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Rising Damp Problems

Rising Damp problems, Rising damp problems and treatments, Rising damp problems in houses, Dorset, Bournemouth, Poole, Weymouth, Dorchester, Wareham, Shaftesbury, Christchurch, Bridport, Swanage, Ringwood, Blandford, Wimborne, Ferndown, Verwood

The results of rising damp in walls leave characteristic signs. There is usually a fairly regular, horizontal tide mark, up to a couple of metres above the floor. Below it, the wall is discoloured with general darkening and patchiness; there may be mould growth and loose wall paper. Hygroscopic salts brought up from the ground tend to concentrate in the tide mark. In severe cases, it may cause rot in skirting boards or dados.

If there is a physical DPC, it is unlikely to have failed. But it could be bridged by pointing or rendering, or by soil, or by paving or rubbish heaped against the wall outside, or by plaster inside. In a cavity it could be bridged by a build up of mortar droppings.

If there is no DPC, the presence of rising damp must be confirmed by correct diagnosis before deciding to put in a remedial DPC.

Rising damp can affect solid and suspended floors. In solid floors, it is occasionally due to a faulty or missing DPM. Dampness in suspended timber floors often becomes evident by the discovery of wet or dry rot, starting in joist ends.

Rising Damp Problem, What is Rising Damp?

Rising damp is normally the upward transfer of moisture due to capillary action. Masonry has a complex pore structure in which the diameter of the pores varies widely and influences the ultimate height to which moisture can rise but it can be over 1 metre. Other relevant factors include the degree of saturation of the soil, the rate of evaporation from the wall surfaces and the presence of salts in the wall. Normally, for new construction, a sheet material is incorporated close to the base of the wall to resist the passage of water. In older buildings, there may be no such barrier or the material may have failed. It may also be made ineffective by defects in construction or use where the DPC is bridged.

Rising damp problems in walls

Rising damp problems in walls

Water which can potentially move from the ground through the base of the wall, or which can be conducted into the remaining parts of the structure from wet external leaves, must be prevented from doing so by effective damp proofing. For new buildings, there are provisions in Building Regulations and British Standards for continuous DPCs between masonry in contact with the ground and the structure above, in order to meet the functional requirement. For traditional solid walls, DPCs have been compulsory in dwelling houses since the Public Health Act 1875.

Rising damp problems in solid masonry walls

Most solid walled houses built between 1875 and 1950 and some older ones, were built with a DPC in the external masonry walls. Some DPCs may have deteriorated and failed but bridging around a DPD is far more common cause of rising damp. Buildings with a suspended timber ground floor generally have a DPC located at, or above the wall plate supporting the floor joists typically 175mm below finished floor level, while those with a solid floor will often have a DPC coincident with the top of the structural floor (typically 50 mm below finished floor level). This difference in level of DPCs can promote bridging problems when solid floors are substituted for suspended floors, or where solid and timber floors abut (for example solid floors in kitchen or scullery and timber floors elsewhere).

Damp bridging of DPCs is a common problem caused by external rendering, internal plastering, raised external ground, solid floors and bonded in external walls(such as screen or boundary walls). Previously installed remedial DPC systems may be damaged or ineffective; problems are commonly encountered with osmosis, evaporation tube and poorly installed chemical systems. Failure of physical DPCs, particularly those formed by engineering bricks or over lapping slates, may result from breakdown of the bedding mortar. Some bitumen felt DPCs become brittle with age; some can soften in hot condition and exude from the wall under pressure, although this seems to make little difference to performance unless actual fractures occur.

Rising damp problems and brick cavity walls

Few buildings constructed with cavity external walls will have been constructed without a DPC of some kind so, if rising damp is suspected, the cause is likely to be breakdown or bridging of the DPC rather than its omission. Bridging is much more common than failure, as most DPC materials have a long life in the protected inner leaf of a wall. The outer leaf should also have an effective DPC but localised failure here is unlikely to cause dampness internally in the dwelling.

Rising damp problems in floors.
Rising damp problems in floors

Rising damp in floors is much less common than in walls; it is often confused with excess residue construction moisture, a common problem in new buildings. In both cases, symptoms are damp patches on porous in situ flooring, rucking, curling and loss of adhesion of sheet and tile flooring, or expansion and disruption of woodblocks. Lifting and loss of adhesion can also be caused by excessive use of cleaning water.
Not all floors are subject to dampness problems; those in contact with the ground in basements or ground floors will clearly be most at risk and measurements should be made to determine the scale of any defect. But the risk should not be discounted altogether with suspended floors, particularly at bearings on external walls. Information from Property Mutual indicates that about one in ten of newly built dwellings inspected by them during the early 1990s were not adequately protected against rising damp.

Damp problems in Chimneys
Damp problems in Chimneys

Dampness is common around chimneys. They should have a capping, a flashing to prevent rain passing between the chimney and adjacent roof covering and in exposed locations, one or more DPCs built into the chimney. The bottom one should be at the lowest intersection between roof and chimney. Rain can penetrate into the stack through eroded pointing or through cracked or detached rendering on the outside of the stack.

There must be adequate provision for damp proofing a masonry chimney where it penetrates the roof line. Not all old chimneys were fitted with DPC and some of these chimneys can be sources of continuous problems.


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