The traditional Beijing courtyard house: Assessment of its...

Plea2004 - The 21th Conference on Passive and Low Energy Architecture. Eindhoven, The Netherlands, 19 - 22 September 2004 of 7

The traditional Beijing courtyard house: Assessment of its environmental performance under changing

historic circumstances

Barbara Muench1

1Beijing Institute for Civil Engineering and Architecture, Beijing, P.R.China

ABSTRACT: In the context of the redevelopment plan of the city for the Olympic Games 2008, large areas of the old city have been declared as protected areas. This areas are characterized by a carpet like maze of one storey courtyard houses and narrow lanes. Still, a major part of Beijing's inner city is covered by this typology of housing. In the inner city alone, more than 1.5 million people still live in courtyard houses. However, the living conditions have changed dramatically since the time these buildings were built. While in the past, one courtyard house belonged to one large family, today many families share that space and have almost eliminated the courtyard itself by numerous building additions, in order to gain living space. The houses are deteriorated and lacking basic facilities like individual bathrooms. They are mainly heated with coal fired stoves, a fact that contributes very much to the heavy air pollution of the city. The government wants to change this until the Olympic games in 2008. The redevelopment of the courtyard areas has given rise to a wide range of conflicts of interests between inhabitants, preservationists and the government, i.e. between the protection of a building typology which forms a strong part of the identity of the city and today's requirement of modern living standards. In China, these standards are represented by the new apartment blocks which are built in more or less the same form al over the country, taking little consideration of climatic differences. The paper assesses the environmental performance and living comfort of the courtyard house in its traditional and modified form. It shortly looks at the measures proposed by the city in order to improve the housing conditions of the large courtyard areas in the course of conservation planning and the planning for the Olympics, and examines their implications in terms of sustainability. Conference Topic: 8 Traditional solutions in sustainable perspective Keywords: Beijing, housing typologies, energy, comfort

INTRODUCTION

For hundreds of years the courtyard house was

the prevailing form of housing in Beijing. The old city was almost completely covered by a carpet like maze of one storey courtyard houses and narrow lanes.

Since the first half of the 20th century the living conditions have deteriorated considerably because of the dramatic overcrowding of the foremost spacious courtyard houses. Many building additions have filled the courtyards almost completely.

A large part of the courtyard housing typology has been demolished over the past 20 years in order to make space for new constructions including many modern apartment house. However, about half of Beijing's 62,5 km2 large inner city is still covered by the old courtyard typology, housing more than 1.5 of the 2.4 million people living in the city centre [1].

Today the demolition of the old town is officially stopped and there is a fierce debate about the advantages and disadvantages of the courtyard house compared with today's apartment blocks.

This study describes the transformation of Beijing's traditional housing typology, the classical

courtyard house, into its overpopulated, modified form, the so called 'da za yuan' (big mixed yard) and assesses both in terms of their environmental performance and the living comfort of indoor and outdoor spaces.

At the end the paper shortly comments on the effect the measures proposed by the city in the run up to the Olympic Games 2008 will have on the environ-mental performance of the old courtyard areas.

2. THE CLIMATE OF BEIJING

The city lies at a latitude of 39°48' N. It has a continental climate with cold dry winters and hot, rainy summers. The four seasons are quite distinct, but spring and autumn are very short, so there is about five months of summer as well as of winter. The annual average temperature is 11.5°C with coldest monthly average temperature of –4.3°C in January and maximum monthly average temperatures of 25.9°C in July, average precipitation amounts to 630mm, about 75% of which is concentrated in July and August [2]. In summer, daytime temperatures can


get as high as 40°C while in winter -15°C are reached during nights. Prevailing winds come from north-north-west in winter bringing cold dry air form Siberia and the Mongolian plain and from south-east in summer bringing warm, humid air from the coastal regions (fig. 1 and 2).

Figure 1: Minimum, average and maximum daily temperature of Beijing [3].

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mean daily global solar

radiation 0

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average monthly temperature (deg.C)mean daily global solar radiation (kWh/sqm)mean monthly relative humidity (%)

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Figure 2: Climatic data of Beijing (temperature, solar radiation, relative humidity) [2]. 3. ANALYSES OF DIFFERENT HOUSING TYPOLOGIES

In the inner city of Beijing there are three main different forms of housing: the traditional courtyard house, the overpopulated, modified courtyard house, called 'da za yuan' (big mixed yard) and the modern apartment block.

In order to limit the scope of the paper the modern apartment block is not analysed in detail, but only used for comparison at the end of the paper.

The focus of the analyses lies on the courtyard house and the 'da za yuan'. Therefore, one typical example of each has been chosen as a case study: ! a courtyard house, which has been build during

Qing Dynasty and is preserved in its traditional form. Today, only a young couple is living in the house, so that there is enough space to use one of the three building units as kitchen and bathroom.

! a small home which has been built as an addition to a former courtyard house in the 1970s and is a typical example for the overcrowded, low quality structures in today's 'da za yuan'. It is inhabited by three persons, a couple and their ten year old son. It has no bathroom or toilet, but an own kitchen.

3.1 Traditional courtyard house

The form of the vernacular courtyard house of Beijing has evolved over more than thousand years and produced building patterns best suited to local cultural and climatic conditions. Still today, many

courtyard houses from the Ming and Qing Dynasties are preserved. (1368-1911) [4].

3.1.1 Building form

One courtyard house consists normally out of different - one storey high - housing units which are grouped around one, two or more courtyards. It is totally closed towards the outside and the whole complex is accessed through a single gate (fig. 3).

Figure 3: Traditional courtyard houses [5]

Each courtyard was inhabited by a single large family. The main building with the rooms for the parents and the main hall - which was the main living space and the place where ancestors were worshiped - are always south orientated. The subsidiary buildings formerly containing the rooms for children and servants are located at the eastern and western side of the courtyard. All courtyard houses and the yard were entirely closed towards north.

The houses have no basement, a stone floor, 30-50 cm thick walls out of grey brick, and a pitched wooden roof structure that is covered with a thick layer of clay and grey tiles. They have large openings facing the courtyard and none or only very small ones on all the other sides.

3.1.2 Thermal performance The thermal performance of the old houses depends very much on the way they are used. Therefore, I first will describe how the courtyard houses performed when used in the traditional way and how they perform today being subjected to modern living comfort requirements. 3.1.2.1 Winter conditions

The fact that all housing units and the yard are entirely closed towards north helps to protect them from the cold winter winds.

Traditional way of use:

The large wooden window screens facing the courtyard normally were covered with one layer of window paper on the outside (fig 4). In winter a second layer of window paper was added on the inside which also covered the cracks and gaps between the windows, so ventilation heat loss was reduced.

All living rooms of the courtyard houses were equipped with a 'kang'. A kang is a brick pedastal that


works like a hypocaust sys-tem. It still exists in the outskirts of Beijing today, where the heat from the cooking stove is used in winter to heat the 'kang'. (fig 4).

Fig. 4: Courtyard house with wooden window screen and ‘kang’

The 'kang' serves as the main living area in winter. Not only do people sleep on top of it during night, but also most all of the daily indoor activities take place on it. The 'kang' works like a radiant heating system with a large area of low surface temperature. Since the perceived temperature by human beings is the sum of radiant temperature and air temperature, the latter one can be kept quite low, thus reducing heat losses through high temperature differences. Moreover people were used to wear several layers of warm cloths. In this way the energy consumption of the houses when used in the traditional way of life was kept low in winter. Today’s use

Today most of the old courtyard houses that have been preserved or rebuilt in their original form are converted into luxury housing due to the high value of land in Beijing’s inner city. They are refurbish with modern bathrooms and kitchens and have modern heating and air conditioning systems. The window paper has been replaced with (in most cases) single glazing, like in the courtyard house analysed in the case study (fig 5 and 6).

Fig. 5: Plan of the small courtyard of the case study. While in the past the courtyard houses worked in

a very energy efficient way, they are not energy efficient any more if subjected to today's living conditions and today's way of use because of the following reasons:

1) Today, electrical heating devises are used instead of the traditional kang-system, because of the absence of any other modern infrastructure, like gas supply, in the old lanes. Therefore, the system of the kang – low air temperature combined with high radiant temperature does not work anymore. Consequently all rooms are constantly heated to about 20 deg.C air temperature.

2) In this way, the air temperature difference between the inside and the outside is much higher and so are the heat losses, because the houses are neither airtight nor isolated. The replacement of the window paper with single glazing increases the heat losses because there is no isolating air gap between the two layers of paper anymore like in former times.

3) Therefore, the energy consumption of the courtyard houses today is very high. The fact, that electrical heating systems are used in most cases today, leads to a even worse energy balance in terms of primary energy. 3.1.2.2 Summer conditions:

Most parts of the courtyard house including the yard itself are shaded by high deciduous trees, which in summer form a dense canopy above the maze of lanes and houses.

The exact south-orientation allows easy shading of the main façade, the south façade, from the high summer sun with relatively shallow roof overhangs. The stone floors and the 30-50 cm thick walls provide high thermal mass, just like the roof which has a thick layer of clay and tiles above the otherwise wooden structure (fig. 5).

Figure 5: Natural shading, natural ventilation from the green courtyard and high thermal mass provided a comfortable climate in summer.

Figure 6 shows that while the outside temperature fluctuates between 17.4 deg.C and 33.5 deg.C, the inside temperature only swings between 20.5 deg.C and 25.8 deg.C, thus not exceeding the comfort range.

Figure 6: The heavy thermal mass of the courtyard house unit (fig. 5) levels the high fluctuation of the outside temperature [6]

The temperature curve of the courtyard house unit follows the outside temperature very closely, i.e. the peaks are just about one hour apart because the small room has a very big single glazed and not air tight façade towards the courtyard. However the temperature curve is much flatter, because of the heavy mass. This high thermal mass, which is shaded all day by trees and thus kept cool, can further cool


down during night, store the coolness and release it slowly during daytime towards the inside.

The fact that the average temperature inside the courtyard house is 22,8 deg.C over the measured period of 10 days, while the average of the tempera-ture outside is 24,0 deg.C can also be attributed to the heavy mass and to the fact, that the stone floor is directly connected to the shaded ground that acts as a large radiant cooling device in the hot season.

3.1.3 Natural ventilation

Large parts (more than 2/3) of the facades facing the courtyard are made of fine openable wooden screens, so that the narrow houses can be almost entirely opened towards the green courtyard for ventilation. The green plants and the low ground temperature from the shaded courtyard, help to provide comparatively cool, fresh air for ventilation even on hot summer days.

3.1.4 Daylight

Fig. 7 shows the measured illuminance levels and the respective daylight factors of the eastern housing unit of the courtyard house on a sunny morning (88000 lux in the sun). However, the entire house is heavily shaded by trees (about 4500 lux under the trees taken as basis for daylight factor calculations). It can be seen that the daylight conditions of the relatively small houses are very good, as one would expect.

Figure 7: Illuminance levels and daylight factors of the bedroom unit.

Figure 8: Private outdoor space in the middle of the city.

3.1.5 Quality of outdoor space: The courtyard space is very pleasant: Shaded in summer, protected from the strong winds and other people's eyes from all sides, does it offer a green, private space in the middle of the city centre (fig.8) 3.1.6 Basic facilities:

Towards the end of the Qing dynasty and during the republican times many of these courtyard houses got their own toilette in the yard.

Today most of the few well preserved courtyard houses belong to rich people and have modern bathrooms and kitchens as mentioned above.

3.2 Da za yuan (big mixed yard)

However, most of the formerly spacious courtyard houses, have become heavily overcrowded. Many different families share the space and have almost

eliminated the courtyard itself by numerous building additions. The traditional courtyard houses thus became so called ‘da za yuan’, ‘big mixed yards’. Today, not only the families are mixed but also the functions of the building units- including housing, small shops, workshops, etc..

After the foundation of the P.R. of China many of the private courtyard houses, formerly belonging to one family, were nationalized and the number of families in the courtyards were increase. After the earthquake in 1976, temporary shelters were built in the courtyards. They have never been demolished and have become welcome additional living space for the constantly growing population. Additionally, many families built their own small kitchen in the yard. At the end of the 1970s the average living space (shiyong mianji) per capita was down to 4.75sqm [7] and that figure has not changed a lot in many of these mixed yard until today (for comparison: in newly built apartment blocks in Beijing the average living space per capita today is about 50 sqm [8]). The houses are deteriorated and lacking basic facilities.

Figure 9: Comparison of the courtyard space in 'xi zhuan hutong no.27 in its original form and today.

Fig. 9 shows a 713 sqm big courtyard in its original layout 1911 and today [9]. In the original courtyard there lived one family with 10-15 people. They had one kitchen and one toilette. Today, there live 17 families with 73 people. They have17 kitchens and no toilette,

i.e. they have to use the public toilette in the lane.

A bird eye view on the same area shows that the building additions have totally elimi-nated the open courtyard space (fig.10).

Figure 10: The open court-yard space has been totally filled up by building additions 3.2.1. Quality and form of building additions

Due to their temporary and informal nature, the building quality of these additions is very low and the used materials are manifold. Walls are mostly made out of brick or concrete and only have minimum thickness and no insulation, windows are single


glazed, neither windows nor doors nor the roof are air-tight. The roofs are sometimes covered with simple tiles, sometimes with all kind of thin, cheap materials like corregated steel, foil, etc. (fig. 11).

Figure 11: Low quality building additions in the 'fa yuan si' area 3.2.2. Thermal performance 3.2.2.1 Winter conditions:

The heat losses of these living units are very high as a consequence of their poor construction. However, because of the high building density they ratio of envelope area exposed to the outside to floor area is very low. Additionally there are high internal heat gains because of the high population density. So overall, the energy balance is better then that of the classical courtyard houses. Even so that cannot really be regarded as advantage since the price for it are very poor living conditions. The homes are mainly heated by individual coal fired stoves, a fact that contributes very much to the heavy air pollution of the city in winter. Inhabitants also complain about the coal dust everywhere.

3.2.2.2 Summer conditions:

Just like the traditional courtyards most of the units in the ‘da za yuan’ are very well shaded by a dense canopy of trees in summer.

Figure 12: Comparison of the temperatures outside, in the courtyard unit, and in the building addition.

However, their thermal performance is very different as the measurements in fig. 12 show. As mentioned above the building units are often very deep and have little façade area. Therefore, their inside temperature does not follow the fluctuations of the outside temperature as much as it is the case in the classical courtyard houses. The average

temperature in the building addition is also higher than in the courtyard house because of the higher number of people per sqm. Therefore, internal heat gains are higher than in the spacious courtyard houses. In the case study, where 3 persons, a young couple and their son, live on 26 sqm (fig. 13), the average temperature is one degree higher than in the courtyard house, that is much bigger and shared by only 2 people.

Figure 13: Building addition chosen as case study In the case study, for example, that was built in the 1970s (fig. 13). Thus, the average temperature However, in most of the units of the da za yuan the living area per capita is even smaller. Some of the units use air condition for ventilation and cooling. 3.2.3 Natural ventilation

Due to the density of buildings, natural ventilation is not very good and many of the houses have problems with fungus.

3.2.4 Daylight

Daylight conditions in the 'da za yuan' are generally very poor because of the following reasons:

1) The small spaces often only have a single facade and are further subdivided by interior divisions to create individual rooms for the family members. These rooms often have no window at all or are lit through small windows in the interior partition walls (see e.g. case study, fig. 15)

2) The distances between the living units in one courtyard are so small that there gets no light to the windows anymore (fig. 14).

3) Because of this small distances and the fact that many people have to pass by the windows to get to their units further back in the yard, people cover the windows with curtains or translucent foils, in order to have some privacy (fig.14).

4) To reduce the high heat losses in winter many windows are covered with cardboard.

Figure 14: Poor daylight conditions in the 'da za yuan'


Compared to the daylight conditions inside the units shown in the photographs, the daylight condition in the case study are still quite good, because the small building is added at the corner of a big yard, facing the lane. However, even there daylighting is very poor, because the unit is shades by large trees, the windows are barred and partly covered with translucent foil to give some privacy. And the bedroom has only a small internal window (fig. 15). The measurements were taken at the end of May on a sunny day at 11.00 am. There were 90000 lux in the sun, 4500 lux under the thick canopy of the trees , and no more than a maximum of 75 lux near the windows. The family uses artificial light all day in all rooms but in the little kitchen.

Figure 15: Measured illuminance levels and daylight factors in the building addition 3.2.5 Basic facilities

Kitchens: Chinese people do prefere to have a separate room for cooking because of the heavy oil fumes. The increase of families in the courtyard houses also increased the need for kitchen spaces in the yards Therefore, most families built a small often unheated building addition to accommodate the kitchen.

Water: The individual units often do not have running water. One water tap in the courtyard is normally shared by many families. Neither the houses nor the courtyard do have a grey water drainage system in many cases.

Toilettes: For ideological reasons and in order to gain living space, individual toilettes in the courtyards have been demolished during the era of Mao Zedong. Today tens to hundreds of people share the public toilettes outside the courtyard in the lanes. 3.2.6 Quality of outdoor space Quality of outdoor space:

Due to the many building additions there is no courtyard left anymore but only small narrow passageways between the houses and the building additions within the yard.

However, the courtyard is still kind of a semi-private space, because it is only accessible through one gate and under the social control of its inhabitants. This has advantages and disadvan-tages: on one hand there is a very close relationship between the neighbours and not the normal

anonymity of a big city. On the other hand there is high social control and no real privacy.

People use the narrow spaces in front of their homes to dry their laundry in summer, to grow potted plants or to hang the cages of their birds out. (fig. 16).

However, due to the lack of space, large part of people's life today takes place outside the former courtyard complexes, in the lanes. There, in the shade of the large trees, people meet to play Chinese chess, to chat, or to do some of the daily works. In this way the former introverted lifestyle has changed today out of necessity and the lanes have become very lively. Fig. 16: Space for birds

4. COMMENTS AND CONCLUSIONS

When asked about the advantages and disadvantages of the different housing typologies in terms of their environmental performance and living comfort, people bring the following arguments [10]: ! Da za yuan:

Disadvantages: living area too small; lack of space in general; unheated kitchen additions, often not connected to the living unit; lack of basic facilities; lack of privacy; coal fired heating not convenient and too dirty, electrical heating too expensive; bad building quality, difficult to keep clean because of muddy courtyards.

Advantages: cheap rent; cooler than apartment blocks in summer, thus less need for air condition; possibility to regulate heating oneself; 'earth spirit' (tu qi), believe that it is better to be able to feel the ground; better neighbourhood relations, not so anonymous; closer to nature, space for birds and potted plants. ! Classical courtyard houses:

Almost all people interviewed agreed that a classical but modernized courtyard house just inhabited by one family would be the best way of living, if one could afford it.

A comparison of temperature measurements in

the courtyard house and the building addition chosen as case studies as well as in one of the flats of a five year old apartment block - that is quite typical for the kind of mass produced apartment houses that mushroom all over China - confirms the statement of the people interviewed (fig 17).

Cleary, the average temperatures in both the courtyard and the building addition in the 'da za yuan' are lower than the average outside temperature while the average temperature in the flat is one degree higher. Especially, when the outside temperature went down for two days between 24 May and 26 May the temperatures in the courtyard house and the building addition went down much more significantly than the temperature in the flat.


Surprisingly, none of the people interviewed complained about the poor daylight conditions. Most people do not really have a problem with the low levels of natural lighting but just switch on artificial light instead. Even in the new deep-plan apartment blocks daylighting is often not satisfactory, but there too, many people do not really mind.

Figure 17: Comparison of the measured hourly temperatures of all three case studies.

A problem in terms of living comfort and micro climate of the city is the fact that only large green areas of lawn are considered to be green space but not the well shaded private and semi private small scale spaces in the old yards with their thick tree canopy. Therefore, the city plans to create more of this 'green areas' even in the old protected parts of the city, with the intention to give itself a 'modern green look' for the Olympic Games 2008, which promotes itself with the slogan "Green Olympics, Great Olympics" [11]. However, these 'green' lawn spaces can neither be used by people nor do they have near as much filtering and shading effect as the large trees, that are there already.

A real environmental problem is not the lack of such type of 'modern, green area' but the lack of a modern infrastructure in the old city: The coal fired heating systems severely pollute the air. In order to improve the air quality until the Olympic games, the government has proposed to use gas heating and electrical heating systems instead. However, probably most of the coal fired heating systems will be converted into electrical heating systems for the following reasons:

1) there is no infrastructure in vast parts of the old city in terms of gas supply

2) it is unlikely that gas heating will be installed in all the building additions of the 'da za yuan' without solving all the other problems of this housing typology and there is no quick solution of how to solve the many problems of the heavily overcrowded old houses. Considering the facts that a) China has already a problem of meeting the growing electricity demand and b) that electrical heating is extremely inefficient in terms of primary energy consumption, the change from coal fired to electrical heating systems is no improvement in environmental terms. It just improves the air quality in the city in the short run but does not provide a sustainable solution at all. If the very low building quality, the lack of insulation and of air tightness is taken into account, a huge amount of energy with high exergy is used to heat Beijing's air.

Another problem is that the city wants to show its own cultural heritage to the visitors and has therefore protected about 40% of the old city. However, at the same time it wants to present in a 'modern look', i.e. it does not want to present the visitors the run down conditions of the 'da za yuan'. But restoring their original form would mean to resettle hundred thousands of people and build new apartments for them on the outskirts of the city. Regarding the environmental consequences, this approach is problematic in several ways: 1) in terms of energy and material and land consumption for the new buildings; 2) in terms of transport: most of those people work near there old homes and once relocated would have very long ways to work or loose their job. 3) It is questionable if it is sustainable to convert large such parts of the city centre, about 12,5 km2 into luxury, very low density housing, while the mass of the people live on the edges of the city and commute to the centre every day.

Although the energy consumption per sqm is very high in the 'da za yuan', the energy consumption per capita in not so high at all because of the low area of living space per capita. In the new apartment blocks and luxury courtyard houses however, the situation is very different. In the new apartments the average living space per capita equals about 50 sqm (2002) [8]. Even if the energy consumption per sqm in the new houses is lower, the energy consumption per person is comparatively high. This is even the more worrying, since building standards and thermal performance of the new buildings are not very satisfying either [12]. Due to a lack of energy efficient design and a lack of the most basic energy saving measures, like shading devises or a reasonable amount of insulation, even newly constructed buildings have high energy consumption. Especially the constantly increasing depth of these buildings and the equal large scale glazing of all facades leads to a constant rise of consumption of electrical energy for lighting and cooling in summer.

REFERENCES [1] Beijing Municipal Statistical Bureau, ed., Beijing Statistical Yearbook, China Statistics Press, Beijing, (2002). [2] Royal Observatory Hong Kong, Summary of Meteorological Observations in Hong Kong, (1995) [3] Meteonorm, Version 4.0. [4] Beijing Municipality City Planning Commission (ed.), Conservation plan for the Historic City of Beijing, China Architecture & Building Press, Beijing, (2004). [5] L. Wu, Rehabilitating the Old City of Beijing. UBC Press, Vancouver, (1999). [6] Temperature measurements have been taken over a period of 10 days in the eastern bedroom of the house. [7] J. Lü, P. Rowe and J. Zhang, Modern Urban Housing in China 1840-2000, Prestel Verlag, München, (2001). [8] Interview with Prof.Ye Jianping, Renmin Daxue, (2003) [9] Location of the courtyard: Xi zhuan hutong no.27, in the fa yuan si area in the southern part of Beijings old city. [10] Interviews have been made by the author on various occasions between spring 2003 and 2004. [11] www.ebeijing.gov.cn/Government/OlympicPlan [12] B. Muench, Environmental assessment of the pattern of urban growth in Beijing, China, Conference Proceedings PLEA 2003, Chile.

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