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   Home      Common Defects in Timber Structures

Common Timber Defects fall into 4 Main Categories

Fungal Attack
Pest Attack
Deformation
Splits


Timber defects are often accompanied by of other structural defects that must be rectified in conjunction with the timber defects.

 
Serpula Lacrimans
Commonly known as
Dry Rot
Dry rot can be recognised by white strands that cover the surface of the wood and can spread over and through brickwork and other inert surfaces

Wet Rot
The term applied to all rot that is not Serpula Lacrimans
Brown rot feeds from condensation on the top surface of floor boards below an impermiable underlay gives rise to brittle cubic dark brown patches of wood that easily breaks away

brown rot that developed in roof beams in the presence of rainwater from the leaking roof

Pest Attack

Commonly referred
to as Woodworm
Beetle attack leaves surface holes and runs


Wane  
Volume loss and defects in timber taken from the outer part of the log known as wane
Splits and Shakes
Splits develop in wood subject to excess deflection caused by long term overloading
Warping
Hardwoods used while still green (not cured) warp significantly on drying

Creep

 
 

Dry Rot thrives in humid, poorly ventilated spaces.  Spores may be present for years without causing a problem until a change takes place such as an increase in moisture resulting from leakage of block drains, a period of sustained wet weather, or an undetected water leak through a roof or from a water supply pipe.  Spread can then be very rapid.  Dry rot is notable for its ability to spread through walls and across inert surfaces to spread widely throughout a building.
 
Wet rot is found where the surface of the timber is wet for a prolonged period of time.  Some wet rots can spread in a similar manner to dry rot, but on the whole wet rot remains isolated.
 
White rot refers to the action of the fungus and is caused by wet rots.  The wood takes on a spongy feel whilst retaining its overall dimensions.  The timber strength is reduced, but in some cases will retain sufficient residual strength to perform its function possibly with some level of strengthening.  This may enable the timber to remain in place either, as a temporary measure until repairs can be put in hand, or as a permanent solution in which the environment of thew timber is controlled and monitored in situations where replacement is not desirable or practicable.
 
Brown rot, on the other hand, can be caused by dry or wet rot and results in the wood darkening and becoming soft and brittle, often with the surface of the wood splitting into a checker board pattern.
 
Brown rot often occurs at the bearings of beams or joists and results in the contact wood becoming squashed and the sides splitting away .  Its presence will eventually result in loss of alignment of members - in the case of floors a ridge will become noticeable under foot.
 
Treatment is similar to that of white rot but it is likely to be necessary to replace all affected timber.
 
Pest attack is caused by wood boring beetles which lay their eggs below the surface of the wood.  Larvae hatch and grow within the wood at which point they bore their way to the surface causing the characteristic surface holes.
 
 
Treatment is by spraying or flooding the surface of the wood with woodworm killer.
 
 

When logs are cut into sections of timber priority is given to the inner part of the log.  The inner material is older and denser than the outer timber.  Outer sections are also ore likely to be affected by variations in the diameter of the log along its length.  This causes a local reduction in the timber section.  This loss of section is known as wane.
 
Wane is not desirable in structural timber although it may be tolerated in some situations, such as when members are larger than necessary to perform their structural function.

Splits and shakes occur as a result of drying of the timber as it ages and / or over stressing of the material.  These usually occur where high stresses coincide with locations of naturally occurring weaknesses within the timber which become longer, wider and penetrate deeper into the material.

 

Warping is the result of the natural drying of timber. 
Structural timber will normally be dried to preset moisture levels before being graded and passed as structural grade timber.
If timber is warped it can be trimmed to as straight member, but if the warping is excessive it should not be used where it will be required to carry significant load.
 

 
Creep is the elongation of a timber beam under sustained heavy load.  This will progress gradually over time until  the beam is permanently deformed with a pronounced bow.
The beam will normally be satisfactory  with regard to strength but may fail in time as the deformation increases.

 
 
 
 
 
Typically any affected timber is cut out and burned.  Care must be taken not to spread the spores onto previously unaffected timber.  Spray is then applied to kill the remaining spores which could be on timber, in the ground, in masonry or any other natural product.
 
In historic buildings the situation may occur where decorations overlay timber suffering from rot.
 
In these cases it may be preferable to halt (or delay) the spread of the rot leaving the affected timber in place and by dealing with the problem that caused the humid damp conditions.  Once the timber is below the critical moisture level the spores become dormant. They do not die, but they do not cause further damage providing the timber moisture content remains low.
The draw back is that moisture levels need to be routinely monitored  and any increase dealt with immediately if the rot is not to take hold again.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The intensity of the holes is not necessarily representative of the extent if infection.  In hardwoods penetration is often only within the  surface zone, leaving the larger timber sections mostly untouched. Larger hardwood timbers may continue to perform satisfactorily even though they appear to be seriously affected.  Nonetheless it is good practice to kill the beetles to prevent infection of other timbers.
 
 
Timber with wane should not be used a structural material in a building project as it contains less reliable material and a lower cross-sectional area than those required as primary structural members such as beams, joists, or columns
 
 
 
 
 

It is inevitable in a natural material such as timber than some minor deformations will be present. 

These defects may develop over time to an extent that intervention is necessary by strengthening the timber with steel pins or straps.
 
In older buildings constructed from Green Oak or other hardwoods warped material is the norm.  In these cases the situation should be considered holistically to determine the most appropriate action for the whole building rather than just considering a single member.
 
 
If a beam is suffering from creep it is a sign that the beam is carrying more load than its safe capacity. 

Measures should be taken to shed some of the load by introducing new load bearing members or by strengthening and construction being carried by the beam.  In the case of brickwork it may be appropriate to introduce reinforcement into the brickwork bed joints thus enabling the brickwork to support itself to some extent.


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