Timber decay (dry rot or otherwise) as a result of fungal attack is a natural process whereby organic materials (such as woods) are broken down and returned to the earth. While this is all well and good when a tree branch falls to the forest floor, it is not so beneficial where timber is employed within our homes and structures.
Simplistically, a number of conditions have to be met in order for fungal growth to occur. Firstly, a spore (a fungal ‘seed’) must be present, as must a food source (organic material like wood), air or oxygen, reasonable temperatures (i.e. 0 – 43 degrees Celcius), and water.
Spores are generally present all around us, as is air and timber, so why is your dining table not falling apart? The answer is water..
Risk of decay arises when the moisture content in timber reaches a high enough level for germination to occur, and it is this reason why dampness and timber decay in buildings go hand in hand.
We specialise in the identification and treatment of wood decaying fungi (such as dry rot), and the sources of dampness which trigger the decay. While we focus on work within Manchester & North West England, we commonly travel further afield and would encourage you to contact us with your queries.
We include below some example considerations, relating to issues of timber decay. While this might be considered specialist knowledge, we simply want you to appreciate that we are experts in the field and are well placed to advise.
What causes issues associated with timber decay:
Lack of ventilation in a ground floor sub-floor void or cellar.
Refurbishing properties can alter the balance of ventilation that has been adequate for years.
It is common to find that heat conservation measures, fire precautions or additional walls without considering air-flow, results in high atmospheric moisture levels and infestations of wood decaying fungi.
Wood left on damp oversites or within sub-floor voids.
Where timber floors are present at ground floor and oversites below are damp, it is common to find that timber has been left on the oversite and that an infestation has occurred.
Such an infestation may spread to the walls and contaminate the floors and walls at ground floor.
Failure to cut back beyond decay.
This refers to the practice of replacing insufficient timber and leaving contaminated wood to encourage further spread of fungus. Also common are secondary timbers placed alongside retained decayed sections to give added support.
Use of new untreated timber.
This is largely self explanatory, but is endemic in the building industry and often results in decay of recently fitted structural and joinery timber.
Modern softwood timber is farmed with fast growing trees to maximize production. This results in a large pore structure within the wood, allowing easy access for moisture and resulting germination of wood decaying fungi. Conversely, modern wood more readily accepts preservatives when they are used.
Use of new pressure impregnated timber, cutting it on site and not treating the cut ends.
Treated timber is very vulnerable once cut. Joiners seem to be totally unaware of this fact.
Fungus will happily spread through the centre of a piece of wood, leaving the treated surface sound.
Spray treatment of in-situ timber, without treating the embedded ends.
This will also leave the centre of wood vulnerable to decay.
How good is your guarantee? It may not cover decay emanating from the untreated embedded sections. Ideally preservative paste would be used on timber at wall contact.
Failure to remove redundant or decayed embedded timber fixing plugs.
Unnecessary wood in walls will sit there waiting for moisture and resulting wood decaying fungi.
Failure to take account of adjoining buildings.
An adjoining property may be at a higher level or may be in a state of disrepair. Both instances would cause damage to the building being repaired.
Lack of ventilation in roof voids.
Incorrect placement of insulation at the eaves or lack of air vents within roof spaces may result in dampening of the roof timbers, thus encouraging decay. This is aggravated in refurbished properties by insulation between ceiling joists preventing heat escape from below, but allowing sufficient water vapour to enter the roof void.
Inadequate or incorrect targeted irrigation treatment of brickwork.This will result in continuing infestation, particularly if other preventative measures are not taken. While wholesale irrigation is rarely justified, quick kill methods are where areas are being closed back in quickly. Note that irrigation in most cases is employed as a means to address dry rot.
Note: Whilst one cannot be sure that all infestation is completely eradicated, the other measures of drying out, replacement of decayed sections of timber and treatment of sound timber will result in an incipient or isolated infestation being left dormant and harmless.
Decorating of dampened existing windows.
It is common to find that retained windows that have been poorly maintained are decorated with impervious paints without the timber being allowed to dry out. Prior to refurbishment the wood could breathe to an extent because of flaking paint and open joints etc., but once painted the trapped moisture increases the tendency for decay, resulting in breakdown of the structural integrity of the wood.
The use of redundant site debris as hard-core.
Brick hard-core inevitably may contain contaminated material or even wood residue. It is best avoided by using crushed stone. If brick must be used, it should be sorted to ensure it is clean, and treated after laying with a fungicidal wall solution.
Failure to clean out sub-floor prior to laying hard-core.
Failure to remove redundant sub-floor air vents when laying solid floors instead of timber.
This is a most common cause of new solid floors being taken up because of fungus (dry rot or otherwise) attacking low level joinery. Every time such occurs, it is inevitable that wood or wood residue, or only wall paper on discarded plaster, or joist residue in redundant joists pockets, is found within or under the hard-core once the floors are dug up.
The fungus will germinate on such wood because it gains oxygen via the redundant air vents and moisture from the oversite.
Once it spreads to the underside of the d.p.m. where condensation may be occurring, it will travel quickly and search out vulnerable timber above the floor, such as skirting boards, architraves, door frames, stair strings and kitchen units.
When such problems occur, it commonly results in full floors or all floors in a property being dug up at a prohibitive cost.
Negligent inspection and incorrect diagnosis at the time of refurbishment.
If this happens, then any of the above can easily occur.
Repairing the damage but not correcting the cause.
This will call for the works to be started again.
NOT READING THE SURVEY REPORT IN DETAIL
Costs money, jobs not done properly.
George D. Hockey
Specialising in identification and remediation of timber decay in Manchester & North West England since 1974.