Damp and Condensation.
Moisture may enter a dwelling in any of the following ways:
1. Water introduced during construction. Several tones of water are used in block laying and plastering and often the walls remain damp until a period of warm weather.
2. Penetration through roofs and chimneys. Tiles and slate need to be laid at an adequate pitch and securely fixed to avoid penetration of driving rain. There should be a generous overhang at the eaves and the junction between chimneys, walls and the roof need to be damp proofed and sealed with lead flashing.
3. Penetration through walls. Penetration occurs most commonly through walls exposed to the prevailing wet wind or from leaking down pipes. Dense rendering can prevent moisture drying out more effectively than preventing its entry, and this tendency is accentuated in cracked rendering with moisture penetrating by capillary action. Modern building materials and methods such as cavity wall construction, vertical and horizontal DPC and DPM reduce the possibility of dampness. Blockwork and plaster are pervious materials and therefore in single leaf solid walls and older construction moisture can soak from the outside after prolonged rain. Rising Damp can be a problem in older houses where there is no DPM or in new buildings through defective DPM, bridging of DPC by a floor screed internally or mortar droppings on the wall ties.
4. Dampness may also result from leaks in plumbing system and condensation.
In older types of houses much of the moisture laden air from cooking, bath, clothes drying etc., could escape through draughty windows or doors, also these houses traditionally had more chimney flues than is common now. Nowadays, with increased cost of fuels and consideration for energy conservation, homes are now better sealed. This prevents the ventilation of moist air and gives rise to a sharp increase in problems caused by excessive condensation.
Factors that influence condensation include:
Air holds water in the form of water vapour that is generally invisible.
Dampness caused by condensation can be remedied by considering heat and
Ventilation can be achieved by providing:
Ventilation includes background ventilation (a wall vent providing one air change per hour approx.) and rapid ventilation in a bathroom for example where a large amount of steam is generated and a window can be opened momentarily.
In situations where high levels are air change are required (3 -4 air changes per hour) the new air may need to be heated to maintain a comfortable temperature. This means more fuel is used and is expensive, some homeowners then reduce the amount of ventilation and therefore risk dampness.
Heating is equally important in controlling dampness. It should be remembered that warm air can hold more moisture that cold air and condensation forms on cold rather than warm surfaces.
Construction for Condensation
Even when all precautions are taken it is still common for condensation to occur, most likely places being bathrooms, kitchen and on any window. Occasional condensation is not a problem if it is anticipated and reparation made for it. The use of impermeable materials such as glazed ceramic wall and floor tiles in these areas prevents condensation from penetrating the building structure and causing damp.
Interstitial Condensation occurs within the structure or fabric of the
The Dew Point is the temperature at which a fixed sample of air becomes
The Relative Humidity (RH) of a sample of air compares the actual amount
of moisture in the air with maximum amount of moisture the air can hold
at the that temperature.
Unit: Percent R.H. at a specified temperature. It is also common practice to describe humidity in terms of percentage saturation.
In order to maintain a constant temperature within a building it is necessary
to restrict heat loss, keeping heat inside a building for as long as possible
to conserve energy and reduces heating costs.
Where materials of high thermal conductivity pass completely through
a wall, floor or roof without insulation e.g. solid block wall, lintel.
A layer of building material that has a high resistance to the passage
of water vapour.
Damp Proofing Old Buildings
One method involves sawing a slot in a mortar bed joint and inserting
a damp-proof membrane. The membrane is normally in about 1m lengths and
can be slate, bitumen-felt, copper, lead or polyethylene.