Dry rot

[swordpoker]

Anyone here dealt with dry rot before?

I've just bought my first development property at auction and the home report says:

"No evidence of significant dampness or infestation was found within the scope of
inspection.
There is an outbreak of dry rot affecting the flooring near to the window and internal
downpipe in the front bedroom and further inspection must be carried out to establish
the extent of the outbreak."

I'd love to hear some general do's and don'ts and get a rough guide on how long it might take to sort out. Anyone got some cheery news for me?

[Breconeer]

Oh dear. Not good news at all.

WET ROT is relatively straightforward, because the fungus involved in destroying the wood (typically Coniophora puteana, but sometimes others) is only active in untreated wood that remains damp or is routinely wetted - it doesn't affect dry wood beyond the area of wetness, so replacing the decayed parts with new treated timber and eliminating the source of dampness or wetness is sufficient.

DRY ROT is an altogether different beastie. If someone messes with it wrongly they can trigger extensive and expensive damage (phenomenally expensive sometimes). Again it is a fungus (Serpula lacrymans), but although it requires a temporary degree of wetness for it to germinate on timber, having done so it immediately puts out almost invisibly fine hollow hairlike fibres (hyphae) which quickly grow through brickwork and mortar, and behind plaster or under concrete, seeking sources of dampness from which it can then draw the water it needs to slightly dampen adjacent dry timbers sufficient for the fungus to extend its presence - in other words, once established (perhaps taking advantage of a temporary flood or leakage that is no longer there) it can attack dry wood, hence its 'dry rot' name.

The fibres can grow in every direction at a rate of about an inch a week - about 4ft a year. So an outbreak triggered by a overflowed washing machine might easily result in a fungus 8ft diameter in a year. In its search for wood it can spread behind plaster or within walls and can reach timbers 10 or 12 feet away - allowing it to move upwards and downwards through several storeys even if it doesn't have doorframes and stairways to sneak up the back of.

It is absolutely vital to investigate exactly how far it has already spread in every direction - so that traces of it are not accidentally left in the building to regrow. This often involves not just gently removing affected timbers and noting the visible extent of fungal activity behind them (dry rot doesn't like daylight, it normally grows on the dark side and only shows when it has consumed enough wood for the front surface to collapse), but very carefully removing plaster and tiles and examining the mortared crevices of the wall. All debris MUST be carefully bagged up on the spot, not carried through the building where slivers of infected wood might get dropped through floorboards or under skirtings. Identifying the barely visible fibrous hyphae is a skilled job - there will be other fibres that are not dry rot.
Because the fibres at the advancing edge of the fungus are invisible to the naked eye, one has to allow for it being about two feet further than seen - which is why most treatment companies go a yard or metre beyond when removing wood and sterilising masonry. The brickwork and concrete does have to be sterilised with an antifungal chemical pumped into drill holes and sprayed across surfaces.

Where the outbreak is close to a party wall, there is not only a likelihood of the outbreak returning to your house from your neighbour's side, into untreated parts of your own house, but a probability that your treatment of the fungus might actually exacerbate the growth of the fungus on their side if not treated by them. The fungus has a strong survival instinct; if attacked and not wholly eradicated it will produce fruiting bodies that release new spores (they look a bit like fine instant coffee powder). Shining a bright light onto the fungus will also distress it and can trigger similar activity.
As a professional timber inspection surveyor, I have encountered numerous situations in which dry rot, improperly dealt with, has resulted in further outbreaks elsewhere in a building - by when the key evidence of the initial shape of the outbreak has been lost, making further treatment even harder, and involving tens of thousands of pounds of structural disruption.

[Breconeer]

A word of comfort (perhaps!). Even the most experienced surveyors will encounter outbreaks of timber decay in which the surface evidence is insufficient to properly establish whether Wet Rot or Dry Rot is to blame. To cover themselves, some will describe it as Dry Rot and suggest a specialist should look at it. If you are lucky, this might be the situation you have.

[Breconeer]

Swordpoker - if you can describe in detail what you see in layman's terms, or better still can show a photo - I will see if I can add any useful observations. One rule-of-thumb (and not totally reliable) is that skirting boards distorted by fungal decay tend to become convex with dry rot (ie, they take on a 'roll' shape), whereas with wet rot the front face will often go slightly concave or rippled. The roll shape is usually a bad sign.