Arjun Basnet Student no: 725563 . AAR4907 - Sustainable Building Materials and Components COURTAYRDS: Their roles in houses as climatic moderator in hot-arid climates Sustainable Architecture Faculty of Architecture and Fine Arts Norwegian University of Science and Technology (NTNU)
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Arjun Basnet
Student no: 725563
.
AAR4907 - Sustainable Building Materials and Components
COURTAYRDS: Their roles in houses as climatic moderator in hot-arid climates
Sustainable Architecture
Faculty of Architecture and Fine Arts
Norwegian University of Science and Technology (NTNU)
Arjun Basnet
Student no: 725563
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‘They provide a place to bask in the sun or a shady and airy place to be cool, while the
houses are stuffy and either too cool from the night before or overheated by the
afternoon sun’. (Hyde, 2000, p.221)
The description above by Lisa Heschong exactly tells the usefulness of having
courtyards in buildings.
Abstract:
Design responding climate issues is an important environmental approach to building
design in today’s context of enhancing comfort condition with considerations of
sustainability and reducing energy consumption. A number of passive strategies can be
explored depending on the geography of a place and the nature of the climate. Use of
courtyards in building designs is one such efficient strategy whose usage can be
explored for both hot and cold climates. Courtyard is an internal climate modifier
(Majumdar, 2001, p.139), the existence of which will definitely change the surrounding
environment and the air temperature. As climate seems to have a major impact on the
building, there must be relationship between the architectural characteristics and
environmental / climatic conditions in order to achieve a good passive design.
Introduction:
Courtyard in general is an area wholly or partly surrounded by walls or buildings.
Conceptually, courtyard is considered as an open space that is open to the sky and
penetrates the mass of the building. Courtyards (Reynolds, 2002, p.ix) not only serve as
a connecting space to the surrounding rooms as traditionally thought of but also
mediates in filtering daylight, wind, rain and noise. In addition to bringing nature into the
building, they assist in moderating nature’s extremes, i.e., hot and cold. These spaces
are normally not as hot as summer’s afternoon sun and as cold as just before dawn or
late night. Courtyards when planned suitably protect outdoor spaces against winds,
maximise solar access and minimise shading in winter whilst opening to breezes in
summer, maximising shading vegetation and minimising solar access to vertical and
horizontal surfaces in summer. In cooler climates buildings can be arranged to trap
warm air or protect it from cold air in courtyards while in hot places, cooling through
courtyards can be further enhanced with the use of fountains, ponds and growing plants
by evaporative cooling.
In denser settlements especially in urban areas where natural light and ventilation
becomes important and is difficult to achieve, courtyard is necessary (Hyde, 2000,
pp.221-24). In the absence of courtyards, it is usually difficult to achieve passive way of
ventilating and some form of active system is required to provide the physical comfort of
building occupants. From the climatic design perspective, the size and degree of
enclosure have a significant impact on the performance of a courtyard and the building
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around it. If a courtyard starts becoming large, then it loses its identity as a normal
courtyard and instead becomes a square or a park. When it becomes too small, it may
look like a corridor; transferring it into a breezeway or to have the more selective
function of an air and light shaft. The usual function of a courtyard is to bring light and
ventilation into a building. However, it can create a useful micro-climate when combined
with different functions, wall types, building forms, materials and landscaping. The
position, orientation, shape and size of courtyards are important factors for the design of
courtyards. Their relation with other building elements open and semi open spaces must
be considered as well. The concept of space in a courtyard house and a western style
house is different as it is closed and more private in the former while it is open in the
Courtyards (Reynolds, 2002) are special areas that allow the inside and outside to
mingle; where rain, wind, daylight, night darkness, and sound can be somehow
controlled. Since at least 3000 B.C., courtyards have been incorporated into the
architecture of the day as a significant part of the physical and cultural landscape.
Ozkan has also stated that the concept of courtyard dates back to the Neolithic times
(Ozkan, 2006).
Greek houses, (Anon., n.d.) in the 6th and 5th century B.C., were built of stone, wood,
or clay bricks consisting of two or three rooms, arranged around an open air courtyard.
Larger homes had a kitchen, a room for bathing, a men's dining room, and perhaps a
woman's sitting area. Since the Greek women were allowed to leave their homes only
for short periods of time, they could enjoy the open air, in the privacy of their courtyard.
In Islamic culture (Ozkan, 2006), courtyard is an exclusively private part of a house and
is used only by members of the family. The courtyard is a multipurpose space where
Figure 1: Courtyard & Western-style house.
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most of the activities of the family take place. It also provides a climatically controlled
space from many of nature’s unwanted forces, like winds and storms.
The compact nature of planning around a courtyard offers efficient use of the
streetscape, as it is primarily used for accessibility and circulation. Therefore, by its
nature in the historical districts of hot, arid regions, very high densities are achieved by
low-rise architecture and an urban pattern that is humane. Courtyard housing is widely
considered to be a responsive typology to low rise high-density urban housing and is an
appropriate form of housing within contemporary mixed use sustainable urban
developments.
Courtyards are an interesting space in a building that have numerous and significance
importance. Their usages vary from place to place and culture to culture. In some
places, a courtyard serves only as a physical outdoor space or an extra space that
connects the outside street to the building. While in other places, according to their
placement, the function is different. If it serves as the entrance to the house, then it is
placed to the corner or to the side with one side adjacent to the street, separated by a
boundary wall. Some courtyards like the colonial Latin America (Venezuela) (Reynolds,
2002, p.4) have courtyards to the rear side of the building connected by a covered
entranceway from the street (see figure2). Typical courtyards have a direct entrance to
the courtyard like the one prominent in the north side of the Mediterranean as in figure2.
Many courtyards found in Kathmandu Nepal are also of this type. In case of ‘four in one’
Figure 2: Different courtyards (Reynolds, 2002, p.4)
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courtyard house in Beijing, public access is allowed to the first smaller courtyard but a
‘hanging flower gate’ screens the second, large and private courtyard. In some other
courtyards like that of the ancient Greece (figure2), the covered entranceway is placed
such that it leads directly to one arcade along the courtyard rather than the centre.
Scope:
Courtyards serve buildings with numerous functions. These are from providing privacy,
access to nature, serving various household and commercial activities to moderating
the climate. In the essay, I basically will focus on the climatic aspect of courtyards. Even
the climatic aspect of courtyards if researched, would produce books. Hence, the scope
of the essay is mainly to explore the moderating qualities of courtyards with climate
extremes in dwellings in hot-dry and hot-arid climates.
Context: hot-arid climate
Hot-arid climates (Mier & Roaf, 2002) are usually observed in hot dry deserts that
almost see no rain throughout the year with the air and soil being very dry. Summer
days are usually very hot and dry while nights are comparatively cooler. Winter days are
generally sunny with clear skies whereas nights are cold. Dust and sand storms are
common usually during the transition season. Drought is a common phenomenon in this
type of climate. The case of Marrakesh, Morocco is taken as the context.
Figure 3: Courtyard, Trondheim Norway; in cold countries large courtyards are sun collecting spaces. The spaces around the courtyard are also protected from the cold wind (picture to the right; http://kart.gulesider.no)
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Method:
It is a good idea to exploit the advantages of courtyard as a passive means in places
where it suits best. To write this essay, I basically collected information from books,
electronic sources and from supervisors. I have taken two cases as illustrations:
i) Turkey case: description to support the theme of the essay (Bekleyen &
Dalkilic, 2011)
ii) Morocco case: quantitative analysis of the thermal behaviour of courtyards in
hot-arid climatic context. (Raydan et al., 2003, 2006)
Research question and objective:
As mentioned above, courtyards serve as an important means for thermal comfort. In
cold areas like Norway, the courtyards are wider/larger to admit more of the winter sun.
They are usually protected from cold winds by the buildings surrounding it. In the
warmer countries, they are smaller to exclude the sun and its tremendous heat. So, we
see that the shape and proportion of the courtyard has a major role to play in thermal
comfort of a building which incorporates it. Courtyard usually assists in the natural
ventilation thereby creating a comfortable indoor environment. So, on the basis of these
facts, this research essay shall be based on the following research question:
What is the influence of a courtyard to thermal comfort in a building incorporating it in
hot-dry/arid climates?
The following objective can be drawn to reach a conclusion to the above question:
‘To study courtyards and their role in moderating the extreme climatic conditions in hot-
dry/arid climatic context’
Social Aspect of Courtyards
In Islamic cultures, privacy is one of the most important factors in a house. As per the
tradition, the male guests are to be entertained, (Zako, 2006, p.65) while at the same
time avoiding their access and contact with the female members of the house. This has
given rise to additional features to Islamic architecture and the courtyards have been
used in some form or the other. The entrance to courtyard is bent to create more visual
privacy from the street.
In Kathmandu Nepal, the old royal palace called the ‘Hanuman Dhoka’ has ten
courtyards. Until the existence of a king in Nepal, the main courtyard called the Nassal
Chowk just next to the entrance was very important for royal ceremonies like the
coronation. The other courtyard ‘Mul Chowk’ has a temple and so is used for religious
activities. The Mohan chowk has a sunken bath which on earlier days was used by the
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royals for bathing.
Similarly the
traditional settlements
around the palace
and other places in
the valley like Patan,
Bhaktapur, Kirtipur,
the buildings are
arranged around
courtyards. These
courtyards are very
important and are
used as community
spaces. Activities like
bathing, religious
activities in case a
temple exists, drying
grains, basking in the sun, various other social gatherings like marriages, parties and so
on. Even at present, when the houses have changed appearance, the courtyards have
remained unaltered posing themselves even more important as the few remaining open
spaces in the crowed city.
Activities in and around the courtyard
Although temporary, any activity can be carried out in a courtyard. Usually the
extensions of a living, dining and kitchen activities are carried out. Activities like sitting,
eating, gathering, celebrating, playing and even sleeping during hot summer nights is
carried out in the courtyard (Bahammam, 2006, pp.78-79). It is designed to be a
multifunctional family space in the house, drawing the family members out into the
courtyard holding them together while providing favourable atmosphere for social
interaction. The courtyard’s floor could have suitable materials for children to play out in
the nature without being threatened from traffic and other extrusions.
Courtyards function successfully as dwellings for older people. They combine the
advantages of compact, easily maintained living quarters with the provision of
communal outdoor places for public contact. The emphasis on the ground plane
minimizes stairs and permits an unusual degree of interaction among people with
limited mobility (Reynolds, 2002, pp.57-58).
Figure 4: Courtyards in Hanuman Dhoka Royal Palace, Kathmandu Nepal (John Sanday)
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Climate control
Courtyards, as per Reynolds (2000, p.79), represent an attempt to bring the forces of
nature under partial control. They intensify some aspects of the climate such as daylight
and dilute others such as wind. Use of Courtyards (Raydan et al., 2006) in hot-arid
regions fulfil several functions such as the creation of an open sheltered zone, the
adoption of ingenious natural cooling strategies, the protection against wind-blown dust
or sand and the mitigation of the effects of solar excess. However, in cold countries like
Norway, these are designed to create ‘pockets of solar gain’, thus balancing the
harshness of cold northern climates. So, a courtyard is either a sun protector or sun
collector depending on their proportions. A deeper courtyard will stay cooler in summer
but exclude sun for warmth in winter and hence are preferred in hot climates. In cold
weather, (Reynolds 2000, p.79) a common design strategy is to ‘huddle’ that is,
minimize exposure to cold air. Courtyard buildings expose only the street façade, the
four walls facing the courtyard, and the roof. Compared to the building surrounded by
open space, this design strategy works well to conserve heat.
During the day, (Medi, n.d.) solar radiation falling on the surface of courtyard warms up
the air which then rises up. In replacement, there is a flow of cool air from the openings
of surrounding ground level room; thus, creating an air flow. At night, the process is
reversed with cool air dropping to the courtyard from the roof and then flowing into the
living spaces through the lower level openings and then leaving through higher level
openings creating a ventilation pattern. This works best in hot-dry climates where day
time ventilation is undesirable, as it brings heat inside and at night the air temperature
becomes cooler and it can ventilate the building. However, when the courtyard receives
intense solar radiation, much heat will be conducted and radiated into the rooms as
against the induced air draft of air which is often problematic. The intense solar radiation
can also produce glare to the inside spaces.
Strategies
Creating suitable environment to avoid heat gain by using shading is one of the best
options for thermal comfort in hot-climate courtyard buildings. Green plants usually
vines or trellis filters sun and diminishes both daylight and wind. Cooling strategies
include evaporation, radiation and convection. Evaporation cools both building and
human skin surfaces quickly and the drier the air, the faster the evaporation. Dry
climates have much less water vapour in the air, so radiant losses to the cold sky are
much greater. And dry climates enjoy much cooler air by night providing a diurnal
convection ‘heat sink’ that humid climates lack (Reynolds, 2002, p.84).
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Wind
Wind (Reynolds, 2002, pp.88-90)
is sometimes helpful in hot dry
and temperate climates for
cooling, especially for night
ventilation when outdoor
temperatures are lower. Wind
moves primarily horizontally and
thus easily skips over the
horizontal opening to a courtyard.
If wind is to be encouraged,
several strategies are available. A
wind-catching strategy is to raise the height of the courtyard wall downwind (assuming
that a site has a prevalent wind direction). As wind moves across the lower roofs and
the courtyard opening, it then strikes
this higher wall. Most of the wind will
move up and over, but a down draft at
the wall can be enhanced if there is
an outlet at the bottom, that is, if some
wind can continue below the roof as
well as over it. Day ventilation
(comfort ventilation) (Mier & Roaf,
2002) will raise indoor temperatures,
while night ventilation will lower them.
In a building, (Wadah, 2006, p.157)
there are differences in temperature
between solid and void elements;
those open to the sun and those
shaded lead to differences in air
density which causes the following air
circulation: one is between the interior
courtyard and the exterior space at
day and night in summer and winter
conditions. The other is between the interior courtyard and the interior space of the
building (see figure 6). As a result, the wind acts as a positive agent in reducing ambient
temperatures simply because of the nature of the use of courtyard architecture.
However, besides moderating temperatures by the gradients created, wind-cooling can
reduce day-time surface temperatures which then benefits night-time conditions.
Figure 5: Wind strategy in courtyard
Figure 6: Air circulation between courtyard and adjoining rooms (Wadah, 2006, p.156)
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Hassan Fathy (Reynolds, 2002, p.91) describes how two courtyards of unequal size,
separated by a loggia, might induce rather weak air motion. More sun penetrates the
larger courtyard’s opening, creating a hot air space. As this hot air rises out the opening,
cooler air must flow into the smaller courtyard. This air is likely drawn either into the
smaller courtyard’s roof opening, or into rooms through open windows at the street. In
either case, this ‘new’ air is cooled as it passes through the shaded smaller courtyard or
cool room, and for those seated in the loggia between courtyards, a perceptible breeze
of cooled air is available for increased comfort.
Humidity to aid evaporative Cooling
Humidity (Wadah, 2006, pp.157-58) is important in reducing the dryness of interior air.
Excessive dry air can give a perception of excessive temperature while in reality; the
same temperature with slightly more humidity may feel more comfortable. Adding
moisture to the air via fountain or a pond can reduce temperature by evaporation as well
as adding a welcome increase in general air humidity. So a balance is often struck in
courtyard buildings between the shape for maximum temperature control from solar
radiation and that which facilitates wind and that which provides optimum levels of
humidity. Since, the water will need the sun to aid evaporation and hence humidify the
air, fountains and ponds are normally placed in the centre of the courtyards because of
the vertical midday sun in summer. For the air movement to the back of the rooms, the
wind towers and vents are usually at the perimeter of the building. This has resulted in
the distinctive design of courtyard houses with their centrally-placed courts and
peripherally-placed wind towers (Figure 7).
Figure 7: Courtyard house in Saudi Arabia illustrating humidification and ventilation strategy (Al-Saud & Al-Hemiddi, 2006)
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Thermal Mass
Thermal mass is a means to improve the diurnal temperature swings in hot-dry
climates. High thermal mass is the most obvious characteristic of traditional courtyard
buildings, and its primary cooling effect delaying the arrival of the afternoon heat, also
aided by shading. In hot-dry climates, high thermal mass can be cooled by radiation to
the night sky, by evaporation and by ventilation at night. The courtyard floor plays an
important cooling role, because it looks straight up to the cold night sky. The shallower
the courtyards, the more the floor exposed to the sky rather than the walls, and so the
more radiant heat loss by night. Use of thermal mass in a shaded and insulated building
can help lower indoor temperature by 35-45% of the outdoor ones when the building is
unventilated (Mier & Roaf, 2002).
Case1: Diyarbakir, Turkey
Courtyard houses (Bekleyen & Dalkilic, 2011) are common in hot and dry climates.
Environmental and cultural differences inform the diverse characteristics of courtyard
houses because they are used by a variety of cultural groups in a large number of cities.
Courtyard houses which are common in regions with hot and dry climates demonstrate
strict territoriality and attempts to create private space for introversion. This life style is
not only to reflect the culture but also is the result to moderate the effect of harsh
climate.
Diyarbakir is a city located in the South eastern Anatolia Region of Turkey and has a hot
and dry climate. The courtyard houses were surrounded by high walls within the
compact urban texture and were built to protect the inhabitants from both the extreme
heat in summer and unwanted interference from outsiders. In all of the houses
examined within the scope of the present study, a central courtyard exists, providing air
and light for the other spaces surrounding it. The windows of all rooms on the ground
floor have a view of the courtyard and they do not have a direct connection to the outer
part of the building. Planning in this way is suitable for hot climates; the space is
designed for users in a way that blocks sunlight in summer and allows sunlight in the
winter. Consequently, the spaces around the courtyard are designed appropriately for
seasonal usage (Bekleyen & Dalkilic, 2011).
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In the summer, according to Bekleyen and Dalkilic (2011), the spaces in the southern
part of the courtyard are used. These spaces are cooler because they face north and
are not exposed to direct sunlight. The ceilings of the rooms are high, and there are
wide windows that are always kept open in summer. They also have additional upper
windows close to the ceiling. The cool air comes into the room through the windows,
and after it gets warmer, it flows into the courtyard through the upper windows. This
creates a kind of ventilation. Even if the lower windows are closed, the upper windows
are always kept open. In some cases, these windows do not contain glass; instead, they
have ornamented wire fences. Thus the warm air in the room is continuously exchanged
through these openings. The semi open space faces the courtyard for summer comfort.
There is a special room specially designed for very hot days placed underground (one-
third or one-half of its space height is placed under the level of courtyard). The room
gets air and light from the upper windows facing the courtyard, and a small pool is
present to decrease the heat (Bekleyen & Dalkilic, 2011).
Figure 8: Seasonal horizontal movement (left); seasonal and daily vertical movement (right) in traditional Arabian courtyard houses (Bekleyen & Dalkilic, 2011)
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Case 2: Studies with reference to Marrakesh, Morocco
This quantitative analysis of the climatic aspect of courtyard in hot arid climate, is the
results from studies by Raydan, Ratti and Steemers (2006, p.135-145).
Contrary to what most people think,
courtyards fulfil several functions in
hot-arid regions (Raydan et al.,
2006, p.135). These include
creating open sheltered zone,
adopting natural cooling strategies,
the protection against wind-blown
dust or sand and moderation of the
effects of solar excess. Climate is
one strongest element that
determines architectural form and
this applies to shape of courtyards
as well. While in hot-arid climatic
regions, courtyards are created to
gain protection from the harsh sun; in countries like Norway, they are used as sun
collector. It is actually the proportions of the courtyard space that varies its climatic
properties.
Raydan, Ratti and Steemers (2006) tired to find out the suitability of courtyards