Fungal Decay in Building Timbers

Dry rot and wet rot can affect buildings of all ages and if decay is discovered it should be identified and remedial action taken without delay.

Fungal decay occurs in timber which becomes wet for some time and is the result of the attack by one of a number of wood-destroying fungi. The most well-known are Serpula lacrymans – the true dry rot fungus -, Coniophora puteana the Cellar fungus and Poria vaillantii the Pore or Mine fungus. Many other fungi also occur and some have recently been particularly linked with decay in door and window frames.

Dry rot is only caused by Serpula lacrymans and is the most serious form of fungal decay in a building. It can spread onto and destroy much of the timber. Wet rot occurs more frequently, but is less serious; decay is typically confined to the area where timber has become and remains wet.

Fungal decay always arises because the wood has become wet, usually timbers will be in excess of 20 per cent moisture content. Finding the source of dampness and eliminating the ingress of moisture and promoting drying is always necessary.

Common causes of dampness in buildings

The first step after discovering fungal decay is to make a careful inspection of the building to find how and where the water is coming from.

The defect permitting access of moisture must be treated and further entry prevented and the area dried out.

External Causes

1. Blocked gutter especially in the hidden valleys of the roof or defective rainwater goods.
2. Defective surfacing to valley gutters and flat roofs.
3. Missing, broke, displacing or loose tiles and slates.
4. Faulty flashing around chimneys.
5. Deterioration of mortar in brickwork joints.
6. Faulty or missing damp proof course.
7. Bridging over damp proof course by soil in flower beds, plinths.
8. Blocked air-bricks.
9. Cracked or broken pipes (waterpipes or waste pipes).
10. Faulty flashing around windows frames.
11. Continued overflow from cistern or water tanks.

Ivy or other climbing plants may hide many of the above faults and roots may undermine foundations causing breaks in damp courses. Roots of nearby trees may cause similar damage to foundations and damp course.

Internal Causes

1. Solid stone or concrete floors with wooden skirtings and/or covered with timber where the impervious membrane is punctured or of poor quality or non-existent.
2. Condensation caused by unlagged steam pipes (particularly under floors), steam condensate particularly in wet process factories, high atmospheric moisture from normal bathroom and kitchen usage. This is especially important in uninsulated and / or poorly ventilated building and is the cause of much window joinery decay.
3. Trapping of flood water in under floor space and over concrete.
4. Old toilets either from fracture of the pan or defects in the plumbing unions.
5. Close fitting linoleum vinyl or laminate flooring laid over unventilated or imperfectly ventilated wooden floor.

Adequate ventilation of sub floor is important and careful attention must be given to clearing blocked air vents and air-holes in sleeper walls. Pockets of dead air favour fungal growth and should be eliminated.

Steps must to taken to dry out existing dampness and to prevent further entry of water in addition to the eradication of the fungus and repair of damage caused.

Outbreaks of Dry Rot and Wet Rot

Outbreaks of dry rot and wet rot start in similar ways. The mature fruiting bodies of wood-destroying fungi that develop during an attack produce millions of microscopic spores and these are widely dispersed by air currents. If they fall on untreated damp wood, they will germinate by pushing out a hollow tube called a hypha which grows and branches to form a mass of hyphal threads called mycelium.

Mycelium develops inside the timber and breaks down the wood for food. The timber may darken in colour and develop a characteristic cracked appearance. Some wet rots may result in bleaching of the wood; these are more common in doors and window frames. Eventually, the wood loses its strength and, in some situations, may become dangerously unsafe.

The main differences between dry rot and wet rot are the degree of development of mycelium on the wood surface and the ability of the fungus to spread into other timbers via adjacent masonry. It is important that the two types of decay be distinguished since they require different treatment.

Identification and Treatment

As we have shown it is very important that the type and cause of the fungal decay are correctly identified before any corrective action can be considered. It is for these reasons that it is important that a detailed diagnostic inspection is carried out by a competent specialist. This inspection should be followed by the submission of a report that details both the cause of the decay and the proposed remedial action.

Dry Rot

Dry Rot is actually a form of wood-destroying fungus - Serpula Lacrymans. Water droplets are often produced on the surface of the mycelium. The mycelium occurs on the surface of infected timber which, in still humid conditions, appears as a white, cotton-wool like growth.

Mycelium spreads over the timber surface by the continued growth and branching of the delicate hyphal threads growing with time. Specialised strands develop within the mycelium and these supply water and nutrients to the growing fruiting bodies. The strands assume their real significance when the fungus spreads from infected timber onto the surface of adjacent stone or brick walls. The tiny hyphal threads penetrate the mortar joints and plaster layers and large areas of damp wall can then become infected.

Bright lemon-yellow patches may also be seen in less humid situations.

Dry rot can appear where timber has a moisture content of greater than 20%. Possible causes can be a plumbing or drainage leak either immediately in the area, or water ingress from the exterior.

Remedial Work/Treatments:

To remedy cases of Dry Rot, we identify the underlying cause, carry out all necessary repair work.

• Remove affected timber
• Carry out specialised treatments
• Re-instatement work
• Specifications detailed in Survey Report or upon request

Wet Rot

This type of rot is caused principally by Coniophora puteana. Poria vaillantii is another important wet rot fungus and a number of less common fungi also occur. While each fungus has its own unique features, the general appearance of wet rot is similar – as is the treatment. Wet rot is typically confined to the area of dampness because the mycelium does not spread into walls.

Remedial Work/Treatments:

To remedy cases of Wet Rot, it is important to identify the underlying cause and carry out all necessary repair work. Specifications detailed in Survey Report, or upon request.

Identification of the type of infestation.

• Treatment of all infected timber
• Repair or replace any badly-damaged timber

We provide spray treatments to eradicate all wood-boring beetles. Mainly loft spaces - rafters, joists and purloins - and floor joists and floorboards.

Left untreated - can cause serious damage, leading to structural weakness.

Carpentry