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See the design in place.
Sustainability encompasses the social, the environmental and the economic, and the most beneficial solution will be the one that best balances these aspects. We propose to enhance a simple form with features that optimise sustainability and can readily be applied to future designs.
The following is a description of these features, and is broadly split into social, environmental, and economic aspects, but, as with sustainability, everything is interlinked and the categories are nominal.
The space is above all a teaching space, and should facilitate effective learning, whilst allowing children to play and to rest safely.
Teachers are an important and scarce resource in some parts of Uganda; as such it is vital to optimise the space for one teacher to teach a whole class of children, and also to make it easy for the teacher to manage the resources and equipment of the school.
A teacher must be able to see all the children in her care from any point in the teaching area, and that the children must feel connected to her and feel included in the class. As such the teaching area is to have a linear form with dimensions that allow the teacher to see the whole class easily without the length causing problems.
Our design includes a teacher’s annex that doubles as both a secure storage area and an office, allowing the teacher to store valuable commodities such as books and to store furniture when the teaching space is being used for community purposes. It includes a secure window that will provide daylight so that the room could also be used as an office space. The partition between the annex and the classroom is to be flexible enough as to allow the annex to be joined with the main room, adding options to the combinations of space planning.
We have provided flat surfaces on doors and partitions that can be painted with blackboard paint and have the means to attach drawings and other work. This will allow the children to influence their environment and create displays they can be proud of. These areas could also be used for community announcements and communication.
In play, the children will have an external canopy sheltering the courtyard from sun and rain, spaces where care and attention has been paid to thermal comfort and ventilation, and storage areas that allow furniture to be cleared from the main classroom space.
At rest, window seats will allow children to sit outside under the shade of the canopy, and the covered external areas will provide shelter from the elements.
The building of such a classroom represents a substantial investment in a small Ugandan community. As such, we would wish the space to fulfil a range of community functions. We have designed the space to maximise flexibility, as described below.
We would wish the classroom to be a product of the community, built and maintained with local labour, skills, materials and furniture; a well functioning space which the community can take pride in.
The focus of the design solution would be the use of local materials, furniture and skills. Buildability is a key feature, facilitating the involvement of the local labour, as is Placemaking, to provide pleasant interesting external and internal spaces that will attract the local community. Making sure that the local community feel included and feel like stakeholders in the project is important in ensuring that the building is well maintained.
We have promoted flexibility with the simple linear form, large doors opening onto the external heart-space, and the teachers annex which can be joined to the room for increased space usage permutations. This allows the space to be transformed for any use that requires a safe comfortable environment. A range of space usage ideas are provided on our building plan page.
The teacher’s annex is to be partitioned from the main space with a flexible but secure folding door arrangement, which allows the annex: to be an isolated secure or quiet space; to be joined to the room to form one space; or to be joined to the room with the door being used as a partition in the main space to form two smaller spaces.
Another aspect of the design challenge is to produce a single classroom that can be used for incremental development of a larger school campus. This is addressed in our master plan, but in general, we have chosen a simple and adaptable form. By using an L-shape we have provided a useful building block in producing secure courtyards and facilitating Placemaking in the design of a larger school.
The classroom is adaptable to varying landscapes and environments throughout Uganda. We have designed to cope with worst cases in terms of the sun and the rain. We have also avoided using materials that would not be available throughout Uganda.
Daylight and Solar shading
It is important to achieve an optimum balance between natural daylight and solar gains. We wish to avoid the use of artificial lighting during daylight hours, but we wish to prevent the occupied space and the thermal mass of the building being heated up by the sun.
We will provide solar shading from high level sun by extending the roof to form overhangs. This canopy should prevent direct sun shining through the windows or heating up the structure during the hotter parts of the day.
We also wish to prevent the low sun entering the classroom in the late afternoon and early evening. Excessive early morning sun can undermine the thermal comfort strategies in the space, and late afternoon sun can make an already warm classroom overheat. To this end, the class room is orientated with windows facing north and south, and the windows are recessed into the wall, and will act as a brise soliel, cutting out direct low sun from the east and west.
The north-south orientation of the windows is preferred, as it allows the low sun to be controlled with building mounted brise soleil such as the recessed windows. However, any orientations is possible but may require external brise soleil to be used, like strategically planted trees and trellising.
Having provided the means for controlling solar gain, we also wish to maximise the illumination provide by natural daylight. To this end, we have chosen a shallow plan form for the classroom which will make daylighting the whole floor plate as easy as possible. We have also chosen tall windows that will maximise the penetration of daylight into the space, and we wish to apply a light coloured surface finish to the inside of the space.
The openable façade could also be a valuable source of light when weather conditions allow it to be open.
It is important to maintain comfortable temperatures in learning environments.
The outside temperatures in Uganda are generally between 12ºC and 25ºC for most of the year, but reach 32ºC in summer. Obviously, the temperature in the classroom will be heavily influenced by temperature of the air, but the design of the classroom can act to provide an environment that will be resistant to the overheating caused by the high occupancy densities, and their associated heat gains, expected in the space.
Increasing the thermal mass of a building allows it to absorb heat during the day, effectively removing it from the space, and reducing temperatures. We would therefore like to have as heavyweight a building as possible. In order to maximise the amount of thermal mass in the building without increasing the cost or embodied energy we propose that the building be constructed of a combination of vernacular building techniques. The structural elements and those required to withstand water in the rainy season shall be constructed of fired bricks; daub, cob/adobe, or rammed earth shall be used to increase the thermal mass of the building in a cost effective way. The internal surface of the walls shall be coffered to offer a greater surface area for the air to interact with the thermal mass, which will lead to an increase in effectiveness. The external surface of the envelope will be flat, to avoid problems with water in the rainy season.
Given the heat gains associated with the high occupancy densities expected in the space, we wish to remove heat as rapidly as possible; as such, a high ventilation rate is achieved by incorporating as many ventilation enhancing features as possible.
The classroom is to have high and low level openings which will create a passive stack effect, where by warmer, more buoyant air rises and exhausts through high level openings, which in turn creates a negative pressure that sucks in colder air from outside at low pressure.
The main windows and the high level vents are situated on opposite sides of the space; this cross ventilation configuration allows air to flow across the space and encourages high ventilation rates. We also propose to have large doors that open up to the façade into the central heart-space / courtyard; which will also dramatically enhance cross ventilation when open.
The design has significant numbers of openings, many of which are controllable. We are aware that high occupancy densities are expected and wish to give the teacher the capability to remove the heat with high levels of ventilation, but also know that control is very important. To provide this control, the design of the windows allow the teacher to reduce the free area of openings, reducing ventilation, and minimising the ingress of any elements such as noise, dust or rain.
Solar chimneys have been used in Africa to promote extract in WC and cooking applications, and in Europe to enhance natural ventilation systems. One of the original features of this design is the proposal to extend the solar chimney idea and use the tin roof as part of a “Solar Roof” extract system to passively exhaust air from the space. The concept is to build a shallow plenum formed between a false ceiling and the mono pitched tin roof. The plenum will have an opening at the lowest point of the roof in the classroom and at the highest point to the outside. Air trapped between the tin roof and the ceiling will get hot, become buoyant and rise rapidly. As it exhausts to outside, it sucks air in from the classroom space, beginning the cycle again. This ensures that heat from the hot tin roof does not enter the classroom space and increases the air change rate in the room.
It is important to cool the space down as much as possible at night. As such, the means to securely night ventilate the building is included. To this end, the windows will be louvres rather than glass and all the high level vents will have secure grilles to allow night ventilation.
As warm air naturally rises, the space will feature generous ceiling heights, so that the warm air can rise away from the occupied zone, and a mono pitched ceiling that channels the rising air to the exhaust vents, rather than allowing it to pool on the ceiling.
The canopy also covers the external heart-space/ courtyard, and will provide shelter from the sun, allowing the space to be used fully when the sun is strong.
Planting suitable vegetation can work to reduce the ambient air temperature of the buildings surroundings, creating a more thermally comfortable atmosphere. The vegetation will absorb solar energy, using it for photosynthesis, or dissipating it by the process of evapotranspiration, rather than the building absorbing and re-emitting the energy, heating up the air in the process.
With high occupancy densities comes the need for high levels of ventilation, to bring in fresh air and remove CO2. There is also the possibility that cooking equipment or night time artificial lighting that create toxic gases will be used in the classroom. The ventilation methods outlined in the Thermal Comfort section are applicable to delivering ventilation requirements.
The classroom is intended to be a place of concentration; this can be compromised by external and internal sources of noise, and so these must be minimised.
Noise from the external environment and adjacent classrooms is difficult to control in a building reliant on natural ventilation. However, providing windows with varying degrees of opening will provide some level of control. Openings at desk height are most problematic for noise ingress and the inclusion of the high level vents and Solar Roof extract allow the openings in the low level windows to be closed. The external noise can also be controlled by using vegetation, such as trees and trellising, as acoustic barriers, and these are included to provide a quiet external environment and allow the classrooms to be as open as possible.
During the rainy season, the noise of the rain falling on the tin roof can be very loud. The false ceiling used in the construction of the Solar Roof extract system is also designed to provide an acoustic barrier to the noise of the roof. We propose to construct the false ceiling from a sandwich of plywood with a soft sound absorbing centre such as wool or straw.
The internal acoustics of the space must also be considered; a large group of children can make a lot of noise, and designing to minimise this is important. Hard surfaces such as concrete, brick and metal have long reverberation times and will increase the ambient noise levels generated by the children. The false ceiling, detailed above, will help by hiding the surface of the tin roof. The design also proposes to add significant mass to the inside of the brick structure using daub or adobe; these materials are softer than fired brick, and will help reduce noise.
The wettest areas are along the shores of Lake Victoria and the western mountain districts; these receive over 1,500 mm/60 in of rain per year. Parts of central and northeast Uganda receive less than 1,000 mm/40 in of rain per year; this is often much less since rainfall is unreliable from year to year.
The opportunity to collect rainwater for future irrigation would be of significant benefit to the local community. Our design features a mono-pitch roof that will channel rainwater towards guttering, sized to cope with the heavy demands of the rainy season, which can be connected to any future rainwater harvesting tank.
Protection from the rain
One of the fundamental requirements of any building is to provide protection from the elements. We have already described how the design provides shelter from the strong equatorial sun, but protection from the rain in the rainy season is equally important.
The exposure of the building to rain will depend on its location. The west of the country is often affected by moist south-westerly winds bringing rains from the Congo, but the building should be designed for a worst case so that it can be situated anywhere. Much of the rain comes in heavy thunder showers, with large volumes of rain falling in a short space of time. The building should therefore be designed to withstand this torrential rain.
The overhanging roof and the recessed windows will work to prevent rain ingress through the windows. The overhang should also provide some shelter for occupants walking around the building.
The external courtyard is also sheltered by the roof, which will provide a play space and entrance area that will remain dry in the rainy season. The mono-pitch roof is inclined to channel the water away from heart-space. This water can be collected in a rainwater harvesting system.
It is also important that the outside of the building envelope can withstand the rain, and will weather as little as possible. To this end, fired bricks have been used for the building envelope. The external building envelope has also been designed to offer flush non recessed surfaces, as to prevent water collecting.
Vegetation should also be chosen to make the most of the rainy season. Indigenous plants and trees that thrive in the areas should be chosen to maximise the use of the water.
The design has been developed from the outset with the challenging robustness requirements of the rural environment in mind. Protection against the elements is achieved through proven corrugated roofing generously overhanging the building footprint; this provides shelter from rain and direct sun. The large windows, allowing natural daylighting of the space, eliminates the requirement for artificial lighting and a dedicated electrical supply, significantly reducing the risk of fire. The large doorway and single-storey construction provide a quick evacuation route, which is also reflected in the masterplanning layouts.
The feature trusses are constructed of termite-resistant timber, and are designed to have a high degree of structural redundancy to take into account variations in timber quality and workmanship. Using trusses allows small, easily sourced, inexpensive timber sections to form the primary members, and allows the large spans and cantilevers that are essential to the design. They will adequately support uplift loads from high winds and dead and live loads from the roof. They are braced in all directions laterally by tying struts at each end and the kingpost truss over the door which helps prevent racking. The kingpost truss also supports the primary truss which sits over the centre of the large door opening. The trusses are spaced close enough that the counter battens required to support the profiled metal roof need only be small, inexpensive timber sections.
The loadbearing masonry walls proposed include returns and piers to provide adequate support for the vertical loads and flexural stiffness against wind loads. The bricks can potentially be local hand-made, sun-dried clay bricks if the structural properties are acceptable, but these may need to be rendered as they will not be as durable. If the properties are found to be inadequate then locally-sourced fired clay bricks will be used. The walls are tied together at the top by a lightly reinforced concrete ring beam, which additionally serves to evenly distribute the truss loads across the top of the wall and act as a lintel over the window openings.
The proposed classroom includes the option for raising the building level above the surrounding landscape to mitigate any potential flooding. This would involve constructing several more courses of loadbearing masonry below ground, directly off the mass concrete foundations, and raising the internal ground level afterwards.
It would also be advantageous to have the floor covered in a concrete screed, which will allow the classroom to be swept clean and keep dust to a minimum, and will reduce the degeneration of the floor.
It is important to consider both the security of the children and the security of the property belonging to the school.
The security of the children requires them to be visible to the teacher at all times. As previously described, the linear form and dimensions of the teaching space aid visibility and connectivity between the pupils and teacher. There is only one point of entrance to the classroom, of which the teacher has full view from the blackboard. Entrances to classroom of small children are generally near the teacher, however, with up to 50 children expected in each class it would be advantageous to allow the classroom to fill up from the front, with late arrivals allowed to join in without disrupting the class. As such, the doors will be situated towards the rear of the room.
The L-shape form of the building can be used in the master planning to form secure courtyards.
The building is designed to minimise the requirement for maintenance, and so that any necessary maintenance can be carried out by local tradesmen.
Our design restricts the use of carbon intensive materials, such as oven fired brick, steel, and concrete, to the parts of the building where the weather proof and structural properties are required. We will use local, low carbon materials such as daub, cob, rammed earth, and small pieces of wood where possible.
We have also designed the building to have a long life and as such to maximise the gain from the embodied carbon, before it has to be demolished.
Energy in use
It is unlikely that any energy will be used in the running of the building, with the possible exception of lamps in the evening. As such optimising daylighting will minimise energy use, and this is discussed with respect to its social aspects.
Water is an important commodity in both a social context and environmental one. By providing the community with the means to better manage the water that falls in the rainy season, the local environment can benefit. As previously described, rainwater is to be collected from the roofs.
The cost of the classroom is critical to the brief, with $3,000 (U.S) allocated per classroom (materials only, as labour will be volunteered by parents and community members). The design requires use of locally available materials, with the construction technique kept simple, so it can be easily learnt by under-skilled members of the community.
Our classroom is to be constructed mostly from locally made bricks, timber and earth infill. Windows have been designed using timber to avoid the cost of glass, and the only building element that is not listed in the example provided is the plywood required to form the solar chimney. We have assumed a material similar to this can be sourced in Uganda, and assumed a maximum cost of $50.
Construction has been kept simple, with the truss proving the most challenging detail. The window shutters and slat arrangements are unusual without being too complicated. Currently a concrete ring beam is proposed, but this could be a deep timber beam if Building Tomorrow considers that preferable.
A relatively lightly reinforced concrete beam would be shuttered, fixed and poured insitu once the masonry has been built full height, providing masonry restraint in plan. Alternatively a timber beam with robust corner connections would be fixed directly down onto the top of the wall.
We have estimated costs using the example provided by Building Tomorrow, scaling relative proportions of mortar to bricks and sand to cement. It is estimated the classroom will cost just over $2900 (U.S). The tables below outlines the material specification and lists all assumption made in calculations.
For further details please see submitted CAD drawings.
CONCRETE (RING BEAM) UNIT SIZE QTY RATE AMOUNT
Cement bgs 3.5 26,000 91,000
Sand trips 0.24 90,000 21,420
Aggregates trips 0.24 120,000 28,560
Timber [Kirundu] 12 x 1 pcs 12x1 0 5,000 2,398
EXTERNAL WALLS (PLASTER INSIDE) UNIT SIZE QTY RATE AMOUNT
Bricks pcs 6,981 180 1,256,580
Sand (river and lake) trips 6 90,000 502,632
Cement bgs 40 26,000 1,052,735
Pyan rolls 2 35,000 65,970
DPC Layer rolls 3 10,000 27,924
Eucalyptus Poles pcs 7 2,000 13,962
Ropes pcs 7 200 1,396
FLOOR SLAB UNIT SIZE QTY RATE AMOUNT
Cement bgs 15 26,000 390,000
Sand trips 2 90,000 135,000
Aggregates trips 3 120,000 360,000
Timber - kirundu pcs 12x1 5 5,000 24,750
Kaveera mtrs 25 2,000 49,500
ROOFING UNIT SIZE QTY RATE AMOUNT
Timber pcs 3x4 7,000 0
pcs 6x2 8,000 0
pcs 4x2 152 5,000 760,000
pcs 3x2 35 4,000 140,000
Facial boards pcs 1x9 17,500 0
Nails kgs 6'' 10 4,000 40,000
kgs 5'' 20 4,000 80,000
kgs 4'' 40 4,000 160,000
kgs 1 1/2'' 4,000 0
kgs roof 7,000 0
Iron shees G30 pcs Im x 3m 34 20,250 688,500
Valleys pcs 6tf 15,000 0
Gutters pcs 10ft 3 13,000 39,000
DOORS AND WINDOWS UNIT SIZE QTY RATE AMOUNT
Doors - wooden pcs 2 180,000 360,000
Windows pcs 147,000 0
Total Sum of Materials 6,291,327
Solar Chimney - fibreboard / plasterboard 110,000
Tools, store and others cost 130000
GRAND TOTAL (Ugandan shillings) 6,531,327
GRAND TOTAL (US Dollars) 2932.57
Bricks - rules of thumb
0.0058 bags cement required per brick
0.0008 trips of sand (total) per brick
Concrete - rules of thumb
0.068 trips of sand and aggregate per bag of cement
0.137 pieces of timber per bag of cement
Tools and store assumed as example - 1300,000
3000 U.S. dollars = 6.68151448 million Ugandan shillings
1 US Dollar = 2227.171 Ugandan Shillings
Plastering - rules of thumb (halved for inside only)
0.00027 Pyan per brick
0.0008 DPC Layer per brick
0.0002 Eucalyptus poles per brick
0.0002 Ropes per brick
Floor slab - rules of thumb
0.33 pieces of timber per bag of cement
1.65 mts of Kaveera per bag of cement
0.1 trips of sand per bag of cement
0.2 trips of agg per bag of cement
Timber dimensions - assumed a pcs is 1.5m or 5 ft.
Truss = 31.5m total - cross section 100x50mm - 4in x 2in
Total number of pcs = 21 per truss
And @ 5 trusses = 105 pcs
Likely volume of cement bag 120 litres - 0.12m3
Volume of concrete required = 1.05m3
Cement ratio - 0.4 = 0.42m3 cement
Number of bags = 3.5
Window frames roughly 50mm x 50mm @ 10.4m per window
And @ 5 windows = 35 pcs of smallest available pcs
Window slats roughly 100mm x 20mm @ 14m per window
And @ 5 windows = 47 pieces
Net floor area - 43.8m2 @ 100mm deep = 4.38m3 concrete
Cement ratio - 0.4 = 1.75m3 cement
Number of bags = 15
Roof area - 100m2 = 34 pcs of iron sheet
Solar chimney - fibreboard - 81m2 - approx $50
Gutter - 10ft = 3m