The prospect of structural movement can be a cause of grave concern for homeowners. The structure of a building primarily comprises the roof carcass, walls, any framework, floors and foundations. Acting together, these elements provide rigidity, structural stability and strength to the building. When one or more elements begin to shift, those characteristics can be compromised.
Forms of structural movement
Perhaps surprisingly, structural movement is common to every home in the country. Indications of the problem include:
- settlement
- heave
- subsidence
- expansion
- contraction
- bouncy floors
Whilst almost all houses experience some level of at least one or two of these aspects, the effects are usually so minimal as to pass unnoticed.
Old and new homes
When a new house is constructed, for example, the masonry alone contains over a tonne of water. As the structure dries, the loss of this moisture changes the dimensions of the wall. If this change is not planned for by introducing joints with a level of flexibility, then structural cracking will occur.
At the other end of the spectrum, the shallow foundations of a period property, which can usually be simple footings, can cause structural issues as the ability of the property to resist natural soil shrinking and expansion is greatly reduced. In particular, if a substantial tree is located nearby, the result can be subsidence and potentially catastrophic structural failure.
The key causes
The root cause of most structural movement can be traced back to one of the following:
Inadequate strength – Historically, safety factors and tolerances were defined purely by experience. The industrial revolution introduced the structural engineer to more and more projects. In modern day construction, detailing on building projects is incredibly precise. For older buildings constructed without an engineer, the structure may simply have been made without sufficient strength for the inherent live and dead loads.
Material decay – The various processes which can speed decay and undermine structural stability, include: timber rot, beetle infestation, rising damp, water ingress and condensation.
Continuity deficiency – Tying the various elements of a structure (primarily walls and roofs) together allows each element to lend the other support. Ensuring continuity in this way can, therefore, add considerable strength to an older property in which the elements might actually be otherwise separate.
Subsoil / Foundation inadequacy
Medieval walls typically were built straight into the ground. Later techniques evolved to incorporate a corbelled distribution and modern houses utilise strip foundations or, where necessary, piled foundations. A corbel is a short structural cantilever member projecting from a wall or a column for the purpose of carrying loads. Unfortunately, only the modern foundation methods are particularly robust and properties that pre-date the first world war can, therefore, suffer from subsoil changes and the influence of nearby trees.
The solution
Structural movement is such a broad topic that there is no single solution. Suffice to say, it is only active movement that should be of serious concern, beyond the decorative issues of historic cracks.
If you suspect active movement, the symptoms of which can manifest themselves anywhere between the top of the roof surface to the very base of the walls, it is strongly advised that you take professional advice, either from a structural engineer or an independent Chartered Surveyor who is experienced in such matters.
An independent professional will not only be able to talk you through the issues, its causes and likely progression, they will also be able to offer an unbiased solution, not influenced by the need to sell a proprietary product.
Whatever you do, don’t ignore active movement. A problem that may have cost hundreds of pounds to ‘nip in the bud’, can quickly evolve into the tens of thousands of pounds to put right.