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Welcome to the Damp section : Dealing with damp in older houses
How to rectify damp in older houses

There are 3 types of damp often found in older homes which are

1) rising damp,

2) penetrating damp and

3) condensation.

1. Rising Damp
  Rising Damp: often the result of a failure in the DPC (damp-proof course). Bricks are porous and if you think of a brick as a type of sponge, it is able to draw moisture up from the ground. The DPC is normally built into the wall at a level of about 6 inches (2 or 3 courses of brick) above the ground, which should stop the damp rising any higher, but over many years, the original DPC (which could be a thin layer of slate, bitumen, lead…) deteriorates and its effectiveness reduces.
  Examine the external brickwork of the house and identify where the damp-proof course is located. There may be a physical reason why the DPC is not working effectively, such as earth piled above the DPC, or rendering applied over the DPC which would allow the moisture to 'bridge' over top of the DPC.
  The drainage of rain and ground water can sometimes be problematic especially when surrounding land is sloped towards a house (putting more of a strain on the existing DPC). Improve drainage by either channelling water away from the house, or allowing water to more easily absorbed into the ground (e.g. replace paving with gravel or planted areas…).

If your DPC has failed you'll need to inject a new DPC into either the brickwork or mortar layer (depending on the method chosen). This is done by drilling holes into the exterior and interior brickwork (or mortar layer) then injecting a specialist waterproofing fliud. The fluid is absorbed into the porous brick and once set will provide an impervious layer. See our feature on "How to inject a DCP" click here.... 'How to inject a DPC' click here...


Rising damp in floors: old 'earth floors' (i.e. often with clay tiles or stone slabs sitting directly on soil) usually have little or no damp-proofing. To fix the problem: you may need to replace the floor by digging out the soil, laying a damp-proof membrane & insulation, and pouring concrete.

See our feature on "How lay a concrete floor" click here....

2. Penetraing Damp
  Penetrating Damp: this is where water is entering into the house as a result of a 'physical' problem, such as a damaged or blocked guttering & downpipes, roof tiles missing, roof flashing damaged, rotted window sills, damaged brickwork, porous mortar (brickwork may need repointing) etc.
  Penetrating damp is usually easy to identify since it is shown as damp patches in walls or ceilings, which become more noticeable when it rains. Its recommended you fix the problem quickly since penetrating damp can damage plasterwork, rot structural timbers, interfere with electrics and so on.

To fix the problem: identify where the water is coming in and investigate the exterior of the house. You should be able to identify what the cause is and what is in need of repair.

Common causes of penetrating damp are defectives: roof tiles, ridge tiles, flashing, guttering & downpipes...

  ...and of course brickwork mortar. This photo shows that the old lime based mortar is become porous and repointing of the brickwork is required. The property on the left side of the photo has had their repointed.
3. Condensation
  Condensation: Old houses were designed to be drafty. They were built with open chimneys, single pane sash windows, and no insulation. This resulted in a constant supply of fresh air circulating through the house, allowing it to 'breathe' and release trapped moisture.
  Over the years most of these houses have now been fitted with double-glazed windows, draft-free doors, high performance roof insulation, and had those lovely drafty chimneys blocked off.
To fix condensation problems:
Walls: ensure air bricks and vents are clear (you may need to add extra airbricks to increase ventalation). Install an extractor fan in your bathroom/shower room. You may decide to insulate solid brick walls (see our feature click here…)
Roof: ensure loft insulation is not blocking airflow from eaves
Pipe work: if pipes are sweating add pipe insulation (pipe lagging)
Windows: if modern windows are fitted ensure they have a trickle vent.
Chimney: open up and insert an air vent (possibly on the top of the chimney, lets air in, keeps rain out).

If your house has a problem with damp, its best to identify the source of the problem and rectify it. Don't waste money on temporary measures such as specialist paints or crystals that abosorb water.

  © 2006