Is the building you manage a period property or historic building? If so, timber is likely to be an integral part of the structure. If not properly maintained, it can suffer from damage and decay. One example is rot.
For rot to take hold in timber there must be several elements present; the fungal spore which introduces the rot, the timber as a food source and crucially, moisture. The most common types of rot in the UK are wet and dry rot.
Timber rotting fungi can be divided into two groups, according to their effect on timber.
Brown rots cause the timber to become darker in colour and to crack along and across the grain (cuboidal cracking). Dry rot and many common wet rots are within this group.
White rots cause the timber to become lighter in colour and has longitudinal cracking without significant cracking across the grain. All white rots are wet rots.
There are many different types of wet rot fungi, however there is only one dry rot fungus: Serpula Lacrymans. To control an outbreak of rot, it is first important to locate and eliminate all sources of moisture and to promote rapid drying, as timber rotting fungi cannot grow on timber below a 20% moisture content.
It is then essential to establish the size and significance of the attack and to remove and replace the rotted timber with preservative-treated timber and to introduce support measures such as the provision of adequate ventilation or damp proofing membranes to break the contact with damp masonry, for example.
If structural timbers are affected, immediate measures may be necessary to ensure the safety of the building and its occupants. A full structural survey should be arranged to determine if structural repairs are necessary.
A wet rot fungus will feed on damp timber and is prevalent in sub-floors where joists can come into contact with moisture or is often caused by defective plumbing or guttering. Wet rot requires a higher moisture content of around 50% (compared to 20-30% for dry rot) to grow and will be localised to the area of the greatest dampness. Badly affected timbers may need replacing.
The Dry Rot fungus, Serpula Lacrymans, is less common and is commonly found within moist, unventilated constructions. Often the first sign of dry rot is a ‘fruiting body’, which looks like a fleshy pancake, which overtime matures to a rusty red colour. The fruiting body generates a significant quantity of spores, which settle as a reddish brown dusty layer. Dry rot can grow and spread using a mass of delicate strands of hyphae known as mycelium to adjacent masonry, which may appear as white silky sheets. This ability to spread means that the dry rot fungus can also grow on the surface and within other inorganic substrates such as brick and plaster, however the growth is only sustained by continued nourishment from the cellulose in the timber.
In the case of dry rot, all spores should be removed and as with all timber rot, the area ventilated to promote drying. The timbers affected by Dry Rot also should be cut away to at least 300 – 450mm beyond the last indications of rot, however this is not a hard and fast rule.
Deirdre O’Donovan is a chartered building surveyor with Earl Kendrick Building Surveyors. You can get in touch with Deirdre via email: Deirdre@earlkendrick.com or call us on 020 3667 1510.