Dry rot - identification and eradication

DRY ROT - SERPULA LACRYMANS
Identification

The implications of an outbreak of dry rot are significantly different from those of an outbreak of wet-rotting fungus. Wet rots are limited in their attack to timber by the extent of dampness present. They are not able to extend their attack beyond timber of a sufficiently high moisture content to facilitate fungal growth. This is not true, however, of dry rot, Serpula lacrymans, which has the ability to spread and extend its attack over a wide area and frequently into adjoining areas.

Dry rot mycelium is able to grow through permeable bricks and mortar and thus effectively penetrate masonry. Strands subsequently form in the mycelium and enable the fungus to conduct water and nutriants over long distances. Growth will also travel behind plastered wall surfaces or along conduits that are embedded in the masonry. Once such growth has reached other damp timbers; for example, joist bearing ends, timber lintels, door and window frames, a further outbreak will develop.
The mycelium and strands of dry rot have the ability to transport water from the original source to previously unaffected timbers, thus enabling further fungal decay and damage. Such spread can only be from damp, poorly ventilated areas into similar, unventilated adjacent areas. Sensitive to high temperatures (25°C and above) and situations where fluctuating conditions occur, dry rot is seldom found on exposed timbers or within well ventilated areas.

In suitable conditions, the mycelium and strands of dry rot can remain inactive in dry timber for a number of years before finally dying. Dry rot can also remain in a dormant state in masonry, though it is not certain for how long. It is possible for growth to reactivate and affect untreated timbers if suitably damp conditions return.

Dry rot, Serpula lacrymans, is a brown rot which will mostly attack softwoods.
The decayed wood will be a dull brown colour with deep cross grain and longitudinal cracks. It will be light in weight and crumble easily between fingers.

The mycelium will form silky white sheets and/or have a cotton wool like appearance with lemon yellow tinges. Aggregated hyphae strands will be white or grey, branching, brittle when dry and can reach the thickness of a pencil.

With its name derived from the Latin serpere: to wind or creep and lacrimans: weeping or tears; ‘creeping with tears’ is a good description of Serpula lacrymans.

Serpula lacrymans, the only true dry rot, is by far the most destructive of all wood-rotting fungi to be found in buildings. It is the cause of millions of pounds worth of damage to buildings, throughout the United Kingdom, each year. If left unattended, dry rot will invariably develop into a very serious problem frequently affecting the structural performance and integrity of the contaminated building.

Survey and Eradication

The eradication of dry rot is frequently an extremely complex problem and to be successful, requires the attention of a professional and thoroughly experienced, specialist contractor.

Before any remedial works can commence to eradicate the dry rot, a thorough inspection of the building must be carried out. It is essential that this inspection should be done by a fully qualified remedial treatment surveyor. Rudders & Paynes surveyors, when carrying out this type of inspection, will take great care to investigate and report on two main aspects.

The typical fruit-body, often appearing at the juncture of wood and masonry, will be pancake shaped, tough and quite fleshy. When young this will have a yellow ochre centre which, due to the production of spores, darkens to a rusty red as the fruit-body matures. The fruit-body will produce profuse quantities of spores which frequently settle as a layer of fine reddish brown dust on horizontal surfaces.

Often, the first sign of an outbreak of dry rot will be the appearance of a fruit-body. On occasion, the collapse of suspended timber joists or other structural timbers will be the first indication of what has become a serious problem.

Firstly, it is necessary to fully identify the areas of the building affected by dampness and establish the cause. Secondly and requiring considerable expertise, is to assess the extent of the dry rot. This will involve careful examination of all accessible timbers and surrounding masonry. Bearing in mind, as described earlier, that dry rot can penetrate brickwork, travel behind wall plaster, panelling and similar: to properly assess the spread of the outbreak demands great care and experience. Adjoining areas that may be susceptible to attack will be included in the inspection providing access can be gained. In the most serious cases it may be necessary to carry out a programme of ‘opening up’ works to determine the full extent of the attack.

Following our survey we will provide a full report, supported by sketch plans. This will give full details of our findings, our recommendations for remedial works and our estimated price, (see further explanation), for carrying out the works specified.

The remedial works necessary to eradicate dry rot will frequently involve much more than just the removal, replacing and treatment of affected timbers. Additional works that may be necessary can include, for example; the removal of wall plaster and subsequent re-plastering, masonry treatment, replacement door and window frames, repair or renewal of staircases, etc. Such works will also include improving the ventilation to affected areas and eliminating the cause of dampness. Thorough drying out of the affected areas of the building is a vital part of the eradication process.

As will be appreciated, identifying the extent and providing a long term solution to an outbreak of dry rot is not for the amateur or unqualified. Dry rot, as with other problems associated with timber and dampness in buildings, requires the attention of a truly professional company such as Rudders & Paynes.