Top Reasons Why Bay Windows Crack And What To Do About Them

Nothing adds more allure to a property than a nice wide bay window. Staged properly, a bay window adds style, character and charm to living areas; a cozy nook where one could curl up with a book and a hot beverage to lose all sense of time.

Over time, however, bay windows are susceptible to cracking and deterioration which, if not addressed, may affect the structural integrity

So why are bay windows so prone to cracking? And what can we do to fix them?

Why Bay Windows Crack

Cracking around bay windows is a sure sign of some sort of movement. All buildings undergo a movement of some kind or settling. Bay window foundations are often built separately from the main structure and may be shallower than the foundations of the rest of the house.

This is done because the load borne by the bay windows is much less compared to the main building. As a result, differential settlement occurs, where the bay windows settle at a different rate as compared to the rest of the structure. This makes bay windows more prone to climate change and changes in subsoil conditions and is usually the root cause of cracking.

There are many reasons why movement occurs. If movement is caused by initial settlement or thermal changes, it is less likely to progress and requires minimal repair work. However, extensive repair may be needed if the movement is due to severe changes in the moisture levels of the subsoil, or if bay window subsidence is being caused by overloading of the foundations.

Differential Movement

Differential movement occurs when the foundations of the bay window and the house are at different depths. In older structures, like Victorian properties, where the foundations are shallow, builders employed stepped foundations called ‘footings’.

These can cause cracking through the window openings as the footings near the windows were even shallower.  In modern properties, which are built with deeper foundations, due to the different rates of settlement, cracking usually occurs near the interface.

Solution for differential movement

An expansion joint can be inserted in the foundations to allow for future movement. It is then sealed using a flexible mastic sealant that weatherproofs the structure and keeps it water-tight.

Subsidence

Subsidence is the term used to refer to the ground beneath the foundations giving way, or subsiding, due to any external conditions. One of the most common causes of subsidence is a change in moisture levels of the subsoil. The change in moisture may cause the soil to expand or shrink. This could be because of prolonged lack of rain, compounded by trees wicking out the moisture, or a leaky drain or plumbing. Shrinking soil deprives the structure of support and causes cracking to the masonry.

Solution for subsidence

The standard method to tackle subsidence-related damage is to underpin the foundations with concrete. This is done by excavating the foundations till the stable ground is reached and then pumping concrete.

Once the cause of the structural movement is identified and resolved, then you may repair the crack and continue to enjoy your bay window.