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Raising the Roof - The myth of woodworm?

The programme 'Raising the Roof' (BBC2 Thursday, 10th February) was, or appeared to be based around a 'fact' that woodworm was rare in buildings. Indeed, Paul Kenyon is quoted as saying, "Woodworm really only exists in timber in the forest. It's very rare in houses", notwithstanding the fact they found plenty of damage during the programme. David Pinniger, an entomologist, also appearing on the programme, clearly stated, "It is very rare in domestic housing now - because of the introduction of central heating means the conditions in ordinary houses are not suitable for woodworm."

So what is fact and what is fiction especially in relation to the programme?


To evaluate 'woodworm' activity (for our purpose common furniture beetle) it is perhaps best to evaluate the programme.


The Surveys:

Well, with a little exception one can only say that if a report card was to be written in relation to the surveys(?) and professionalism shown, it must read "Must do considerably better!"

There is no doubt whatsoever that the BBC had a case in the message they were trying to get across to the public in relation to woodworm surveys and subsequent recommendations. It appeared likely that the specialist surveyors were competent in knowledge, but it also appeared that as it was only a 'woodworm survey' they went directly into 'sales mode'.

The "Saleman" is a criticism that has been repeated against the remedial treatment industry in the press. Unfortunately, in general, the industry as represented on the TV lived up to that criticism.


The experts:

Dr. Singh :

SinghThe first piece of timber he removed from wall was almost certainly weevil damage, not Weevil?woodworm (common furniture beetle).

It is very difficult to find common furniture beetle larvae in wood especially by taking only a very small sample of what was clearly well attacked wood (it may have taken many years to get to this state). Looking for larvae in a property in that manner is certainly not definitive and is highly unlikely to be productive. One cannot make a definitive statement on insect activity from such a process.

There has been feedback to indicate that there was very likely activity within the cellar of the property; frass was reported on cobwebs and holes were noted to be clean. In probability this does indicate activity which was not surprising given the conditions within the cellar. The floor boards, however, were probably a different matter: the holes appeared old with paint (?) in some. Three cheers, however, for the surveyor that suggested the 'paper over surface test'; this is precisely what the BBC expert should have done - it is the most definitive test for activity.

Dr. Singh is recorded as stating, "Just dry it out and warm it up and it will go away". Wrong! How do you dry a house that is already dry (i.e., in equilibrium moisture content with the environment), and how would you warm it up - the house is naturally warm and dry in the spring, summer and autumn when internal conditions will be much more closely related to the external environmental conditions, i.e., around 7 months of the year. But I suppose he means central heating - more of that later.

Finally, the expert could not smell anything in the roof after the alleged treatment. As a timber treatment expert it is rather surprising that he is not aware of the effectively odourless micro-emulsions. So you can't rely on smell! Furthermore, did they use a suitable method sensitive enough to find the appropriate preservative? We just hope they didn't look for lindane in these new wood preservatives!


David Pinniger:

This was the other expert used in the BBC documentary, and shown in the New Forest.

He clearly stated, "It is very rare in domestic housing now - because of the introduction of central heating means the conditions in ordinary houses are not suitable for woodworm. Many old houses were attacked in the past before central heating". Paul Kenyon replied, "So it's very rare in houses because of central heating".

So what about central heating? Does it play a part? Well, let's look at some facts and data about dynamics of moisture in buildings and timbers.

rhwoodThe moisture content of air-dried wood follows the surrounding relative humidity - the higher the relative humidity the greater the equilibrium moisture content of the wood. In winter the relative humidity is lower than in summer when figures frequently in excess of 65% are obtained. The central heating clearly plays no part in affecting the equilibrium eqilibrium moisture contentmoisture content of wood when it is not in use, i.e., around April to October. This is the period when relative humidities are naturally at their highest and when common furniture beetle lays its eggs. And, of course, central heating will have no effect on roofing timbers, subfloor timbers, cellars and timbers in, say, under stair cupboards isolated against external walls. Central heating may, however, maintain drier timbers at first floor level but only during the winter months when it is in use.

Thus any well ventilated roof space or subfloor area is likely to be subject to the same conditions in a centrally heated house as one with no central heating. In fact there is a lot of evidence, both theoretical and practical, that central-heating may improve conditions for wood boring insect activity in some parts of the building. Why? Usually roofs become better insulated at the same time as central heating may have been installed; this means they remain colder during the winter. Warm moisture laden air rises into the roof from the house, cools and the relative humidity increases, sometimes dramatically, as will the equilibrium moisture content of roofing timbers.

So in roofs and other areas such as sub-floor spaces, central heating is not a major governing factor for control of environmental conditions which would control or prevent woodworm activity.

Where then does this expert get his evidence for his statements? Well, it appears to be taken from Building Research Establishment publications. They undertook surveys into the incidence of common furniture beetle activity in 1963; they repeated the exercise 30 years later. They found that activity had dropped by around 50% during that time. This, they reported, was most probably due to the use of central heating and improved ventilation.

The problem is that the logic and practice are flawed. Frequently central heating is coupled with decreased ventilation; hence the problems of condensation which develop in upgraded buildings. Why? with the advent of central heating comes closed fires, draught exclusion, better insulation.

Central heating will have no effect in roofs/subfloor timbers, etc, as described above, and central heating is not in use for the major part of the year! Indeed, figures and data being obtained at present as part of a long-term project clearly show some very high timber moisture contents in centrally heated houses during the winter; this is for the reasons described above. It also shows insect activity in some relatively dry wood (less than 12%). This data will be published around the end of April/May.

So, if old houses were, "attacked in the past before central-heating" why should the central heating change anything? Common furniture beetle lays its eggs when there is no central heating active, i.e., June to August, and central heating will either not affect or even exacerbate dampness within a roof, and will not affect subfloor timbers, etc.

It is clear that the two experts maybe getting drawn along on a hypothesis which doesn't stand up to objective scrutiny. Indeed, in the south-west of England, as far as can be determined, there is the suggestion that common furniture beetle activity may be on the increase!

In a paper David Pinniger also reports that infestations in buildings probably reached their peak in the late 50's and early 60's, this probably being due to poor quality timber used after the war. Yet it is this period that central heating was being installed in properties. Why then should the infestations have even developed in these properties? Perhaps the apparent decline in common furniture beetle activity in houses examined between Building Research Establishment surveys has been the result of spraying timber preservatives for 30 years. (Subsequent to the middle to late 1960s pretreated timber was being introduced. It is also possible that 'wild' common furniture beetle stocks have declined due to increased woodland hygiene i.e., dead wood being quickly removed from forests and woodlands).

Oh yes, just one final point. It is a pity that the expert didn't tell Paul Kenyon searching the New Forest that he wouldn't find common furniture beetle in living trees!



The specialist surveys:

Most, but not all, appeared to want to sell something rather than undertake a professional inspection for woodborers and woodborer activity.

The performance of these surveyors will only strengthen the position of those activists in the press, etc, who appear to have an agenda against the remedial treatment industry.

Overall - not good, and likely to cause problems for many in the longer term.


The Experts:

It was clear from the programme that the basis of their argument was that if central heating was present then all woodworm must be dead. In practice the evidence is not there to support this theory, especially considering the dynamics of moisture in buildings.

So, at the other extreme the experts were wrong, at least in part, themselves: it was their flawed information that was also in part the basis of the programme.

Oh yes, the 'woodworm' in the damp block was almost certainly weevil!

One must seriously respectfully suggest that the experts actually study the dynamics of moisture in buildings and visit properties to examine what is really going on, especially in roofs and subfloor areas. The overall evidence is not what was suggested in the programme.

And central heating? It will have little if any effect during spring, summer and autumn, and would not affect significantly conditions in roof spaces and subfloor areas at any time; it may even make conditions worse in roofs. Common furniture beetle is common in buildings AND still active in many old properties - centrally heated or not. The experts' statements in relation to central heating may seriously mislead the general public over this perception of woodborer activity.


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