Structural Movement in Buildings

Structural Movement

Buying a new house or selling the house you currently call ‘home’ can prove challenging if a structural movement has been detected as this can affect the property’s resale value and insurers may refuse coverage for the home as they deem it a risk.

 

But how does one detect structural movement in their home? It is usually the presence of cracks that brings the risk to one’s attention.

 

Finding your forever home and seeing cracks in the walls can be alarming, especially when dealing with an older home. But these cracks may not need to be a cause for concern as most buildings move to some degree during their life cycle and this movement is what results in the formation of cracks.

 

All buildings settle after construction or a major structural change i.e. loft conversions, as the ground adapts to the weight applied to it and can leave cracks behind. Also, buildings may move due to temperature changes or there may have been movement in the past that has left cracks as evidence but only when this movement is ongoing or severe should there be concern.

 

The initial appearance of a crack can be misleading, as some can appear serious, leading to assumptions about the condition of the building but concludes to be no more than a decorative issue. Where as some can look insignificant but over time it develops into a sizable, costly problem. Therefore, identifying the cause is a critical first step if you are to find reassurance that your home is safe.

 

To help you to understand structural movement and how it can affect your home, we will explain the different types of structural movement, their causes, and possible solutions in a series of three posts.

Ten Questions To Ask An Architectural Designer

Types of structural movement

Before we discuss the possible causes and solutions, we will first explain the various types of structural movement that may affect your home.

 

These types include: Subsidence, Settlement, Heave, Sway, Bouncy floors, Bulging walls, Expansion and Contraction, and Cracks.

Subsidence:

This is the downward movement of the ground that occurs regardless of the presence of a building on the site. One of the most common signs of subsidence is cracking which is identifiable by it being more than 3mm wide, diagonal and tapered, visible internally and externally, and found near doors and windows. Around the junctions of extensions, cracks can form as the extension tries to rotate away from the original structure due to subsidence.

Other signs of subsidence are the crinkling of wallpaper at ceiling/wall joints and the jamming of doors and windows.

Settlement:

This is the downward movement of the ground due to the presence of a building and its weight. Typically, this is not a serious concern as most buildings settle gradually over time as the ground adapts to the newly imposed loads by slowly becoming compressed. Issues with settlement usually presents itself in the early life of the structure and therefore older buildings rarely experience on-going settlement.

There are two types of settlement, with one being more detrimental than the other. There is uniform settlement where the entire building will settle at a uniform rate and this happens if the entire building rests on the same type of soil or when the loads on a home are uniformly distributed throughout. The more detrimental type is differential settlement, and this is the unequal settling of the soil beneath a building’s foundations. This can lead to the sinking of different parts of the building.

Heave:

This is the upward movement of the ground due to the expansion of previously desiccated or shrunken soil (clay) as it reabsorbs water. Heaving also occurs during freezing conditions as the water trapped in voids in the soil forms ice crystals and expands, this is referred to as frost heaving.

Because the soil generally cannot expand downwards or sideways due to the presence of existing soil, the direction it will be able to move is in the direction of least resistance which is upwards and hence the soil can rise to a displacement generally less than 150mm.

Sway:

All structures experience displacements due to the building swaying but some buildings experience larger displacements than others. Buildings sway when they are exposed to lateral forces, whether it be from wind or earthquakes and this is considered, where relevant, during the design phase by ensuring sufficient lateral resistance is provided.

Bouncy floors:

A reduction in the strength of the floor joists due to cut outs made for fitting services or material decay can increase the deflection experienced. Applying loads to the floors greater than it was designed for, also causes larger deflections and these large deflections are what results in bounciness.

Bulging or leaning of walls:

This can result from the building lacking lateral restraint, walls being too slender, the addition of more stories, the increase of floor loads due to a change of use, roof spread, and vibrations.

Roof spread occurs when the roof is insufficiently designed and the outward, horizontal force at the top of the wall due to the weight of the roof causes the walls to be displaced. This displacement causes cracks to appear at the junctions between the external walls and the ceilings.

Expansion and contraction:

Materials expand and contract when exposed to temperature changes. Often, these changes in temperature take place slowly but the effects are the same where colder materials contract and warmer materials expand. Whilst small changes may be experienced by the singular elements of the structure, the cumulative effects of these changes can be substantial. Moisture changes can also cause expansion and contraction of the building materials.

Cracks:

How can we recognise the patterns of cracking?

Diagonal cracking – upward and downward movement

Diagonal cracking wider at the top– symptomatic of downward movement (subsidence or settlement). Crack runs through the weak points such as windows and door openings.

Diagonal cracking wider at the bottom– symptomatic of upward movement (heave).

Vertical cracks – most commonly associated with horizontal movement (thermal and moisture related). May indicate that structural components such as bricks or blocks have failed causing significant stresses within the building.

Horizontal cracks – routinely associated with corrosion (wall ties for example)

Diagonal cracks above openings can be caused by the failure or absence of a supporting lintel. This is typical in buildings built from the 1940’s to 1970’s as the original steel windows were often produced to support the walls loadings and therefore lintels were not required.

With a better understanding of the types of structural movement that can impact your home, we conclude Part 1 of our three-part series. In our next post (Part 2), we will look at the various causes of structural movement.

Structural engineering drawings