Timber frames

Fungal attack is most likely to be found in areas associated with still air and moist conditions.

Any smell of damp should alert the surveyor to the high risk potential of fungal attack, and further investigation should be undertaken to assess the visible evidence of fungal activity.

Areas of particular concern are under-stair areas, behind panelling, under floors and enclosed framing.

Dealing with fungal attack in a listed building can be a complex. The common remedy used by contractors of stripping out affected wood and replacing it may be diametrically opposite to conservation practice. Stripping out timber floors at ground level and replacing them with a concrete base is a particularly confrontational remedy.

A softer approach is required by many conservationists. This is based on the principle that fungi need a consistent and quite precise environment in which to live, and like all living organisms will seek out new ideal environments to survive. By simply removing the food supply, i.e. damp timber, the environment becomes unsustainable and the fungi die.

By drying timber out, the risk of fungi spread is reduced. Timber with a moisture content of under 17% is considered safe from micro-organism attack. Well-ventilated areas help maintain low moisture levels, so are less prone to attack by wet and dry rots.

Many textbooks and contractors' literature provide dramatic photographs of large-scale wet and dry rot attacks. From experience these pictures demonstrate the exception rather than the rule.

While large outbreaks of wet and dry rot can have a devastating effect on timber, such outbreaks evolve because fungi has been left unchecked. An occupied house is less likely to suffer from such large outbreaks, and by far the most common form of outbreak a surveyor would deal with is the small, localised variety. The need to apply fierce intervention is relatively rare, but some insurance policies insist on such action.

Note: Ensure that all remedial work attempts to miminise alteration/damage to the existing form of the building - refer to BS 7913:2013 Guide to the conservation of historic buildings.

Other threats to the structure

Poor control of rainwater and water vapour is a major cause of defects. Particular attention is needed to recognise the significance of:

• built-up ground levels;
• roads and the potential of road salt spray;
• the vulnerability of pipelines and underground water services; and
• water ingress around chimney stacks, gutters and roofing materials.

Eaves depth and the speed of ground filtration are critical to the performance of walls.