty drains or decreased moisture levels due to nearby trees and plants, often require targeted interventions. Repairing drainage issues, removing vegetation, and trimming trees may be sufficient to prevent further movement. However, in cases of severe structural damage where the foundations have collapsed entirely, underpinning becomes indispensable.
Diagnosing the specific cause of cracking can be a complex endeavour, given the numerous potential factors involved. If you are troubled by cracks in your property, we are more than happy at S Jones Surveying to carry out any assessments needed to identify the root cause of the problem and recommend the most suitable course of remedial action