Cost of damp Proofing

March 19, 2014
Damp Proofing Old house

Damp in the home can have many causes and many negative effects. In addition to the physical structural damage to your property, damp can also cause bad odours, mould, and rot. These side effects can impact the health of you and your family and lead to allergies and illness.

Our modern lifestyles and building methods can raise the relative humidity inside our homes. Measures such as double glazing reduce ventilation, and bathing, cooking, and washing all generate water vapour. This vapour condenses on various surfaces, resulting in damp. Condensation damp can be diagnosed from water droplets and mould growth on internal surfaces.

Penetrating damp is caused by rainfall seeping into houses due to poor roof maintenance and repair, gutter blockages and overflows, and various other points where water can enter. This water seeps into the structure of the building and the timbers and can cause significant damage. This type of damp displays as large patches or stains on walls, ceilings and floors, particularly after heavy rains.

Internal spillage occurs when a bath or sink overflows or an appliance such as a dishwasher or washing machine leaks. Damaged and burst pipes and geysers also result in internal spillage.

Below ground damp causes what is sometimes called rising damp. Moisture in the ground evaporates but is impeded by the impervious coatings used in building, causing the water to drain towards the perimeter walls, where it soaks up through the brickwork by capillary action. This can also be affected by fluctuations in the water table beneath your property. The rising damp caused by below ground moisture can leave a tidemark on the walls indicating salt deposits, although there is seldom mould growth.

Common Causes of Damp in your Home

The causes of damp fall into four categories:

  • Condensation
  • Penetrating damp
  • Internal spillage
  • Below ground damp

What Does Damp Proofing Entail?

or DPCs, a barrier designed to prevent moisture from penetrating your walls and floors. Other methods include application of a paint-on preparation that seals the surfaces. There are also instances of porous ceramic tubes, 50mm in diameter, being inserted into a wall. The theory is that these tubes will collect the damp and allow it to evaporate, but they can be unsightly and there are often problems in application.

Some of the damp proofing methods employed are extreme and require structural alteration to your house.

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How is the DPC Inserted into the Wall?

There are different methods for installing DPCs. In some cases, the DPC is inserted by cutting into the wall or during rebuilding. This can be effective, but it can also result in structural problems and damage to internal finishes, especially where these are custom or antique.

There are chemical damp proofing course solutions available which are injected into holes drilled into the wall. This method is quite widely used today, but it cannot always be applied in older buildings. The cost of chemical DPCs is around £195/m, which includes the cost of re-plastering the holes through which the mixture is applied.

Damp Proofing Costs

This table details estimated damp proofing costs for dealing with common damp situations. These costs are obtained from the Building Cost Information Service, which is part of the Royal Institute of Chartered Surveyors. The costs include everything necessary to carry out the work including labour, material and VAT (correct as of December 2011).

Problem Solution Terraced house – one wall Terraced house – whole house Semi-detached house – one wall Semi-detached house – whole house Detached house – one wall Detached house – whole house
Ground level is above the existing damp- proof course Excavate soil only £204 £268 £262 £594 £437 £1, 446
Excavate soil and lay pre-cast concrete paving slabs £431 £728 £600 £1, 491 £1, 036 £3, 274
No damp- proof course in wall Inject silicone damp-proofing course £221 £350 £384 £469 £1, 899
Internal walls are damp Asphalt tanking to 1.2m height and decorate to full height £1, 631 £3, 250 £2, 435 £6, 477 £4, 858 £15, 346

How to Save Money on Damp Proofing

  • Ideally, damp prevention measures should be put in place during the building stages, but this is obviously not an option in existing homes, especially in older and period houses.
  • If you do discover a damp problem in your property, the first step towards ensuring that you are treating the problem correctly would be to determine the actual cause of the damp. Oftentimes an expensive and intrusive solution is recommended when a simple, cheap one would be as effective.
  • If the damp is caused by condensation, it could be a simple matter of improving the ventilation in your home. Opening windows and doors to allow air flow could help significantly. Installation of extractor fans in high moisture areas such as kitchens and bathrooms can also make a big difference. Proper insulation can also go a long way towards preventing condensation in your home.
  • Penetration damp can have many external causes as mentioned above, and simply repairing the root cause can solve the problem and allow the moisture to evaporate. Gutter maintenance and repair should be carried out at least twice a year to ensure that there are no blockages or leaks that can cause overflow into the structure of your house.
  • Roof junctions are often areas where leaks can occur, and resealing these areas can prevent leaks. Replace missing or broken roof tiles before leaks can cause damage to roof timbers. Re-point any mortar that needs it to prevent cracks and holes forming where water can get in.
  • The same principle applies to damp caused by internal spillage. Often removing and repairing the source of the water will solve the damp problem without the need for drastic and expensive measures.
  • Future damp problems can also be prevented by using lime plaster instead of the anti-sulphate or renovating plaster that is normally use. Lime-based plaster allows greater breathability, which aids evaporation and decreases the chances of damp build up.
  • Proper drainage in the ground surrounding the house can also prevent below ground damp, especially in basements and cellars. French drains can be effective for this purpose, but need to be set up properly to avoid compounding the problem.
  • Rising damp is often the most difficult and expensive to fix, as the damp has permeated the walls and floors deeply and can be difficult to fully remove. However, investigations have shown that this damp is actually far less common than popularly believed. Often what is diagnosed as rising damp is only condensation, and can be solved as described above.
  • Make sure that you know exactly what type of damp you are experiencing before embarking on an expensive damp proofing solution.
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