Fungal decay

The dry rot fungus, Serpula lacrymans (Schumach. ex Fr. Gray), (previously known as Merulius lacrymans), is the most important timber decay fungus in buildings in northern and central Europe. It is also of serious concern in Japan and Australia. Serpula lacrymans - in Latin Serpula 'to creep', lacrimans (lacrymans) from the Latin 'tears'. The difference between the wet and dry rot fungus relates to two aspects of the organisms:

• the dry rot fungus tends to decay wood at lower moisture contents (i.e. 20% to 30%) than the wet rot organisms (i.e. 30% to 50%); and
• the wood tends to be left in a dry state after attack by a dry rot fungus.

Not only does the fungus bring about the dramatic decay of timber, but it is also able to spread through a building from one timber location to another across non-nutritional surfaces. The fungus has a serious impact on UK housing stock and causes concern when dealing with the conservation of buildings of architectural or historic value. Timber decay investigation and eradication is therefore big business in Britain. Serpula lacrymans is the most virulent form of fungal attack in building timbers, and buildings of traditional construction are particularly vulnerable to this form of decay.

The vast majority of properties in the UK contain a significant amount of wood, ranging from structural timbers (such as trusses, perlins and joists) to finishings (such as skirtings and panelling). To detect the type and extent of fungal decay, remedial measures may entail the loss of decorative finishes, and extensive exposure of and damage to the fabric of the building; such work can be very expensive. It is therefore not surprising that the estimated annual expenditure on timber preservation works in Britain is over £400 million.

Building surveyors and other professionals have to consider the factors that may indicate the likely causes of internal decay, whether past, present or future. In addition, correct early diagnosis will help the surveyor to avoid a negligence claim in the event of a future outbreak of the rot. It also minimises the chance of carrying out inadequate or excessive treatment where Serpula lacrymans is mistaken for wet rot or vice versa.

The fungus has occupied a specialised ecological niche in buildings in Europe with its unique biology, and is only known to occur in the wild in the Himalayas. For detailed information please refer to The search for wild dry rot fungus (Serpula Lacrymans) in the Himalaya on the origins of dry rot in the Himalayas.

It first became recognised as being of economic significance in the UK in the 17th century when ships of the Royal Navy were decomposing faster than they could be built, culminating in the case of the Queen Charlotte, launched in 1810, which cost far more to repair in 1812 than to build 2 years before. The damage to the ship was almost certainly caused by dry rot fungus S. lacrymans. The causative organism of these early attacks is sometimes recorded as Boletus lacrymans though by the 18th century the organism had been more formally named as Serpula lacrymans, by von Wulfen (1781). In 1912 S. lacrymans was renamed Merulius lacrymans (by Falck, 1912). In recent decades, a return to von Wulfen's nomenclature has occurred.

The ravages of the dry rot fungus are familiar, as is the destruction caused by attempts to eradicate it, particularly involving the use of chemicals. Remedial chemical timber treatment can cause damage to the health of building occupants and is a cause for concern to environmental health authorities. It is the lack of understanding of the biology and ecology of the dry rot fungus that has led to this radical treatment and hence considerable damage to building fabric.

The author has led several Himalayan expeditions for the search for wild dry rot in the Himalayas with a view to gathering information on its biology, ecology and genetics in the wild. It is hoped that the fundamental scientific knowledge gained through multidisciplinary research should enable us to reach a better understanding of the fungus and to develop safer, more effective, ecological control techniques and strategies. Not only is fungal infection of timber unsightly and potentially hazardous to human health, it can also adversely affect the structural integrity of the timbers as well as disrupt the use of the building. Dry rot fungus has an unenviable reputation as the cause of one of the most expensive and destructive problems associated with timber in the built environment. To understand why the organism can cause such destruction it is necessary to understand its biology, ecology and physiology, and its natural environment.