Wind and rain
The hazards dealt with in this section are principally of three types:
• Sand and dust
• Tropical downpours
• Cyclonic storms
Sand and dust
• These are common hazards in hot dry regions, capable of causing problems of durability of building components and great discomfort for the dwellers.
• Continuous attack by wind-blown sand causes abrasion of materials and dulling of surfaces; sand and dust can enter buildings through cracks and gaps between materials; accumulation of sand in parts of buildings can be a nuisance, but also a hazard, if loads increase on weak components; rainfall mixed with sand and dust can produce a messy sludge.
• Under normal conditions sand particles roll or bounce on hard surfaces to heights between 1 and 1.5 metres, while dust can be carried to any altitude in the earth's atmosphere.
• These can occur suddenly and with great intensity, producing floods in a very short time.
• Heavy rains in the tropics can loosen and dislocate building components; cause breakage and penetration of water; wash off coatings, insecticides and fungicides; create unbearable noise on some types of roofs.
• Inundation of buildings causes people to seek refuge on the roofs, which can collapse under the extra load.
• The softening of soils and exposure of foundations can cause severe building damages.
• Rain penetration in buildings can encourage fungal growth and corrosion of metals.
• These storms, commonly called hurricanes (in Atlantic and Caribbean regions), typhoons (in the Pacific region) or tornados (in all inland regions), can reach wind speeds exceeding 300 km per hour. Hurricanes and typhoons are generally accompanied by torrential rains and, since they occur mainly in coastal and island regions, create storm surges, which send seawater several kilometres inland, causing floods and destruction.
• The high wind pressures affect all parts of the building, so that light structures are the most vulnerable. Roofs with slopes less than 30° can be torn off by the high negative pressure (suction) on the leeward side.
• Flying debris also cause considerable destruction; due to the lashing rain, water penetrates unprotected parts of buildings; components get dislodged and a rewashed away; trees, power transmission poles, chimneys, etc., fall on houses and people; and a number of other effects of tropical cyclones can account for thousands of deaths and total devastation.
Sand and dust
• Wind-blown sand is effectively excluded by surrounding houses with sand barriers (eg masonry walls) of at least 1.60 m height. Better still are houses with completely enclosed courtyards, whereby the outer walls have no openings, or just small ones located at a high level.
• Vegetation around houses can greatly reduce the amount of flying sand and dust. Narrow, zig-zag streets with high walls on either side have a similar effect.
• Projecting components and cavities should be avoided on outer walls to prevent accumulation of sand and dust. Surfaces should be smooth and resistant to abrasion.
• The siting of buildings should facilitate quick drainage of water. Houses raised well above the ground surface and drainage channels surrounding them are important.
• Wide overhanging sloped roofs are required to protect outer walls and openings, and discharge the rainwater at a sufficient distance from the wall base, avoiding dirt and erosion by splashing water.
• Tight, waterproof joints and water-resistant materials or surface treatments are essential to avoid rainwater penetration. Facilities for cross-ventilation to remove indoor moisture are equally important.
• Insecticides and fungicides applied externally can be washed out, losing their function, but contaminating the surroundings; hence they should be used with great care or avoided, if possible.
• Metal connectors and components that can corrode should be protected from rainwater and well ventilated to prevent moisture retention.
• To prevent noise problems on sheet metal roofs, shorter spans between supports, bitumen coating on the underside of sheets, rubber washers at the suspension points, and an insulating layer or suspended ceiling, all contribute towards noise reduction, and are effective in combination with each other. Quite often layers of straw are placed on the roof, but must be tied down, as winds can blow them off.
• In flood prone areas, roofs must be especially strong to carry the load of dwellers seeking refuge. Provision of storage space just under the roof and openings for trapped air to escape are further useful measures. House constructions that permit the house to float on flood water can avoid a lot of damage, providing it is anchored at the same spot.
• Building sites should preferably be at higher levels, sufficiently distant from the seashore, and topographies or the surrounding buildings should not cause a funnel effect or increase wind velocities. Clusters of trees act as natural wind-breaks.
• Foundations should be generously dimensioned and wide at the base to resist uplifting forces or tilting due to pressure from the side. Connections between foundations and walls or columns need to be exceptionally strong.
• Stability is increased by division of floor plans into smaller rooms, the walls teeing strong enough to resist lateral forces (eg strong corners, diagonal bracing, etc.) and securely fixed to the foundations and roof; outer walls should be smooth and streamlined (eg rounded corners, no projections) to provide least resistance to winds.
• Roofs should be sloped at least 30°, to reduce the danger of lift-off; for the same reason, wide overhangs must be avoided (which contradicts the requirement for rain protection); connections to the substructure must be particularly strong and rigid, as forces act from all sides.
• Openings should be small and provided with shutters (folding or sliding, rather than hinged); glass panes, especially thin varieties, should be avoided.
• In general, good materials and workmanship are the principal protective measures, and designs should permit easy access to vulnerable parts for regular inspection and maintenance.
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