There are few things that put a buyer off a property more than seeing Dry Rot or Wet Rot appearing on a survey report. And fewer things to sink a seller’s heart at that!
What’s The Difference?
The main thing to get clear is whether it is Wet Rot or Dry Rot. They may sound similar, but Wet Rot, yes, you’ve guessed it, only affects timbers that are very wet, i.e. where they have a moisture content of over 24%, and Dry Rot prefers a slightly lower moisture content of between 18% and 22%.This dampness may be caused by inadequate ventilation to sub-floor areas, the proximity of the timber to wet or damp walls, rising or penetrating dampness, and water leaks such as from sinks and baths, poorly maintained roofs, and general unwanted water ingress. The spores for all types of timber fungi are in the air, in the same way as are pollen, mould and viruses, and, in the same way, they are harmless until they land on a sensitive host.
There are several different types of Wet Rot, each having its own characteristic growths, strands and fruiting body (the fleshy ‘mushroomy’ part). Damage to the timber causes it to become very weak and can even be broken up by hand once the attack has developed. The strands, coloured depending on the type of Wet Rot, can grow on to adjacent brickwork or plaster, but cannot damage this. Wet Rot can be a brown rot or a white rot; the white or brown does not refer to the colour of the fungal growth. The brown rot causes the wood to darken and break in to smallish cuboidal cracks, whereas white rot causes a lightening of the timber, and damage is manifested along the grain.
Fibroporia (courtesy of The Wykamol Group)
Wet Rot Treatment
Whatever the type of Wet Rot, they all require the same treatment – find out why it’s damp, remove the source, make sure the surroundings dry out quickly, and remove or repair damaged timber. Damaged parts of the timber will need to be cut out as they will no longer be strong enough to do their job. Most wet rot is seen around window and door frames where flaking paint has let rain water in, or floors and skirting boards next to damp walls, or joist ends set in to damp walls. If the rot is seen in an enclosed area, you’ll need to increase the ventilation to ensure the area dries out quickly. (Note: de-humidifiers can be a bit strong and can sometimes warp the remaining wood – natural ventilation is preferred if possible.
Fibroporia (courtesy of The Wykamol Group)
Dry Rot is different in as much as it can travel through masonry in its search for food. It will affect timber that has been made damp in the same way as for Wet Rot. When Dry Rot spores land on something suitable they develop into a soft cotton-wool like form, from which white strands are produced, extending along the timber or masonry. Eventually a part of the cotton-wooly area thickens and darkens, and produces reddish dust. This is called the ‘fruiting body’, and this dust is the new spores.
Strands of Dry rot found growing between plaster and brickwork
Dry rot strands and mycelium cover this destroyed timber, which was removed from a door casing.
The Dry Rot eats all of the nutrients in the timber, causing large cracks as it is emptied of its strength and fibres. When the initial food source is exhausted the strands travel through masonry and between plaster and brickwork, in search of the next friendly host. Usually when the new host is found, the older fruiting body dies, and a new one is grown, starting the process again.
Sheets of dry rot mycelium grew below the cladding on this pillar
Dry Rot needs to be stopped as it can travel throughout a property, taking its own moisture supply with via these strands. It can cause severe damage if allowed to get a hold on wall plates and other structural timbers. But do not fear - it CAN be treated!
A sheet of Dry rot mycelium grows across the sub-soil under this (removed) timber floor.
Dry Rot Treatment
Dry Rot treatment requires that the extent of the outbreak is identified. Unfortunately this can be a bit disruptive, as floorboards may need to be lifted, paneling removed, etc. It is better for this to be done at the outset, rather than a half-treatment undertaken. Again, you will need to determine the source of moisture, and halt this. All affected timbers will need to be cut out to ensure that any signs of growth within are gone (to approximately half a metre beyond the last signs), and the area needs to be dried as quickly as possible.
The reddish-brown at the centre of the photo is the new 'fruiting body' of the Dry rot where spores are produced.
The similarity to the treatment of Wet Rot ends here, as the characteristics of Dry Rot require more severe action.
Any masonry in contact with any strands etc., and this includes the soil below ground floor timbers, needs to be thoroughly cleaned, and treated with a masonry sterilizer, or biocide. Thicker walls require drilling so that this biocide can be injected in, as well as surface sprayed.
All surrounding timbers that can remain need to be sprayed with a biocide to ensure that any strands or spores are killed. Usually, a dual purpose chemical is used here. Even though you may not have had any insect attack, many types of woodworm are associated with partly decayed wood, and it is recommended, and preferred by contractors who may have to insure this work, to use a combined Dry Rot treatment and Insecticide at this point.
It is for this reason also that contractors will frequently recommend a dual-purpose spray to follow Wet Rot works.
Although many contractors can issue a guarantee for the Dry Rot treatment, this is invalidated if you allow the timbers to become re-wetted for any reason. Ensure that regular maintenance checks are carried out, so that in a worst case scenario you catch the regrowth quickly.
Dry rot mycelium grows across the sub-soil and up the party wall. This attack had affected the skirting and floor boards in both properties. (The bottom edge of the plaster can be seen in the top right, the floor boards have been removed.)
Many old buildings will show signs of Dry or Wet Rot. Often the attack is long gone, leaving little but a bit of crumbly wood and old, brittle white strands. Like defunct woodworm, this does not mean an on-going problem. Trained, experienced surveyors will be able to tell the difference in live or dead strands, and recommend treatment.