Report: 104

Building Type: Adobe / Earthen House

Country: IRAN

Author(s): Mehrdad Mehrain, Farzad Naeim

Last Updated:

Regions Where Found: Buildings of this construction type can be found in the Middle East. This type of housing construction is commonly found in both rural and urban areas.

Summary: This building type is typically one or two stories and used for single-family housing. It is more predominant in the desert, in cold-weather, or other inhospitable climates. It has a large mass and basically no strength, particularly against out-of-plane wall forces. These buildings are the most seismically vulnerable. In the 2003 Bam earthquake, collapse of these buildings was widespread and contributed to many of the 43,000+ deaths. The typical mode of collapse is out-of-plane failure of the walls, resulting in loss of support for the roof. Adobe construction is widespread throughout Iran, and is used both by wealthy families in luxury residences, as well as by poor families in more modest dwellings.

Length of time practiced: More than 200 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Single dwelling

Typical number of stories: 1

Terrain-Flat: Typically

Terrain-Sloped: 4

Comments: Adobe construction is widespread throughout Iran, and is used both by wealthy families in luxury residences as well as poor fami

Plan Shape: Rectangular, with an opening in plan

Additional comments on plan shape: Small windows, one entrance door and one entry for each room.

Typical plan length (meters): 12

Typical plan width (meters): 12

Typical story height (meters): 3

Type of Structural System: Masonry: Earthen/Mud/Adobe/Rammed Earth Walls: Adobe block walls

Additional comments on structural system: The vertical load-resisting system is earthen walls . The roofs are usually adobe domes or cylindrical arches, supported on adobe walls. Sometimes flat adobe roofs with wood joists are used (as described in section 1.9, if these buildings are built on hillsides, the ground floor of one building can be the roof for another.) . The lateral load-resisting system is earthen walls . The lateral load-resisting elements are adobe walls, typically 3 m high, 4 m wide and 0.80 m thick. The walls do not have any additional system (such as crown beam or pilasters) to restrain their out-of-plane movement. That is one reason why the buildings are so vulnerable in earthquakes. If the walls move out of plane, the roof loses its support, and collapses .

Gravity load-bearing & lateral load-resisting systems:

Typical wall densities in direction 1: >20%

Typical wall densities in direction 2: >20%

Additional comments on typical wall densities: The typical structural wall density varies from 10% to 35%. The walls are very thick, typically +/- 70-80 cm.

Wall Openings: Small windows, one entrance door and one entry for each room. Opening area is about 30 percent of total wall area .

Is it typical for buildings of this type to have common walls with adjacent buildings?: Yes

Modifications of buildings: No modifications are made to the building .

Type of Foundation: Shallow Foundation: Wall or column embedded in soil, without footingShallow Foundation: Rubble stone, fieldstone strip footing

Additional comments on foundation:

Type of Floor System: Vaulted masonry floorOther floor system

Additional comments on floor system:

Type of Roof System: Vaulted masonry roofRoof system, other

Additional comments on roof system: The roofs (and walls) typically have a 5 cm (2 inch) layer of straw reinforced mud to provide protection against rain .

Additional comments section 2: The typical separation distance between buildings is more than one meter, if not connected to adjacent buildings.

Who is involved with the design process? None of the above

Roles of those involved in the design process:

Expertise of those involved in the design process: No special expertise . None .

Who typically builds this construction type? Other

Roles of those involved in the building process:

Expertise of those involved in building process: No special expertise . None .

Construction process and phasing: Sun dried adobe units are used to build walls and roof. A 2-inch layer of straw-reinforced mud covers the walls and roof for rain protection. Every 4 to 6 years, this layer is washed away from the roof and requires replacement. The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size.

Construction issues:

Is this construction type address by codes/standards? No

Applicable codes or standards:

Process for building code enforcement:

Are building permits required? No

Is this typically informal construction? Yes

Is this construction typically authorized as per development control rules? No

Additional comments on building permits and development control rules:

: Building Maintenance and Condition: : Typical problems associated with this type of construction: Who typically maintains buildings of this type?: Owner(s) Additional comments on maintenance and building condition:

Unit construction cost: $20/m2 (this is a rough estimate. A lot of people build their own houses, using their own dirt to make adobe blocks.) .

Labor requirements: It takes about 100 days for 2-3 persons (200-300 person days) to complete the construction.

Additional comments section 3:

Patterns of occupancy: Just one family, possibly with married son and daughter-in-law, lives in each unit .

Number of inhabitants in a typical building of this construction type during the day: <5

Number of inhabitants in a typical building of this construction type during the evening/night: <5

Additional comments on number of inhabitants:

Economic level of inhabitants: Very low-income class (very poor)Low-income class (poor)Middle-income class

Additional comments on economic level of inhabitants: The ratio of price of each housing unit to the annual income can be 10:1 for very poor and poor families, and 20:1 for middle class families .

Typical Source of Financing: Owner financedPersonal savingsInformal network: friends or relativesSmall lending institutions/microfinance institutions

Additional comments on financing:

Type of Ownership: Own outrightOwn with debt (mortgage or other)

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: No

What does earthquake insurance typically cover/cost:

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: No

Additional comments on premium discounts:

Additional comments section 4:

Damage patterns observed in past earthquakes for this construction type: Iran has a long history of devastating earthquakes that have affected adobe structures. In the 2003 Bam earthquake, over 40,000 people died; in 1997 over 1,568 people died and in the 1990 earthquake in Manjil over 40,000 people died. In the Bam area, there have also been other significant earthquakes: in the Gisk-Zarand 1977 earthquake–665 people were killed; in the 1981 Golbaf earthquake–between 1,000 and 3,000 people were killed; in the 1981 Sirch earthquake- -1300 people killed. Many people were killed in adobe structures .

Additional comments on earthquake damage patterns:

The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.

Additional comments on structural and architectural features for seismic resistance:

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: They are weak in the out of plane direction. The walls tips over or bend outwards.

Earthquake-resilient features in walls: There are no earthquake resistant features. If the adobe walls can be kept in place, the seismic performance of the building will improve significantly .

Seismic deficiency in frames:

Earthquake-resilient features in frame:

Seismic deficiency in roof and floors: It is made of weak materials. If the walls move out of plane, the roof collapses.

Earthquake resilient features in roof and floors: The roof consists of arches and domes which provide integrity.

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

Additional comments section 5:

Additional comments on seismic strengthening provisions:

Has seismic strengthening described in the above table been performed? None in Iran .

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? Not applicable .

Was the construction inspected in the same manner as new construction? Not applicable .

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? Not applicable .

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? Not applicable .

Additional comments section 6: