When to Specify Woodworm Treatment

Was woodworm treatment necessary?

timber decay

A screwdriver is useful for assessing timber decay but appears to be the diagnostic tool of choice for this particular damp proofing company.

I was recently asked to review a report, supplied by a large National damp proofing company, on behalf of a client, who spent thousands of pounds on unnecessary treatment, including timber preservatives. I say ‘unnecessary’ but perhaps it would be more correct to say that the woodworm treatment wasn’t proven as being necessary.

Perhaps it might be first useful to explain what woodworm are…

Woodworm

Woodworm is a collective term, which is used to describe all classifications of wood-boring insects.

Wood-boring insects use wood as a source of food, and in the UK at least, mainly consist of beetles.

Furniture Beetle, Woodworm

Furniture Beetle (Anobium Punctatum)
(Source: https://www.naturespot.org.uk/species/common-furniture-beetle)

The most common type of wood boring insect in the UK is the ‘Furniture Beetle’, or ‘Anobium Punctatum’ to give its latin name. It is brown, usually about 3-4 mm in length and has a prothorax that resembles a monk’s cowl.  Whilst less common in the UK, timber can also be infested by the much larger Death Watch beetle (Xestobium Rufovillosum) (which is considerably larger at 7- 8mm long), the House Longhorn and the Powder Post beetles. In all species there is a grub like larvae stage, lasting several years, whereby the larvae bores around under the surface of the wood. This is where the most damage occurs.

Note insect flight exit holes in timber

Note insect flight exit holes in timber

A furniture beetle’s Life cycle

The infestation process starts when the female beetle lays its eggs directly into the timber through cracks, crevices or even existing flight holes. The eggs are oval in shape and laid in batches of between 20-60. After about 5 weeks, the eggs hatch and the larvae (woodworm) tunnel down into the wood and spend the next 1- 5 years digging their way around munching through the timber until the next stage in its life cycle. It is in this stage that the greatest structural damage to the wood takes place, and this damage goes unseen due to its location within the timber. The larvae then carve out a ‘pupal’ chamber near the surface of the wood in which the larvae ‘pupates’ into a beetle over a 6-week period. The fully formed beetle then burrows its way to the surface and out, leaving a circular ‘flight hole’ about 1-2mm (roughly the size a dart would make in a dart board). This is the final stage of the beetle’s life cycle, with the females living for around 14 days, and the males only 4 days.

Wood boring beetles thrive in damp conditions; indeed many living trees can have beetle infestation. Species such as the furniture beetle prefer the softer ‘sap’ wood from which they feed off the cellulose, whereas the larger Death Watch beetle is especially fond of hard woods such as oak and beech. It is worth pointing out that the ‘heart wood’ of say, a piece of oak, is usually left untouched by beetles and just the outer sap wood is subject to beetle attack.

Signs of beetle attack

Again, the screwdriver is used in support of woodworm treatment with insecticide.

Again, the screwdriver is used in support of woodworm treatment with insecticide.

Apart from the obvious flight holes left by the beetles, a powdery dust called ‘frass’ can often be seen on floorboards and other wooden surfaces. Frass is the excreted wood that the larvae produce.

In old historic timber framed buildings, especially thatched cottages, there may be signs of beetle attack, evidenced by frass on the face of the timbers, in a honeycomb pattern. If the wood has clearly suffered beetle attack, there is a need to determine whether the timber still has structural integrity. The frass must be scraped off and the heart wood of the timber examined. It is very rare for a beetle attack to penetrate deeply into the heartwood of a piece of oak, so its structural integrity usually remains.

Old bore holes or new?

To establish whether beetles are still present in timber, where there is evidence of frassing, is quite straightforward. Once the frass has been scraped off, a piece of tissue paper can be stuck over several suspected areas of wood and sealed round all edges with a water soluble glue, and left from April to August (this is the flight stage in the lifecycle). On inspection, there may be larvae and beetles trapped or flight holes puncturing the tissue paper. All of these point to an active infestation. Also, checking spider webs in old timber framed buildings to see what’s entrapped can help to establish the types of insects that are present. You should also recognise, that many timbers were installed with insect flight exit holes, because wood boring insects also attack trees as well as cut timber. The majority of flight holes observed on timber from historic buildings are often at least 100 years old. This is because the infestation took place within the living tree before it was even felled, due to the moist conditions present in nature. Needless to say, whether the bore holes are old or new, forms a critical deciding factor in whether or not woodworm treatment is required.

Case Study

In august 2017, the property in question was subjected to a damp and timber survey, by a large national damp proofing company. The client knew they’d be expensive but wanted the assurance of dealing with a ‘brand’ name.

Damp & Timber treatments specified costing over £22,000

Damp & Timber treatments specified costing over £22,000

In total, this company specified over £22,000.00 worth of work, which included over £3000.00 for treatment of wood boring insects and timber decay. Post completion of the work, another surveyor attended the property and informed my clients that he was of the opinion that this work wasn’t necessary, and that my clients had been mis-sold these treatments. Obviously alarmed, they asked me to carry out a review of this companies survey report and survey methodology.

The Survey

There were many issues, both with their investigation for rising damp, and their assessment of timber decay, but for the purposes of this blog, we’ll remain focussed on their assessment of wood boring insects and the treatment specified.

The surveyor repeatedly made claims in his  report that there were, “current attacks by wood boring insects,” and of course used the word ‘current’ to justify his specification for timber preservative treatment.

In fact, no evidence whatsoever was presented proving a current attack, failing to even take or record timber moisture contents; a significant omission. BRE Good Repair guide 13, highlights the following as indicators of live infestation:

Indicators of insect activity are:

  • Freshly cut exit holes and recently ejected bore dust (frass), although dust may have been shaken from timbers by foot traffic.
  • Insect larvae extracted by probing the tunneled timber. In practice the larvae are difficult to find.Identification of the insect causing the damage is important, not only in deciding if any wood preservative treatment is necessary, but also in deciding if any other action is required.

From the flowchart below, it could be seen that the company concerned failed to demonstrate or prove that insect infestation was active, and therefore failed to reasonably comply with this guidance. If no live infestation was present, then the next step is to assess whether timbers contain more than 20% sapwood; if the answer is no, then no treatment is required.

BRE Good repair guide 13

Flowchart taken from BRE Good Repair Guide 13.

Further guidance is given in BRE Digest 307, which states that; ‘The presence of damage by wood boring insects does not always indicate a need for remedial treatment.’  The common types of damage found in building timbers have been divided into three categories:

BRE Digest 307

Taken from BRE Digest 307

Again, the table above highlights the importance of identifying the species before deciding on treatment measures, and throughout the report, wood boring insects were only discussed in general terms, with no identification being made. What we know unequivocally, that no proof. whatsoever was provided to demonstrate this timber treatment was necessary.

As discussed earlier, the client was charged over £3000.00 for timber preservative treatments, the insecticide, being a Permethrin based product. If you want to understand the mark up on these products, 5 litres of Permethrin based product, can be obtained from a brand name company, for around £9.00; enough to cover around 15-20 square meters of timber.

How we deal with woodworm organically

It is vitally important to get to the root cause of the woodworm issue so that a long-term solution can be implemented. Since the woodworm larvae thrive in damp timber, it makes sense to identify and remedy the cause of that damp, and by doing so the infestation will cease, and more importantly, not come back.

Generally speaking. woodworm like their meals with a little ‘gravy’ so you should focus on the root cause of the damp in timber and we would generally look to treat this issue in the following simple manner…

  1. Eliminate the source of moisture and introduce rapid drying
  2. Assess the severity and depth of timber infestation and damage
  3. Replace any structurally unsound timber
  4. If required improve ventilation to the affected area

It is a treatment plan almost identical to what we’d specify to deal with an outbreak of fungal decay such as dry rot.

It is a sad fact that the damp proofing industry has enjoyed great success by unnecessarily recommending that damp timber infested by woodworm is covered with litres of toxic chemicals. The main issue with this method is that it does not address the primary reason as to why the timber is infested in the first place, Since the timber is still damp after being treated with chemicals, there is a likelihood of re-infestation occurring.

Furthermore, these toxic chemicals can cause environmental damage and might even require a licence if being used in close proximity to any protected species. Thankfully though, the inadequacy of this practice is now becoming better understood and is well documented in BS7913: 2013 “Guide to the conservation of historic buildings”. It also identifies that chemical treatment does not actually penetrate deep into the timber, but only just under the surface and therefore any larvae, which are active inside, won’t necessarily be affected.

Is this what passes for a survey and damp proofing report?

How damp proofers sell unnecessary DPC injection work. 

Typical of the Reports used by the damp proofing industry to sell unnecessary retrofit DPC injection work and re-plastering.

Fig 1. Typical of the Reports used by the damp proofing industry to sell unnecessary retrofit DPC injection work and re-plastering.

We’ve had to do one inspection this week and one detailed survey relating to production of a Part 35 compliant expert witness report; in both cases this involved checking a survey Damp proofing report that were recently provided by an East Midlands damp proofing company, Preserva. Our last involvement with this company was when we were called to re-survey a property in Nottingham after the same company had diagnosed rising damp and hacked off all the low level plasterwork from the clients walls up to waist height. It was at this point the client got suspicious and called us in. What we found was that this company had done no diagnostic work to prove that rising damp was present, they further stated that a damp proof course comprised of blue engineering bricks had failed and failed to point out where the damp proof course was bridged by soil banked against the wall. We did the diagnostic work and in fact proved that the property did not have rising damp, or indeed any significant moisture present at depth in the masonry. The property was suffering from chronic condensation damp and we specified works to deal with this issue. Preserva reinstated the plasterwork at their own expense and my client saved circa £2500 by not having unnecessary remedial treatment carried out for rising damp.

Qualifications

We’ve said this before but if you invite a CSRT ‘qualified surveyor’ into your home then you invite a chemical  salesman into your home. It took me many years to get letters after my name, whereas the CSRT (Certificated Surveyor in Remedial Treatment) can be achieved in three days with no previous experience of buildings or surveying, but apparently after three days they are now experts in damp.

It would appear that nothing has changed because again we reviewed two recently completed reports that fail to prove the cause of damp and make incredibly tenuous claims that rising damp is present. Lets analyse the first one…

Despite damp proofers specifying remedial work for rising damp, there was no significant moisture present at depth.

Despite damp proofers specifying remedial work for rising damp, there was no significant moisture present at depth.

In fact the 8 page ‘report’ is fairly standard generic text with a few comments inserted to vaguely satisfy the unsuspecting public that they have diagnosed rising damp; though they stop short of ever saying this, which is a feature we’ve found in all their reports, that we’ve reviewed. In this report their CSRT ‘qualified’ surveyor makes the following statement… “At the time of our inspection visible signs of dampness, supported by moisture profile readings obtained using an electronic moisture meter, indicated the presence of dampness to all accessible ground floor walls. This is apparently due to salt contaminated plasterwork and an apparent possible breakdown of any existing damp proof course.”

Never has the word apparent been more incorrectly used because quite clearly it wasn’t apparent since no diagnostic work had been done. The ‘surveyor’ had not carried out salts analysis to prove that salts were present in the plasterwork and in fact there was no salt migration visible on inspection of the plasterwork. Additionally, he had not carried out testing to prove that moisture was present at depth in the masonry; this is a pre-requirement before even suggesting that the existing damp proof course has failed.

Incidentally, damp proof courses do not fail, please read this… http://buildingdefectanalysis.co.uk/conservation/do-physical-damp-proof-courses-fail/

He briefly discusses moisture profiles despite the fact that you cannot obtain any useful moisture profiles using an electronic moisture meter and further fails to even mention what that moisture profile is! Is it a rising damp moisture profile, a reverse rising damp moisture profile or just a random profile? We’ll never know but since he specified unnecessary remedial work for rising damp then I think we can assume it was a rising damp moisture profile. Critically, since it was only a relative reading then the results are unreliable and more importantly they are only moisture profiles at the wall surface. Even scan meters can not provide useful or reliable moisture profiles at depth in the masonry, and this is what we are fundamentally concerned with when investigating the potential for rising damp. The unnecessary work quoted for as a result of this report would have cost the client £2996.00 plus vat and to add insult to injury they were expected to pay £75.00 for an insurance backed guarantee if they wanted optional long term protection on this unnecessary work.

Second Review

Our second review concerns a property in Derbyshire that was surveyed by Preserva in December 2015. Their observations are limited to the following internal observations, ” Chimneys were open encouraging direct rainfall to enter the building fabric. These should be capped with a vented cowl by your builder. External brickwork was very porous and was rendered on the front and gable ends. This render was in a poor condition and it was suggested that this should be removed. The property did not appear to have been constructed with any sort of damp proof course.” 

In fact these are reasonable but limited comments and whilst it’s reasonable to comment that buildings don’t have an existing physical DPC, this was not entirely true. The rear extension in fact had a physical DPC comprising of blue engineering bricks and there were a large number of other external damp related defects that were not commented on; probably because they would not facilitate the sale of retrofit chemical injection. The main part of the building may not have a physical DPC, none was visible. However buildings can manage moisture perfectly well without a physical damp proof course and in fact there are thousands of buildings in the UK that do not have a physical damp proof course but do not have a problem with rising damp.

Internal observations were limited to the following, “Dampness was noted around all external walls of the dining room and lounge areas. Moisture profiles taken with a moisture meter confirmed that dampness was a problem within these walls. This was clearly due to the defects noted above and could also be attributed to some rising moisture from the ground also.” 

Timber moisture content of 26% means that timbers are at risk of timber decay.

Timber moisture content of 26% means that timbers are at risk of timber decay.

The operative word here is “could”… works were specified for rising damp on the basis that some dampness could be attributed to rising moisture from the ground, so again we see an assumption being made in the complete absence of any credible diagnostic results. Moreover, there were internal issues that would have been obvious to any reasonably competent surveyor, not least of which was incredibly high moisture content to the timber floor joists in the cellar. We do not know what the value of this work was but you can be sure that it was a substantial sum, we rarely see quotes of less than £2.5k for this sort of unnecessary work and frequently quotes are substantially higher. We have not yet encountered a case where the work has been required.

Also please read http://buildingdefectanalysis.co.uk/damp/diagnosing-rising-damp/

Damp Proofing is Almost Never Required! 

 

We’ll say it again… ‘Specialist treatments for damp are almost never required and the vast majority of damp can be cured with nothing more than minor and often inexpensive building works.’

You should view any report you receive from a damp proofing company with extreme scepticism.