Wet Rot

Dealing with Wet Rot


Wet rot, like dry rot, can damage a building. The damage can affect the structural strength of timber which could ultimately harm the occupants of the said building.  When decay is discovered it should be immediately identified so as to that the problem could be properly addressed.

What is wet rot?

Wet rot is the decay of wood caused by its exposure to high level of moisture. For wet rot to grow a constant source of moisture is needed.  The moisture could be caused by leaks in the plumbing system or leaks from the roofing system. The moisture could also be the result of faulty construction or any structural defect. A wall that is adjacent to a timber could be consistently damp because of moisture seepage from the exterior. The constant high level of moisture would ultimately transfer to the timber. Moisture and wood equals wet rot.  A wet timber is the ideal breeding ground for wet rot fungi like: coniophora puteana; Poria vaillantii and Phellinus contiguous. Unlike dry rot fungi, wet rot fungi are generally confined to the afflicted damp area because the thread-like mycelium does not spread out to neighbouring timber. Damage caused by the fungus is limited to the host timber.

Different Types of Wet Rot Fungus

There are three types of wet rot fungi. The most common wet rot fungus is the coniophora puteana or the cellar fungus because it is usually found in damp basement.  This fungus causes timber to darken and produces longitudinal cracks usually under a very thin layer of good wood. This fungus thrives in very damp areas like the basement, roof and solid wood floor.  Strands that look like black ferns can be observed on the surface but do not spread to adjoining timber but confined to the damp area.

The poria vaillantii (pore fungus) causes wood to shrink and rift into cubical sections. This fungus is also a common in houses.  Its strands are white and quite flexible. Infestations of this type of fungus sometimes manifest itself in fern-like growths on the surface of the wood.

Phellinus contiguous are mostly found in exterior joints.  The fungus bleaches wood which eventually turns fibrous and stringy.  This fungus is a major concern for it causes   decay on structural joints.

Where to Spot Wet Rot

 The most susceptible parts to wet rot are areas that are most likely exposed to damp and where there is no through ventilation.  Suspended timber floors are likely to develop wet rot because of poor ventilation under floor joists. The supporting masonry on ends of joists might be damp (either by rising damp or penetrating dampness) thereby transferring moisture to the floor joists. Roof timbers are also susceptible to damp due to water that might penetrate from leaks on the roofing i.e. valley, gutters, ridges and on the roof sheeting itself.

Window frames especially the lower sills are more prone to wet rot because of the tendency of water to collect at the bottom of the window. Sometimes, wet rot is hidden below a very thin surface of wood or paint.  Professionals usually push a thin blade on suspected wood. The blade should meet resistance at after a few millimetres. If the blade goes halfway through the wood then there is definitely wet rot. Timber with wet rot will look darker and feel spongy. A wet rot infested timber will crumble to the touch when dried.

Can Wet Rot be Prevented?

Wet rot is highly preventable. There are certain measures that you can do to check a possible infestation. The first thing that you should do is check for possible rising damp and other sources of penetrating damp. If rising damp is a problem seek the advice or services of an expert. If penetrating damp is the issue, see if you can fix the cause. If you can't, then get a qualified handyman to do the work.

Make sure that external timber frames are all adequately painted for protection against moisture. Check that the roof has no leaks.  It's better to check the roof when it's raining. Access the roof and shine a torch. Any moisture would be easily reflected.

Check for wet rot under the kitchen sink, the washing machine, bath and shower and all other areas where there's a possibility for the timber to get damp. Preventing wet rot is easy enough.

Treatment for Wet Rot

Good house design and construction are the best protection against decay caused by wet rot. However, proper maintenance is another story. It is therefore advisable that all wood be treated with some form of preservative. Most modern homes have their wooden floors nailed to battens on concrete. Although the concrete is treated for rising damp, it is still ideal to treat the battens with preservatives. If wet rot is discovered trace the source of dampness. Unless you know where the moisture is coming from it would be useless to treat the affected wood. Repair the structural problem that is causing the wet rot. If the source of moisture on the floor joists is a rising damp on the masonry, sort out the rising damp first. If moisture is coming from a leaky water supply pipe in the kitchen, have a qualified plumber to fix the problem. If wet rot is found on roofing members it is best to seek the services of an expert.

Rotten and mouldy timbers should be replaced.  If the damaged wood is very small, you can just cut the rotten part and splice a new treated piece.  In any exposed area where wind could possibly drive in rain, it is best to treat the wood with preservative too.  Note that as with all fungal infection, eliminating the source of moisture and complete drying of the infected timber are the effective "treatment".