DRY ROT & WET ROT

DRY ROT AND WET ROT

There is a long tradition of using wood in buildings and a recent resurgence of timber frame in off-site construction. The extensive use of wood brings with it the risk of rot and fungal infestation which can cause significant damage and require substantial, costly repairs. Modern buildings are not immune from the risk of decay, as any pre-treatments have limited durability.

The challenge for surveyors, with so much of a building’s structure concealed, is identifying the risk of water penetration, knowing where to look, and identifying the wood rot/fungal growth if discovered. With this knowledge, surveyors should not be surprised with the timber defects found in cellars. You can not only see the rot, but sometimes smell it.

Dry Rot

Dry rot tends to grow at lower moisture content at around 20 to 30% in wood. In other words, it does not require a lot of moisture to develop and spread, which is what makes it so dangerous. It thrives on warm and unventilated spaces. It is the after-effects on damaged timber which the term ‘dry’ relates to.

Dry rot can be far more aggressive than wet rot and spread extensively from its source, even spreading up or through brick walls. The lack of ventilation to sub-floor areas can only aid the growth of dry rot so a surveyor will always be checking for air vents to external walls.

Depending on conditions, dry rot can spread rapidly, from 1 to 4 metres per year. The fruiting body discharges its spores at a phenomenal rate, up to 800 million per day!

Treatment

Treating dry rot tends to be expensive and more involved than wet rot, dependent upon how extensive the outbreak is. The treatment can be more disruptive as it invariably requires cutting out the defective timber with chemical treatment to adjacent areas and improving the overall ventilation.

Wet Rot

Wet rot and dry rot are two completely different types of fungi. Wet rot fungus tends to grow on timbers with a high moisture content of around 45 to 50% and above. It is far more common than dry rot.

Wet rot can be due to defects with external guttering, plumbing defects, rising damp, penetrating damp, and lack of routine maintenance. It can be found in roofs, cellars, floor timbers, skirting boards and external joinery.

Treatment

To eradicate wet rot depends on the severity of the wet rot.  In most cases the affected timber will need to be cut away and replaced with new timber.

Consequences for Mortgage Valuations

As stated above, wet rot is often relatively easy to rectify by removing the source of water ingress and replacing the rotten timber. Therefore, this is less likely to have a significant impact on the value of the property. The rotten timbers are also likely to be more evident and their condition is often reflected in the valuation figure. 

Dry rot is often hidden and concealed within inaccessible parts of the construction making it more difficult to repair. The unknown element makes it difficult to estimate likely remedial costs and, therefore, further investigations are often required before the impact on property value can be determined and before the valuation figure can be provided.