samedi 9 janvier 2016

The Casbah

The Casbah

      The courtyard houses are the most turban element in the traditional building, then the public baths and last the mosque to complete the selection. But during the last century, these elements have been neglected, their importance decreased and their decay started.
     Modern vs. traditional buildings
    Modern buildings are very energy intensive because they rely too much on mechanical and electrical systems for heating, cooling,   and lighting. Traditional, vernacular, or indigenous buildings, on the other hand, used little energy for heating, cooling, and lighting,   and what energy they did use was natural and renewable. Because modern buildings use about 50% of all energy, they are a major cause of energy depletion, pollution, and global warming [3]. More efficient mechanical and electrical systems are not the primary way of reducing the energy consumption of buildings. Rather, it is the design of the building itself that will have the greatest impact on reducing the energy requirements of buildings. For example, modern buildings rarely use shading, natural ventilation and heating devices, while traditional buildings usually did. As such is the case of the courtyard house, the mosque, the suq and  the urban  amenities such as the public bath, the school and the hospital. Vernacular architecture around the world is impressively rich with ingenious techniques early dwellers used to protect themselves from the diverse weather conditions they were subject to. Great examples of  well-thought vernacular architecture are located in the Middle-Eastern region and North Africa where a hot and arid climate zone prevails. This climate condition is probably a good example of extreme weather conditions and studying the architectural techniques that allows the creation of independent microclimates in these regions is worth exploring. Some of these traditional techniques are being slowly rediscovered today and slowly applied  to modern forms of architecture. However, sustainable features in general and  passive climate control in particular, even though newly rediscovered, are starting to limit the architectural expression of the buildings. This work explores, as stated earlier, the use of passive design devices such as heating and cooling, day lighting, ventilation in Casbahs, courtyard houses and traditional public amenities (i.e. mosque, suq and hammam). Reaching this major aim would enable architects, restorators and specialists attend an optimum of efficient management of energy in historic building restoration-renovation and their future reuse.
    The Casbah  is of a very dense, tightly packed system of courtyard buildings organized along narrow streets and alleyways (figure 2). The streets are too narrow for cars and the major streets are lined with shops, workshops and public facilities. There is  no car pollution as these cities evolved at times when transport was done using animal such as donkeys, horses and camels. All buildings are inward looking onto courtyards which provide good access to natural light and ventilation and provide both visual and acoustic privacy. High residential densities are achieved within a mixed use tightly
knit urban fabric. There are few if any windows on the street. The entrances on the streets and alleys are usually small (even the entrances to the larger courtyards).

     The houses constituting the Casbah have small size windows and are built usually high and very close to each other. Indeed, the primary purpose of these constructions was to protect the inhabitants and the animals from the extreme sunny days of the summer. Through studying this type of architecture, it is clear that every single feature of these dwellings is well thought in order to contribute to the creation of a microclimate within the town: the layout of the Casbahs, their height, their orientation, the use of materials in addition to the inner migration within the dwelling All play a major role in the temperature regulation inside. It is important to note that The plan of a Casbah is introverted, with a major atrium on the inside, typically referred to as a courtyard. These urban and architectural element (the courtyard) play a major role in the climatic control of these houses at the building scale, but also  at the urban scale (i.e. the Casbah).Being special in its inception and in generosity vernacular architecture, rely on the four  main natural or classical elements: water, air, fire and earth.

 The Natural Elements & Sustainability Indicators
         1. Air
The houses are  usually accessed from the street through a bent entrance which prevents visual intrusion into the internal spaces. At the entrance there is a lobby. Also we find  it in the hammam  and is the largest and most decorated space. This large space allows cool air to enter the hammām and facilitates the natural ventilation of the first passive zone of the structure. The hot rooms I Islamic baths are characterized by multiple circular or star-shaped openings over the whole surface of the dome and closed by glass caps. Some of these glass bulbs are removable in order to allow for natural ventilation to take place when the bathing spaces are not used. They allow natural day light to enter the bathing spaces where the highly concentrated steam helps the diffusions of light rays inside the bathing spaces with reflective and diffusing effects. 

       2. Fire
The heart of the hammām is the furnace. It is built against the longitudinal wall of the hot room. It has its own entrance for the delivery of the fuel and only communicates with the bathing spaces via the under floor heat tunnels. The furnace is also used for other socio-economic functions such as the cooking of meals for families living in the neighborhood. The warm and hot rooms are heated using the hypocaust system traditionally used in the Roman baths. The hot smoke from the fire travels under the floor of the hot and warm rooms before rising up a chimney in the walls. Once the air has passed under the floor, it is drawn into the walls and up the flues due to the hot air already rising in the flues creating a partial vacuum. The heating  system is a labour intensive device as it requires constant attention to feed the fire  and remove the ashes. It used to act as neighborhood recycling centre for local by-products such as wood chippings, olive stones and combustible rubbish which are used as environmental-friendly fuel for the furnace.
      3. Water
Water is one of the main elements keeping alive the hammām. Sustaining its use is important. The majority of bathhouses were equipped with their own well, however they still needed to have additional quantities of water to fill their cisterns and tanks. Hence their location next to main transportation routes but also to the water distribution system. The use of water inside the hammām is regulated on the basis of the quantities of water heated by the furnace. Basins and pipes are designed in a way to reduce water consumption accordingly to the number of clients, but also to the human body needs for washing and cleaning.
Traditional public bathhouses are half buried in the ground. The consequences of this half burying of the hot room spaces in the hammām is the pit effect. It allows heat gain, passive heating and helps concentrating the cool air at the bottom of the lobby and keeps warmer air in the upper layers by a thermo-dynamic movement. One of the main requirements of the building envelope is to have a high level of thermal mass in order to keep the heat in. Another reason is to support the roofing structures and ground pressures when buried, and give a strong inertia to the building [16]. The walls are traditionally built of a base of thick stone topped by brick construction and the domes and vaults are built with bricks. Special water-proof renders and plasters are made from a lime mortar to which ashes from the furnace are added. Brick and brick buildings are sustainable because they’re highly durable; Offer long term life performance; Are low maintenance Are energy efficient; Provide healthy and comfortable environments and; Are recyclable.


  The features of Mud Brick
Basic mud brick are made by mixing earth with water, placing the mixture into moulds and drying the bricks in the open air. Straw or other fibres that are strong in tension are often added to the brick to help reduce cracking.
 Structural capability
With thick enough walls, mud brick can create loadbearing structures up to several storey’s high. Vaults and domes in mud brick that it can be used for many situations other than vertical walls. It may be employed as infill in timber frame building or for loadbearing walls. Although its compressive strength is relatively low.
Contrary to popular belief mud brick are not good insulators. Since they are extremely dense they lack the ability to trap air within their structure. The attribute of bulk insulation that allows it to resist the transfer of heat.
One way of dealing with mud brick’s lack of insulation is the construct some or all of the outer walls with framed construction and use mud brick for partition walls and as an internal ‘reserve brick veneer’ on some external walls. 
Traditional earth building of used walls up to a metre thick. These would provide reasonable insulation and enormous mass to stabilize internal temperatures.
Sound insulation
A well-built mud brick wall has very good sound insulation properties. In fact, it can be almost equivalent to a monolithic mansory structure in its capacity for attenuation. Some modern mud brick homes use mud brick for external walls and high partition walls internally, it is some effective for thermal and acoustic performance to use mud brick for the partition walls and light weight.
 Fire and vermin resistance
Since earth does not burn and earth walls don’t readily provide habitat for vermin, mud bricks generally have excellent fire and vermin resistance.
Durability and moisture resistance
Mud brick walls are capable of providing structural support for centuries but they need protection from extreme weather or continuous maintenance.  Although some soils are very resistant to weathering, as a general rule mud brick needs protection from driving rain and should not be exposed to continuous high moisture.