national maintenance week heading

Advice & Guidance

Timber Decay

Few people would dispute the prudence of identifying the nature of a problem first, before throwing money at a solution. Yet homeowners continue to spend vast sums on unnecessary chemical timber treatment that would be better directed towards appropriate repair and improved maintenance.

Misdiagnosis of fungal and insect attack is rife and the mention of ‘death watch beetle' alone can induce panic. Inactive woodworm holes are re-sprayed each time a property changes hands and excessive treatments applied to mild decay that poses no real threat. Additionally, surveys for mortgage lenders are frequently undertaken by remedial treatment contractors with a vested financial interest in their own recommendations. Therefore, always question the need for treatment.

Air grille

The Cause:

Dry rot, the most aggressive wood-destroying fungus, thrives in unventilated voids. It often has a musty smell and can develop into grey/white cotton wool-like sheets with tiny orange spots. Wet rot sometimes produces brown strands and commonly causes exposed wood to soften and lose strength. Wood-boring insects include furniture beetle (‘woodworm') and the larger death watch beetle, with the latter only usually affecting hardwoods. Flight holes and bore dust are symptoms. These fungi and insects all have one thing in common: they only usually cause significant damage where dampness exists. Their presence indicates an underlying building problem.



The Remedy:

Because dry timber will not be vulnerable to attack, successfully arresting decay involves eliminating moisture and promoting drying - for example, rectifying faulty gutters, providing extra ventilation and possibly isolating vulnerable timbers. Decayed timber only requires removing as far as is necessary to carry out repair. The eradication of dry rot in particular is best entrusted to independent specialists.

Chemical treatments just address the symptoms of decay, not the causes. They should only be used where an attack is serious and dampness will be hard to eliminate quickly or effectively. Spray-, brush- and injection-applied products are amongst those available. Some are restricted for use by specialist applicators.

Spitalfields houseA step-by-step approach to avoiding unnecessary treatment:

  • Commission an inspection by an appropriate specialist familiar with old buildings.
  • Assess the evidence - the cause, type and extent of decay, its current activity and the need for monitoring and/or non-destructive investigation.
  • Carry out repairs to eliminate dampness and improve ventilation. Monitor the fabric condition.
  • Decide whether treatment really is necessary. It must be justified, targeted and applied safely. Keep a record of all chemicals used.
  • Undertake regular and appropriate maintenance. This is the key to preventing any serious future problems.

Top Tips:

  • Do employ an independent specialist, such as a chartered building surveyor.
  • Do eliminate the source of moisture as the first priority - without it wood-decaying fungi and insects cannot survive.
  • Do retain and repair as much old timber as possible. More is generally removed than strictly necessary.
  • Don't employ a remedial treatment contractor with a vested commercial interest in their own recommendations.
  • Don't use chemicals merely to buy peace of mind or obtain a guarantee.
  • Don't carry out timber treatment where dampness has been diagnosed solely with an electrical resistance meter.
  • Don't shot blast timbers or cut back ('defrass') surfaces attacked by beetle in an attempt to aid inspection or treatment. This is unnecessary and highly destructive.

© SPAB 2007