Hong Kong Builder
PLANNING FOR
FOR COOLNESS
By Geo. W. Grey, F.S.L.. F.R.L.B.A.
In addition to air-conditioning and the electric fan, there are structural and decorative devices which tend to maintain coolness in interiors of buildings.
Colour has its influence, experiments indicating that white gives greatest coolness, red comes next, greys and greens not being so good.
It is claimed that painting white the hulls of ships that were previously black, reduced the interior tem- perature from 12 to 15o.
In an official test, copper sheets, placed in boxes having a tin plate lid with a black paint surface exposed to the sun and a whitewashed under-surface, reached a maximum temperature of 112, while that under a tin plate having a whitewash upper surface and its metallic under-surface reached only 60°.
This experiment endorses the value of the practice of whitewashing or limewashing roofs, particularly those of galvanized corrugated iron, the galvanizing giving the metallic desired underside.
Asphalt, and to lesser extent tiles, will all benefit from the point of coolness if whitened.
With corrugated surfaces, not only does whitening reduce the solar radiation, but it also reduces the reflec- tion of heat from one corrugated surface to another, a corrugated surface not only reaching a higher temper- ature by reflection from one corrugated surface to another, but there is a greater surface exposed to solar radiation than the area covered.
Chinese tiles, which are so often covered with a black solution, will absorb a considerable amount of heat and transmit this heat, the inside being both black and Corrugated,
The Building Research Board states: "Slab cork is an excellent heat insulating material; in order to obtain equivalent insulation to a cork slab 2" thick at least nine inches of any normal concrete would be required. and probably considerably more,'
," but the value of cork
and other insulating materials is largely reduced if used inside, and not outside, as the lesser heat radiating material should be exposed.
Insulating materials need to be carefully chosen for vermin proof qualities. They must have no food value for vermin, and they must be so made as to afford no harbour for them.
Flat roofs of concrete covered with asphalt or mem- brane waterproofing which have been given a thickness of earth and sown with grass have been very successful in keeping rooms cool. Potted plants on a roof also tend to keep cool the rooms underneath.
Surroundings
Pavements surrounding buildings are to be avoided as these radiate heat.
The surroundings to a residence laid out with lawns, with the minimum allowance for vehicular and foot traffic, make for coolness.
Native policemen in tropical countries have found this out as, when regulating traffic, they can sometimes be seen to have collected leaves and other vegetation upon which to stand.
Verandahs
A verandah is usually looked upon as somewhere to sit out, and perhaps take tea, it being forgotten that it is the most usual means of keeping interior rooms at a low temperature by protecting their enclosing walls from the direct rays of the sun. Further, in those climates where the hot season and the rainy season coincide, the windows may be kept open without admitting the rain.
In contrast to the verandah, Southern Europe and South America obtain their coolness by paved rooms,
11
thick walls and a low overhanging eave, with compara- tively small window openings filled in with shutters which can be thrown open in the cool of the evening. It is claimed that this arrangement provides a cooler loung- ing place and that, by excluding the hot air during the daytime, the premises are kept generally cooler than they would be if a verandah were provided.
From the point of view of heat from the sun's rays, the verandah has not as great a comparative value as a protection when near the equator as it has in more northern or southern latitudes. The sun, as the equator is approached, becomes more directly overhead, and there- fore near the equator comparatively slight projecting eaves prevent the sun shining through window openings and directly upon walls. Verandahs, which actually act as wide eaves, then have greater value.
Orientation of a building is of importance for the maintenance of coolness of the interior but the nearer to the equator the building is situated the less important this aspect becomes.
Height of Rooms
Nothing will convince many people that height from floor to ceiling is not inducive to coolness, and that a low room can be anything but stuffy.
High rooms, by the very fact of their height, may form large spaces for the storage of hot and foul air by the difficulty of obtaining ventilation at, or near, their ceiling level. If windows, or ventilating openings, are supplied at, or near, ceiling level, it is often found that
sash, or gearing being out of order. they are seldom opened owing to the weight of a large
Large rooms, containing good cool air, without the means of replacing the air, will remain pleasant for a fairly long period as they contain a greater quantity of air to foul and heat up, but there is no value to the space above the heads of occupiers unless the air there is in circulation, and to keep it in circulation, windows should be as near ceiling level as circumstances will permit.
Air Space
One way of maintaining coolness is by the use of a false ceiling, a very common method being by suspending metal lathing from the floor above, leaving an air space between floor and ceiling, or between roof and ceiling, as the case may be.
On the flat roofs, the use of large concrete or clay tiles on concrete or brick supports, providing an air space, is also common. Nowadays, the construction of hollow tile reinforced concrete slabs incorporates a fair measure of insulation directly into the roof covering.
Air spaces are advantageous, even if only by reason of the additional thickness which results but, when the air is confined, efficiency is not as great as with air in circulation. The confined air gradually heats up during the day and might communicate the heat to the rooms adjacent. Given free inlets and outlets, the hot day air will be replaced by the cooler night air; further, during the day circulation will be set up by reason of the dif- ference between the temperatures on the shady and the sunny sides of the house.
Unless there is a cooling plant, or heating apparatus, a building is neither a refrigerator nor hot-house. In a refrigerator where cold is "generated," or in cold cli- mates where the interior of a building is heated and in which it is wished to retain the temperature created, cavity walls through which the external air is permitted to circulate reduce the value of the outer wall as an insulator, owing to the air from outside coming in con- tact with the inner wall. Where there is no artificial cooling or heating, circulation in the cavities give a better result,