Investigating defects

In building surveying terms, a building is made of a series of elements. Each element has its own material properties. Defects can occur when different elements come into contact with one another – different combinations of materials result in different reactions.

Understanding how elements behave under stress and how they interact with surrounding materials and the environment can inform an understanding of how a defect has occurred. Take, for example, a timber plank that is cracking. The surveyor first needs to understand what caused the timber to crack, before whittling down these causes by delving deeper. It could be, for example, that on further examination a rusty nail has caused the cracking. Why would this be the case? Has water penetrated to the nail causing it to expand and therefore exert a stress on the timber causing it to crack?

So, the questions to ask are:

• How do building elements behave when they come into contact with one another?
• If one has a defect – how would this affect the other materials around it?

The first question comes back to design and whether these elements and materials work well together. For example, steel and concrete have qualities that when put together form a single strong structural element. However, staying with this example, if the steel reinforcement within the concrete corrodes and therefore expands it will cause the concrete to spall. This is further complicated by porous concrete.

Metal corrodes when in contact with water, so anywhere there is a metal element that is exposed to water will risk damaging those components around it. Further examples of this are cavity wall tie failure, filler joists floors used as roofs and, back to the main point, steel framed buildings that have been unmaintained where water has been able to penetrate.

Timber on the other hand is affected by fungi, which is a living organism. Fungi needs food and warmth and, most importantly, moisture to survive. Timber needs 20% moisture content for a prolonged period for these conditions to be perfect for fungi to use it as a source of food. Once the fungi has taken hold the structural integrity of the timber will then be compromised. A typical example of this are floor joists resting within an outside wall that has failed, causing water to infiltrate the wall and rot the timber joists. The failure of the building’s envelope therefore has a detrimental knock-on effect.

Modern day building materials, such as engineered bricks and modern cements, are strong and inflexible. This means that if there is movement within a building, these elements are normally the pivot point of damage as they do not have the flexibility to move with other elements attached to it.