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Time to stop the rot

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technical & practice - When your project is confronted by evidence of timber rot, do you panic, spend loads of money, or defy the report?

mical remedial treatments for timber decay and damp problems are an unnecessary, avoidable expense in the vast majority of cases, yet architects and other construction professionals continue to waste thousands of pounds on treatments for refurbishment or redevelopment projects throughout the UK.

At best, chemical treatments are expensive, and at worst totally unjustified. Thousands of woodworm treatments are specified every year, many of which are simply not needed.

Inaccurate damp diagnoses frequently lead to money wasted on injected chemical damp courses. Our modern understanding of decay organisms such as dry-rot and wet-rot fungi has enabled building techniques to evolve, and traditional approaches - for instance, chemical treatments of dry-rot infected masonry - have been shown to be completely unnecessary.

There are far 'greener' and more cost-effective methods of dealing with timber decay and dampness problems.

So why haven't architects woken up to this fact?

The combination of a lack of understanding of the decay organisms on the part of architects and others and, possibly, comments from salesmen working on behalf of the chemical treatment firms, have doubtless led to the slow rate of uptake by construction professionals of the lower-cost eradication and prevention methods available.

The tendency for construction professionals to stick with familiar methods also contributes to the problem, and this needlessly adds to redevelopment/ refurbishment costs.

A wider appreciation of the conditions required by wet-rot and dry-rot fungi would help. Dry-rot 'lives' in damp walls and consumes damp wood that is in contact with the wall. In the past it was thought that the fungus could transport water from damp areas to attack wood that was otherwise dry.

Timber scientists now know that the dry-rot cannot transport sufficient water to attack dry wood, and that the wood has to be damp due to water from another source. Often the source is dampness in the wall soaking into the wood, or water ingress from defective roof coverings and rainwater goods, cracked renders or plumbing leaks. Dry-rot also needs unventilated conditions to thrive. If the wood is prevented from becoming damp, and ventilation is provided, then conditions in the building will be such that dry-rot will simply not occur. Any ongoing decay will be eradicated, and future out-breaks avoided.

Isolation and ventilation techniques are the best and most cost-effective methods of dry-rot prevention and cure. These include the use of joist hangers combined with damp-proof membranes, instead of building timbers into the masonry.

Joist plates could be isolated from the masonry using a damp-proof membrane, thus preventing the wood from becoming damp enough for rot to occur, even if the wall is damp. Combined with ventilated dry-lining details or the installation of airbricks at floorvoid level, this approach can easily prevent dry-rot.

Increased ventilation also minimises the risk of wet-rot, which requires that the wood be wet for prolonged periods. Ventilation details allow wood to dry quickly, even if wetting occurs in the future. If detailed correctly, these methods are fail-safe and can make buildings virtually rot-proof without any chemical remedial treatments.

Most buildings have a degree of wood-boring insect damage. However, the lack of understanding of the conditions needed by the insects, those persuasive chemical-treatment salesmen, and unfamiliarity with the 'problem', result in money being wasted on insecticide treatments by architects and their clients.

In the absence of fungal decay, only the sapwood of timbers, structural or otherwise, is vulnerable to insect attack. The moisture content of the wood is also critical, and must be above a particular threshold or the insects cannot survive. In most cases, drying infested timbers to below the threshold for attack will ensure that the insects die out naturally.

If wood-boring insects were not selective about the wood they attacked and the condition of the wood in terms of moisture content and decay state, then all timber in buildings, particularly older ones, would have been entirely eaten away. But self-evidently, this has not happened.

It simply does not follow that because a building has a degree of insect damage, then chemical 'woodworm' treatments are needed.

Damage from an insect attack is permanent, but insect attacks are not, and the culprits may have died out naturally many years ago. It may also be the case that the wood is now too dry to support insect attacks, so is no longer vulnerable. The breakdown of starch in sapwood cells over time also makes wood less attractive to 'woodworm'. In the vast majority of buildings, insect damage is historic, and no longer ongoing, so remedial treatments are not necessary, but when was the last time a chemical treatment firm advised you that no work was required?

'Preventive' treatments may be offered. However, it is not due to luck that a building which has stood for a century has little or no 'woodworm' damage; it is because the condition of the timber (sapwood/ heartwood, decay state, moisture content and age) is not attractive to the insects and will not be attractive in the future. It seems crazy to pay for a 'preventive' treatment against a problem that will not occur anyway. It is money wasted.

Chemical remedial dry-rot and wetrot treatments are always avoidable, but 'woodworm' treatments are not.

It is fair to say that in some circumstances chemical treatments are the best approach. Take the example of a built-in bearing end of an oak beam in an external wall of an old cottage or mansion house. Over the years, dampness in the wall has soaked into the wood and caused the beam, including the heartwood, to partially decay, allowing a deathwatch beetle attack. Given the location, it is not possible to encourage drying of the bearing end by increased ventilation, so the fungal decay and therefore the deathwatch attack may continue.

Insecticide pellets or pastes inserted deep into the core of the timber would be the best option available, although even this would not be 100 per cent certain to eradicate the insects. That said, chemical treatments along the full length of the beam would be unnecessary, as only the damp and partially decayed parts of the wood are at risk. If specialist timber surveying techniques have established that structurally significant damage is present, the affected bit of the beam should be cut back and then resupported clear of the wall face.

Architects may think that chemical remedial companies can always be relied upon for good advice about 'woodworm'. Think again. Unfortunately, this is not always the case, as a recent condition survey of a church roof in Kent suggested. The roof comprised oak trusses, dating back 150 years or more. The sapwood of the truss components had been entirely eaten away by woodworm and deathwatch beetles, but the heartwood remained virtually unaffected and in reasonably good order, with very little fungal decay and no evidence of structural movement. It was likely that the insect damage had occurred soon after construction, or in the following decade or two, and there was no evidence of any recent or ongoing infestation. In fact, given the general absence of fungal decay, there was virtually no risk of insect damage to the oak heartwood. Nevertheless, representatives of two well-known and widely used remedial treatment firms both recommended that smoke treatments be carried out.

One even suggested that the treatment should be repeated annually for five years in order to guarantee results.

Such advice is barely credible. In reality there was very little risk of further insect damage to the wood, and the client could have wasted thousands of pounds on the treatments if he had not sought independent advice. Any self-respecting timber expert could have told the client this, but the representatives of both of the chemical treatment companies did not. One would have to seriously question their representatives' expertise.

Dry-rot and wet-rot are inextricably linked to dampness, and damage to internal decorations due to dampness is common. It is therefore important to address damp problems in buildings, and this means that an accurate assessment of the extent and source(s) of any dampness is vital in order to avoid them.

The 'surveyors' employed by chemical treatments firms commonly use electrical capacitance-type moisture meters to 'diagnose' dampness in buildings. Architects take note: these meters can be prone to false readings - they can give high readings on masonry that is bone dry, which often results in misdiagnosis, the most common of which is for rising damp. Chemical treatments for rising dampness, such as injected dampcourses, are expensive, and may well be very profitable.

In the vast majority of cases like this, it is far more likely that penetrating dampness is the cause. Even the manufacturer of a very widely used damp meter seems to be aware of possible problems with misuse and misinterpretation of readings from its meters, judging by the caveats on some websites.

In some instances, accompanying salt-tests are needed for a more reliable diagnosis, but have you ever seen a damp contractor carrying out salttests? Rarely, I would suspect.

Without question, there are respectable chemical remedial treatment contractors. But, if a damp treatment company diagnoses rising damp on one of your projects and recommends an injected dampcourse, it might be advisable to get an independent dampness assessment done, for confirmation or otherwise, by people who do not rely on profit from the sale of chemical damp treatments. Spend money to save money.

The ultimate method of damp measurement is oven-dry testing of masonry samples, in accordance with BRE guidelines. This method enables an accurate moisture profile for the building to be established, and any necessary remedial works to be recommended. In short, this is the best way of avoiding unwarranted expense. Even if dampness problems are diagnosed using oven-dry testing, chemical damp treatments are rarely the most cost-effective control method. Consideration should always be given to the use of breathable plasters, ventilated dry-lining and isolation of vulnerable timbers from damp walls, to avoid the problems caused by dampness in buildings, and as an alternative to chemical treatment.

The use of French drain details, for example, can also help control dampness while minimising costs.

If architects and other construction professionals do not wake up to the problems that relying only on 'advice' from some of those who profit from chemical treatments can bring, then they continue to risk wasting many thousands of pounds every year on completely unnecessary remedial treatments. They must recognise that membership of a chemical treatment industry body is no guarantee that they are assured of getting sound advice from contractors. Architects should always seek truly independent advice about timber decay, insect attack and dampness, from experts.

Respected independent authorities such as the Timber Research and Development Association (TRADA) agree that chemical remedial treatments for dry-rot, including irrigation of infected masonry, are by no means an absolute requirement, and that a non-chemical approach can be just as effective. It is time architects also recognised this. After all, the nonchemical approach is far cheaper.

Failure to question the common assumptions could be costly, yet many persist in sticking with what (they think) they 'know'. For years, construction professionals, such as Jeff Howell, who writes for the Sunday Telegraph, have been highlighting the problem of unnecessary treatments for woodworm, dry-rot and damp (see www. ask-jeff. co. uk). But it remains a big issue.

So, come on architects, you wouldn't buy a house solely on the basis that the estate agent, who stands to profit, said it was in good condition.

Truly independent expert advice is a far better prospect. Such advice could well save thousands of pounds, and avoid even more money being wasted on chemical remedial treatments for refurbishment/redevelopment projects in the UK.

Nick Clifford is a former TRADA technical consultant and buildings investigator, and is managing director of Checkwood Environmental Solutions. For further information, email info@checkwood. co. uk or telephone 020 8393 7997

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