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.

Construction

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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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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Training in Damp Investigation and Remediation

Why chartered building professionals need their own supplementary damp training qualification and why Housing Providers should have their staff trained. 

Damp Training

Damp Training

We delivered another 4 hour lecture to undergraduates at Coventry University on November 23rd to supplement their academic learning with pragmatic site experience and to teach them a damp investigation process that can be used throughout their careers. Coventry University run one of the best RICS accredited building surveying degree courses in the UK and their statistics show that they are now one of the leading universities in the UK  for student satisfaction. We believe passionately that future generations of chartered building professionals should not be deferring specialist damp survey work to a damp proofing industry who are significantly less qualified than they are and hopefully drive home the message by using humour to make a serious point. We offered course attendees our D.A.F.T qualification, or ‘Damp and Fungas Technician,’ because we thought that after attending a short course they deserved letters after their name to show that they were damp specialists. Unsurprisingly, there were no takers but we are hopefully influencing the next generation of chartered surveyors to not defer survey work because in fact, they themselves are the future experts in this field. Building pathology is a core building surveying skill and you cannot practise isolated elements of pathology without first having a detailed knowledge of construction technology. Assessment of the building type is a critical part of any damp investigation and you need a construction related degree to underpin any further specialist knowledge you gain relating to damp investigation and remediation.

A supplementary qualification

We have also believed for some time that Chartered professional bodies should be pro-active in developing a professional supplementary qualification for Chartered building professionals interested in damp investigation and remediation. Perhaps not D.A.F.T but maybe something like D.I.P or Damp Investigation Professional. You would need to be a Chartered professional to gain this qualification so as to ensure you have the pre-qualifying knowledge of buildings and building technology. In our opinion, a comprehensive course could be delivered in two days because no supplementary training in site health and safety would be needed.  I would also suggest that a professional damp report is reviewed to ensure it complies with a recognised survey process and protocols before being awarded the final qualification. This will ensure that professionals have both the knowledge and the full range of diagnostic tools required to carry out a professional damp investigation.

We are in discussions with Chartered bodies to deliver CPD training in damp investigation & remediation and this will possibly start in February of 2016 so please watch out for this. Our aim is to give Chartered professionals, or those working towards chartered status,  the knowledge and confidence to stop deferring ‘specialist’ damp survey work, because in fact, it is not specialist at all, it is a fundamental part of any chartered professionals job role.

Damp Training within Social Housing

We have also been training social housing technical staff in damp investigation and remediation since 2006 and I wrote our course in damp investigation and remediation because as a senior manager working within social housing I saw tens of thousands of pounds being poured down the drain every year on unnecessary damp proofing works caused by incorrect diagnosis of rising damp. Moreover, these costs were repeatable at some future point in time because damp proofing companies have no interest in curing damp, they simply want to sell systems that manage damp. It was always very difficult for me to understand why an industry so concerned with cost efficiencies did not understand that this was one of the biggest potential areas to make savings on the both planned and responsive maintenance costs. Larger social housing providers cannot employ chartered professionals every time they encounter a damp property because the budget would be blown very quickly but they should have a clear focus on curing rather than managing dampness. That being said, many providers have retained our services to deal with the more complex cases or legal disputes relating to alleged disrepair or statutory nuisance.

Many housing providers carry their own technical teams, often HNC or degree qualified in a construction related discipline. We have trained hundreds of industry surveyors since 2006 and have been delighted to see these organisations completely change their approach to dealing with damp properties, they now take responsibility and have a focus on correct diagnosis to ensure they achieve a cure for the damp rather than throwing money away on unnecessary damp proofing works.

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