Biological agents that can cause problems in buildings are:
• insects (termites, borer beetles, triatomine bugs, cockroaches, mosquitos, flies, etc.), which either attack and destroy building materials (such as timber, bamboo, some plastics, etc.), represent a health hazard or are simply a nuisance to the occupants;
• animals (rats, bats, birds, snakes, etc.), which can nest in uncontrolled cavities, and can not only create health problems and disturb occupants, but also restrict important functions of the building, for example, by building nests which block ventilation openings or clog drains;
• fungi (moulds, stains, rots, etc.), which develop in moist dark conditions on timber and other vegetable building materials, some fungi being non-destructive (blue stain), while others (dry rot, wet rot) lead to decay and destruction.
Many methods of protecting buildings and occupants against these agents exist, but some protective measures can create new problems, if implemented without sufficient care and consideration of the consequences. Good building design and use of materials should always be considered before resorting to using chemicals, which can destroy fungi, insects, rats, pets, children .......
• Maintenance of clean conditions on the building site is vital, as dense vegetation, debris, dirt and moisture provide ideal environments for biological agents to thrive in. If termite colonies are found in the vicinity, the use of vegetable building materials should be avoided as far as possible, or used only for non-structural components.
• Good drainage of the site is essential, to avoid moist conditions (which attract insects) and standing water (in which mosquitos breed).
• Soil poisoning below and around buildings is advocated in most publications, but it should be remembered that the poison will sooner or later be washed into the ground water, losing its protective effect against termites, but contaminating drinking water supplies.
• A continuous reinforced concrete floor slab under the entire building can effectively keep out subterranean termites. If joints are necessary, these should be rough and sloping or tongue and groove joints.
• Termite shields fixed continuously around the base of the building, V-shaped grooves (45° angle) and metal caps projecting 5 - 8 cm around pipes and columns, provide sharp corners, around which termite tunnels cannot be built. These are also visible barriers that help to detect the development of tunnels, which can then be destroyed.
• Buildings raised 80 - 100 cm off the ground on poles or columns (not continuous footing wall) permit visual inspections underneath the floor (to keep away termites and other insects, and maintain clean conditions), and also facilitate ventilation (keeping the floor dry). Exposed foundations and columns should be painted in a light colour to help detect termite galleries easily from a distance.
• Foundations and floor slabs must be constructed with great care to avoid the development of cracks through differential settling. Cracks can also develop due to drying shrinkage, thermal and mechanical stresses, or bad quality materials and workmanship, and these should be carefully sealed, especially in walls, to avoid nesting of insects, such as triatomine bugs, which are responsible for the Chagas disease (an illness from which more than 20 million people in the rural areas of Latin America are suffering).
• Certain timber and bamboo species have a natural resistance to insect attack, and should be used wherever possible. However, these species are usually rare and expensive, so that less resistant species are mostly in use. Hence proper seasoning and some form of chemical treatment is necessary to avoid early deterioration. (Please refer to the sections on Bamboo and Timber.) Under no circumstance should bamboo or timber components be embedded in the ground.
• Mosquitos, flies, flying termites, and numerous other insects can be kept out of buildings by covering all openings with fine wire mesh, but this also causes a reduction of cross ventilation.
• New methods of termite control by natural means are being investigated in the Federal Republic of Germany (Bibl. 25.12): by special cross-breeding and elimination of the reproductive capacity of termites; by producing sexual hormones to disorient the termites or alarming pheromones and repellents to start a reaction of escape; by subjecting termites to certain toxic fungi (effective only in the first 3 weeks of the fungus' life). However, these biotechnical and microbiological methods still present problems that warrant extensive research.
• Rats and mice are eliminated by depriving them of nesting places and every possible source of food. Rubbish heaps, piles of stone or wood, tall grass, etc. should be removed.
• Food stores can be made rat-proof if the entrance is high enough above the ground and thus inaccessible to rats. Metal sheet strips about 30 cm wide, running parallel to and 60 cm above the ground, prevent rats from climbing up walls. Metal termite caps, projecting farther outwards (about 20 cm), prevent them from climbing up columns and pipes.
• Concrete floor slabs prevent animals from gaining access to the building from below.
• Birds and bats, which nest under roofs or in cavities, and snakes and other animals that can enter through ventilation slots and pipes, are kept out by covering all openings with a wire mesh.
• In general, smooth, hard surfaces, clean conditions and regular inspections are very effective in keeping a place free from pests.
• Fungi are simple plants which cannot produce their own food from air, water and sunlight, but live on dead organic matter (timber, bamboo, etc.) located in damp, dark, warm and poorly ventilated places. Therefore, the best protection against fungi is to maintain clean, dry, light and well ventilated conditions. Moisture contents of timber should be less than 20 % (achieved by proper seasoning).
• Temperatures below 0° C (unrealistic in the tropics) and above 40° C also prevent fungal growth, as well as complete submersion in water.
• Designs with timber and other vegetable material should ensure quick drainage of water and avoidance of direct contact with concrete or masonry (achieved by placing a damp-proof membrane to separate the materials).
• Timber, affected by dry rot, should preferably be replaced by a fresh, unaffected component, while the affected timber should be burnt.
• Chemical treatment can help to eliminate fungi, but here again the comments in the sections on Bamboo and Timber apply.
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