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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The worst brickwork we’ve ever seen?: A new contender.

Declining Standards in New Build Highlighted by the worst brickwork we’ve ever seen.

Norwich New Build

Norwich New Build

Back in July we were called to carry out a snagging inspection to a David Wilson Homes site in Norwich, which had the worst brickwork we’ve ever seen. Our clients had signed up to buy a new build ‘off plan’ but started to have grave concerns relating to the quality of their potential new home as they watched the build progress. Our initial discussion related to the fact that the brickwork colour was mismatched and that the developer had employed someone to tint the bricks to match; when I arrived on site to carry out the snagging inspection the specialist was at work  painting individual bricks with a pot of red tint solution and a paint brush, a quite laborious task as you can imagine.

We’d agreed to inspect before the build was complete because our discussions with the client, and indeed pictures sent to us, gave enough cause for concern that this was necessary.  The following image slider will give you a feel for the quality of the work and the sheer volume of defects we encountered. Please view the slider on full screen to fully appreciate the illustrated defects.

Would you have bought this house?

Norwich new build
OLYMPUS DIGITAL CAMERA
Bridged polyethylene DPC
Oversailing brickwork
Cracked bricks
Failed mortar joint
Poor pointing
Cracked bed joint
Poor standard of pointing
Protruding perp weeps
Poor setting out
Perps out of alignment
Overly wide mortar perp
Inconsistent mortar joints
walls out of plumb
Smeared pointing work
OLYMPUS DIGITAL CAMERA

Significant Defects

As you can see the defects were significant and we commented in our report that we found it difficult to believe that this brickwork was completed by a fully qualified brick layer. Of particular concern was the incredibly poor setting out, failed mortar bed joints, inconsistency in width and depth of mortar joints and last but not least, walls that were significantly out of plumb, well beyond the 8mm maximum allowable NHBC tolerance. As often happens in these cases it was relayed back to us from our client that the developer didn’t agree with our report and that a site manager of 20 years experience knows more than us and his view is that the brickwork was perfectly acceptable. I thought it may be useful to balance the Chartered professionals view with a second opinion  from a master bricklayer and obtained the following commentary from an acquaintance who is also a master bricklayer…

The master bricklayers view

“My name is Bill XXXXXX and I have been a brick layer for the last 30 years.  I have City and Guilds  NVQ level 3 in brick laying  and NVQ level  6  in site management. I’ve been asked by Joe Malone  for my opinion  about the workmanship of Plot XXX in Norwich.

There seems to be wide and inconsistent perpendiculars and significant variation in bed joints.

The pointing is of a very low and poor standard i.e. holes and not perps not ’top and tailed correctly’

Weep holes are protruding out of the brick work and should be flush.

Also bricks have been laid upside down allowing moisture to catch on the face leading to premature failure through ‘spalling’ aka frost damage.

The walls are significantly out of plumb. Variation in plumb should on good brick work be a maximum of 4l mm out of plumb one way or another. Brick courses seem to wander. Chipped bricks have been used rather than discarded. The Brick work is over sailing be 10mm in places below the DPC

There are large gaps around some windows which implies poor setting out.

Some bricks are cracked and should have been discarded. Two failed bed joints are apparent.

The brick work has not been washed or cleaned down.

The mortar colour varies implying it has not been ‘gauged’ and makes the building look patchy.

The damp course is protruding through the mortar.

Back straps for the garage have been missed. Roof ridge work is poorly finished and there appears to be no mechanical fixings

The brick work does not appear to be ‘fair faced’

In all a very poor standard of work has been delivered with a significant amount of snagging already required.

On a site managed by our company this work would be condemned and the brick layers replaced or forced to do the work again to our own companies’ standard.”

The only point on which we don’t agree with on this second opinion is with regard to the DPC being pointed over. DPC’s should not be pointed over, they should be exposed and clearly visible and if they are not then they are bridged.

The worst Brickwork

Our clients reached something of stalemate with their developer, because they were insisting that sections of the building were taken down and rebuilt, whilst the developer was offering minor remedial works that fell well short of dealing with the significant defects in this build. Their complaint was ultimately elevated to the managing director of David Wilson Homes and our client eventually informed us of the following outcome, “We have decided not to proceed with the purchase of the house. I think we always knew this was the outcome deep down. I have received a reply letter from the MD of David Wilson East division offering to rescind the contract and contribute towards ‘reasonable’ conveyance costs.”

When we last spoke our clients were looking to purchase an old traditional property and we completely understand why, moreover, we believe that they made absolutely the right decision to withdraw from this contract. A brave and sensible decision, especially when you consider that many clients purchase with their heart rather than their head.

 

 

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