Damp proof courses defined
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Damp proof courses defined
We would refer you to wikipedia.org, the excellent free online encylopedia. It says:
A damp-proof course (often abbreviated to DPC) is a horizontal barrier in a wall designed to prevent moisture rising through the structure by capillary action - a phenomenon known as rising damp .
Interestingly, they say:
This technique has been used since ancient times. The Romans used a horizontal course of slate inserted in a wall to act as an impervious barrier.
Building standards in many countries require most new buildings to incorporate a DPC at the time of construction. This may consist of a thin strip of plastic, a course of engineering brick or slate, or a layer of bitumen.
It would be interesting to know what the person who put the Wikipedia definition up does for a living?
Wikipedia definition under damp proof course for properties without a damp proof or a failed damp proof course
Where a DPC is absent or inadequate, there are various means of retrospectively fitting one. A common method in masonry walls is to drill holes into the wall at regular intervals and inject a penetrating chemical (e.g. silicone) into the holes. The chemical is absorbed into the masonry where it dries to form a waterproof barrier. Some irregular stone walls cannot be drilled for a chemical DPC, so an osmotic electrical system is often fitted.
Alternatively the cement joints can be drilled and the chemical injected there instead, although this is a less satisfactory method. A larger volume of chemical will be needed.
Some forms of the chemical are odour free, some have a strong odour, this should be taken into account when purchasing.
We would reiterate this is a definition from Wikipedia and isn't one that we agree with.
The construction definition from Wikipedia
This is interesting too.
The DPC known as Damp Proof Course is usually a thick plastic strip bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin plastic line in the mortar near ground level.
A DPM is usually a thick polythene sheet laid under the floor slab, to allow the slab dry out and keep out groundwater. It is often laid on a bed of sand, to prevent the sharp edges of the hardcore damaging it.
To create a continuous barrier, pieces of DPC or DPM are welded together. In addition, the DPC is welded to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground under it.
In a cavity wall, there is usually a DPC in both the outer and inner wall. In the outer wall it is normally 150-200mm above ground level (the height of 2-3 brick courses). This allows rain to form puddles and splash up off the ground, without saturating the wall above DPC level. The wall below the DPC may become saturated in rainy weather. The DPC in the inner wall is usually below floor level, (under a suspended timber floor structure), or, with a solid concrete floor, it is usually found immediately above the floor slab so that it can be linked to the DPM under the floor slab. This enables installation of skirting boards above floor level without fear of puncturing it. Alternatively, instead of fitting separate inner and outer DPCs, it is common in commercial housebuilding to use a one-piece length of rigid plastic, (albeit an angled section), which fits neatly across the cavity and slots into both walls (a cavity tray). This method requires the need for weep vents to enable rainwater ingress to drain from the cavities otherwise rising dampness could occur from above the DPC.
In old buildings there may be a DPC made from lead . The DPM may be non-existent, leading to damp problems, or it may rely on an impermeable floor finish such as ceramic tiles to keep most of the damp out.
Again, we must stress that definition of a damp proof course comes from Wikipedia and not us.
Different types of damp proof course
There are many different types of damp proof courses, which can be broadly divided into two sections:
Original damp proof courses have been built in as the property was constructed, and
new damp proof courses that have been added after the property was built. They may be into a property that originally had a damp proof course, or with many older properties (prior to the late 1800's), when damp proof courses were first required.
We would refer you to our article on Damp proof courses, why? for more information
Many sources say it was from the Public Health Act 1875, however, Jeff Howell from the Sunday Telegraph and the excellent website askjeff.co.uk , has researched the subject and in his brilliant book The Rising Damp Myth believes the first legislation to be from the local government board's model by-laws of 1877. We are sure in some areas of the country the practice of adding a damp proof course was long established if it was formed as part of a by-law and in other areas of the country it no doubt took some further years these methods were adopted.
Damp proof courses built in as the property was built
|During the course of our surveys on older Victorian and Edwardian properties, where we can see a damp proof course these tend to be the edge of a slate. In many instances we can't actually see any damp proof course at all, as there is a rendered plinth at the base of the property.
|White painted rendered plinth to the base of the property, built in the 1800s
Lead damp proof course
We have read about these being used but we have only seen them used retrospectively and this was to a timber frame property, where the sole plate, which is bottom most timber, meets the brick plinth and makes up the very base of the property. The lead flashing had been added relatively recently and we can see this as being both good and bad, depending upon the detailing. Unless the lead was well formed with a suitable slope it would allow water to sit on a ledge, which would ultimately cause problems.
Modern plastic based damp proof courses
A variety of different styles have been used over the years, such as plyload, which their website informs us is a bitumen free polymeric damp proof course.
It is flexible to low temperatures, resistant to ageing and shrinkage and can withstand superimposed loads.
Interestingly, it comments:
Traditional damp proof courses were made from textiles with bitumen or pitch and suffered from creep under heavy load and therefore have limited life spans.
They then go on to say that these were superseded by high performance rubber products, but these were generally high priced. Alternative cheap polythene products were used in lower specification applications, despite the low strength of the mortar/polythene bond and an example of a modern damp proof course.
Information from the supplyload.co.uk website.
Another manufacturer is Anderson and they do a variety of damp proof courses; from a standard one that is bitumen free and uses a blend of polymers and elastimers, to a high load variety, to a bitumen and polyester based damp proof course that is advertised as being very robust, to a high performance DPC, that is capable of both gas and damp proof course existence.
Funnily enough, whilst we looked for manufacturers of damp proof courses, the Internet offered us far more companies that inserted damp proof courses as a remedial service. We may have been using the wrong term, or the inserting of a damp proof course may simply be bigger business.
New damp proof courses that have been added after the property was built
Damp proof courses that are added at a later date
These fall into four areas:
the insertion of a damp proof course
the repairing of a damp proof course
magic tubes tubes
the electronic barrier system
DIY inserted damp proof courses
If you look to remmers.co.uk website, who offer drill and cartridge kits for your house for under £100!
Damp-proofing cream soaks in over an hour and reacts with the water in the masonry to form a complete DPC. BBA Certificate /4202. This is based on a silane/siloxane paraffin emulsion and all you do is:
Drill a whole into the wall, along the line of the mortar joint.
Slot the cartridge into a silicone gun and attach the nozzle, which you will need to buy from them.
Squirt the cream into the hole.
Job done; no more damp.
It says it is suitable for stone, brick masonry rubble on most walls, a full proof DPC every time!
There are many companies offering the insertion of a damp proof course; from large companies, such as Kenwood Plc kenwoodplc.co.uk , RentaKill rentakill.co.uk , Protim protim.ie and Pass & Co. Timber Preservation: londonline.co.uk and many other local companies; search on the Internet or in your Yellow Pages to see that there is plenty of choice.
The physically inserted damp proof course
Although we have never seen it, we have heard it talked about. This is where, literally, a section of the wall is removed and a slate damp proof course is inserted, although we can't see why it can't be any other sort, and the building is gradually worked around (we assume) until the damp proof course is in place.
Magic tube system (the Knapen system)
Often advertise on the front of national newspapers, so we assume they sell a lot of them to make them worthwhile, although we can't say we've seen more than a dozen over 20 odd years.
We found the gist of this explanation in a book called Damp Walls by R W Castle, and on http://books.google.com .
This system involves a tube of approximately 2.5cm diameter being inserted into the wall (not an easy task in itself). The frequency of these tubes depends upon the material into which they are being inserted, the ideal being that it increases the evaporation of moisture by ventilating the property better.
This article utilised:
The Rising Damp Myth by Jeff Howell: Bricklayer, Chartered Surveyor and Chartered Building Surveyor
Mike Parrett's information from the SPAB (Society of Protection of Ancient Buildings) website, particularly in relation to annual maintenance work
The article by Tim Hutton MA MSc MRBs on Building Conservation 1998.
Dr Jagjit Singh, the excellent ebssurvey.co.uk
remmers.co.uk , who provide a do-it-yourself damp proofing kit, Tel. No. 0845 373 0110, local contact Ashley Palmer at firstname.lastname@example.org Tel. No. 07545 330675.
You may also be interested in these other articles about dampness issues:
Resolving Dampness in your Basement
Dampness in Buildings - Basics Article
Dampness in Buildings - Technical Article
Dampness Defects Report
Shared Freehold and Problems with Damp
Damp Proof Courses - What are these for?
Damp Proof Specialists - Talk to us First
How do Older Properties keep dry without a damp proof course?
Rising Damp and Independent Reports
Please see our section on:
Specific Defects Reports
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