[FDArchitects]

Following are the main causes of dampness in a building

Rain penetration
It is the main source of dampness. Heavy rain of short duration is less dangerous. rain water enters through joints, cracks and porous bricks or stones.

Level of site
Low laying building sites are effected by the depositing surface water and underground water.

Drainability of the Soil
Course grained soils like Sandy or gravely soils provides good drainibility conditions and fine grained soils like clay retain water and cause dampness.

Climatic conditions
In cold climatic condition dampness causes due to condensation of water vapors.

Defective Orientation
If building is exposed to direct rain showers and less sun rays then it cause dampness.

Entraped moisture in the building
Due Over soaked bricks and use of salty or alkaline water results dampness in building.

Defective construction material
Porous bricks, soft stones, alkaline water etc. cause dampness of building.

Defective construstion
Through defective joints of parapet, copping and masonry joints moisture can enter in the building.

Moisture originates in the building.
It is due to the leakage through water supply or sanitary system of building.

[Mili Jain]

what are the effects of this dampness in building ..?? what happens if it persists for a long time in building

[FDArchitects]

Effects of Dampness

Following are the harmful effects of dampness in buildings:

Building becomes aesthetically poor.
It causes dry Rot to the wooden members provided in the building.
It causescorrosion of metals used in building.
Plaster peels off.
Paint blistered and bleached and the surface disfigured.
Holes and pits are formed in topping of floors.
Efflorescence occurs and bricks disintegrate and turn in to powder.
Unhygienic conditions in building.

[fdaforum]

basically what is dampness :

Dampness :
The excess entry or penetration of moisture inside a building through its Floors Walls and Roofs is called Dampness.
Dampness is dangerous both for Inmates and Building
Due to dampness the building become unhygienic.
Dampness in buildings is a risk factor for health effects.