Driving Rain

• Driving rain is rain carried along at an angle to the vertical by wind so that it impinges on the vertical surfaces of the building .
• The effect of driving rain is that the vertical surfaces facing the wind now receive rainwater , although at an angle . The run-off from the vertical surfaces will increase the loads on any abutting horizontal or sloping surfaces unless the water is drained away separately .
• When a droplet of rain driven by wind strikes the building surface , it fall apart & its kinetic energy may force part of the droplet into the pores of the material used in the construction .
• The accumulation of moisture within the material may cause expansion of the material while slower surface drying cause contraction . The resultant stresses set up may laead to disintegration of the surface layer .