4. Bioclimatic Design
The equator runs across East Africa, through Kenya and Southern Uganda. Along the Equator the sun at midday is directly overhead throughout the year. This means that in East Africa roofs receive far more solar radiation than walls. Glazing acts as a heat trap by permitting short wave solar radiation to enter but not allowing longer wave thermal radiation to escape. Direct sunlight on windows will consequently cause buildings to overheat. The basis of solar shading principles is to allow diffuse daylight into buildings while shading from direct sunlight.
Orient buildings to reduce east and west elevations which receive the most direct solar radiation
North and south elevations receive hardly any direct solar radiation, though the further north you travel the more the south-facing walls need shading and vice versa. East and west elevations receive low-level solar radiation in the morning and afternoon respectively. This means that these walls by preference should not contain window openings, which should be kept to the north and south façades. Energy efficient masterplanning often results in an east-west grain to the layout of buildings.
Use elements of the building such as colonnades and projecting overhangs to shade windows and walls from direct sunlight.
A large overhanging roof will shade windows from direct sunlight and reduce the external surface temperature of the building, which can have a corresponding effect on local air temperature.
Overhangs are particularly important where buildings cannot be orientated on the east-west axis due to topographical constraints. In these circumstances, overhangs can be exaggerated by creating a colonnade around the full circumference of the building or on particularly exposed façades.
Trees and Planting
Trees and climbing plants can be used to shade exposed windows and walls particularly on the east and west elevations.
Vegetation can be strategically planted to provide shading for windows, walls and roofs of buildings which would otherwise be exposed to high levels of solar radiation, such as the east and west façades.
The Umbrella tree for instance, has dense and overarching foliage and will easily shade walls and single storey roofs. Climbing plants can also be grown alongside or up buildings, and trained along wires or poles to create a living shading device.
Climbing plants have been trained to grow on the east and west façades of Mubuga Primary School by MASS Design Group
A shiny or very light roof finish will reflect solar radiation, helping to reduce radiant heat transfer to interior spaces.
One of the most simple and effective methods to protect against interior solar gain, is to select a reflective roofing material that helps to limit thermal transfer to the interior spaces. Shiny metal sheet roofing is far better at reflecting solar radiation than any alternative. White or very light coloured roofing is much better than dark colours, which will actually absorb the sun's heat. Clay tiled roofs are less absorbent than metal and will transmit radiation at a far slower rate.
Create a second skin beneath the roof to reduce the radiant temperature and help to cool the roof through enhanced ventilation.
Considerable improvement to the thermal performance of a roof can be made by installing an internal lining or ceiling and ventilating the space between the two. Generally the larger this space, the better the ventilation and cooler the internal surface of the roof will be. The ceiling should ideally have some insulation or thermally absorbing characteristics but a ventilated airspace alone provides a significant improvement compared to an exposed single-skin roof.
Gando School by Kéré Architecture has a barrel vaulted brick ceiling sheltered by a secondary oversailing metal roof