CZDG-Hot and Humid Climates
Climatic Design, Zoning, and Guidelines for
Hot and Humid Climates (Hormozgan Provence)
Morteza Kasmaei
Building and Housing Research Center
Affiliated to the Ministry of Housing and Urban Development
BHRC Publication No. R-653: Tehran, 2010
Summary
Creating healthy and comfortable spaces is one of the main objects in Sustainable Design. In present research, the climatic data of meteorological stations of Hormozgan province and its adjacent areas has been used to study the climatic effects of main populated areas of this province on the architectural design of residential buildings. Based on the results of this study, guidelines for architectural design of residential buildings and built environments in the populated cities of Hormozgan province has been proposed. These guidelines, which can be used in all Hot and Humid climates of Iran, provide recommendations on the site selection, orientation, and layout of buildings, the size, and position of openings, and shading devices, and most suitable building materials for building’s envelope.
Climate: The Given Conditions
High temperature, intensive solar radiation, and high humidity are the main climatic features of almost all of the meteorological stations of Hormozgan province.
Economic Geography and Population
Based on the latest estimates of total population, Hormozgan province had 1,403,674 inhabitants in 1385 (2007). The priority of Hormozgan cities in relation to housing need are as following: Bandar Abass, Kish Island, Bandar Lengeh, Qeshm Island, Minab, Bandar Kong, Dehbarez, Bandar Khamir, Bandar Jask, Dargahan, Parseyan, Fin, Hajiabad, Bandar Charak, Jenah, Hormoz, Bandar Soza, Sirak, Bastak, Zeyaratali, Fareghan and Abomossa Island
Traditional architecture
Traditional architecture in Hormozgan is the outcome of centuries of optimization of material use, construction techniques, and climate consideration. The main features of this architecture are summarized in the following paragraphs.
– Buildings are built on a platform that is about 100 cm above ground.
– Exterior walls are very thick and are mostly were built from stone and mortar and were covered with gypsum.
– Windows are large, completely operable and are built from wood and glass. Although windows are large, but the glass portion of them is very small and in some cases, there is now glass in windows and doors and they are completely covered with solid boards.
– Sun shades are the most common and important element of the building and effectively provide desired shade. Since the solar radiation is very intense and shading the whole opening is one of the priorities in protecting the interiors from the harsh climate, wide and high porches were placed in front of interiors to eliminate solar radiation on all openings and exterior walls.
– Roofs are flat and are made of timbers, and branches and leaves of palm trees. Usually roofs are projected from one two or all sides of floor plan to protect exterior walls from solar radiation.
– Covered balconies or porches, which are the semi outdoor spaces, are the most significant part of traditional buildings.
– Interior yards (hayat) which are large and surrendered by other elements of the house, are one of the main architectural features of the residential buildings in this climate. The finish floor of the yard is below the finish floor of the porches and rooms. In the middle of the yard, a court has one or more trees to provide the necessary shades.
– Wind catcher (Badgir) is one of the other main features of traditional buildings in this climate. For a long period, they have been used to modify the interior climate of the houses by getting advantage of the prevailing winds.
– In order to get the advantage of cross ventilation in moderating interior climates, the main openings of the traditional buildings in this climate are faced the prevailing winds. By having the covered balconies in front of all openings, these openings are protected from the intense solar radiation.
– The plan layout of traditional buildings is central courtyard. However, the interior yards in this climate are unlike the yards of hot and dry climates or even cold climates of the country are very large; area of the interior yard is much more than the footprints of the covered spaces. All the house elements that surrendered the courtyard have linear layout.
Design Guidelines
For climatic design of outdoor spaces, three main goals have been outlined:
1- Provide shade in over-heated periods
2- Provide airflow in over-heated periods
3- Provide sunny exterior spaces in under-heated periods
Based on Mahoney Tables, for all parts of Hormozgan, in relation to building layout, two different groups with different goals have been recognized.
Group 1, islands and cities close to shoreline, like Bandar Abass and Bandar Lengeh:
1- Buildings should be elongated along the east-west axis
2- Open space layout for breeze penetration
3- Single banked rooms for permanent air movement
Group 2, areas far from shoreline and with high altitude, like Hajiabad and Minab:
1- Compact courtyard planning
2- No permanent air movement required
Regarding other aspects of design, like size of openings and construction materials, different parts of the province has different needs.
Concerning the Climatic design goals of residential buildings, based on climate analyses, there are two different climatic groups in Hormozgan. The first group consists of Islands and cities close to shoreline. In some parts of this group, there is no need for heating; in other parts, there are some heating needs, which can be provided by passive means. Therefore, this group is divided to 2 sub groups.
Group 1-1, including Siri Island, Abumossa Island, and Jask:
For this sub group following design goals are formulated based on climate analyses:
1- Protect indoor spaces from sun penetration in over-heated periods
2- Protect indoor spaces from outdoor heat penetration
3- Provide indoor exposure to the outdoor climate
4- Provide permanent ventilation
5- reduce indoor air humedity
6- Protect building from monsoon rain
Group 1-2, including Bandar Abass, Qeshm Island, Bandar Lengeh, Kish Island, Bandar Dayer, and Minab
For this sub group following design goals are formulated based on climate analyses:
1- Protect indoor spaces from sun penetration in over-heated periods
2- Protect indoor spaces from outdoor heat penetration
3- Provide indoor exposure to the outdoor climate
4- Provide permanent ventilation
5- Use solar radiation for heating
6- reduce indoor air humedity
7- Protect building from monsoon rain
Group two, areas very far from shoreline and with high altitude, like Hajiabad and Tashkuyeh:
For this group following design goals are formulated based on climate analyses:
1- Protect indoor spaces from sun penetration in hot periods
2- Protect indoor spaces from outdoor heat penetration
3- Use outdoor temperature fluctuation to moderating indoor climate
4- Provide indoor exposure to the outdoor climate
5- Use solar radiation for heating
Based on the above design goals, protection of indoor spaces from the sun and the outdoor heat penetration in over-heated periods of the year are the first and second priorities in building design for all parts of Hormozgan province.
The following design guidelines are formulated based on climate analyses and the study of traditional architecture of the Hormozgan province.
Site selection
From climatic design point of view, the best sites for residential building development in hot and humid climate are those sites that are not in leeward sides or are not in low lands. The best location for buildings in sloped sites is the windward mid portion of the slopes. It is preferred the westerly and easterly slopes are not be selected for building development. Best sites are large sites and those that have not surrounded by tall building or elements. On Greenfield sites, disturbance including earthwork and clearing of vegetation should be limited to the boundaries as close to the building perimeter, surface walkways, patios, surface parking, and primary roadway curbs.
Site Design
Disruption of natural hydrology should be reduced by reduction of imprevious cover and use of pervious materials in site surfacing, including sidewalks, parking lots, and roads that are not used by heavy vehicles. In site design, the following goals should be considerd.
– Location of buildings and site elements should be determind in relation to the prevaling wind dirction.
– Site elements shoud be located in a way that allow use of prevalling breezes in natural ventilation.
– In locating site elements for those parts of Hormozgan that solar heating is suitable, there shoud be nothing left in southern part of the building and within 30 degrees of the south elevation.
Site Pattern and Density
In this region and all hot and humid climates of Iran, since provision of continuous and efficient ventilation is necessary, open planning and wide, free spaces between buildings that help to achive good ventilation is beneficial. In ditermening the necessary distances between buildings, wind shadows have to be considerd. In this regard, and for buildings with flat roofs and equal hight and dept, the distance between 2 buildings should not be less than 3.75 times hight of the windward building. If the dept of the same buildings are 2 or 3 times of their hight, this distance should not be less than 3 or 3.25 times of the hight of the windward building.
The most beneficial site layout is when the windward row of buildings cosists of low detached houses, the midel row consists of mixed height apartments and the leeward rows consists of long and tall buildings.
Building Orientation
In selecting suitable building orientation in places that are close to shoreline, it is important to respect to the sun and wind. The objectives are to minimize solar penetration to the interiors in over-heated periods, and to consider the effects of wind in providing cross ventilation. To minimize solar penetration to the interiors, the building should be oriented in a way that receives minimum amount of solar radiation in over-heated periods and in a direction, that reduces the size of necessary shading devises.
In relation to the effects of winds in cross-ventilation, best orientation is the one that makes larger incident angle with the direction of prenailing winds (between 45 to 90 degrees). In Bandar Abass, and with respect to the sun and prevailing wind, the best orientation for double-banked buildings is north-south direction and the worst is 75 degree east of south. In all parts of hormozgan and with respect to the solar radiation, north-east orientation is the best direction for building orientation.
Orientation of street network
The best direction for streets in Hormozgan is the one that provides adequate shade on the street and provides adequate airflow in streets. To increase the amount of sunshades in over-heated periods, the best direction for streets is north-south and 15 degrees east of south. 15 and 30 degrees west of south and 30 degreesare east of south are second, third and forth priority. To provide adequate airflow in streets and good natural ventilation for the adjacent buildings, the prevailing wind should be oblique to the streets, the angle between the wind direction and the street could range about 30 to 60 degrees. In Bandar Abass with respect to the solar radiation and the prevailing wind direction, the best direction for the strets is 30 degrees west of south. 15 and 30 degrees east of south are the second and 15 degrees west of south is the third priority.
Building Form
In this region, the effect of solar radiation on selecting building form is much more important than the efect of prevailing wind in providing cross ventilation. In this respect, building plans that are elongated on their east-west axis with wide porches are preferred. In places close to shoreline, the planning should be directed towards optimum ventilation conditions. In general, detached houses are the best and two story town houses with open stairwell are the next best building type for the humid regions. Buildings with internal, double-loaded corridors should be avoided in hot-humid regions. Singel-loaded corridor buildings that have also windows on corridor silde of the apartments, which severely interferes with the privacy of the occupants, are the other priority of building form in this reigen. Multistory apartment buildings with staircases or elevators serving only two units per floor, which can provide cross-ventilation, are suitable building type for housing development in Hormozgan.
Main Building Spaces and Plan Organization
From climatic design standpoint, three main spaces are necessary for residential buildings: interior, semi outdoor and outdoor spaces. Balconies are very useful in this climate for both shading the windows and walls and providing a suitable semi outdoor space. In cases that the building is air conditioned, the best plan organization for the building is dense and compact form. However, when the objective is to cool the building with enhancing natural ventilation in some over-heated periods, the plan of the building should be open and elongated to the east-west axis. In this case, interior of the building should be open and windows should be large and operable. It is possible to design a building with special details, which will enable it to be compact when it is air-conditioned and to be widespread and irregular in shape when it is naturally ventilated. (A building with porches recessed inward and flanked by adjoining rooms, which should be equipped, with operable large windows or insulated shutters).
Relation of building to the ground
In all parts of this region, building should be raised from the ground. Raising the building on the stilts also is advantageous in humid climates. Firstly, this enables better ventilation by locating the windows above the zone of maximum wind damping by the surrounding vegetation, and secondly, it enables cooling of the floor from below. In addition, the building is better protected from floods created by the monsoon rain.
Size and location of windows
Based on Mahoney’s tables, in all places close to shoreline, size of openings, doors, and windows should be about 25% to 40% of the area of related elevation. In islands, larger windows, about 20% to 80% of related elevation, are preferred. In places far from shoreline, windows should be small, about 10% to 20% of the related elevation. Generally, large openings are advantage in this climate if they are effectively protected from penetration of sun during the over-heated periods.
The most effective height of the windows from the human comfort aspect, which is important in this climate, is about 0.5 to 1.5 meters above the floor (the occupied zone). In bedrooms, it is particularly important to bring the windowsill as close as possible to the height of the beds, thus ensuring adequate airflow around the occupants’ sleeping area. When upper windows have to be used, it is preferable to use horizontally pivoted windows with upper hinges, which, when open, would direct the airflow downwards. It is important to select a type of window that is 100% operable. In many instances, solar protection not only with respect to the windows but also for the whole area of the elevation may be provided by extending the roof beyond the floor area and creating wide porches.
Sun Shading devices
Since protecting the interior spaces from intense solar radiation during the over-heated periods is one of the main climatic design goals in this region, all transparent openings should have some mean of shading device. To design such a device one can use the available recourse that has been prepared for all main cities of Iran.
Color of Exterior surfaces
In all parts of Hormozgan province and all hot-humid regions of Iran, in order to reduce the effects of intensive solar radiation in thermal condition of the buildings interiors, light colors should be applied to all exterior surfaces.
Building Materials
Refer to section 19 of Iran National Building Code to select type and thickness of insulation layers for building shell in desired areas of the region. As an example, based on the prescriptive recommendations that are given in the mentioned code, type and thickness of insulation layers for suggested and common envelope materials in the region are as following.
– Composite walls with a layer of concrete blocks, and a layer of brick, with cement mortar facing: For Group 1, 8 cm expanded Polystyrene with density of 30 Kg/m³ or more. For Group 2, 5 cm of the same insulation material
– Solid flat roof: For Group 1, 10 cm expanded Polystyrene with density of 30 Kg/m³ or more. For Group 2, 6 cm of the same insulation material
– Floor on ground: For Group 1, 4 cm expanded Polystyrene with density of 30 Kg/m³ or more. For Group 2, 3 cm of the same insulation material
Climatic Zoning of Hormozgan Province
In relation to the main climatic design goals, all cities and populated areas of Hormozgan province are classified in two zones or two groups. Group 1 has two sub groups. The geographical boundaries of these two zones are shown in Climatic Zoning map of Hormozgan province, which could be used in determining the design recommendations for different parts of the region.
Climatic Zoning map of Gilan and Mazandaran provinces
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