So far in this series, we’ve looked at damp and timber defects, in their various forms. Now, we move on to structural movement – a cause of grave concern for homeowners across Britain.
The ‘structure’ of a building primarily constitutes the roof carcass, walls, any framework, floors and foundations. Acting together, they 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. Forms 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 all 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 (usually just ‘footings’) of a period property can cause structural issues, as the ability of the property to resist natural soil shrinking and expansion is greatly reduced. Particularly 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 and, in modern day construction, materials and building projects are incredibly precise. For old 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 articles published so far in this series have looked at various processes which can speed decay and undermine structural stability, including 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. Unfortunately, only the modern foundation methods are particularly robust and older properties (pre-WWI) can therefore suffer from subsoil changes and the influence of nearby trees.
The solution
Structural movement is such a broad topic that there cannot possibly be a 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 be anywhere between the top of the roof surface to the very base of the walls, it is strongly advised that you speak with a professional – either a structural engineer or a chartered building surveyor 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 to put right.
*Back to September 2016 Newsletter*
© www.propertysurveying.co.uk    SJ