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CAUSES OF DECAY AND DAMAGE TO CULTURAL PROPERTY

Gravitycauses buildings to falldownExternal Causes of Decay. The sun produces light with ultraviolet and heat radiation

Climatic causes Biological and botancialcauses

Natural disasters

Seasonal temperature changes Animals TectonicsDaily temperature changes Birds Earthquakes

Wind Insects Tidal wavesPrecipitation of rain and snow Trees and plants FloodsIce and frost Fungi, moulds, lichens LandslidesGround water and moisture in soildust

Bacteria Avalanches

Dust Volcanic eruptionsExceptional windsWild fire

Internal Causes of Decay(Note: the building modifies andprotects)(Courtesy: Plenderleith, H.J. and Werner, A.E.A., 1971)

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Climatic causes ofdecayIntroduction

Previous chapters have dealt with theeffect of gravity, one of the principalcauses of structural decay. This chapterdeals mainly with geographical causes,i.e. with climate and its side effects.

Earthquakes are given a separatechapter.

Climate, in all its aspects, is one of thefundamental causes of the decay ofbuildings, through failure of theirmaterials which in turn affects thestructure. To give a simple example, mud

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brick or adobe may last thousands ofyears in extremely dry, arid desertconditions such as found in North Peru orNubia, but less than a decade in the hot,humid climate of southern Nigeria. Theresistance of building materials toclimatic agents of decay decreases withtheir exposure and age. Even intemperate zones, solar radiation is foundto be more destructive than frost. Water,in all its forms, is the agent thatpromotes chemical actions and gradualdeterioration of building materials andactively damages buildings when heavyrainfall overflows gutters and rivers risein flood.

Whereas the macroclimate of the worldhas been classified according to thegrowth of different types of vegetation orannual rainfall, this information is only ofindirect value to the architect examining

an historic building. The activecomponents of macro- climate that affecta building particularly are radiation fromthe sun, seasonal temperature changes,rainfall, particularly storms which maycause flooding on both a micro or macroscale, wind and the transportation ofground moisture.The siting of a building and the soil it

stands on affect its microclimate whichcan modify the macro- climateconsiderably and so increase climatic

hazards. For example, the ruined VillaJovis on the island of Capri, built by theEmperor Tiberius c. A.D. 70, stands on apromontory rising about 300 m (1000 ft)from the Tyrrhenian Sea, exposed to thewinds and salt spray as well as beingliable to attract lightning strikes in anarea noted for its thunderstorms. It hasbeen shown that cities modify themacroclimate, being warmer in winterand also much more liable to heavyconcentrations of atmospheric pollution.Other examples of microclimatic effects

are frost ponds, shading by hills ormountains, and the ameliorating effectsof water on temperature extremes, aswell as that of the moisture content ofthe soil.The architectural form and structure of

a building will influence the microclimateof its parts. Indigenous or vernaculararchitecture shows how buildings wereused as 'spatial environmental systems'to modify the external climate, one

example being the wind towers andwater-cooling chambers used in Iran andthe Gulf States. Courtyards with waterand fountains modify a hot, arid climateby providing shade and evaporation, asdo trees when growing around a building.Particularly in hot humid climates, aircirculation is important both for comfortand prevention of fungal attacks onorganic material which often precedesinsect attack, and in such cases one findsthat the vernacular architecture of thecountry responds to its climate by havinglight, open structures with roof shapesdesigned to encourage air movement. Ifan historic building is to be used as amuseum, both the external and internalclimate will need careful considerationand the architect has a responsibility fordefining and assessing the climaticfactors which will affect the exhibits.

Solar radiation

Solar radiation is the prime cause ofclimatic conditions, and its wavelengthsrange from the ultraviolet (0.2 ^m),through the narrow band of visiblespectrum of light (0.4-0.9 ^m) to up toinfrared (8 ^m), which

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Figure 7.1 Mean annual temperatureworld(Courtesy: McGraw-Hill Book Co.; from Koeppe, C.E. and De Long, G.C., Weather and Climate, 1958)

Figure 7.2 World temperature ranges(Courtesy: McGraw-Hill Book Co.; from Koeppe, C.E. and De Long, G.C., Weather and Climate, 1958)

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