How much for new Damp Proof Course.

between 60 and 90 pounds per metre linear we charge here in south of london though, before any work you need to look at the obvious ones... failed guttering, little trees and green around the walls, etc.
chemical damproofing is not usseless..though it needs to be done properly and many things to be taken into account , not just inject and render and go

I had an independent survey on my last house. The surveyor said the most expensive job he had ever seen in his 20 years was £5K.

Hi,
The function of a chemical damp proof course (dpc) is solely to control moisture rising up through the wall by capillarity. Due to the limitations of the chemical dpc system there is usually a reliance upon the associated re-plastering to hold back a certain amount of moisture that may continue to rise up the wall once the chemical dpc is installed and also for this plaster to hold back ground salts that may be present within the lower areas of the wall that had previously suffered rising dampness.

It is not the function of the chemical damp proof course to address other moisture sources such as condensation or penetrating dampness.

The existing dpc the house was built with may itself be affective but dampness / degrading plaster appear to the lower parts of the wall for a number of reasons other than the dpc breaking down. Examples of this may be debris within the cavity of external walls bridging the dpc or dampness emerging at gaps between floors and walls.

A Chartered Building Surveyor (RICS) may be familiar with general principles of dampness and associated problems but they are not usually a specialist in these subjects unless they have undertaken additional training. A specialist surveyor in dampness and timber problems should be CSRT or CTIS / CRDS qualified. A list of suitably qualified persons may be found upon the Property Care Association (PCA) website be they a contractor or independent Freelance / Consultant surveyor. Hope this helps, kindest regards, David Aldred Independent damp and timber surveyor.

Hi Bricks,
Thank you for the reply and I know Jeff having spoke and exchanged information with him on a few occasions. You asked when a chemical dpc should be installed and I feel I gave a fairly reasonable answer to this particular question.

As to your further question of whether dampness will rise up a wall by capillarity, the answer is yes in some few cases it can and I have had this proven by laboratory analysis of wall samples on a few occasions for court work. When it is proven by such laboratory analysis to have occurred the height of the moisture rise varies due to a number of reasons and the last time I spoke with Graham Coleman who undertakes such laboratory analysis I think he said that he had found in one particular case where rising dampness had been proven to occur by such analysis up to a height of 2.4m which is well beyond the 1m typically associated with half brick thick walls.

Perhaps of more concern is the frequency of confirmed occurrences. Laboratory analysis to investigate rising dampness is both disruptive to undertake and expensive such that it is impractical for anything other than where the client is prepared to sanction such investigation (i.e. a dispute / court work) and is not therefore normally undertaken for say pre-purchase surveys.

Where such such laboratory analysis is not sanctioned by the client you are left with the judgement of the surveyor and their level of skill with both electrical and carbide damp meters used on site during their inspections but since neither on their own will prove moisture rise by capillarity this is not the same as confirming whether or not such moisture rise by capillarity is occurring by laboratory anlaysis.

In my own experience of inspecting in excess of 20,000 houses from all over the country with dampness problems for more years than I care to remember, then in cases where it could be confirmed the house was built with a damp proof course, be that slate or bitumen, or some other relatively impervious material and where that material was relatively intact and continuous, then I myself have never been able to prove significant failure of that material such as to produce full wall lengths of moisture rise by capillarity. Other surveyors may have been able to prove different by laboratory analysis but that is my own experience over a reasonable sample of UK housing stock.

Statistically when looking at all the dampness problems seen within properties then true rising dampness is by far the least common, especially where an existing dpc is present and it is also the most difficult, disruptive and expensive moisture source to prove compared with condensation, leakage / penetrating dampness. In view of this I would recommend those inspecting a dampness problem to have an open mind and where possible to approach the problem by way of resolving all other obvious moisture sources / plaster problems first, then monitor for drying down (25mm wall thickness per calender month) before considering whether the cost and disruption of laboratory analysis of wall samples to investigate any dpc failure was justified.

If this approach is not taken and a dpc is installed simply as a precautionary measure because areas of high electrical damp meter readings were found towards the base of the wall without actually proving failure or lack of a dpc then one runs the risk of not resolving a different type of moisture that may be present and wasting both time and money with inappropriate treatment in addition to having damp / degrading walls and risk of associated decay etc.

Where a chemical dpc is proven to be justified then it should be appreciated that these type of damp proof courses are not the same as an impervious sheet materials of modern pitch polymer, or lead / slate / bitumen etc. The chemical dpc's are by their nature installed blindly and where done correctly the intention is to establish a continuous layer of material throughout the depth and length of the wall that will hopefully control any true rising dampness present to a point that is considered to be negligable.

As indicated in my previous post they do rely on the associated re-plastering to hold back a certain amount of dampness that may continue to rise up the wall due the inherent limitations of the system and also to hold back any ground salts that may be present within the wall. Because the chemical dpc and re-plastering are a system 'joined at the hip' the recommendation is for the same contractor to undertake both the chemical injection and the re-plastering to avoid any split liability and especially since such re-plastering requires a high standard of workmanship. It is not uncommon where a third party has undertaken associated re-plastering to see the chemicla dpc working but the re-plastering not covered by guarantee has degraded due to being of an inadeqaute specification.

Chemical dpc's are not appropriate for all cases and the experienced specialist surveyor should advise where this is the case. For instance they may not be appropriate for large thickness walls and some types of wall construction. Also some chemical dpc's are pore lining materials and not pore blocking materials and in the case of the former it should be appreciated that if any hydrostatic pressure is present such as say a property close to the sea and significantly below sea level then this may cause moisture to push up through and / or across the chemical dpc.

Perhaps one can see from the above that dampness and associated problems are specialist subjects and hence the recommendation for appropriately qualified persons to inspect the problem as detailed above. Kindest regards, David Aldred Independent damp and timber surveyor.