Fungal decay

The correct and early diagnosis of dry rot requires knowledge of:

• the physiology, morphology and pathology of the fungus;
• building structure and construction;
• environmental conditions;
• moisture mapping in the building fabric; and
• wood science and pathology.

Determining the presence of hidden or built-in timbers in cavities and voids is crucial to a full and accurate detection of the infestation. There are a number of techniques the surveyor can use to help in arriving at a correct diagnosis and these are listed in the table below.

Primary detection methods
Detection methods	Types	Examples
Human senses	Visual	Warping or cuboidal cracking in wood, strands and sporophores
	Aural	Hollow sound when tapped
	Olfactory	Musty/mushroom smell
	Touch	Spongy, friable when felt or probed
	Taste	Acrid
Non-human senses	Sniffer dogs	Trained dogs to locate active dry rot outbreaks (but dogs cannot trace dead dry rot or wet rot decay, which is very important to trace).
	Electronic noses	Specially developed electronic instruments for the detection of moulds claim to detect dry rot.
Artificial detection	Moisture meter	Necessary to confirm damp areas
	Hand mirror/torch	To help inspect awkward voids
	Ultrasonic hammer	Can help to indicate the soundness of large joists
	Endoscopes	To inspect inaccessible areas, e.g. cavities and voids
	Genetic	DNA analysis of rot samples

Although dry rot primarily attacks softwoods, it can also infect hardwoods such as oak. There are various timbers within a building that are susceptible to dry rot (see the following table), to which the surveyor should give particular attention.

Timbers vulnerable to dry rot
Location	Common timbers affected
Walls	Safe lintels (windows and doors, timber safe lintels) Bonding timbers Strapping and boarding of dado panelling Lathing behind plaster Skirting boards
Roofs	Rafter feet and ends of ceiling ties, particularly behind 'beam filling' Truss ends and ceiling joists Ceiling ties built into wall heads Wall plates
Floors	Joists built into masonry Bressummers (large support beams) Wall plates Floorboards Skirting grounds and skirtings

Figure 1: Dry rot pancake shape fruiting bodies to the ceiling; also note salt efflorescence to bricks due to moisture ingress

Figure 2: Dry rot fruiting bodies to brickwork at ground level

Figure 3: Dry rot fruiting bodies at ceiling level

Figure 4: Water ingress and dry rot fruiting bodies

Figure 5: Typical pancake shape dry rot fruiting bodies

Figure 6: Dry rot Serpula lacrymans mycelium, strands and fruiting body infesting the basement wall

Figure 7: Extensive dry rot Serpula lacrymans strands and mycelium on brickwork

Figure 8: Extensive growth of dry rot Serpula lacrymans strands and mycelium

Figure 9: Dry rot Serpula lacrymans fruiting body to the skirting board

Figure 10: Extensive dry rot Serpula lacrymans mycelium, fruiting bodies

Figure 11: Extensive dry rot Serpula lacrymans mycelium on brickwork and developing fruiting bodies

Figure 12: Extensive dry rot Serpula lacrymans mycelium growth to ceiling joists, wall plate and brickwork in the basement

Figure 13: Peziza fruiting bodies in the brickwork (sometimes misdiagnosed as Serpula lacrymans fruiting bodies)

Figure 14: Close up of Peziza fruiting bodies in the brickwork (sometimes misdiagnosed as Serpula lacrymans fruiting bodies)

Dry rot in its early stages is difficult to distinguish from other wood fungi without the benefit of laboratory analysis. This involves growing samples of the fungi on an artificial medium under incubated and controlled conditions. Various media based on oatmeal, wheat flour and malt extract can be used as a nutrient to encourage fruiting of the fungus.

In its terminal stages, when the fruiting bodies or sporophores have developed brown spore dust, dry rot is relatively easy to distinguish from wet rot. The former, however, can spread to other timbers, even through masonry materials, whereas the latter is always restricted to the locus of the moisture source. This ability to spread is one of the distinguishing (and menacing) features of Serpula lacrymans.

Other techniques used in the identification of fungi include optical and microscopic, laboratory culture and various non-destructive techniques, which can be used on site to aid the surveyor to make an accurate judgement, e.g. hot wire anemometry or electronic relative humidity measurement.

For early warning and management of insect and fungal infestation and decay in buildings, more exotic techniques may sometimes be useful, including:

• pheromone insect traps for beetles;
• infrared thermography;
• short-wave radar;
• automatic weather stations;
• ultrasonic detection of timber-boring insects; and
• total building monitoring using specialist data loggers.

Any technique must be carefully justified because the value of the information from techniques not routinely used or properly calibrated can be very limited.