Do physical damp proof courses fail?

Why DPC Injection Work is Rarely Required. 

The damp proofing industry in the UK commonly promote two statements that are fundamental to this industry. Firstly, they promote rising damp as a common occurrence and we can comfortably state that this is simply untrue. It is an academically proven fact that  rising damp is incredibly rare.

The second claim, which is also fundamental to an industry that sells retrofit chemical injection and re-plastering is that physical damp proof courses commonly fail.  We have reviewed many many reports from these ‘specialist’ companies and the absence or failure of an existing physical DPC is commonly cited as justification for installing a retrofit chemical injection system. Moreover, you have all commonly seen retrofit chemical injection work installed where physical DPC’s already exist.

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There are of course legislative requirements for the insertion of a physical dpc in new buildings. Approved document C, Section 5.2, states that walls should: resist the passage of moisture from the ground to the inside of the building; and not be damaged by moisture from the ground to any part which would be damaged by it. This requirement is met if a damp proof course is provided of; bituminous material, polyethylene, engineering bricks or slates in cement mortar or any other material that will prevent the passage of moisture.  However, relatively speaking this is modern requirement and we have many thousands of properties in the UK that do not have have a physical damp proof course installed and yet they manage moisture perfectly well despite non-compliance with the modern requirement for a physical DPC.

I personally carried out a comprehensive review of this very question and  what became clear is that the majority of academic commentary cited bridging rather than failure as the key issue, in fact it is fair to say that there was general agreement on this point. We  found only two cases where commentators cited their view that DPC’s fail, in both cases these were unproven opinion rather than proven fact. Here is an opinion given by Trotman P, Sanders C, Harrison H (2004)…  Physical dpc’s can fail occasionally, particularly those formed by engineering bricks or overlapping slates, following breakdown of the mortar; bitumen felt dpc’s can become brittle with age.  The ‘breakdown of mortar’ is the most interesting point in this statement but the idea that an engineering brick can fail is simply wrong. The authors do not go on to explain their point but we can only assume that this idea is linked to occasional building movement that results in cracked engineering bricks at DPC level. A crack in a brick or a slate DPC will not result in capillary rise in those units and we are firmly of the opinion that engineering brick DPC’s do not fail. Moreover they are the simplest physical DPC to visually inspect. The key controversy must focus on hidden DPC’s installed to the mortar bed joint. These can be formed from a wide range of materials including poured bitumen, bitumen felt, lead, copper, overlapping slates and probably one or two more that currently escape my mind. They are  often not even visible at the bed joint and this may be due to being hidden by high external ground levels, or more commonly, they have been pointed over. Both issues are clearly bridging issues rather than DPC failure and if you have a bridge then the simple solution to that problem is to remove the bridge.

To my knowledge no one has carried out a piece of research into alleged DPC failures and published their findings. It can’t be done by the damp proofing industry because they have a vested interest in promoting the idea of DPC failure. It would need to be an independent piece of work  that to my mind would be a valuable piece of research. I have considered co-ordinating this with a demolition company so that every time a building is taken down we can thoroughly inspect the DPC in the process. We have removed bricks from walls on many many occasions to inspect cavities and where we do this we have consistently found the old physical DPC to be intact and fully functional.

We have previously written that Portland cement degrades over time, initially it is resistant to rising damp until after many years of degradation it then becomes the major moisture pathway for rising damp. Where a continuous physical barrier is installed then clearly this is not a problem but this fact may well form at least a partially valid argument towards a claim that an engineering brick DPC has failed. Technically there would be nothing wrong with bricks but the mortar perps may allow rising damp via diffusion. Interestingly we have seen where perp joints have been left open on engineering brick DPCs and this would completely mitigate for this potential issue.  However, in all alleged cases of DPC failure,  what we commonly recommend is that so long as there is a provision for adequate wall base ventilation then this does not become an issue. It is all about maintaining moisture equilibrium, which is ensuring that moisture is evaporating off the wall as fast as it is rising.  Similarly, where we find that physical DPC’s are hidden we simply treat the building as though a physical DPC is not installed so that if external finished floor levels are a minimum of 200mm below internal finished floor level then this need not be a problem. There are thousands of properties in this country that perform perfectly well without a physical DPC and they generally do so because moisture equilibrium is maintained in their walls due to the fact that they are left bare, they are correctly  repointed with lime mortar, there is adequate subfloor ventilation, external finished floor levels are not too high and local ground moisture is managed.  You can of course apply all or most of these principles to a building that has a physical DPC installed, even one that has allegedly failed and you would mitigate for the alleged failure.

We are lucky enough to carry out a great deal of survey work on the Crown Estate. We deal with some very old historic buildings that were originally built to a very high standard. We are seeing properties over 150 years old where ordinarily we would not expect to see a physical DPC installed but on this Estate they do,  and this gives us a rare insight into some quite unique properties. Many of the images contained within this blog are from the Crown Estate and we are consistently finding perfectly functional DPC’s in some of the oldest properties to have physical DPC’s installed.  I may not have proven through this blog that physical DPC’s don’t fail but I can state with certainty that no one has proved that they do. We do not believe that physical DPC’s fail so if one is installed then you should give careful thought as to why you would even consider installing another unproven retrofit chemical injection system in the absence of any proof that the existing physical system has failed. We have always taken a balanced view on retrofit DPC injection because pragmatically there are times when lowering external ground levels may not be an option but the fact remains that we very rarely have a need to specify these management solutions because our focus is always on curing rather than managing or hiding the problem.



10 responses to “Do physical damp proof courses fail?”

  1. David avatar

    A useful article. Thank you.

    I’ve got a garage which has what seems to be a bitumen felt DPC like the one shown in your third photo. Originally there was pointing over the DPC but over the last couple of years this has come away so the edge of the DPC is now clearly visible between the two courses of bricks all the way round the building. So it looks like the first photo in your carousel of images (where you say extrusion has blown the mortar) except that in my case the pointing covering the DPC has come away pretty much everywhere rather than just in a few places.

    Will that potentially give me a problem with damp? Do I need to rush to get it repointed or is this nothing more than a cosmetic issue?

  2. Alexander avatar

    Wonderful to see a surveyor who understands the futility of injected dpc’s, which frequently mar historic buildings and the importance of using lime mortar. Unfortunately I regularly see surveyors recommending damp proofing firms to give damp surveys, being happy with their methods and neglecting the importance in the difference between lime and OPC mortars.

    I have argued it out with a building surveyor who had a house built in 1720 repointed in OPC, damp proof courses injected and cement render installed. He also had a dpc injected on a rear wall of the house due to damp under a window, ignoring my pointing out the state of the cill which was causing water to run down the wall. Unsurprisingly after this the wall was still damp over the injected dpc and coming through the wall. However when some time later the cill was replaced at my suggestion the wall became dry…

    1. Joe Malone avatar
      Joe Malone

      Thank you for the kind words Alexander, and it is equally wonderful to see that others like yourself understand the problem.


      Joe Malone

  3. Lee Trevethan avatar
    Lee Trevethan

    Joe Im from Australia I have a double brick house. Some of the brick mortar joints are loose and falling out. Some sections of the house have darker coloured bricks. Im thinking of just repointing with a lime based mortar. Can you advise the mixture and do you think the damp course is no good?

    1. Joe Malone avatar
      Joe Malone

      Lee, no one could possibly answer that based on such scant information.


      Joe Malone

  4. Robert Purkiss avatar
    Robert Purkiss

    I have a serious problem with black mould in many of my rooms. I have just bought a hygrometer and it seems the readings I am getting are over 70 %. Is this the cause of the black mould as I have been told by 3 company’s that my dpc has failed.

    1. Joe Malone avatar
      Joe Malone

      Hi Robert,

      How could they possibly know that your DPC has failed? Did they remove bricks to check the DPC? Did they even test for moisture at depth in the masonry, by drilling the walls, and using deep wall probes or calcium carbide testing? Both are rhetorical questions, because I know the answer is no.

      As I’ve stated in this article, DPC’s are usually just bridged or compromised in some other way. However, if they are citing alleged failure of a physical DPC, as a causal factor for mould, then this is completely wrong, and high humidity levels are indeed a significant factor. Remember that condensation damp is still the most common form of dampness in properties, and you should consider the following factors.

      1. Have you got effective mechanical extraction installed in the property?
      2. Does the building have a fully controllable central heating system, and are you using it effectively.
      3. Is the building envelope well insulated? Old solid walled properties tend to suffer more from cold surface condensation.
      4. Are there any occupancy issues that would contribute to high humidity levels? I’d point out that occupancy issues are incredibly rare.

      Regards. Joe Malone

      1. David P avatar
        David P

        I also must add that lack of roof ventilation can lead to high humidity and condensation issues, notably mould, particularly around North facing window recesses. Some properties have felt membranes under the roof tiles that don’t breath, or there is a lack of roof ventilation in general, eg no ridge tile vents. If a property has a non- breathable membrane then it needs to be replaced with one that does breath, such as the ” air open” spec and nhbc approved. Also consider the need for clay ridge tiles with vents or even a dry ridge system. I’d take my time to get independent advice from a number of sources; a roofing company might be happy just to sell you something.,but you need to do your research before parting with your money.

  5. William avatar

    Have lived since new in 1999 det 2-bed bungalow with unfilled cavity walls. Have had no damp issues whatsoever until now.
    Most rooms are papered, now lounge – 2 external and 1 stud walls – have wavy damp stains from skirtings upwards. I suspected faulty dpc but accept verdict of enlightening article.
    Carpeted floor is 5C colder than mid height, with CH room thermostat always at comfortable 21C (corresponds with adjacent thermometer).
    A complete layman, I need ask, why, after 23 years has this problem just arisen?
    If condensation is cause, how to better ventilate without losing warmth in extreme cold when lounge windows face north and east? Only radiator is beneath north window. Thanks in anticipation.

    1. Joe Malone avatar
      Joe Malone

      Hi William,

      I’ve made it clear that there is no evidence that DPC’s fail, however they can be bridged or compromised in some other way; for instance debris in the wall cavity. If you have unfilled wall cavities then I’d have bonded polystyrene beads cavity wall insulation installed.
      Regarding ventilation, ideally, have a Kair K-HRV150 single room heat recovery fan installed in the bathroom. This will recover much of the heat that would otherwise be lost using a standard extractor fan. Have this wired to run continuously on trickle speed with boost speed wired to the lighting circuit. Obviously do not open windows or trickle vents in the bathroom when the extractor fan is installed or this will let in cold air and short circuit the extraction process.
      Why are you having this problem now after 23 years? I cant answer that because I haven’t investigated the issues but we have had unusually cold weather lately. Has there been a change in occupancy levels lately?


      Joe Malone

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