Britain’s climate is wet all year-round. Our islands are home to some of the wettest places in Europe – for example, the moors on the South West coast of England and the Scottish Highlands. Our weather has a tendency to cause excess moisture in buildings through penetrating or rising damp, or by overwhelming blocked water management systems such as gutters and drainpipes. This is a particularly serious problem for timber-framed properties, where excess moisture can lead to rot.
Timber frames are cost-efficient, easy to construct and when combined with insulation panels great at locking in heat. There are however, certain measures that construction industry professionals need to follow in order to ensure their longevity and structural integrity, by preventing the natural wood fibres from being damaged by weathering and rot.
Dry rot or wet rot?
Dry rot is a form of timber decay caused by fungal growth as air-borne spores germinate when they come into contact with a food source such as timber, which has become damp. It is one of the most damaging conditions you can encounter in a property. It severely impacts structural integrity as it aggressively spreads from one area of timber to the next.
Contrary to its name, dry rot needs moisture to flourish and grow, and it can be hard to spot because it often grows where people do not look, such as under floorboards, behind panelling, in lofts or behind plaster away from light. Affected timber will be covered in a white growth of fungal strands (mycelium) on its reverse side and have large cracks across the wood grain called ‘cuboidal cracking’. Orange/red spore dust may be present too when the fungus produces a fruiting body (mushroom) on the affected timbers too. Dry Rot can spread many metres away from the original source of moisture
Wet rot is not as harmful as dry rot, but it can still cause substantial damage to properties. It attacks timber in much wetter conditions, making it a common cause of structural defects, particularly when allowed to go untreated. When excess moisture is absorbed by timber it can allow fungal spores to germinate and produce enzymes which break down the cellulose in timber leading to the timber losing its strength. Wet rot can by identified by a damp musty smell, small cracking across the grain and softening of timber and noticeable discoloration of the wood. Wet rot will only occur where the moisture source is located.
Tackling both dry rot and wet rot
The primary action is to locate and cure the cause of the moisture ingress.
Dry Rot: ‘Exposure work’ is required to trace the full extent of the outbreak because Dry rot can spread behind wall plaster and travel along other construction materials such as steel. To treat the fungus growing on the walls and timbers (known as mycelium), affected wall plaster is removed. Holes are drilled in to the wall around the perimeter of the affected masonry and a masonry biocide is pumped in to them. A surface application is then applied to all the exposed masonry. The treatment has the effect of ‘sterilising’ the masonry to prevent further dry rot mycelium growth.
Wet rot: The decayed timber needs to be cut back to what is called ‘sound’ timber (wood that remains in safe condition and structurally intact), and any decayed sections repaired. Finally, the timbers should be treated with a fungicidal spray that is quick to dry, low odour, non-flammable and HSE approved.
Decayed or structurally weakened timbers must be removed and replaced. The most vulnerable sections of timber are usually those that bear into the wall structure because it is at those points where the timbers typically tend to absorb moisture
This means it’s often only the ends of the timber which need to be replaced. The traditional method to achieve this is to splice in new sections using steel plates or bolts, and timber connectors fixed through the timber. While this is effective, the steel plates can be quite unsightly if the timbers remain exposed. Also remember to check ventilation especially under timber floors. Blocked airbricks contribute to moisture condensing on timbers causing them to rot, not just at their ends but mid-span too
For large section beams an alternative is to use epoxy resins for carrying out structural repairs to these large sectioned damaged timbers. This is an aesthetic and economical method, since repairs can often be carried out relatively quickly, without having to cut out large areas of the existing timber and with minimal disturbance to the surrounding structure and the presence of unsightly steel plates.
Timber plays an important structural and aesthetic role in most buildings, so some care and attention is important to prevent damage and maintain a property’s value. A professional survey is the first step towards identifying the extent of any damage caused by wood rot or woodworm.
By Richard Walker, National Technical and Development Manager at Peter Cox