Bay Windows - common defects…

Many of our London streets are characterised by terraces of Victorian houses featuring bay windows. Whilst inspecting these properties, we will often find defects to the bay structures. As such, we thought it may be useful to share a few of the more common issues identified, some possible causes and ideas on how to prevent these from occurring (where possible).

Movement/deflection/subsidence…

Victorian and Edwardian properties famously feature shallow foundations. Considering a standard two-storey terraced house, where properties often feature cellars, these parts of the building have the deepest foundations (and will therefore be the most stable). The foundations to the main structure of the building will be shallower in contrast and there may, in fact, be very shallow or no foundations to the bay itself. This, in tandem with London’s clay soil (which will expand during the wetter months and contract during drier seasons), can lead to movement of the building in differing proportions. Often, this movement results in cracking and a separation of the bay structure from the main body of the property.

Whilst it is not usually necessary to undertake invasive (and expensive) underpinning works as a preventative measure, other steps can be considered to mitigate the risks to these vulnerable structures.

Trees…

Mature trees in close proximity to the building can prove problematic. Root growth, in particular, can cause desiccation of the soil and subsidence of the property, as well as increasing the risk of damage to the sub-surface drainage. This can lead to leaking and saturation of the ground, resulting in heave or other movement. Some trees (such as Willows) have greater water requirements and can remove large amounts of water from the ground. This action can result in shrinkage of the soil, again, leading to movement. It should be noted that evergreen trees have fairly consistent water requirements, whereas deciduous trees remain dormant during winter months and become more ‘thirsty’ during the summer.

Guttering and drainage...

Saturation of the ground can be caused by an incorrect arrangement or failure of the rainwater goods (including rainwater gulleys). In some cases, downpipes are found to discharge directly over the ground to the side of the bay, again, causing saturation of the ground. In other instances, rainwater gullies may become cracked or damaged by plant growth and slowly release water into the soil. This is mostly preventable through regular inspection and maintenance of the rainwater goods and when inspecting, we pay particular attention to these elements - the cost of repair is comparatively small to the larger fix if left to leak over the longer term!

Damp…

Dampness to bay wall structures is relatively common. If allowed to persist, dampness can lead to water penetration into the property and poses a risk to the timber structures (timber floors) in contact with the damp surface. Typical causes of dampness include:

• A failure of the rainwater goods: Leaking from guttering and downpipes allows rainwater to run down the face of the brickwork. As many of these properties are constructed using soft red bricks, damp penetration will invariably result.

• Window sills: Many bays feature large stone window sills. A failure of the decorations to these elements can lead to water penetration into the dwelling and these surfaces should be kept in good decorative condition.

• Homeowners may want to enhance the attractiveness of the bay through the addition of plant pots to window sills, however, their presence can also contribute to an early failure of the decorations.

• In good practice, window sills feature a drip detail, which comprises a narrow groove cut into the underside of the sill. The groove casts water away from the face of the building and helps to prevent water from running over the surface of the wall below. These elements are often found to have worn away or, in some instances, have been inappropriately filled in.

Roofing…

Bays often feature their own roof structure. Just as for the roof serving the main body of the building, these roof coverings can fail due to age and they should be well-maintained. Any slipped or damaged tiles/slates or failing coverings should be repaired as part of routine maintenance of the property. Any moss growth on the surface of the roof coverings should also be cleared to prevent water from becoming trapped beneath the roof coverings which can lead to their premature failure.

In addition, the weathering at the abutment between the roof coverings of the bay and the main body of the property should be well-maintained. Typically, the opening between the bay and the front room is supported by a timber beam and leaking of the weathering to the bay roof can lead to timber decay. This may require replacement of the beam to resolve. Diagonal cracking above the bay can indicate failure of this element.

Window fittings…

As mentioned, bay windows will often feature a stone surround and will originally have featured timber framed windows. The window frames are structural elements and when these are removed (to allow for the fitting of new windows), new posts must be introduced to support the bay. The lack of such support leads to deflection of the bay and the new windows.

Ventilation…

In good practice, a bay structure will feature sub-floor vents to allow for cross ventilation of the sub–floor structure. Where modernisation has occurred and/or relandscaping of the garden has taken place, hard paving may have been laid to abut the face of the building. In this new arrangement, rainwater then splashes against the paving and adjacent wall surfaces. Over time, this can lead to water penetration and gives rise to the risk of water entering the sub-floor void. If this is allowed to persist, it can cause damage of the ground floor structure and increase the risk of wood boring beetle infestation.

A word of reassurance…

Cracks and leaning to bays can be a cause of concern to homebuyers, however, when we inspect, we take into consideration whether any movement or cracking is historical (having occurred during normal settlement of the building) or of more significant concern. In many cases, the potential defects are of no great concern and can be addressed as a part of routine maintenance.