Study on the Visual Performance of a Traditional Residential Neighborhood in Old Cairo

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Study on the Visual Performance of aTraditional Residential Neighborhood inOld CairoSura Almaiyah & Hisham ElkadiPublished online: 08 Aug 2012.

To cite this article: Sura Almaiyah & Hisham Elkadi (2012) Study on the Visual Performance of aTraditional Residential Neighborhood in Old Cairo, Journal of Urban Technology, 19:4, 59-86, DOI:10.1080/10630732.2011.649913

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Study on the Visual Performance of a Traditional

Residential Neighborhood in Old Cairo

Sura Almaiyah and Hisham Elkadi

ABSTRACT Traditional dwellings located in the hot arid zone in Egypt are well known fortheir sensitive architectural response to the region’s climatic conditions and socio-culturalnorms. The majority of these dwellings are well recognized for their courtyard arrange-ment and perforated fenestration systems that evolved to control the harsh solar, climaticconditions without compromising the aesthetic quality of the space and the occupants’well-being. The unique visual characteristics of these structures cannot be fully appreci-ated by assessing the visual performance of buildings in isolation from their urbancontext. Much of the character of the traditional urban fabric of this region came fromthe collective visual perception of its architectural components as well as urban patterns.This paper examines daylight behavior of a well-known historic alleyway and of a court-yard house in the Old City of Cairo. Using the Radiance IES simulation modeling tooland a scaled model under an artificial sky dome, the paper investigates the visualcomfort in a typical pedestrian street and a selected house. A comparative analysisbetween simulated results and measured values at target points was conducted. Theresults indicate a reasonable agreement with the simulation results. The paper gives aninsight into the overall visual experience in the traditional settlements in the Old Cityof Cairo in relation to daylight components and hence their contribution to the uniquesense of identity of the place.

KEYWORDS Daylight; architectural heritage; place identity; visual comfort; daylightmodeling

Introduction

The influence of climate in shaping the uniqueness of the traditional architectureof the Arabian region is widely recognized (e.g. Al-Shareef et al., 2001; Baker andSteemers, 2002; Salama, 2006; Warren and Fethi, 1982). Many scholars have dis-cussed the environmental performance of traditional buildings and settlementsin the Arabian region, which were formed under the influence of the physical,technological, and socio-cultural structure of a society and in harmony with itsclimatic conditions. Hassan Fathy’s pioneering writings in the early 1970s andmid 1980s provided detailed descriptions of the environmental aspect of tra-ditional dwellings of the region in general and of Egypt, in particular. The majority

Correspondence Address: Sura Almaiyah, Senior Lecturer, Portsmouth School ofArchitecture, Portland Building, Portland Street, Portsmouth, PO1 3AH. UnitedKingdom. University of Portsmouth, UKE-mail: [email protected]

Journal of Urban Technology, Vol. 19, No. 4, 59–86, October 2012

1063-0732 Print/1466-1853 Online.Copyright # 2012 by The Society of Urban Technologyhttp://dx.doi.org/10.1080/10630732.2011.649913All rights of reproduction in any form reserved.

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of these dwelling units are well recognized for their courtyard arrangements andperforated fenestration systems that evolved to control the harsh solar radiationwithout compromising the aesthetic quality of the space and the occupants’well-being. However, the unique visual characteristics of these dwellings or struc-tures cannot be fully appreciated by assessing the visual performance of buildingsin isolation from their urban context. Whereas research on the thermal perform-ance of traditional Arabian dwellings has received constant attention (e.g.,Ealiwa et al., 2001; Scudo, 1988, Sharif et al., 2010), research on visual comfortand daylight performance of these buildings and settlements has receivedrather less attention. The few published studies that dealt with this subject tendto focus on assessing the daylight performance of buildings or certain fenestrationsystems in isolation from the urban context. For example, in 2001 Al-Shareef et al.,presented a computer based-model for predicting the daylight performance of acommon shading system found in the traditional architecture of Saudi Arabia(the traditional parallel shading system, Rowshan). In a more recent article, Al-Sallal and Dalmouk (2011) evaluated the daylighting performance (in terms ofmuseum lighting requirements) of a traditional residential building in the UAEthat was recently converted to a museum.

Given the fact that much of the character of the traditional settlements of thisregion came from the collective visual perception of their architectural as well asurban components, this paper presents a comprehensive daylight analysis of oneof these traditional neighborhoods by assessing the daylight behavior of two of itsmain components: a typical dense narrow street and a courtyard house arrange-ment. One of the well-known traditional residential neighborhoods in the OldCity of Cairo was used as a core for investigation. The variability in the visual per-ception and comfort for a typical pedestrian street and the occupants of the housewas predicted using the Radiance IES simulation modeling tool and a scaledmodel under an artificial sky dome. The paper gives an insight into the overallvisual experience, sense of comfort, and daylight microclimate in the traditionalbuildings and settlements in the Old City of Cairo where daylight has contributedto the place’s unique sense of identity. The paper also presents a methodology thatcan be used to assess daylight behavior at an architectural level as well as at anurban scale.

The article is structured into three main sections. It starts by providing a briefdescription of the study area, the main architectural features and urban com-ponents that shaped its local microclimate. The second section provides a detaileddescription of the methodology and the validation exercise. The third partincludes results of the first phase of analysis that dealt with assessing the intensityand diversity of illuminance in the two examined forms: the alleyway and thecourtyard. The results of the second phase of analysis, in which illuminancevalues and lighting requirements of a selected number of core spaces in thehouse were investigated, are given in the second part of section three.

The Study Area: Old Cairo

The historical significance of the Old City of Cairo is globally well recognized. SirBanister Fletcher (1996), for example, put Cairo high on the list of cities of out-standing historic value with an immense legacy of buildings dating back to theMiddle Ages. Grabar (1984) raised the same point, yet ascribed the city’s character

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and sense of place to the way in which historical monuments and towers hadshaped the physical fabric of the city, forming a network of visual signs thathelps passers-by to navigate the city. In Tung’s view, it is the “adaptivity” of themetropolis to its climate that most accounted for Cairo’s unique appearance. InPreserving the World’s Greatest Cities (2001: 105) he wrote:

in a part of the world where the sun was intense and nearly vertical, one ofthe few forms of relief was shade. Thus as the density, height, and popu-lation of the city increased, the streets were not widened, since deep,narrow canyons resulted in an environment of cool shadow.

Cairo is the capital of Egypt and has served as the capital of numerous Egyptiancivilizations. It lies between latitude 308 north and longitude 318east where a highintensity of solar irradiation predominates for a large part of the year. The averageannual global radiation can reach 2600 kwh/m2/year in the southern parts of Egypt,and the direct normal solar radiation varies between1970 and 3200 kwh/m2/yearwith low levels of cloudiness. The annual sunshine duration hours vary between3200 and 3600 hr/year (Ministry of Electricity & Energy, 2006). In such a geographi-cal context, the hot arid climate was vital to the development of certain architecturalfeatures and urban patterns. In addition to the compact configuration of the med-ieval urban fabric that shaped the local microclimate at the street level, traditionalCairene architecture exploited different masonry devices to promote thermal andvisual comfort including the use of courtyards, mashrabiyya (perforated screens),malqaf (wind-catchers), internal gardens, and many others. Brief descriptions ofsome these traditional motifs that can be traced to the medieval residential buildingand neighborhood examined in this work are given below.

Urban Layout

In hot arid climatic regions, protecting the building blocks from intense solar radi-ation was one of the main problems facing local builders. For that reason,enclosed, compactly planned urban forms, such as internal narrow alleyways,were among the most suitable urban forms developed in this type of climate toreduce the heat problem caused by excessive direct radiation. By placing build-ings close to each other, surfaces exposed to the sun were often reduced with alarge amount of shade and coolness that decrease the heat gains on externalwalls (Koenigsberger et al., 1974). Like many other cities in the Arabian region,tight busy streets and narrow winding alleyways are the most recognizableurban components that form the urban fabric of old Cairo. Among the outstandingexamples of these indigenous urban components are those alleyways that lie inthe heart of the historic spine or “heritage corridor” where nine clusters of monu-ments worthy for conservation were identified by the The United NationsDevelopment Programme (UNDP) in the late 1990s. The selected alleyway, ElDarb el Asfar (See Figure 1), is one of the alleyways that occupies the arealocated between the main historical thoroughfares leading from the north gatesof the old Fatimid wall towards the south: al-Mu’iss Street and al-GamaliyyaStreet. It is part of al-Gamaliyya district, which itself has gained special historicvalue, including the highest density of historic monuments in the area (Meinecke,1980). The alleyway was renovated in the mid 1990s, and today it is part of the

Study on the Visual Performance of a Traditional Residential Neighborhood 61

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tourist center of the Old City, close to many Islamic monuments and Cairo’s prin-cipal historic bazaar, Khan el-Kalili.

Building Form: The Courtyard House Arrangement

The courtyard house type is another well-known architectural arrangement thatcharacterizes the traditional architecture of Cairo. The main feature that differen-tiates this house style from other types of houses is the outdoor space that isenclosed within the interior volume to act as the heart of its morphology andspatial organization. Among the few surviving traditional courtyard houses inthe region are those located in the heart of the Old City. The significance of thehouse selected in this study lies in its historical value. El- Suhaymi House,located on the northern side of the examined alleyway, presents a completeexample of the traditional Cairene residential buildings of the seventeenth andeighteenth centuries (See Figure 2). It has all the traditional components of thehouse of the period and according to the Egyptian Ministry of Culture (2002) itis the only remaining complete example of private houses of that period. Exca-vations in the courts of the house also indicate that the site on which it waserected had been populated and built on since the Fatimids founded Cairo inthe tenth century. The house covers an area of over 2,000 square meters, with atotal of 115 spaces distributed on five levels surrounding a main internal courtwith an area of more than 200 square meters. Its structure suffered from variousnatural and man-made deterioration factors for several decades. In 1931, owner-

Figure 2: El- Suhaymi House, internal view of the courtyard showing the takhtabush facade on thenorthern side of the House (left) and the maka’ad at the first floor (right)Source: http://ocw.mit.edu/ans7870/4/4.615/images/16/image12.html

Figure 1: View of the alleyway of El Darb el Asfar showing its western entrance (right image), thecentral section (second from right) and the eastern side


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http://ocw.mit.edu/ans7870/4/4.615/images/16/image12.html

ship of the house went to the Egyptian government and around five decades laterit was added to the list of historical monuments, recorded as number 399. Whereassome of its vulnerable sections underwent various phases of restoration, the fullrestoration of the house was only completed in 2000, and it subsequentlybecame a museum.

As a house type, traditional Cairene houses with central courtyards involveda certain spatial arrangement that was composed of several space types. Addingto the central courtyard arrangement, they were typically characterized by fivekey space types. These core space types are: the dihliz (bent entrance), qa′ a (recep-tion area), takhtabush (covered outdoor setting area), maka’ ad (covered loggia), andharamlekor harim(female quarters). Operational definitions of some of these spacetypes are given below adopted from a previous study by Salama (2006) and theirlocations within the house are shown in Figure 3. Given the value of these coreelements in shaping the overall architecture of the house, three of these corespace types were selected here as a base for evaluating the visual performanceof houses of this type.

Fenestration System: Latticework

Whereas the courtyard arrangement can been seen in the traditional residentialarchitecture of many countries across the Arabian region, mashrabiyya is one ofthe few elements solely associated with the traditional residential houses ofEgypt. It is a complex perforated fenestration system made of highly craftedlattice screens of unvarnished wood, fixed over the openings. Traditionally, mash-rabiyya was used as a device for lightening and ventilating the domestic spaceswhile at the same time protecting women’s privacy. To control the passage of

Figure 3: Ground and first floor plans showing the three key selected spaces


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light and airflow while maintaining privacy, a typical mashrabiyya was composedof two parts presenting different lattice arrangements. While the lower part of themashrabiyya was constructed with a tight lattice pattern of turned wood to satisfythe visual and social demands of the “conservative residences,” the upper partabove eye level was constructed with a more open lattice pattern of turnedwood to compensate for the reduction in light and air caused by the lower part(Abdel Gelil, 2006). Baker and Steemers (2002: 6) have described the use of thisdevice in accommodating the inhabitants’ privacy while maintaining theirvisual connection with the outside environment. In their description,

Privacy and view out are the result of the relative intensities of light oneither side of the screen, where from the lighter side you see the screenbut are unable to see detail through it to the darker interior, thus provid-ing privacy. Conversely, from the darker side, the screen allows viewsthrough to the lighter and more public spaces.

Shading Strategies

In addition to the narrow winding streets and central opening courtyard housetypes that dominate the Old City urban fabric, covering the streets is another strat-egy that complements the traditional architecture of Cairo. In residential areas,shading the facades of buildings is often achieved as a result of the cantileveredvolumes of the projecting latticework or mashrabiyya. Shade is also brought tothe commercial streets and tight alleyways by means of various types of urbanroofing, including temporary shading devices. For a single building or courtyardarrangement, shade is often obtained by architectural elements such as projectingroofs, covered loggias, open galleries, and supplementary plants or by projectingthe lattice screens that shield the openings.

Orientation

The orientation of street and internal courtyard plays an important role in thelevels of shading and daylighting. The long axis of each form can be directed tothe N-S, E-W, NW-ES or NE-SW, all of which have varying impact on the pro-duced shading or exposure patterns in both spaces and hence on their daylight be-havior. In a study on the influence of different street orientations located inSouthern Europe over the solar gain (Littlefair et al., 2000), the findings suggestedthat the NE-SW/SE-NW typical grid pattern of the streets has significantly lesssun penetration than an E-W/N-S grid. This is the result of the changes of theangle of the sun, which varies widely with the time of the day and time of theyear. Although the same amount of direct solar radiation enters the top of eachalley, with the E-W alleyway more solar radiation reaches the ground, whilewith the N-S alleyway the direct radiation is more likely to strike the east-andwest-facing buildings at an oblique angle, resulting in less solar gain. It is alsoevident that in hot regions courtyard forms with an orientation between theNE-SW, NW-SE, and the N-S can provide extra shade as they stop the access ofdirect solar radiation at ground level for most of day (Littlefair et al., 2000; Muhai-sen, 2006). As illustrated in the ground floor plan (See Figure 3), the orientation ofthe examined house is within 15 degrees of North, thus representing one of themost preferable orientations of a courtyard building form in a hot arid climate.


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By contrast, the alleyway shows one of less successful streets orientations in termsof blocking direct solar radiation in this type of climate (See Figure 4). The impactof orientation on the intensity and diversity of illuminance in both forms is dis-cussed below.

Assessing the Daylight Performance of a Traditional Settlement of Cairo

The Building Research Energy Conservation Support Unit (BRECSU) (1997) classi-fied the design parameters that have an impact on daylight levels in buildings,urban spaces, and settlements into three levels. These are the “micro scale,”where the interest is concentrated upon the geometry of fenestration elements;the “meso scale,” deals with the significance of openings within the externalfabric of the building and the effect of building depth; and the “macro scale”where the considerations are at the level of urban planning. The main design par-ameters related to the urban space configuration and affecting daylight levels atthis scale (the macro scale) are the orientation of space, compactness ratio (enclo-sure ratio), reflection properties of the surrounding surfaces, and the geometry ofthe sectional profile of space (Al-Maiyah and Elkadi, 2007). Besides the influenceof these spatial parameters, the daylight levels in buildings also depends upon aset of design parameters related to their geometry (the meso scale). Among theseparameters, the form, the size, the orientation of building, and the size andlocation of light openings in the building envelope are the most influential (e.g.,Baker and Steemers, 2002; Baker et al., 1993). As this paper aims to provide anunderstanding of the overall visual experience found in traditional urban settle-ments by assessing daylight levels in a typical dense narrow street and courtyard

Figure 4: Distribution of reference points along the alleyway


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house in Cairo, a similar framework is adopted by this study in which two mainphases of daylight analysis are conducted. While in the first phase of analysis,parameters related to the macro scale were considered, the second phase of analysisfocused on the elements of the meso scale by assessing daylight behavior of aselected number of internal spaces of the house (See Figures 3 and 5).

Methodology

The study went through several stages: firstly, due to the absence of the requiredarchitectural drawings of the target buildings a photo survey was conducted as apart of the site visit to identify the geometry of the case study. Around 100 digitalphotographs of the alleyway (See Figure 1) and the house were recorded to outlinethe geometry of their facades. Simple tape measurements were also conducted todetermine the scale of the digital model and assess its accuracy at a later stage.This is referred to as a photogrammetric approach. It was previously introducedby Mantzouratos et al. (2004) as part of an illumination study of one of the nine-teenth-century neo-classical buildings in Athens and also adapted by the authorsin a previous study (Elkadi and Al-Maiyah, 2007). Historic maps and two-dimen-sional drawings that were collected during the site visit were also used in buildingup the digital model. In the second stage, the three-dimensional model of theexamined configuration was created using Model IT (the building modeler) in

Figure 5: Distribution of reference points in the three spaces (the bent entrance- upper left and right,the takhtabush-lower right and the maka’ ad-lower left)


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an IES virtual environment, and a preliminary phase of daylight simulation wasconducted. Daylight illuminance values at target points along the alleyway andinside the courtyard were predicted using the Radiance IES simulation tool. Radi-ance is a powerful highly accurate simulation tool that is increasingly being usedto simulate complex lighting environments (e.g., Balocco and Frangioni, 2010; Kimand Chung, 2011). Although the physical accuracy of Radiance in simulating lightbehavior in a complicated internal environment has been rigorously validated(e.g., Mardaljevic and Lomas, 1995; Ng et al., 1999), its capability in providingaccurate calculation at the urban scale is yet to be tested. Therefore, a validationexperiment that is based on a physical model and an artificial sky dome was con-ducted in the third stage of the work to provide more confidence in the simulationmodeling. This approach is developed based on a recent work by Kim and Chung(2011) who have used a physical model under real sky conditions to validate thepredicted illuminance values of a museum building in South Korean. Similar tothe digital model created in Stage 2, a 1:50 physical model of the alleyway andthe house was carefully constructed using light plastic materials. The actual alley-way measures 7.5 m in width at its western end, 3.2 m at the central section,around 5.8 to 3.8 m at the east, and is 166 m long (See Figure 1). Due to the limit-ations set by the size of the sky dome simulator and the practical difficultiesassociated with building up a 1:50 model of such a long street, only the centralpart of the alleyway where the house is located was constructed and tested. Itmeasures 46 m in length and presents the most compact sectional profilesfound in the alleyway with a height to width ratio of 3.2:1. The model was thentested using the artificial sky dome at the Bartlett, University College London(UCL) (See Figure 6). This large-scale facility comprises a 5.2m diameter hemi-spherical dome, covered with an array of 270 compact fluorescent luminairesthat are individually controlled to adjust the luminance distribution; thus model-ing various sky conditions.

Figure 6: Images of the scale model, the digital model and the sky simulator facility


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Four main phases of measurements were carried out in which a system ofreference points was used to assess daylight illuminance values at target pointson the model. A total of 18 points that were assembled on three main axes wereused to measure illuminance values in the courtyard and another nine pointsthat were assembled along the main axis of the alleyway were selected tomeasure the values at the street level. The distribution of the measurementpoints along the alleyway and in the courtyard is shown in Figures 4 and 7.

Illuminance data at the target areas were recorded respectively using a Mega-tron light meter that can measure illuminance levels at12 different points simul-taneously. The illuminance data at each target point was recorded four times intwo measurement sessions over two days on May and June 21 and the averageilluminance value at each reference point was then calculated. A KonicaMinolta LS-110 luminance meter was used to measure the reflectance value ofthe physical model, and the data logger and controlling PC were programmedto take measurements at the two sessions. At the same time, simulations usingovercast sky conditions similar to those assigned to the sky simulator weremade and comparative analysis between measured and predicted data was con-ducted to validate the simulation exercise. The scale model measurements andthe results of the Radiance simulations are given in Table 1. The agreementbetween simulated and measured values was quite acceptable. The comparativeanalysis shows that the absolute relative difference between simulated andmeasured illuminance values along the alleyway and in the middle of the court-yard lay in the range of _14 to 36 percent and _11 to 22 percent, respectively (SeeFigure 8). Part of the high discrepancies observed at specific spots, such as point1of the alleyway and point 1 of axis 1 in the courtyard, may be attributed to somepossible errors in the sky simulator dome, differences between the physical modelconstruction and the digital model, as well as to the differences between thelocation of the physical photocells and the digital one. Overall, these figures arein agreement with those recorded by Mantzouratos et al. (2004) using other simu-

Figure 7: Distribution of reference points in the courtyard (right)


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Table 1: The results of the physical and the simulation-based measurements

The Alleyway

Point 1 Point 2 Point 3 Point 4 Point 5 Point 6 Point 7 Point 8 Point 9

Measured data-test 1 3663 2608 2283 2326 2729 2890 4119 5695 7446Measured data-test 2 3492 2654 2097 2344 3010 2939 3919 5384 7157Measured data-test 3 3408 2568 2058 2320 2983 2912 4023 5390 7152Measured data-test 4 3526 2534 2114 2348 3034 2958 4016 5375 7120Simulated data 2248 2035 1961 2004 2152 2437 3631 6185 8232RE1 (Relative error) 0.39 0.22 0.14 0.14 0.21 0.16 0.12 20.09 20.11RE2 0.36 0.23 0.06 0.15 0.29 0.17 0.07 20.15 20.15RE3 0.34 0.21 0.05 0.14 0.28 0.16 0.10 20.15 20.15RE4 0.36 0.20 0.07 0.15 0.29 0.18 0.10 20.15 20.16Average RE 0.36 0.21 0.08 0.14 0.27 0.17 0.10 20.13 20.14The Courtyard- axis 1 (ax1)

Point 1 Point 2 Point 3 Point 4 Point 5 Point 6

Measured data-test 1 3647 4833 4940 5256 5004 4788Measured data-test 2 4000 4964 5053 5309 5258 4826Measured data-test 3 3925 4959 5113 5321 5288 4843Measured data-test 4 3942 4958 5094 5303 5261 4823Simulated data 2380 4265 5285 5660 5637 4951RE1 (Relative error) 0.35 0.12 20.07 20.08 20.13 20.03RE2 0.41 0.14 20.05 20.07 20.07 20.03RE3 0.39 0.14 20.03 20.06 20.07 20.02RE4 0.40 0.14 20.04 20.07 20.07 20.03Average RE 0.39 0.13 20.05 20.07 20.08 20.03The Courtyard- axis 2 (ax2)


Measured data-test 1 4272 5006 5242 5516 5299 5034Measured data-test 2 4591 5164 5281 5596 5359 4904Measured data-test 3 4568 5157 5282 5593 5340 4900Measured data-test 4 4556 5166 5276 5588 5341 4915Simulated data 3499 4872 5788 6151 5900 4883

(Continued)

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Table 1. Continued

The Alleyway

Point 1 Point 2 Point 3 Point 4 Point 5 Point 6 Point 7 Point 8 Point 9

RE1 (Relative error) 0.18 0.03 20.10 20.12 20.11 0.03RE2 0.24 0.06 20.10 20.10 20.10 0.00RE3 0.23 0.06 20.10 20.10 20.10 0.00RE4 0.23 0.06 20.10 20.10 20.10 0.01Average RE 0.22 0.05 20.10 20.10 20.11 0.01The Courtyard- axis 3 (ax3)


Measured data-test 1 3826 4294 4674 4947 4540 3873Measured data-test 2 4177 4446 4758 5040 4583 3734Measured data-test 3 4176 4465 4770 5055 4575 3785Measured data-test 4 4104 4475 4782 5049 4528 3736Simulated data 3151 4110 4771 4974 4677 3773RE1 (Relative error) 0.18 0.04 20.02 20.01 20.03 0.03RE2 0.25 0.08 0.00 0.01 20.02 20.01RE3 0.25 0.08 0.00 0.02 20.02 0.00RE4 0.23 0.08 0.00 0.01 20.03 20.01Average RE 0.22 0.07 20.01 0.01 20.03 0.00

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lation software and much lower than the average errors reported by Kim andChung (2011).

The digital model of the alleyway was then adjusted to include the other sec-tions of the original setting, and the examined internal spaces and simulationswere carried out to predict the illuminance values on the summer solstice andwinter solstice at three time intervals (9:00 AM, 12:00 PM and 3:00 PM). Thesummer simulation was carried out under clear sky conditions and the winterscenario under the CIE overcast sky. A high quality and medium-resolutionsetting was used in the simulation modeling depending on the complexity of

Figure 8: Comparison of simulated and measured illuminance values in both space configurations


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the target spaces. For the internal spaces simulations the ambient bounces wereapplied to the value of 5 and on average each rendering takes 24–36 hours torender on a Windows XP Professional workstation.

Daylight Simulation

Phase One: Daylight Performance of the Courtyard and the Alleyway

As stated before, a total of 18 points that were assembled on three main axes wereused to predict the illuminance values in the courtyard. Whereas axis 1 wasarranged to assess the illuminance levels on the eastern side of the courtyard,the other two axes (2 and 3) were arranged along its central and western side(See Figure 7). The analysis of the early morning scenario on the summer solsticeclearly showed the impact of the courtyard’s north-south orientation on its day-light behavior. The internal envelope of the courtyard blocked the low angle ofthe sun in the early morning to reach the points located at its eastern side(axis 3) while allowing direct sunlight to reach the other two axes. The averagedaylight illuminance values received into the courtyard at 9:00 AM on thesummer solstice were about 1269 lux at the eastern side, 1770 lux in the centralpart, and about 2004 lux at the western part. These figures suggested a variationof around 37–40 percent in illuminance values between the shaded eastern side ofthe courtyard and its exposed parts. However, despite this variation in the inten-sity of illuminance, the 9:00 AM simulation results showed that overall there was asmooth transition of daylight distribution across the courtyard, which in turn hada direct impact on the visual experience for the uses before midday. The quartiledeviation is a strong indicator of variability within a population of data; the lowerthe value, the less variation in the mean or the average. This metric is used here toassess the diversity of illuminance in both forms before and at midday on thesummer solstice. Table 2 provides summary results of the illuminance values inboth space configurations including average illuminance and quartile deviation.Whereas a large spatial variation in illuminance is predicted along the alleyway,the courtyard showed less variation among its illuminance values. At 9:00 AM,the upper and lower quartiles of the mean were around 12 percent of the meanin the case of the courtyard and more than 40 percent in the alleyway. The largevariations of illuminance along the alleyway before midday are the results ofthe partial obstruction of the low sun by the alleyway’s internal envelope,leading to a wide range of light and shade spots along its main access. As aresult, the pedestrians of the alleyway tend to experience different ambient day-light conditions from those of the users of the courtyard with sharp changes inilluminance values moving from dark to lighter daylight areas. At a point intime when the average illuminance value in the courtyard is about 1700 lux, theintensity of daylight in the alleyway varies between 4200 lux in the exposedbright spots and as low as 1300 lux in the shaded areas. While the human eyecan adapt to a wide range of lighting conditions, sharp shadows and suddenlarge changes in illuminance in the field of view may affect visual comfort bycausing transient adaptation problems. Unlike the 9:00 AM case, when the obstruc-tion of the low angle of the sun by the courtyard’s internal envelope has helped inreducing the intensity of its illuminance, the noon sun angle has led to a significantincrease in the intensity of illuminance in both the alleyway and the courtyard.The average intensity of illuminance received by the alleyway and the courtyard


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Table 2: Summary of illuminance in both space types

Alleyway Courtyard

Axis 1 Axis 2 Axis 3

0900 1200 1500 0900 1200 1500 0900 1200 1500 0900 1200 1500

Summer solstice

Intensity of illuminance (average) 2962 6068 3031 2004 5468 1752 1770 5793 2380 1269 4308 2884Uniformity of illuminance (quartile deviation) 0.44 0.30 0.28 0.16 0.10 0.10 0.10 0.17 0.10 0.11 0.15 0.13Winter solstice

Intensity of illuminance (average) 2656 4072 2367 2126 3230 1894 2342 3585 2088 1918 2919 1713Uniformity of illuminance (quartile deviation) 0.35 0.33 0.34 0.14 0.08 0.11 0.14 0.09 0.11 0.13 0.08 0.12

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at noon on the summer solstice was 6068 lux and 5190 lux, respectively. This is theresult of the high solar angle at noon that allowed more intense sunlight to reachmost of the target points in both forms. It is however, important to point out therole of the temporary covers that are usually used (and still in use in the originalsettings) during the summer time in areas with low aspect ratios (width-heightratio). Such temporary shading elements would play a major role in reducingthe intensity of solar radiation and thus improving the uniformity of illuminanceat the street level. Courtyards were also often planted to further improve thevisual experience by providing a pleasant transition between shades andshadows particularly during midday. However, the impact of these supplemen-tary shading elements on the intensity of illuminance in both spaces has notbeen considered in the simulation modeling. After midday, the change in theshading conditions as the sun moves to the west allows the overall values of illu-minance in both the courtyard and the alleyway to fall by around 50 percent frommidday values. The average illuminance values along the alleyway and in thecourtyard at 3:00 PM was 2339 lux and 3031 lux, respectively. However, despitethis identical reduction value in the two spaces, the intensity of illuminanceremains more uniform in the courtyard than in the alleyway (See Table 2).

Unlike the summer solstice, when the constant change in the shading conditionsover the course of the day led to a wide range of illuminance values between the alley-way and the courtyard, a difference of less than 20 percent in the average illuminanceis observed between the two spaces on the winter solstice. This is the results of thehigh contribution of the diffused skylight component to the total energy of daylightduring winter. In urban open spaces, the intensity of illuminance relates to a combi-nation of direct sunlight, diffused skylight, and the reflection of daylight from the sur-roundings. Previous research by Al-Maiyah (2006) on daylight behavior in selectedtraditional urban forms in Cairo demonstrated that the diffused component accountsfor around 70 percent of the total energy of daylight during winter. The predomi-nance of the diffused component also led to a more homogenous distribution of illu-minance along the alleyway on the winter solstice than on the summer solstice,particularly before midday (See Figures 9, 10, and 11).

Phase Two: Daylight Performance of Selected Spaces of the House

Recommended Illuminance Values for Examined Spaces: As above stated, three of thecore spaces characteristic of this house type were analyzed in terms of their illu-minance values and lighting requirements. Each of these spaces was designedto serve a specific social activity where various levels of privacy and daylight con-ditions were required, and therefore assessing their visual performance shouldprovide an interesting base for illustrating the influence of these social and func-tional demands in shaping the architecture of the house.

In terms of establishing lighting requirements for this phase of analysis, at themoment there are no illuminance recommendations for residential buildings inEgypt (Mohammed, 2004). On the other hand, the Illuminating EngineeringSociety of North America (IESNA) (Rea, 1999) established an illuminance selec-tion procedure on the basis of factors such as the type of activity within a spaceand characteristics of the visual task, not on the basis of space type. Given thefact that the space types examined in this work are unique in their configurationand there are no regional regulations that can assist in assessing their perform-ance, therefore the illuminance recommendations set according to this procedure


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were useful in setting up the recommended illuminance values for this phase ofanalysis. Accordingly, the recommended illuminance values for evaluating thedaylighting performance of the three examined spaces were established basedon the IESNA lighting guides (See Table 3). In general, a 50–100 lux is rec-ommended for simple orientation (such as the bent entrance) and areas wherevisual inspections are occasionally performed and a 300 lux for residential appli-cations where more common visual tasks are performed such as reading in theground floor meeting place and sewing in space type 3 (the first floor loggia).The Chartered Institute of Building Services Engineers (CIBSE) (CIBSE 1994,2009) also provided a set of lighting guides for residential buildings. However,the recommended illuminance values were designed to assist with lighting plan-ning and illuminance selection in communal residential blocks (such as studentresidences) and not for conventional residential units or family homes. Therefore,these values are not appropriate for the current application and space types.

As with the first phase of analysis, the system of reference points was againintroduced to assess the illuminance values in each space type at the same timeintervals on the summer and winter solstices. The distribution of referencepoints in the three spaces is illustrated in Figure 5.

Results and Discussion

Space Type 1: The Bent Entrance

In most of the traditional houses in Cairo, entrances were usually bent. Becauseresidents lived within a rigid social pattern, protecting their privacy from

Figure 9: Illuminance levels (lux) in the courtyard at midday on the summer and winter solstices


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pedestrians on the street was a prime consideration in the design of their dwellingunit, which had its impact on the doorway’s design. By bending the mainentrance, local builders managed to provide privacy for the house residentsthrough preventing pedestrians from seeing the inside of the house. In additionto providing such a threshold separating the inside from the outside, bententrances exerted another practical role protecting the interior of the house fromwind, dust, and noise. Attached to the entrance lobby is a doorway which wasusually designed so that it led directly into the covered sitting area in the court-yard without allowing exposure of the private spaces to visitors to the house.The size of the examined entrance lobby is 2.7 m x 4.0 m and of the doorway is1.8 m x 8.9 m (See Figure 5).

The analysis of the simulation results on the summer solstice revealed that formost of the day, daylight conditions received into the bent entrance were almostconstant. Average illuminance values predicted before and after midday werenearly identical, ranging between 117 lux and 136 lux, respectively. Unlike themorning and afternoon hours, a higher illuminance with an average value of210 lux was predicted along the entrance during midday. This increase in the illu-minance values is the result of the high intensity of daylight at midday when thesun is at its highest point in the sky as well as to the high contribution of the lightreflected from the surrounding surfaces. As for the daylight performance of thespace, the analysis of the results on the summer solstice showed that there isonly a limited time in the day during which natural light exceeds recommendedillumination levels for personal orientation. Apart from the 210 lux in the middle

Figure 10: Illuminance levels (lux) along the alleyway at the three examined times on the summer andwinter solstices


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of the day, the average illuminance values before and after midday are well withinthe IESNA recommended values.

As previously stated, this space type played an important role in the architec-ture of the house not only in providing a transitional focal point between twoenvironments but also in protecting the privacy of the residents. While assessingthe daylight levels of the space itself against the current IESNA standard valuesmight help us in evaluating its efficiency in terms of meeting the visualdemands of the users, its role in meeting the social/privacy demands of the

Figure 11: Illuminance levels (lux) in the courtyard (axis 1) at the three examined times on the summerand winter solstices

Table 3: Illuminance categories and illuminance values given in the IESNALighting Handbook for generic types of activity in interior

Type of Activity Illuminance

Public spaces 30 luxSimple orientation for short visits 50 luxWorking spaces where simple visual tasks are performed 100 luxPerformance of visual tasks of high contrast and large size 300 luxPerformance of visual tasks of high contrast and small size 500 luxPerformance of visual tasks of low contrast and small size 1000 luxPerformance of special visual tasks 3000 to 10,000 lux

Recommended Illuminance Values for Examined Spaces

The bent entrance 50 luxThe takhtabush 100 luxThe Maka’ad (covered loggia) 300 lux


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residents cannot be explained by assessing its light conditions in isolation from itssurrounding context. Therefore, a further analysis was made comparing the illu-minance values of the entrance to those of the alleyway. The analysis of the resultsshowed an average ratio of 26:1 between the illuminance values of the entranceand those for the alleyway on the summer solstice. The calculated illuminancevalues in the entrance were 96 percent lower than the values calculated alongthe alleyway. Similar results were also found on the winter solstice with consider-ably higher illuminance values along the alleyway than in the entrance (SeeFigures 12 and 13). This excessive variation of illuminance between the entranceand its adjacent brightly daylit alleyway should have contributed to the senseof privacy for occupants. The sharp contrast of illuminance between the insideand the outside does not allow for an instant comfortable visual adaption.

Space Type 2: The Takhtabush (a Covered Outdoor Sitting Area)

The second selected space type is the takhtabush. It is a“type of loggia, or a coveredoutdoor setting area at the ground floor level located between the courtyard andthe back garden, opening completely onto the courtyard with a mashrabiyya ontothe back garden” (Fathy, 1986: 63–64). As a space configuration, it played animportant part in ameliorating the extremes of temperature in the traditionalcourtyard houses of Cairo. It was initially introduced to ensure a cool meetingplace for the residents and their visitors since it allowed for air circulation viaits mashrabiyya from the courtyard to the back garden. The takhtabush in the El-Suhaymi house is north-oriented and located in the center of the house directlyopposite the main entrance at the front of the house. It is a rectangular space,which is typical in this type of houses, with a width of 8.6 m and a length of 6.0m, and has two lattice screens or mashrabiyya(s) that measure 2.9 m wide and3.6 m high, covering its rear elevation (See Figure 2).

Figure 12: Illuminance values along the entrance at 09.00 on summer solstice (left) and winter solstice(right)


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As this space is an extended part of the courtyard, comparing its daylightbehavior to that of the courtyard seems to be more informative than assessingits performance separately, and hence, a comparative analysis was conductedbetween the two spaces. At 9:00 AM on the summer solstice when theaverage illuminance value in the courtyard was around 1681 lux, the averagevalue in the takhtabush was about 778 lux, giving a variance of 54 percent.The highest average illuminance values received into the takhtabush was inexcess of 1500 lux, which as expected was observed at noon on the summer sol-stice. While this may seem very high around twice the figure estimated beforemidday, it only comprises 30 percent of the average value received into thecourtyard at midday. At 3:00 PM, the average illuminance values received intothe takhtabush and the courtyard was about 897 lux and 2339 lux, respectively,giving a variance of 62 percent. Overall on the summer solstice, the averageilluminance values received into the takhtabush was estimated to be 62percent lower than the values calculated in the courtyard. Similarly, on thewinter solstice, it was found that the average illuminance values receivedinto the takhtabush was around 74 percent lower than the results predictedfor the courtyard. As for the diversity of illuminance in the space and apartfrom the first two points of axis 2, a uniformly distributed pattern was observedin most of the takhtabush in both seasons. This uniform distribution contrastedwith the various illuminance values observed at the target points in the court-yard due to change in the shading conditions as discussed previously. It is theresult of the complementary effects of the north orientation of the space and the

Figure 13: Illuminance levels (lux) along the entrance at the three examined times on the summer andwinter solstices


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configuration of its north-facing lattice screens providing the users with a con-stant flow of diffuse light (See Figures 14 and 15).

Space Type 3: The Maka’Ad (Covered Loggia)

Whereas the takhtabush usually provided a seating area for the house’s casualguests the maka’ ad was originally used as a gathering space for the house resi-dents and close friends, acting as a family area. It was usually rectangular orsquare in shape, elevated from the ground floor, opened with its entire facadeonto the courtyard, and essentially oriented to the north in favor of the softbreeze (Salama, 2006). In the selected house, the loggia is located on the firstfloor and measures 4.75 m wide and 5.15 m long. It has two north-facing archedopenings that measure 2.25 m by 4.0 m (See Figure 2).

As for the general lighting trend in the space, the results on the summer sol-stice revealed that daylight levels received into the loggia were almost constant inthe morning and the afternoon hours. An average illuminance value that rangedbetween 650 lux to 700 lux was observed in the space at 9:00 AM and 3:00 PM,respectively. When these values were compared to those predicted in the court-yard at the same hours, the results suggest a 2.9:1 ratio between the illuminancevalues of the two spaces. The highest average illuminance values predicted forthe space was over 1200 lux, which as expected, occurred at midday on thesummer solstice when the sun is almost vertical in the sky. Although this figureis much higher than the average illuminance values received into the spacebefore and after midday (around twice these values), it only represents onequarter (25 percent) of the average value received into the courtyard in themiddle of the day. In the winter solstice, the average illuminance values calculatedwere in the range of 680 to 610 lux in the morning and afternoon hours and inexcess of 1000 lux at midday. Interestingly, and despite the wide variations insky conditions between June and December, these values were only slightlylower than those predicted on the summer solstice (a variance of 14 percent). Alikely reason for such a constant illuminance value received into the space inboth seasons is due to its north-facing orientation. This is a very interestingoutcome that might suggest that the orientation was fundamental in the mindsof the house builders when selecting a location for the family gathering space.As for the lighting requirements of the space, although the north orientation hashelped in maintaining constant illuminance values in both seasons, none of the

Figure 14: Illuminance values in the takhtabush at 15.00 on the summer solstice (left) and the wintersolstice (right)


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recorded values fall within the recommended values. On the summer solstice, theaverage value recorded in the morning and the afternoon hours were aroundtwice the values defined by IESNA for residential applications and those pre-dicted at midday were around four times the limits. At present, this space ismainly used as a viewing platform and hence, such a high amount of daylight illu-minance might not be an issue for short visits, but if the use of the space is to bechanged in the future, it might be worth considering introducing some form ofshading devices to reduce its daylight levels to a more actable level (See Figures16 and 17).

Conclusion

This paper is part of an ongoing research project designed to assess daylight be-havior in the traditional settlements of Old Cairo. The unique visual experiencecharacteristic of these settlements is well documented and often described aspart of the overall identity of the city. However, assessing the characteristics ofthese settlements in terms of their daylight behavior is a rather difficult task

Figure 15: Illuminance values in the takhtabush at 15.00 on the summer and winter solstice


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Figure 16: Illuminance values in the first floor loggia at 15.00 on the summer solstice (left) and thewinter solstice (right)

Figure 17: Illuminance values in the first floor loggia at 15.00 on the summer and winter solstice


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that requires an understanding of the diversity of illuminance at various architec-tural scales as well as urban patterns. Accurate simulation modeling tools,on the other hand, such as Radiance that is increasingly being used for illumina-tion studies in internal spaces can assist in standardizing the diversity of illumi-nance at various scales and across different spatial typologies. Accordingly, asimple methodology for the study of the daylight behavior of traditional settle-ments in Old Cairo was proposed and tested using a combination of simulationand physical-based measurements.

Analysis of daylight performance shows large variation between the alley-way and main open living areas within the house. The paper shows a largespatial variation in illuminance along the alleyway. The courtyard, on the otherhand, showed less variation among its illuminance values. The paper explainshow pedestrians of the alleyway have a different visual experience as a conse-quence of different ambient daylight conditions from those of the users of thecourtyard. The model shows sharp changes in illuminance values moving fromdark to lighter daylight areas. While a more visually comfortable environmentis maintained in the courtyard and the adjacent spaces, it is believed that tra-ditional temporary shading devices were major tools in adjusting the variationthrough the alleyway. These temporary shading devices, which are still usedduring the summer time in areas with high illuminance values, are, therefore,key to harmonizing daylighting levels across the alleyway and thus improvingthe uniformity of illuminance at the street level.

Examination of the impact of solar angles in summer and wintertime showsidentical reduction value in both the courtyard and the alleyway. However,despite this identical reduction value in the two spaces, the intensity of illumi-nance remains more uniform in the courtyard than in the alleyway. The papershows that direct sunlight is the main component of daylight in both the alleywayand the courtyard during the summer. This is one of the reasons for the sharp vari-ation during the summer season. The predominance of the diffused componentduring the winter solstice, on the other hand, led to a more homogenous distri-bution of illuminance along the alleyway.

More detailed analysis of open spaces adjacent to the courtyard within thehouse highlighted the value of careful design in achieving excellent visual andthermal comfort levels. The paper also shows that design layout and orientationare also used to achieve social objectives. The bent entrance, for example, notonly acts as a visual threshold but also exerts another practical role: protectingthe interior of the house from wind, dust, and noise. The visual transformationfrom the bright alleyway to a more comfortable level of the courtyard is dramati-cally accentuated through an area of dimmed light levels.

The design of the takhtabush, which is used to entertain casual guests who areneither formal nor close family friends, provides an excellent comfortable, wellventilated, and reasonably lit environment. The takhtabush receives a daylightlevel that comprises 30 percent of the average value received into the courtyardat midday.

The maka’ ad, where family and friends, spend most of the outdoor times,received particular attention in the design and details. The paper shows that themaka’ ad has a constant illuminance value received into the space in bothseasons due to its north-facing orientation. The design of a north-facing loggiawas fundamental in achieving this outcome.


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The proposed methodology in this paper proved capable of predicting andanalyzing illuminance values in a heritage context. The predicted results suchas those presented above can be used by town planners or support localdecision-makers by assessing, for example, the implications of interventionschemes on daylight conditions in a dense urban fabric. The paper shows howcareful and successful design can lead to social and cultural considerations aswell as responding to environmental factors, particularly daylight levels.

Note on Contributors

Sura Almaiyah is a Senior Lecturer at the University of Portsmouth in the UnitedKingdom.Hisham Elkadi is a Professor of Architecture and Head of School at DeakinUniversity, Australia.


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Documents

Study on the Visual Performance of a Traditional Residential Neighborhood in Old Cairo