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How much for new Damp Proof Course.

1356712

Comments

  • Bricks wrote: »
    In what circumstances would a chemical DPC be the solution?


    I don't claim to be an expert, but judging from my own experience;

    If rising damp is a fact why is it not universal?
    I own two Victorian houses, both of which have no Damp Proof Course. The internal floor is 2 courses above ground level which is often soaked with rain. Yet there is no evidence of rising damp! The internal plaster is direct onto the 9" solid wall.
    The plaster is in perfect condition and my moisture meter confirms that they are dry.
    The sad thing is that I can see many of the other houses in the street with the telltale holes which indicate that a chemical DPC has been installed.
    I strongly suspect that this has been due to condensation on the internal walls.
    One of my houses did have damp and fungus growing on the plaster of an external wall. It was let to a tenant. Since it was cold they had sealed up the windows and even blocked the vent for the kitchen extract, which they refused to use since they said it caused a draught.
    A new tenant installed,vent unblocked and extract fans used the problem was solved.
    I believe an extract fan in both the kitchen and bathroom is essential, together with heating, removing the moisture laden air as near as possible to the source
  • Hi Toptenor,
    For rising damp to occur it requires a certain set of conditions to be met, not least of which are the amount of moisture present within the subsoil beneath that particular house, the height of the water table and the pore size of both masonry and mortar. It is believed that shrinkage cracks within house walls may provide some of the major pathways for rising dampness to occur where there is no effective barrier to this moisture source.

    Although you say your property has no damp proof course it may well be constructed with such materials that provide an effective control of rising damp to a point that is considered insignificant, especially when an appropriate type of plaster is also present.

    Whether the chemical damp proof courses were indeed justified or were installed as a result of misdiagnosis to the other properties within the street you mention we simply do not know and each would have to be investigated upon a case by case basis but it would be interesting to look at whether the walls that were treated in those houses with a chemical dpc have any ground salts associated with rising dampness within them, which may indicate whether or not a rising dampness problem had previously been occurring.

    As you quite rightly indicate resolving any obvious moisture sources that are readily apparent such as condensation especially occupancy induced before rushing to blame everything on rising dampness is a common sense approach. Condensation would however be unlikely to occur on an internal wall between rooms as it is doubtful you would hit the dew point unless the situation was extremely chronic. Hope this helps, kindest regards, David
  • Sorry when I said internal walls I meant the inside of the external walls. However I must say that when in a small bathroom which may not be particularly warm and a hot shower is run the air within the bathroom can quickly become saturated ie 100% RH. Condensation will occur on almost any surface provided the surface temperature is below dew point. When one of my tenants left there was fungus on external and internal walls not to mention the ceiling.
    Regarding the chemical DPC's on the other houses. Come on David. These are exactly the same as ours. The same bricks and mortar sitting in the same ground. They called in a company who cures dampness. What did they say was needed? A Chemical DPC surprise,surprise.
    Most "experts" even agree - Rising damp is very very rare.
  • Hi Toptenor,
    I agree that in my experience true rising dampness within properties is rare, particularly where the property was built with some type of dpc be that a sheet material or band of masonry that acted as a control to rising dampness. I could not defend any misdiagnosis where this resulted in a chemical dpc being installed where it was not required but you would have to look at it on a wall by wall basis. Kindest regards David
  • Further to my previous post the University of Portsmouth has just completed a study into rising dampness within buildings where there is no effective damp proof course and this document gives excellant information upon the subject including the many factors that influence not only how this problem can occur but also the height to which it may rise. This study was comissioned by the Property Care Association (PCA) which is the leading trade body for amongst other things damp-proofing and structural water-proofing. Kindest regards, David Aldred Independent damp and timber surveyor.
  • Ok David sounds intriguing. Has it been published on the web?
    I'd like to read it!

    Cheers Ian
  • Hi

    I have a question regarding damp proofing. I am in the process of getting quotes to get some damp proof work done to a house that might be a victim of what is described in this thread. The wall paper is coming off at the lower end of the walls. Outside bricks are severley weathered and the structural surveyor recommended replacing the lower 3 rows of bricks.

    The house is end terraced and was built in 1880, with 9 inches solid wall. The planned work is to remove 3 rows of bricks from the ground level on the outer wall, then cut through the mortar of the inside wall, then insert a 9 inches damp proof membrane while building the outside rows of bricks. The plan is to do 1 meter and leave 1 meter to maintain structural stability of the wall.

    What are your thoughts on this process? Is it safe? Worth it? What about alternatives, such as electric damp proof?

    Many thanks
    Be nice, life is too short to be anything else.
  • David_Aldred
    David_Aldred Posts: 371
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    edited 18 December 2010 at 11:00AM
    Hi Toptenor & Thunderbird,
    The Portsmouth study as far as I am aware is currently within the Members section on the Property Care Association website so is not fully out there on the web at present but I guess it will only be a matter of time before it is. There is nothing secret or particularly new within the document and basically it just discusses the mechanisms for how rising dampness can occur in walls under the right conditions when no effective dpc is present both here and abroad including examples of how others have looked at the problem. It does not really cover how common the problem is within UK housing stock, the difficultly for people to properly confirm rising damp without laboratory analysis, nor how common true rising damp to properties that already have a dpc is within the UK but when the study does filter through to the web in general it is worth a read if you are wanting to know a little about how water can rise by capillarity. Other than that there is plenty of good information on the subject already out there both in books and on the web.

    With regard to Thunderbird's query installing a physical sheet dpc of say pitch polymer in the way you describe if done correctly should give a very effective dpc. It is not as common as the chemical dpc's due to the disruption and labour costs. As regards it being safe ;again it comes down to the skill of those undertaking the work but again if done correctly it should be quite safe. If you are having to replace the outer brickwork in any case and you can put up with the disturbance / stand the costs then it would make sense in that case to go with this option given the pitch polymer dpc is a physical barrier to rising dampness compared to the other remedial systems which when done correctly at best will only control rising dampness to a point that is perceived to be dry, that is to say some degree of rising dampness may still occur that would have to be held back by a reliance upon the re-plastering system.

    One thing to bear in mind is the external 9" solid walls will still be cold and prone to condensation / penetrating dampness and rather than simply re-plaster internally you might want to consider waterproof grade insulated dry lining with appropriate vapour barriers to improve the situation in addition to ensuring the outside face of the wall is breathable including mortar / render. Hard dense cement mortars / renders should be avoided because of this issue and true lime mortars / renders are preferred.

    The 'electrical' elctro osmosis method of controlling rising dampness has been out there for a good while and has been around since about 1930. The electrodes in damp walls have an electrical potential relative to earth which can induce rising damp and if you remove or short out this potential the theory is you will stop rising damp occurring. It is a well established process for drying clay soils.

    On the downside as far as I am aware the system lacks a British Standard, BRE or BBA approval as a means of controlling rising damp possibly as a result of lack of hard evidence that the system will work in all situations. The lack of such standards can be an issue should a dispute arise at a later date as you have little to compare with what was actually done with what should have been done other than the manufacturer's own literature. Problems reported by others include the system stopping working during drier periods then failing to re-establish itself during the next damp period and corrosion failure including metal services that may incorrectly have come into contact with the system. Again there is often a heavy relaince upon the re-plastering to hold back any dampness that may continue to rise up through the wall. Regards, Dave
  • ukmike
    ukmike Posts: 751
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    In my own experience of inspecting in excess of 20,000 houses from all over the country
    20,000 houses??How old are you!
  • When I first worked for a dpc contractor we were in the boom of the chemical dpc injection years and I had an assistant where we would survey each property as a pair and do 1200 inspections per year on average - a good many years of that when demand was really high and there was a lot of grant work on offer is a lot of houses and was a crazy workload combined with a secretary batting out standard paragraphs and our quick hand drawn sketches for any work required - even for the contractors those boom days are gone and contrasts even more sharply with the level of inspection I have done for the past few years as an independent where I typically look at the house as a whole and are on site a good couple of hours minimum for a standard semi detached and all the next day to do a single report hand written specific to that property with CAD drawings, photographs etc.
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