A damp proof course 

A damp proof course is a course of some impermeable material laid in the foundation walls of building near the ground to prevent dampness from rising into the building. The damp proof course may be horizontal or vertical to prevent moisture rising through the structure by capillary action. Damp proof course is usually made from bitumen coated aluminium, plastic sheets, PVC, copper or lead sheets, cement concrete.

 

Material used for damp proofing


An effective damp proofing material should have the followingproperties
  •  It should be impervious.
  •  It should be strong and durable and should be capable of withstanding both dead as well as live loads without damage.
  •  It should be dimensionally stable
  •  It should be free from deliquescent salts like sulphates chlorides and nitrates
  •  The material should be reasonably cheap.
  •  The material should be such that it is possible to carry out leakproof joining work.

Dampness in buildings

What Is Damp?

Damp is generally defined as unwanted water or at least, moisture, in quantities that are unsightly or likely to cause deterioration in the fabric or furnishings of a building. Dampness can be divided into 3 areas or causes,

  •  rising damp,
  •  penetrating damp
  •  condensation damp

Rising damp

This is water soaked up from the ground and is only a problem if the damp-proof course or dampproof membrane is either damaged or bridged. Rising damp is prevented by isolating the concrete footing from ground moisture. While it is normal to protect the foundation wall from ground moisture with a damp proof membrane, no effort is made to protect the footing concrete. However most moisture is located at the bottom of the excavation, where the footings are located. With impervious subsoil it is important to prevent water ponding from occurring at the bottom of the excavation.


Penetrating damp

This is where water leaks into the building through a building defect. Sometimes a defect may be obvious. An example of this could be a missing roof tile which allows water to ingress. A less obvious example could be a leaking rainwater pipe that may not be apparent until the water soaks completely through the wall. Penetrating dampness can be many different defects in the external fabric of the building. The effect is to allow water to get through the fabric of the building.


Condensation

This is moisture generated in the home. It is the dampness formed when air laden with water vapour is cooled by contact with a cold surface. Household activities such as cooking, bathing, washing and drying of clothes, even breathing are major sources of moisture generation. Other causes of moisture can be from flue less paraffin or bottle gas heaters, and un-vented tumble dryers.To reduce condensation from forming, keep doors closed, when these rooms are in use. This stops moisture reaching other rooms, especially bedrooms which are often colder.Condensation and its related problems (such as mould growth) generally occur during the winter months when the outside temperatures are colder than those inside a building. As a result condensation will normally form on external walls and windows.

How to prevent Damp

1) Produce less moisture


Simple things make a huge difference, like covering pans when cooking, drying clothes outdoors, venting your tumble dryer to the outside and not using paraffin heaters or flue-less bottled gas heaters.

2) Let the damp air out and the fresh air in


Consider installing extractor fans in your kitchen and bathroom if they don’t have one already, and shut the doors between these rooms and the rest of the house when they get steamy. Open your windows when you can, and allow the air to circulate behind furniture and through cupboards and wardrobes.

3) Insulate and draught-proof your home


Warm homes suffer less from condensation, so you should make sure your house is well insulated. Your windows and external doors should be air-tight, and you should consider secondary glazing if your windows are draughty.

4) Heat your home a little more


Keep a low background heat in unused rooms. Use a thermostat on the heater or radiator, and remember to air the rooms from time to time.