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Stephen Boniface - Stephen Boniface specialises in building conservation providing multi-disciplinary consulting services. He is Chairman of the Building Surveying Faculty and member of the Residential faculty. He serves on the RICS Building Conservation Forum Board and is the 'Agony Uncle' on the Period Property UK website (

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In response to the huge number of questions on damp and alleged timber infestation Period Property UK has taken the unique initiative of providing answers to three damp and timber treatment questions. The questions are answered by Stephen Boniface a leading conservation surveyor and the BWPDA who represent many of the companies providing damp and timber treatment surveys in the UK today. A brief overview of both parties are show below.

If you wish to discuss or debate the issues raised please use the discussion forum or email your thoughts to us on the feedback page.

Stephen Boniface: Period Property UK agony uncle expert.

  • Chairman of the RICS Building Conservation Forum 2001 -
  • Surveyor to the Georgian Group 1992 -1995 & 1997 - 1998
  • Chairman of the RICS Working Party on the affect of the Mortgage Valuations process on historic buildings 1995 - present
  • Full member of the Institute of Historic Building Conservation (IHBC) 1998

Stephen Boniface says 'these questions all raise important issues, but without inspecting the properties only general advice can be given. Wherever timber or damp problems are suspected there should be an inspection undertaken by an independent professional who understands historic buildings and how they function and does not have a vested financial interest in the outcome of any advice given. This means that you will probably have to pay for the inspection and independent advice'

All the views expressed in answering the questions are Stephen Boniface's personal and professional opinions and may not necessarily be the views of the RICS. Stephen Boniface can be contacted on 01279 421 500.


The British Wood Preserving and Damp-proofing Association is the largest association of its kind in Europe. The BWPDA has, over the past 71 years, set the standards for timber treatment and damp-proofing companies operating in the UK and overseas. Becoming a member of the Association requires much more than basic ability. All contractors must not only satisfy stringent tests on their skills, methodology and knowledge of safety and environmental legislation, but also on their financial soundness. Members include manufacturers and distributors of preservatives and damp control products, flame retardants and timber treatment plants; producers and users of treated timber and specialists in remedial timber treatment and damp proofing. They work to an OFT-approved Code of Practice and must regularly demonstrate that these standards are being maintained. The association operates an Arbitration Scheme in the event of a complaint arising. The BWPDA can be contacted via their website on


o All ready treated for damp but a new survey indicates a complete new chemical dpc is required? Kevin Thornton (West Midlands)
o Does the Electro Osmosis system work and should I have my internal walls tanked? Philip Hunter (Essex)
o Survey indicates wordworm infestation & wet rot - what are the effective remedies for these problems? John Aitken (Strathclyde)

SUBJECT: All ready treated for damp but a new survey indicates a complete new chemical dpc is required?
FROM: Kevin Thornton (Wolverhampton, West Midlands)
I am currently considering the purchase of a late 1890's Victorian End Terrace House. It is in need of considerable modernisation even though it has been used as Bedsits/Flats for about 30 years. A recent damp and timber survey indicated that a complete chemical injection damp course was needed even though the current owner assures us (and has a warranty) that this has already been done except to an internal party wall and the rear wall of the property. These are the only areas where visible signs of rising damp can be found. My questions are:

  1. Do I just have the obvious areas treated i.e. the party wall and the rear of the property?
  2. Should I have the whole house treated again to be on the safe side?
  3. Will having the treatment again cause other problems?

Also, I have been quoted a price of £2000 for the treatment including plastering, as well as some wood boring beetle protection. Is this a reasonable quote?

Kevin Thornton

Stephen Boniface : Period Property Agony Uncle Answer

If the property has been treated in the past and there is still a problem one has to question whether the causes of dampness have ever been properly and fully assessed? Too often treatment companies rely solely on a hand-held moisture meter to tell them whether there is a damp problem. This indicates a total lack of understanding of how the meter works and what it can and can not tell us. In timber it can give a reading that indicates the likely levels of moisture content, but even then it is not an absolute reading. I have obtained 100% readings and yet there is clearly still timber - it has not totally turned to water! Further, the meters are far less accurate when used in wall plaster, etc. They can only give an indication of the possibility of dampness. For accurate damp levels one has to take core samples from the wall and test them. How many of the treatment companies have offered to undertake such work? How many have undertaken tests for the presence of hygroscopic salts? How many have identified the nature of the plaster? How many have investigated ALL possible sources of moisture (including internal condensation)?

In some late Victorian houses the construction did rely on the presence of a physical damp proof course to give some protection to the ground floor timbers from dampness, because the floors were set low in relation to ground levels and sometimes the sub-floor ventilation was poor. If further investigation reveals that an effective damp proof course is necessary to protect ground floor timbers, etc from dampness and the original dpc has failed you might have reason to consider the insertion of a new dpc. Ideally this should be a new physical dpc cut into the wall, but a chemical dpc is often a cheaper quick alternative, provided appropriate plastering is included (as the chemical dpc is not always 100% effective by itself). That said, I would only advise the insertion of a dpc if there is clearly evidence that one is necessary and that what exists has failed. Only further investigation will reveal this.

There are many possible causes of damp in a building that can come from above (e.g. rain, snow, leaking gutters, leaks around windows or doors, leaking downpipes, defective pointing), from below (e.g. ground water, high ground levels, blocked gullies), and from inside (e.g. condensation - from washing, cooking, breathing, etc -, pipe leaks). All damp problems are exacerbated by a lack of ventilation or where moisture is able to become trapped within a building or the fabric itself. As mentioned in other answers, the beetle infestation is probably allied to the damp problem. Deal with one and the other will be dealt with. Nevertheless, you may have to undertake localised treatment and/or repair of timbers. Only by accurate assessment of precisely what is happening will the problem finally be treated without worrying about the possibility of returning to this matter again in a few years.

BWPDA answer

1. If the owners have a guarantee relating to the walls where there is no sign of rising damp that should be sufficient assurance. The owner should have disclosed the fact of an existing guarantee to the damp and timber surveyor before the survey was carried out. If the fact was disclosed, the surveyor must be able to justify his recommendation to re-treat and in any case the company that issued the guarantee should be given the opportunity to inspect their original work first.

2. Treating the whole house again to be on the safe side is probably unnecessary but a choice you have.

3. Having the treatment again shouldn't cause any problems.

It's difficult to comment on the quote without seeing what is included. However, plastering is likely to be a significant proportion of the total and if the plaster on the previously treated walls is in good condition as your question suggests, restricting work to that which is necessary will result in a price reflecting the extent of the problem. Being on the safe side comes at a price.


SUBJECT: Does the Electro Osmosis system work and should I have my internal walls tanked?
FROM: Philip Hunter (Dunmow, Essex)
I am in the process of buying a period property approx. 400 years old, I have had a survey recommending Electro osmosis damp proofing system. There was an extension put on the back of the property and this is about 12 inches higher than the front of the house and the survey also said there may be horizontal damp due to this but did not recommend tanking so as to allow the sole plates to breath. I called in specialist damp proofers who quoted for the Electro and the tanking and quoted to tank the wall. My questions are firstly is Electro osmosis any good? And secondly should I get the walls tanked?

Philip Hunter

BWPDA answer

Introducing a modern damp-proof course should only be considered if it has been demonstrated that rising damp is occurring and there is damage/disfigurement of internal decorations and/or external wall surface and/or internal structural timbers are becoming wet and so at risk from fungal decay. If the building has lasted for 400 years without a dpc then the question should be asked what has changed to cause my problem? - of course it may be modern expectations of a perfectly dry internal environment with surfaces suitable for modern decorative finishes - quite legitimate aspirations for a home owner but perhaps not what the building is capable of without intervention. The debate will no doubt go on this one. Once an informed decision has been taken, the choice of dpc is very much one for the surveyor and homeowner. The electro osmosis system does not hold an Agrément certificate of performance unlike many liquid or slurry injection systems and the more recent 'cream' formulation but it has been used successfully for many years and like any system must be installed and maintained in accordance with manufacturer's specifications. On tanking, the only purpose it seems in this case would be to protect sole plates (in the original building presumably) due to poor installation of the extension - poor because that should have been taken into account in the design of the extension. If the sole plates are becoming wet something needs to be done to protect them - if not leave well alone. Sole plates if original will probably be naturally durable but even in such cases long-term wetting up above previously sustained moisture levels will place them at risk of decay.

Stephen Boniface : Period Property Agony Uncle Answer

I have yet to see a property where this has been used effectively and have never recommended it. If the damp proofing system proposed is so effective why do they want to tank the walls internally? The first question to ask is why are the walls damp? In the properties I inspect of this age the ground levels have usually increased over the centuries and the bases of the walls been covered, usually with impervious modern render finishes. Sometimes the ground floors are also finished with impervious modern concrete. The result is dampness trapped in the walls. The best solution is surely to ensure that any trapped dampness is released, rather than sealing it in with tanking? If the building has functioned for most of the past 400 years without a damp proof course, why does it suddenly need one now? Address the basic problems and get the bases of the walls functioning properly and it is unlikely that you will need to have any specialist treatment undertaken. In any event, what evidence of a problem is there? If plaster is crumbling and timbers rotting there is need for some work, following careful assessment of precisely what is wrong. However, if there are no visible defects one has to question the validity of the assessment of 'rising damp' that has led to the recommended specialist treatment. In most buildings I inspect of this age, where modern renders and finishes have been applied, where ground levels are high and where concrete floors installed, there are problems of trapped moisture (even if not visible or manifest in terms of damage). However, I have successfully dealt with such matters by carefully considered building works rather than resorting to quick-fix systems that do not address the basic problems.


SUBJECT: Survey indicates wordworm infestation & wet rot - what are the effective remedies for these problems?
FROM: John Aitken (Cambridge)
We have been looking at buying an "upper quarter villa" (1902) and have been advised that there is woodworm infestation in the roof timbers and damp rot around a fire place in the bed room and in the floor boards of the main public room (under a bay window. There has been extensive upgrading to the property but these problems have not been addressed. Can I ask if there are any effective remedies to these problems and if work on the exterior of the property could help reduce the dampness etc?

John Aitken

BWPDA answer

If a live woodworm infestation in the roof timbers has been identified you have two choices:

  1. Assuming risk of structural collapse has not been suggested, do nothing in the expectation that the quality of timber in the roof will be such that perhaps attack is limited to sapwood portions of the cross sections and providing you can live with a few beetles every summer and are not storing valuable wooden items which might be damaged or even destroyed in time in the loft. Such a course of action is a legitimate choice for the homeowner, depends on an understanding of the biology of the insect in question and the owner's willingness to ignore the infestation based on an informed choice. The downside of going this route is that when the property is being sold the discovery of a live beetle infestation in the roof is likely to cause the buyer to ask awkward questions and either lose interest or probably seek a reduction in the price. Don't be taken in by recent suggestions that keeping the roof dry will cause beetle infestations to die out naturally - investigations, observations and experience shows that idea to be in the wishful thinking category.
  2. Have the roof timbers treated in accordance with a specification drawn up by an experienced and/or qualified (CSRT) remedial surveyor who understands his obligations under the COSHH Regulations and the appropriate treatment protocols. Woodworm treatments have been required to be approved under the Control of Pesticides Regulations since 1986 and those legally on the market can be assumed to offer safe and effective long-term protection for treated timbers when applied in accordance with manufacturers' instructions. Modern formulations include the high-tech microemulsion systems that are very low odour and treated areas may be safe to re-enter within as short a time as one hour. Treatment will normally result in a guarantee for up to 30 years, which should be kept with the deeds or house file or logbook. In addition, BWPDA members can offer their clients' protection for the guarantee from Guarantee Protection Insurance should the contractor go out of business during the guarantee's life.

Damp rot around a fire place in the bed room indicate either penetrating damp via a faulty chimney (requiring an inspection and decision on correcting the problem based on reason for damp build up) or internal condensation if chimneys have been blocked up without adequate ventilation. For the floor boards of the main public room (under a bay window) a careful inspection is needed to identify the cause of the dampness which in such cases may equally be, penetrating damp (in properties of this age a solid brick wall is likely and under bay windows it may be a single skin) due to failure of the drip beneath the outer sill, deteriorating pointing especially if facing prevailing weather, faulty rainwater goods etc, or rising damp (is there an original dpc? - the age of the building indicates there might not be one) both possibly aggravated by condensation. All of which can be put right provided the diagnosis is correct - use a qualified surveyor.

Stephen Boniface : Period Property Agony Uncle Answer.

The first question to ask is whether the infestations identified are active or historic? Let us assume that there is an active problem. The woodworm is probably continuing because of a suitable environment, including perhaps some dampness. Ensure the roof is well ventilated and that any sources of damp (i.e. leaks, etc) have been dealt with. Localised targeted treatment of the affected areas might be appropriate to ensure that the infestation does not spread whilst the environment is gradually changed to one that does not support such an attack. This principal applies to most infestation attacks.

As a general rule, beetle infestations are rarely sustained in a well-ventilated dry atmosphere. Rot is not dissimilar in many ways, in that a well-ventilated dry atmosphere would not normally sustain a rot outbreak. The rot around a fireplace suggests that the original source of damp was the chimney. Ensure that there is no continuing damp problem before any other work is undertaken. If timbers have been weakened by the rot they need to be replaced, strengthened or repaired. However, since the 1950s it has been recognised that it is not necessary to cut out surrounding sound timber (a common practice even though not supported by research and observation of cases in situ). Rot will only thrive if the conditions are appropriate. It will not usually spread far beyond the source of moisture. Rot is a generic term for fungal growths that require nutrients from timber to grow and survive. However, like their cousins (mushrooms) they die if the conditions are not conducive. Generally they require a dark, humid damp atmosphere. Remove the conditions and the fungal growth dies.

Regarding the rot by the window, it is likely that the window/window sill was allowing water penetration and that this was the source of moisture that sustained the rot outbreak. The first rule of any rot treatment is to identify the source of moisture and deal with it. Otherwise no amount of treatment or other work will be effective. If the area in question is likely to take time to dry out or may remain damp the timbers and surfaces nearby may require localised chemical applications to help reduce the vulnerability to the rot continuing. Timbers in contact with damp surfaces should be isolated from them with a suitable membrane. Voids that are prone to dampness should be well ventilated. Finally, any work to the exterior that ensures the property is well maintained and that unnecessary water ingress does not occur is a good thing. However, it is not appropriate to use modern impermeable finishes, etc to try to totally exclude moisture in a building such as this. The reason, quite simply, is that such methods usually only result in moisture becoming trapped, thus perpetuating the problem. The building should function traditionally and should be allowed to breathe.