THE French word doucement has an onomatopoeic sensuality that is entirely absent from any English synonym. When Arthur Rimbaud, therefore tells us that Il pleut doucement sur la ville, he conjures up a whole mise en scene that seems to merge the soft drizzle of a Connemara autumn with the demi monde of the seedy suburbs of a nameless town in Normandy. "It rains softly on the town" fails utterly to convey the same impression.
But Connemara rain is often far from doucement. Sometimes it is very heavy and when combined with the penetrating force of a strong wind it results in a phenomenon known to meteorologists as "driving rain", whose penetrating power can be a severe test for even the most sophisticated of building methods and materials.
In calm conditions, raindrops fall vertically at a speed depending on their size. When a wind is blowing, however, the drops are also carried horizontally. With very strong winds the rain is swept along at angles close to 45 degrees, and vertical windward walls receive substantial wetting. During a prolonged spell of such conditions, water may penetrate through tiny cracks, the structural fabric of the building may be affected and damage may be caused to interior decoration. At the very least, the absorbed rainwater increases the thermal conductivity of the walls, and by lowering the temperature inside may lead to condensation on the inner face. It also increases the fuel consumption required to maintain the house at normal temperatures.
Difficulties of this sort, however, are not inevitable; they can be minimised where driving rain is frequently a problem. Careful choice of site and orientation, for example, reduces the exposure; special architectural features, like large roof overhangs, provide good protection; and special methods of construction, or a protective coating applied to a finished surface, help to avoid the most unpleasant consequences.
To gauge the extent of the problem in different regions, meteorologists have devised a "driving rain index" to quantify susceptibility. It is based on annual average wind speed and rainfall and a look at the resulting map brings no surprises. High values of the driving rain index, between 10 and 15, are common in the western counties; values of six or seven are the norm along the south coast, while four or five is typical of the midlands, and Dublin has a driving rain index of slightly less than four. As one might expect, there are also strong variations with local topography, mountain areas having much higher values than their neighbouring lowlands.