Rising Damp in 3 Year Old Extension

This week I attended a property in London where the client was suffering from quite significant decorative spoiling, caused by rising damp above the skirting boards in the rear extension. She had only recently purchased the property and given that the rear extension was only around three years old, and works were signed off by her local building control department, understandably, she was a little worried by this.


The extension was of cavity walled construction, with a lightweight concrete block inner and outer leaf of masonry, and an 80mm cavity, fully filled with Rockwool batts. One initial observation showed that the sidewall of the extension was unfinished concrete blockwork, where even the mortar joints had not been pointed up. External ground levels were also significantly too high.

Exposed concrete blockwork
Exposed and highly porous concrete blocks left exposed to the elements. The wall had not even been pointed up.

Moisture Readings

Moisture readings to the hard plaster system were only slightly elevated, but high enough to warrant further testing for moisture at depth using calcium carbide.

High damp readings
Protimeter MMS2 shows slightly elevated readings above the 20% trigger point, where testing for moisture at depth is required.

We carried out testing for moisture at depth using calcium carbide and found a very high reading of over 20% total moisture content at wall base, and 12% at the next highest level. A rising damp moisture profile, showing that moisture is being sourced from the ground. Of course, you have to contextualise these readings in light of the material being tested, and these highly porous concrete blocks will soak up moisture very quickly. Had these been brick walls, then moisture readings would have been significantly reduced.

Calcium carbide testing
Saturated concrete block walls with rising damp moisture profile

How could rising damp affect relatively new construction?

Since we know that ‘Part C’ (Resistance to Moisture) of the building regulations requires the damp proof membrane (DPM) in the floor to form a continuous barrier with the damp proof course (DPC) in the wall, then clearly, if those guideline had been followed, then the property would not be suffering from rising damp. Invasive work was now required to locate the damp proof course in the wall, to firstly ascertain if a DPC was present, and if so, was it linked to the DPM in the floor, and was it possibly bridged?

We started to remove plaster from the wall base and thankfully, located the DPC in the wall, which proved to be bridged by the internal plasterwork. This also showed that the floor DPM was not linked to the DPC, a clear breach of building regulation requirements.

Bridged damp proof course
Bridged damp proof course not linked to DPM in floor.

Bridged Wall Cavity?

External observations showed high ground levels and with the render extended down to ground floor level, then clearly any DPC present in the outer leaf of masonry had to be bridged.

Bridged DPC
External render will bridge the physical DPC

This issue should not present a significant issue with regards to moisture transferring to the inner leaf of masonry, so long as the wall cavity is clear of debris, since the cavity will form a ‘moisture break.’

However, with the high moisture content recorded to the inner leaf of masonry, we suspected there was a problem with the cavity and opened the cavity up for inspection. As suspected, we found significant amounts of debris, bridging the cavity at wall base. The debris serves to transfer moisture across from the outer leaf of masonry, to the inner leaf of masonry.

Debris in wall cavity
Debris in wall cavity

Incidentally, the wall cavity was inspected with a borescope, but full fill insulation prevented a proper view of the wall cavity, which is why I decided to open up the cavity at the door reveal base.

Should we call in the damp proofers?

Had the client called in the damp proofers, it is almost certain that they would have diagnosed rising damp, using a hand held electronic moisture meter, recommended that the walls be injected with a retrofit damp proof course, and re-plastered the internal walls with a waterproof tanking plaster or render. The water proof tanking, may have provided a dry wall surface for a while, but would no doubt have failed in the not too distant future, since the underlying problem had not been addressed.

It will be almost impossible to remedy the lack of bond or connection between the DPM in the floor and the DPC in the wall but addressing the issues that can be easily dealt with should remedy this problem. Key actions to address this problem will include:

  1. Remove the skirting boards and remove all plaster from the internal wall base to fully expose, and un-bridge the physical damp proof course.
  2. Opening up the wall cavity to remove all debris, which is transferring moisture from the outer leaf of masonry to the inner leaf of masonry.
  3. Ideally, reduce external finished floor levels, so that they are a minimum of 150mm below internal finished floor levels.
  4. Remove external render from the wall base, ensuring that the render is a minimum of 150mm clear of external finished floor levels.

None of this is specialist work, and can be carried out by any reasonably competent builder., as is often the case when it comes to remediation work for damp.

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Magnesite Floor Failure

Property In London W7, with Magnesite Floor Failure
Property In London W7, with Magnesite Floor Failure

I’ve recently just completed a long Roadshow for the RICS, ironically, I was giving a talk on solid floor defects, and included a section on Magnesite floor failure, as a refresher. In the last talk I gave, I asked an audience of about 70 Chartered surveyors, how many had seen a magnesite floor recently; the answer was none. I myself have not seen for for quite a few years but only a week later, I attended a property in London to investigate an alleged problem with sulphate attack, and guess what I found?…

What is Magnesite Flooring?

Magnesite, or Magnesium Oxychloride, was a product widely used by the flooring industry between circa 1920 and 1960. It was especially used in industrial premises, as it was resistant to oil spillages; however, it was frequently used in residential premises.

It is a water based product, commonly reddish pink in colour, though can be pale yellow, or any other colour specified.

Magnesite Flooring
Magnesite Flooring

Magnesite flooring was made from a mixture of calcined magnesite and magnesium chloride solution with various fillers (e.g. wood flour, sawdust, asbestos).• It was typically laid between 10 and 25mm thick, but two coat applications could be up to 50mm thick. 

What’s wrong with Magnesite?

Firstly, Magnesite contains chlorides, so if there is any embedded steel reinforcement within the floor slab, then the concrete can be affected by Chloride attack, which will corrode the embedded steel. Corrosion is an expansive reaction, and cracking of the concrete is likely to occur, as the steel corrodes. You should also consider, that steel water pipes may be buried in the concrete, and these are equally at risk.

Many old concrete floors, do not have a damp proof membrane installed, DPM’s came into common use in the mid 60’s, but prior to this, many concrete floors had a waterproof oversite, a layer of bitumen was commonly used. It would be wrong to assume that Magnesite provides that same protection against damp, and in fact they are very vulnerable to dampness. Magnesite is water soluble, and will return to its previous state if exposed to enough water.

The Asbestos Risk

As discussed earlier, Magnesite can contain asbestos fibres, as a filler. Commonly, the way to deal with asbestos, once identified, is to remove it, using a licensed contractor, or to encapsulate it. However, you can’t encapsulate a Magnesite floor, as they are so vulnerable to deterioration when exposed to water. Obviously, if you tried to encapsulate by pouring a screed over the top, then you’d be introducing large amounts of construction moisture into the Magnesite. The underlying Magnesite, would then most likely turn to a Weetabix type consistency, and start to break up, leaving you with no suitable substrate support below the screed.

Magnesite Floor Case Study

In this particular property, a Chartered surveyor had recently attended, for a pre-purchase survey and noted heave, or an uneven concrete floor below the carpets; he then of course raised the alarm for a potential risk of sulphate attack.

I attended to sample the floor, but on pulling up the carpet, the cause of this uneven floor, was clearly Magnesite floor failure; the Magnesite having got saturated, subsequently expanding and causing large blisters in the floor.

It was still important to investigate the situation with the underlying concrete and I excavated a hole through the slab to sample both the concrete, and the underlying hardcore. However, on breaking through the 8″ thick concrete slab, we found that there was no hardcore, and the slab sat directly on wet clay, with no DPM installed. This of course means that the concrete is in direct contact with ground sulphates.

Concrete slab sitting directly on clay
Concrete slab sitting directly on clay

The concrete was also notably wet, and this moisture had transferred to the Magnesite, causing it to heave up, blister, and crumble. From the image below, you can see how the magnesite had delaminated from the concrete substrate, forming large blisters, which crumbled when you stepped on them.

Failed Magnesite Flooring
Failed Magnesite Flooring

We did take samples of the concrete for sulphate tests, but with a saturated slab and widespread failure of the Magnesite, my advice was to renew all the solid floors, with the only test required being for asbestos. Testing the magnesite for asbestos, was critical before any works to remove the flooring could proceed.

One final note worth mentioning for any surveyors looking to check for dampness in Magnesite. Magnesite is electrically conductive, so if using a hand held electronic moisture meter, it will always give a high reading for damp.

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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 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.

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Timber Frame Defects

Common Timber Frame Problems

Neo-Georgian with Timber Frame

Neo-Georgian with Timber Frame

We were recently called to investigate some damp and structural issues to a 12 year old timber frame Neo-Georgian 3-storey apartment block across the water from mainland UK. The building had been affected by both water ingress and a number of structural issues for quite some time and two previous technical reports had reached broad agreement of the fact that the timber frame was showing signs of distortion due to shrinkage, shrinkage commonly occurs in timber frames after construction and one engineer estimated the height of the timber frame may reduce by up to 30mm, a degree of shrinkage that wouldn’t be replicated in the outer non-structural leaf of masonry. In fact the outer masonry leaf tends to expand as it takes up moisture during the first couple of years after construction, so it is in fact moving in the opposite direction to the timber frame.

Wall Ties

It is for these reasons that timber frame movement ties are specified for developments over four storeys, as these are required to accommodate the additional vertical movement in the timber fame and differential movement between the inner and outer leaf. However, this is a 3 storey development and so long as vertical movement stays within expected limits then a standard fixed wall tie should suffice.

Standard Timber Frame Wall Ties

Standard Timber Frame Wall Ties

Timber frame movement tie

Timber frame movement tie

 Structural Cracking & Movement

Significant structural cracking

Significant structural cracking

Structural cracking to the outer masonry leaf of timber framed buildings can often occur where this differential movement between the inner and outer leaf falls outside of acceptable limits due to inherent design flaws or poor build quality.

When inspecting the building externally we noted that door and window frames were often slightly deformed and out of square, which resulted in extreme difficulty in opening the softwood timber french doors leading out onto the apartment balconies. We also noted significant stepped cracking in a number of areas to the outer leaf of masonry.

Starting from the Top

It was initially thought that defective balcony detailing and waterproofing arrangements were the cause of water ingress into the building and in fact the initial instruction was very much about investigating potential balcony defects, but of course you must approach these investigations with a blank canvas and an open mind. Whilst there were a number of relatively minor issues with balcony upstand detailing and parapet wall box gutter outlets, it was clear that these were not responsible for the water ingress or the structural defects seen.

Logically, I like to start from the top and work my way down once I start the internal inspection  and starting from the top meant inspecting the balcony that fully surrounded the building at top floor level.

Keeping the Timber Frame Dry

Open bed joints to parapet copings and no throating detail to underside

Open bed joints to parapet copings and no throating detail to underside

I found a number of serious and critical defects relating to the high level parapet walls that in my opinion have been allowing rainwater ingress into the wall cavity for a number of years, possibly since the building was constructed. Of course, if this was the case and water ingress was as bad as I believed it to be then the the greater probability is that the timber frame has swelled and expanded, rather than shrunk. The net result of course is the same, which is the potential for excessive differential movement between the inner and outer leaf. Moreover, there is a further potential for timber decay in the structural timber frame and perhaps even structural failure as timbers are affected by fungal decay.

Open perp joints between coping stones

Open perp joints between coping stones

Defects Causing Consequential Damage

Adhesive and cohesive failure of sealant to coping bed joint

Adhesive and cohesive failure of sealant to coping bed joint

We noted that the parapet wall copings were not fit for purpose and had been poorly installed off centre so the outer wall face had a 70mm overhang, whilst the inner parapet wall face only had a 30mm overhang. To meet the requirements of BS5642 then a minimum 45mm overhang was required to either side. However, more critically there was no throating detail to the underside of the parapets meaning that rainwater would flow along the underside of the coping overhang and straight into  cracks or open joints that may exist to the coping mortar bed.

Lead apron proved not to extend across the width of the cavity

Coping stone removed. Lead apron proved not to extend across the width of the cavity


Of course, this shouldn’t be a problem, because there’s bound to be a physical damp proof course installed under the copings as a secondary line of defence… or at least there should be!  We removed a parapet coping and as we suspected there was no physical DPC installed. So water was entering the wall cavity from the underside of the failed bed joint to the copings and the open joints and cracks in the coping mortar perp joints.

On finding these defects we of course had serious concerns as to what effect this long term water ingress was having on the timber frame. On checking the timber moisture content to the head of the timber frame we recorded a moisture content of 21.2%, proving the real current and ongoing risk of timber decay to the structural timber frame.

High moisture content to timber frame

High moisture content to timber frame









We recommended and specified urgent works to correctly waterproof the balcony parapets and further recommended opening up sections of the wall cavity where cracking had occurred to inspect the integrity and condition of the structural timber frame.

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The incidence of true rising damp Vs Induced rising damp

I  am often asked how common rising damp is and after being asked again today I wanted to outline my thoughts on this issue, since we have a damp proofing industry operating in the UK, which operates on the premise that rising damp is a common occurrence. In fact it is incredibly rare and a review of the academic text relating to this question led to the following academic review…

How common is rising damp?

 It’s important to examine the incidence of rising damp in order to understand the size of the problem. Oxley T A, and Gobert E G (1999, p.7,8) state that awareness of dampness has also been stimulated by the rise of a service industry of ‘specialist’ firms devoted to curing it. This is an industry largely directed towards curing rising damp. This is a competitive industry which uses a lot of publicity; it has spread quite widely the impression that rising damp is the main cause, or at least a very frequent cause of dampness in buildings. In fact rising damp is a relatively uncommon cause of dampness in buildings.

The 1991 English House Condition Survey carried out by The National House Condition Survey Group (1993, p.54) found that one fifth of the stock is reported as experiencing problems associated with damp. In almost two thirds of these dwellings the problems relate to rising or penetrating damp, in the remainder the problem is condensation.

Table 2.1 (below) further clarifies this by showing that 12.6% of damp properties are affected by rising damp.


Table 2.1 Problems with Damp                            

                                                                               Thousand dwellings (%)


Problem                                                             Number of Dwellings     %

Condensation/mould growth only                                 1560                     (39.8)

Rising damp only                                                          494                     (12.6)

Penetrating damp only                                                   780                     (19.9)

Combination of the above                                             1087                    (27.7)

Any problems                                                                 3921                   (100.0)


% of total stock                                                                                           (19.9)

Source: English House Condition Survey (1991)

Oxley T A, and Gobert E G (1999, p.1,2) state that, we have good reason to believe that only about one third of all dampness problems are due to rising damp. They further explain; in the Protimeter laboratories specimens of wallpaper and plaster are received almost daily from surveyors and local authorities for chemical analysis for the presence or absence of certain nitrate and chloride salts, which are typical by-products of rising dampness. Salts are consistently found from year to year to be present in only about one third of all specimens tested. An even lower incidence is reported by Trotman P, Sanders C, Harrison H (2004) who state that rising damp featured in 5% of the 510 occurrences during the period 1970-74; 4% of the 518 occurrences during the period 1979-82 and 5% of the 520 occurrences during the period 1987-89, an average of about one in twenty of all (damp) investigations.

Oliver A, Douglas J and Stirling S (1997, p.186) give three reasons why rising damp is not as pervasive as other forms of damp:


  1. The majority of buildings in the UK have some form of original dpc. Even bridging or lack of continuity between dpc’s/dpm’s would cause only localised rather than widespread incidences of rising damp in a building.
  2. Failures of these dpc’s would need to be severe and extensive to cause major and general manifestations of rising damp in a wall. There is no evidence that suggests that such failures are occurring on a large scale.
  3. The problem of rising damp in walls caused by defective or missing dpc’s can be combated by reducing the sub-soil moisture content.


More induced rising damp caused by damp proofers.

More induced rising damp caused by damp proofers.

General academic consensus puts the incidence of rising damp in all damp properties at around 5% but our own view based on pragmatic experience of carrying out hundreds of detailed damp investigations, using the full range of diagnostic tools puts the incidence at significantly less than 5%. General speaking I believe that earlier investigators failed to understand the difference between true and induced rising damp, which would give a falsely high incidence. Lets assume 5% is correct though, even if this were true, one in twenty damp properties affected by rising damp is relatively rare. Practically speaking, we do not find true rising damp in anything like 1 in 20 damp properties. We may encounter three or four cases a year and for each case we almost always identify subterranean leaks and consequential high ground moisture levels as the cause.

Induced Rising Damp

Theres a great irony in that an industry, that promotes the incidence of true rising damp is in our experience, primarily responsible for causing it. However, this wouldn’t be true rising damp, rather, it is what we call ‘induced’ rising damp. Whenever waterproof coatings are applied to walls that prevent moisture evaporating from that wall then the moisture has nowhere to go but up. In these situations there is no limit to the rise height, as academically accepted to be the case for true rising damp and often the first sign of this problem is damp staining breaking through at the top of the finished waterproof plaster or render system, such as in the image below. The solution for this is to undo the work done by damp proofers and remove the cementitious render from the wall to reinstate wall base evaporation. We commonly encounter induced rising damp wherever we follow in the steps of damp proofers but we rarely encounter true rising damp and where building technical details are correct then it is usually caused by high local ground moisture caused by leaking drains (foul and storm) or leaking incoming water mains.

A classic case of induced rising damp

Unexplained damp patches at high level explained when plaster was hacked of to reveal an underlying waterproof render. A classic case of induced rising damp caused by damp proofers.

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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.


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.


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Damp in Old & Historic Buildings

Managing damp problems in old buildings

CPD Session in Nottingham

There will be an opportunity to attend a talk I’ll be giving in dealing with damp in old and historic buildings on the 19th of May in Sandiacre, Nottingham. Full details can be found on the following link

The event is being organised by Jane Newton at the CIOB, whose contact details can also be found in the link above. The event is £5 to non-members of the CIOB and free to members and students. Whether you are a practising surveyor or just have an interest in old buildings then I’m sure you’ll find it fascinating.

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The talk should last about an hour with a Q&A afterwards. Topics that I’ll be covering are:

1. Tools of the Trade
2. The principles of moisture management
3. Back to basics: A focus on critical technical details.
4. Understanding moisture equilibrium
5. Cure or management solution
6. The holistic damp investigation process
7. A brief update on rising damp
8. Condensation damp & ventilation strategy.

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Ventilation Strategy for Managing Condensation : Part 2

Looking at Ventilation Strategy & Options

Mould caused by ineffective ventilation and poorly insulated loft space.

Mould caused by ineffective ventilation and poorly insulated loft space.

In the absence of a modern whole house MVHR (mechanical ventilation and heat recovery) system, which few of us have, then your choices for how best to ventilate your property fall to single room options such as extractor fans or vents, or a PIV system may be recommended. The vast majority of properties that we deal with will rely on standard extractor fans, which more often than not are poorly chosen, poorly installed and poorly understood.

General Principles for Ventilation

In part one we explained why opening windows is a terrible idea for managing condensation damp and why is was crucial to place equal emphasis on managing heat losses as well as air changes. With that principle in mind, where extractor fans or single room heat recovery fans are installed, they should be wired to run continuously on trickle speed 24 hours a day with boost speed wired to the bathroom lighting circuit or pull cord. In our view fans with humidistat switches or over run timers are ineffective and we never specify them. Humidistat switched fans are particularly unreliable as the humidistat sensor often gets fouled with airborne debris.

It is absolutely critical that there are no open windows, wall vents or trickle vents in any room containing an extractor fan because if there is, then the fan will simply draw air from this open vent, short circuiting the extraction process and preventing air changes in the property. The key is to ensure that air is being drawn from other rooms so ideally trickle vents should be open in other rooms not containing a running extractor fan.

Ventilation Options

Positive Input Ventilation (PIV)

PIV system in loft space

PIV system in loft space

Until recently very little research had been done to prove the effectiveness of PIV and yet it widely specified. The BRE recently set up a parallel study to investigate the performance of PIV systems and carried out trials in their Watford test house and field studies in 16 Welsh properties. The study concluded with the following key findings:

  1. PIV did not directly save any energy but may save a little when compared to conventional extraction providing the same level of ventilation exchange. This is because roof space temperatures are usually a minimum of 3OC higher than outside.
  2. Input ventilation was found to be effective in reducing relative humidity levels by around 10%RH in the test house, even when internal doors were closed. Vapour pressures reduced overall by 0.2kPa. The unit was shown to be more effective upstairs than downstairs.
  3. In the field monitored houses input ventilation was not consistently effective in reducing relative humidity. When internal humidity levels over those outside was examined, PIV was found to be effective in the most humid houses but did little in the dryer houses. Even in the cases where it was effective there were often inconsistencies between rooms in the same house.
  4. In both the test and occupied houses, the roof space was consistently more humid than outside (excess vapour pressure of about 0.1 kPa), implying that moisture was being transmitted to the roof space from the rooms below. The results showed this moisture transfer regardless of whether input fan was operating or not.This demonstrates that PIV may actually recycle higher levels of RH back into the habitable space.

I’d be understating the case if I said that results were not particularly encouraging and an interesting point that was made  is that the occupants perceived improvements or benefits were far greater than were actually proven. Clearly for some occupants there was a psychological benefit or placebo affect taking place. The last time I wrote about the proven poor performance of PIV I had damp industry salesmen stating their disagreement and commenting about how great PIV was and how they’d had a ‘masterclass,’ not just a class, but a masterclass in ventilation from someone at the BRE involved in this study but this doesn’t change the findings and we simply don’t ever specify PIV and have never needed to.

Passyfier Vents

Passyfier vent

Passyfier vent

Passyfier vents are a relativity new product, again of unproven reliability. Essentially they are an improvement on a standard open wall vent in that they are packed with rockwool which is moisture permeable but retains heat and prevents drafts  within the property. The tubing connecting the inner and outer face of the vent is sloped to the outer face of the wall to allow for drainage  of any moisture that is collected in the rockwool packing. In their own right we cannot believe that these vents will provide an effective ventilation strategy but they have to be an improvement on a standard open wall vent since drafts and heat loss will be massively reduced. In fact where open wall vents are installed we have frequently packed these vents with rockwool  insulation and received very similar benefits at very low cost.

Single Room Heat Recovery Fans

Single room heat recovery fan

Single room heat recovery fan

These are our preferred option for ventilation but are often ruled out due to cost. A  good standard centrifugal fan may cost circa £70.00 whilst a single room heat recovery fan may cost around £250.00. However they do merit one or two words of warning. 1. Some units  come with heat exchangers that occasionally require them to be removed and cleaned in Miltons fluid or similar; this may be a prohibitive requirement in specifying for the social housing sector. 2. Manufacturers claim amazing performance of up to circa 90% heat recovery but they fail to mention that higher efficiencies are only achievable at low trickle speeds. Heat recovery is incredibly poor at high speeds because the air moves across the internal heat exchanger too quickly. However given that we generally recommend continuous running at trickle speeds then this principle is perfectly geared towards installing, and getting the best from single room heat recovery fans.

Single Room Extractor Fans

Crude but effective test for extractor efficiency

Crude but effective test for extractor efficiency

These can still be fairly effective in managing condensation so long as you avoid the pit falls that most installers fall into and follow our general principles for running extractor fans… silent & continuous running at trickle speed. We commonly see cheap axial fans installed to ceiling mount locations, yet generally, axial fans are not powerful enough to move air through the length of ducting in the roof space.  We generally specify a centrifugal rather than an axial fan (though high powered axial fans are available) because we know it will be effective for ceiling, as well as wall mounting.  A crude but effective test we often carry out is to simply see if the running extractor holds a sheet of paper, if it doesn’t then in all  likelihood it is ineffective. It is also critical that silent running fans are installed because if they are noise intrusive in operation then they will be turned off. We commonly see  cooker hoods installed to deal with extraction at first floor or kitchen level but these are ineffective purely due to the noise they produce. They’ll be ran infrequently during cooking and often are not even piped to an external wall so actually contain nothing more than a charcoal filter to deal with cooking smells. They should not be viewed as a suitable replacement or alternative for a silent and continuous running extractor fan.

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Plaster Beetles

                                                                         A less well publicised visitor



We’re all heard of woodworm, the term used for the larvae of the destructive furniture beetle, precisely for the reason that they can be destructive but there are other forms of infestations not generally considered harmful that you may not be aware of, the plaster beetle is one such visitor. Of course, if you’ve suffered from a plaster beetle infestation then you’ll be well aware of this pest. We recently took a call from a client asking for advice on a plaster beetle infestation in a new build property. The constructor had called in a pest control company who had fumigated but the client experienced re-infestation within two weeks of the treatment.

Plaster beetles get their name from the fact that they are often seen in new properties where damp plasterwork often provides ideal environmental conditions for these visitors. Also known as scavenger beetles, plaster beetles are part of  the lathridiidae family, a family with over 1050 described species.  This particular visitor is an unpleasant nuisance rather than being harmful but nevertheless, no one would want a plaster beetle infestation in their home. The problem is not often reported on because they are relatively innocuous however we found this report relating to a new build infestation that gives a feel for how unpleasant a plaster beetle infestation can be…

“In September, the couple spotted tiny insects in the kitchen. “I went into the bathroom and saw plaster beetles all over the wall,” says Jane. “As fast as I cleaned them away, they kept on coming. They were all over the bedroom and in the kitchen. The microwave, toaster and a television were so badly infested that I had to throw them away.”
The couple were told by the council’s environmental health department to open the windows and turn up the heating, which made things worse.
“Barratt said it had never heard of this method and recommended we used fly spray. I was using 10 cans a day – and still they kept coming. We discovered orange mould under a picture frame and thick green mould under the sink,” says Jane.
At the beginning of November, they consulted an independent environmental adviser, who said that they should have just left the trickle vents open and turned the heating down to 14-16C all day. This seemed to have an effect, but they also had to buy two dehumidifers. “I can’t afford to go on paying for the dehumidifiers to be on 24 hours a day,” says Jane. “We are so upset, as this was our dream house and we just want to enjoy it.” The couple are hoping the infestation might finally be over. “But we can’t be sure, if the conditions change, they might be back.”

What we noted from this newspaper report is how badly the homeowners were advised and how wide the difference of opinion as to how these pests should be dealt with.


A range of plaster beetles. Source: bugguide.net

Since plaster beetles thrive in damp conditions then they are more prevalent during the wetter seasons but essentially, if you have damp conditions that lead to mould colonisation then there is a small risk of plaster beetle infestation. They have been a particular problem in some new homes where properties have been handed back to new owners without being properly dried out; particularly where properties have been flooded due to careless plumbers; an issue we have seen many many times in new build. Residual  construction moisture can be a temporary issue in new build properties but in the main, properties should be relatively dry unless there is or has been some additional underlying issue. Indeed, it may be that the building fabric is relatively dry but you are suffering from high levels of relative humidity that support fungal growth. Interstitial condensation can be a particular problem since mould formation can occur in hidden voids, thereby providing a hidden food source for beetle colonisation.

Plaster beetles can be anything from 0.8mm to 3mm in length and have a life cycle of 13 to 28 days. Adult beetles deposit their eggs near a food source (mould) and when larvae emerge they feed on the mould spores before eventually pupating into adults. Pupation can take up to five months dependent on the availability of food. Some types of plaster beetle are reasonably good fliers and can be attracted to light, which is why you may see them congregated around a light source or near windows.


Generally speaking we are not great believers in chemical treatments and prefer to deal with infestations like this in a more natural way that avoids spraying harmful chemicals in the home. Since plaster beetles feed on mould and mould is caused by damp conditions in the home then doesn’t it simply make sense to deal with the issue at source by removing the source of moisture and the source of food? Chemical treatments can never deal with the underlying cause of the problem, which is dampness and subsequent mould colonisation. Moreover we simply do not like the idea of spraying harmful chemicals in the home and the chemical effects will reduce over time, thereby requiring re-treatment since the underlying cause has not been addressed. There is also an option of heat treatment, whereby the property is heated to 45 degrees C. This temperature should kill off any plaster beetle colonies in the home but again our main concern is that this does not address the underlying cause so there may well be a risk of re-infestation.

You will need to address the underlying cause and in simple terms you should consider 5 factors:

  1. Identify and eliminate the source of moisture
  2. Promote rapid drying
  3. Eliminate the food source (If possible)
  4. Ongoing management of high relative humidity in the home.
  5. Regular cleaning protocol to aid beetle management

The source of moisture may be a plumbing leak, penetrating damp or condensation damp and if you are in a new build property, you may simply have to deal with temporary construction moisture by promoting rapid drying. You may want to consider hiring snail fans to dry out walls and a dehumidifier to mop up the excess humidity. If this is not successful then it is likely that you have a more significant underlying source of moisture that needs identifying.

If mould colonisation is obvious then treat this with a proprietary fungicidal spray to help eliminate the food source and where plaster beetles are seen then they should be vacuumed as frequently as possible to help manage the population whilst the underlying cause of dampness is being addressed.

The underlying cause won’t always be obvious, in which case you may need to call in a Chartered Building professional. If you call in a pest control or damp proofing company then you should expect to be sold chemicals or heat treatments, money that would be better directed towards correct diagnosis of the underlying cause of moisture.

Flour Beetles

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Flour Beetle (Tribolium Castaneum). Source Wikipedia

As an aside to this blog, we were recently asked to advise on a flour beetle infestation in a kitchen. The client complained of frequently seeing larvae on the kitchen worktops but had no idea what they were or where they were coming from. Similar to  plaster beetles, they are another relatively innocuous, but nonetheless unpleasant visitor that can invade kitchen foodstuffs, particularly flour and cereal products. However, the issue of seeing larvae only on kitchen worktops gave us a strong hint as to the source of the problem… “Do you have a toaster on the kitchen worktop,” we asked? “yes, we have a double toaster” came the reply. We advised the client to open up the toaster and clean out all the old breadcrumbs that had accumulated in the base and sure enough it was packed with two years worth of breadcrumbs and a flour beetle infestation that was completely eradicated once the toaster was cleaned out and the food source was eliminated. Some of these toasters have cleaning trays in the base that can be removed for cleaning but they are simply not up to the job. Of course we’d completely understand that many would prefer to simply throw the toaster away rather than clean it out but we’re not advocating mass toaster disposal without first checking that this is the source of the problem.




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Ten Tips to Avoid Buying a Damp Property

Ten simple but valuable checks for potential homebuyers


High external ground levels are a problem, but less so in cavity walled construction.


  1. Check external ground levels are not too high when compared to internal finished floor levels. If a physical damp proof course is installed then external finished floor levels should be a minimum of 150mm below internal finished floor Level. In older buildings, if no physical damp proof course is installed then this is not necessarily a problem, simply ensure that external finished floor levels are a minimum of 200mm below internal finished floor level.
  1. Make sure external masonry is not painted. Brickwork cannot dry out when it is coated with impermeable masonry paint. If it is painted then you should at least have the paint removed from the bottom three courses of brickwork. Similarly, you should generally avoid clear waterproofing products despite claims that they are ‘breathable.’ Cement render can cause similar problems and you should ensure that cementitious render is in sound condition and not bridging the damp proof course at lower level.


  1. Respect the buildings construction type. If it is an old building built with lime mortar then it should be repointed with lime mortar and not Portland cement. Understand that old buildings are meant to breathe if they are to dry out, and Portland cement prevents moisture evaporation and causes spalling of brickwork.
  1. Avoid buying any property that has an original rotten timber floor replaced with a retrofit concrete slab. Retrofit concrete slabs will often cause wall base damp by pushing moisture up the walls under hydrostatic pressure. Again, this is about understanding how the building was originally built.
  1. Measure the wall thickness at a door or window reveal, is it around 240mm or less including the plasterwork? If so then its likely to be solid walled and therefore more likely to suffer from penetrating damp or internal cold surface condensation issues. You may even discover some single skin brickwork, particularly on gable walls in very old buildings. Mortgage companies do not generally like to lend against these properties due to perceived structural and damp issues. Buying an old solid walled property does not mean you are buying a damp property but you should understand the implications.
  1. Find the incoming water main and see if it is Polyethylene pipe. An old building may still be on the lead water main and these are susceptible to leakage that may go undetected under the floor of the property for quite some time. Many of the worst damp problems we’ve encountered have been caused by leaking water mains.


Rising Damp? Technically no, since this was caused by a leaking lead water main buried in the subfloor

  1. If the property is cavity walled, is cavity wall insulation installed? CWI can occasionally cause penetrating damp, particularly the blown fibre variety. However, when correctly specified and installed we still believe it is a worthwhile addition to most suitable properties.
  1. Check your airbricks! Timber floating floors should as a general rule of thumb have airbricks installed every 2 linear metres to ventilate the subfloor and prevent timber decay. These are a critical technical feature so don’t ignore them!
  1. Has the property been treated with retrofit chemical injection? You will know the obvious telltale signs such as a row of plastic plugs installed into the brickwork at low level but what you may not know is that this is a two-part system that includes the application of internal waterproof renovating plaster. This renovating plaster dams in the damp and often gives the appearance of a dry wall at surface when in fact the underlying wall can be saturated. These management systems are almost never required despite the volume sold, and can prevent walls from drying out so don’t kid yourself that these treatments are a good thing. They are a management solution rather than a cure and as such are destined to fail.
  1. Know that condensation damp is the biggest cause of dampness within properties. To combat this, ensure that the property is well insulated, has a fully controllable central heating system installed and has a means of controlled mechanical extraction installed in the kitchen and bathroom areas.
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