Appropriate Building Materials: a Catalogue of Potential Solutions (SKAT, 1988, 430 p.) Fundamental information on protective measures Biological agents Fire Wind and rain Earthquakes

Appropriate Building Materials: a Catalogue of Potential Solutions (SKAT, 1988, 430 p.)

Fundamental information on protective measures

Biological agents

General

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 .......

Protective Measures

Insects

· 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.

Protective measures against termites (T. Se, Bibl. 25.12)

· 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.

Animals

· 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.

A simple ratguard (Bibl. 25.08); Prevention of rat nesting (Bibl. 13.13)

· 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

· 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.

Fire

General

Fire is a chemical reaction which takes place when a combustible material is heated in the presence of oxygen. The liquid or solid fuel gives of fvapour when treated end burns as flame.

The surface area of a material relative to its volume and density is a major criterium of its ability to burn. Thick, solid material is relatively difficult to ignite and burns only at or near the surface. Thin sheets burn rapidly, while finely divided or pulverized material can become explosive when suspended in air.

Fires can break out in buildings by accident (eg when cooking on open fires, as is common in many developing countries), by self-ignition (eg by the discharge of sparks due to friction between materials in very dry conditions, or by concentration of the sun's rays by the lens effect of some glasses), or by natural hazards (eg lightning, or earthquakes).

The damaging effects of fires in buildings depends on the materials used and the design and construction of the building. Some materials merely shrink and crack, while others may expand, melt or disintegrate causing total destruction. Lives are endangered by burns, collapsing walls and roofs, inhalation of toxic gases and smoke, panic and loss of sensibility and vision.

In hot arid zones, houses are normally built with thick, heavy materials, which do not readily ignite. In warm humid zones, combustible materials are commonly used, but humidity and rainfall can have the same effect. Nevertheless, there is always a fire risk in all climatic zones, and must be taken into consideration in all building designs.

Protective Measures

· With regard to planning in warm humid zones, where buildings are generally placed well apart for good cross-ventilation, care must also be taken to maintain a good distance between buildings in the direction of the prevailing winds, to avoid spreading of fire from one house to another.

· Climatically appropriate design in hot dry zones calls for close spacing of buildings, but sufficiently wide escape lanes and access roads for fire-fighting vehicles are essential.

· Combustible building elements should not be used closer than 1 metre to potential sources of fire (stoves, chimneys, etc.); similarly combustible materials stored in and around the house must be shielded from such sources by means of non-combustible materials (eg gypsum, glass, bricks, concrete, metals, stones, mineral wool).

· The design of cavities should take into consideration that they can act as flues, spreading fires rapidly.

· Chemical treatment of timbers and other vegetable products is possible (mainly impregnation with borax compounds), but expensive, and complete resistance is never achieved.

· A fire retardant thatch roof construction has been developed by CBRI, Roorkee in India: a non-erodable bitumen stabilized mud plaster is applied on the upper surface and the drying shrinkage cracks sealed with a slurry of soil and cow dung mixed with a small proportion of bitumen cutback. In this way the dense covering layer stops the passage of air and retards ignition for at least one hour. As an additional advantage, the roof is waterproof.

· As a general precautionary measure, it is advisable to have a water reservoir, hose pipe and pump, and/or hand fire-extinguishers close by.

Combustible and non-combustible materials (from Bibl. 00.14)

Combustible	Non-combustible
- Timber (even if impregnated with flame retardant)	- Asbestos-cement products
- Fibre building boards (even if impregnated with flame retardant)	- Fibre concrete products
	- Gypsum plaster
- Cork	- Glass
- Wood-wool slabs	- Glasswool (containing not
- Compressed straw slabs	more than 4 - 5 % bonding agent)
- Gypsum plaster board (rendered combustible by the paper liner)	- Bricks
- Bitumen felts (including asbestos fibre-based felt)	- Stones
- Glass wool or mineral wool with combustible bonding agent or covering	- Concretes
	- Metals
- Bitumen protected metal sheet	- Vermiculite
- All plastics and rubbers	- Mineral wool

Wind and rain

General

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.

Tropical downpours

· 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.

Cyclonic storms

· 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.

Protective Measures

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.

Tropical downpours

· 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.

Rain protection of stabilized soil block construction 00.12)

Cyclonic storms

· 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.

Aspects of building to withstand strong winds (Bibl. 25.06)

Earthquakes

General

Of all natural disasters, earthquakes cause the greatest amount of death and destruction. They generally occur without any warning and, depending on their intensity, can within a few seconds turn a prosperous town into a pile of rubble.

There are several causes for seismic tremors, the main cause being the movement of large continental plates (a few millimetres per year), which collide, move apart or rub against each other, building up immense tension within the rock formations, which at a certain point readjust themselves with a sudden violent motion, sending out seismic waves in all directions. Another cause is the leaking out of molten magma through faults in the earth's crust, which can happen deep beneath the sea or in the form of volcanic eruption. Quakes beneath the sea give rise to tsunamis (Japanese name for seismic sea waves), which can cause total devastation in coastal areas. Volcanic eruptions affect a comparatively small area and damage is mainly caused by molten lava and ash descending on houses and fields.

Artificial causes of earthquakes have recently resulted from the construction of dams, where the large water reservoirs exert great pressure on the earth's crust and lubricate faults, which release the pressure in seismic waves. The exploitation of oil and gas deposits disrupts the balance of pressures and thus can also lead to seismic tremors.

These causes make certain regions more prone to earthquakes than other areas, but exact forecasts of tune and intensity are not possible so far. Special measures to minimize damage to lives and property are recommended in these regions, but complete safety cannot be achieved.

Seismic waves comprise horizontal, vertical and torsional (twisting) movements acting simultaneously. Weak, non-elastic components break apart or disintegrate; elastic materials vibrate and absorb the tremors; while tough and rigid materials can remain unaffected. Destruction of buildings mainly begins with walls falling apart; the ceilings and roofs, lacking support, follow suit, burying the dwellers and property beneath them. However, far greater damage results from secondary effects of earthquakes, such as fire, landslides, damburst, epidemics, etc. A series of smaller tremors follow major earthquakes and can lead to further collapse of buildings, greatly complicating rescue work.

The greatest casualties occur where the population is poorest and houses are built with cheap, sub-standard materials and methods, on dangerous sites, such as slopes, sea shores, valleys below dams, etc. Earthquakes of comparable intensities cause far less destruction and deaths in industrialized countries and rich areas of Third World cities, than in the poor rural areas and slums of developing countries. Hence, earthquakes are often called "classquakes".

Typical earthquake effects and damage (drawings by John Norton, Bibl. 25.10)

Protective Measures

· Building sites should not be on or close to hillsides (danger of landslides, avalanches), or near the sea (risk of tsunamis); sufficient distance from neighbouring structures (danger of collapse), especially in prevailing wind direction (fire risk), and downstream from reservoirs (danger of dam-burst) should be maintained. Filled ditches and watercourses should be avoided.

· Building forms must be simple and symmetrical (both horizontally and vertically); complicated forms are possible, if subdivided into independent, simple components.

· Foundations should be of reinforced concrete, constructed on solid ground (preferably rock), maintaining uniform depths (no stepping on sloping ground) and having continuous reinforcement. On poor soils, strong slab foundations have the advantage of "floating" on seismic waves, thus avoiding damage.

· Walls should be relatively light (to lower the centre of gravity of the building and reduce the damaging effects of collapsing walls), capable of absorbing vibrations, but with rigid connections to foundations, adjoining walls and roof. Frame structures (timber, bamboo, reinforced concrete, metal) with light infill walls are most resistant to earthquakes, conventional masonry structures require a strong, continuous ring beam on top of the walls, to prevent them from falling apart.

· Openings should be small, not less than 50 cm from corners or other openings; glass panes should be avoided.

FIGURE

· Roofs should be as light as possible, either monolithic (with high tensile strength, eg reinforced concrete), or of strong, flexible members, firmly tied to the supporting structure; compact symmetrical shapes with spans as small as possible. Roofs must be securely fixed to the ring beam or building frame. Alternatively, roofs can be fixed to independent supports, structurally separated from the walls, which, in the event of failure, would not cause the roof also to collapse.

· Appendages (eg parapets, chimneys, water tanks), if they cannot be omitted, should be very securely fixed, to avoid their being shaken off.

Strengthening of masonry walls with reinforced concrete (Bibl. 25.10)

· Stone, earth and clay brick walls generally perform poorly in earthquakes. Improved resistance to collapse is achieved by strengthening and reinforcing corners; ring beams are essential. Masonry walls and domes should be avoided in earthquake zones. Clay tile roofs need strong and heavy timber substructures, which are a hazard when they collapse, and the tiles tend to fall down under vibration.

· Reinforced concrete and ferrocement are ideal materials for seismic resistant constructions, if the qualities of cement, aggregate and workmanship are good, and the metal reinforcements are protected from corrosion. Concrete frames and thin shell structures are best, but heavy ceiling and roof slabs must be avoided.

· Timber and bamboo frames with light infill walls or cladding provide optimum earthquake resistance, and cause less destruction than heavier materials in case of collapse, but represent a fire hazard, which is of significance during earthquakes (due to breakage of chimneys, power and gas supply lines, etc.). Protection against biological hazards is essential to avoid weakening of the construction.

· Metal frames permit light, flexible constructions, but design and dimensioning should take into account the risk of buckling; fire protection and good resistance to corrosion are essential. Metal sheet roofs generally perform well in earthquakes.

· General precautionary measures are in all cases good workmanship and regular inspections of critical parts for maintenance and repairs; also all protective measures against fire.