Water damage in buildings and the prospect of timber decay
Should timber decay be expected without question, and what can be done to minimise the risk?
by Dr Matthew Green
The following popular, but quite erroneous, wisdom has arisen from investigators’ unquestioning but misinformed belief that the fungus has a name that accurately describes its biology, namely that:
• Dry rot produces enough water from the wood it is decaying to
sustain it, so that the fungus continues to spread and cause damage even
if the source of moisture that caused it is removed.
• Dry rot strands conduct water to make dry timber wet enough to
attack.
• Buildings dry through a moisture zone where there is a risk of
dry rot developing.
All of these ideas are nonsense, but widely believed and the consequence has been massive destruction. The treatment of dry rot has usually caused far more damage to our building heritage than the fungus. There are several archival cases where stately homes have been demolished due to financially prohibitive dry rot treatment quotations.
Photograph 3: Commercial dry rot treatments: they often inflict more damage to a building than the fungus.
There is no doubt that dry rot, growing in a damp and neglected building, can cause considerable damage, but it will still be restricted by the local environment. A dry rot spore needs to land on timber with high moisture content (in excess of 28%) in order to germinate. Once growing, it will not spread to the dry parts of the house, a fact recently described by a German researcher, Tobias Huckfeldt, who also found its growth rate to be comparable to that of other building fungi. The fungus needs a substantial amount of fresh water to grow and thrive. Without that, it poses no threat to a building. Such potential sources of water should be considered before any suspended floor deemed insufficiently ventilated has the walls supporting it riddled with airbricks (with more loss of the building fabric).
‘Dry rot’ as a term to describe Serpula lacrymans is an unfortunate and inaccurate legacy of 200-year-old observations misapplied to an organism that does not warrant the infamy it has achieved.
Return to part one of this article