Description

The World Housing Encyclopedia (WHE) Report Database contains 130 reports on housing construction types in 43 seismically active countries. Each housing report is a detailed description of a housing type in a particular country. The description is prepared from a number of standard closed-ended questions and some narrative that have been provided by report authors. Each report has five major categories including architectural and structural features; Building Materials and Construction Process; Socio-economic Issues; Past Performance In Earthquakes, Seismic Features and Vulnerability; and Retrofit. All of the housing reports in this database have been contributed by volunteers. If you are interested in writing a housing report please contact the WHE Editorial Board.

About

The World Housing Encyclopedia (WHE) is a collection of resources related to housing construction practices in the seismically active areas of the world. The mission is to share experiences with different construction types and encourage the use of earthquake-resistant technologies worldwide. The technical activities of the WHE are steered by an international team of 22 professionals specializing in different aspects of seismic safety of buildings and structures. They bring relevant experience from 16 seismically active countries across the world. For more information about the World Housing Encyclopedia, visit http://www.world-housing.net/.

General Information

 

Report #:14
Building Type: Vivienda de Adobe (Adobe house)
Country: El Salvador
Author(s): Manuel A. Lopez
Julian Bommer
Gilda Benavidez
Last Updated:
Regions Where Found: This construction practice is widespread throughout the country. San Salvador, the capital of El Salvador, is perhaps the only area where this construction type does not exist. The San Salvador Metropolitan building and planning agency (OPAMSS) has prohibited the construction of adobe housing due to its poor seismic performance in San Salvador Metro area. However, the Vice Secretary of Housing (ViceMinisterio de Vivienda) has issued a group of technical norms, in 2014, as a complement of the Adobe building law, dated in 1946; such norms were developed after a 8 research year project finaced by JICA named "Taishin" (http://taishin.wsiefusion.net/inicio).
Summary:

This housing type can be found in rural and urban ...

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: Occasionally
Comments: This construction practice was, and still is, widely used in ElSalvador although this region is highly seismic. El Salvador's ea


 

Features

 

 

Plan Shape Rectangular, solid
Additional comments on plan shape
Typical plan length (meters) 30
Typical plan width (meters) 15
Typical story height (meters) 3
Type of Structural System Masonry: Earthen/Mud/Adobe/Rammed Earth Walls: Adobe block walls
Additional comments on structural system Roof loads are directly transmitted to the shear walls by wood purlins or beams. The beams directly rest on the top of the walls. Walls take the entire gravity load. Walls transfer the load to the foundation.The adobe walls that act as shear walls providing the lateral stiffness. In urban areas, the thickness of the walls can be as much as 1 m. In rural areas, the thickness can be between 0.3 and 0.5 m. The roof can be considered as a flexible diaphragm and is supported directly on the walls.
Gravity load-bearing & lateral load-resisting systems
Typical wall densities in direction 1 >20%
Typical wall densities in direction 2 15-20%
Additional comments on typical wall densities The typical structural wall density is more than 20%. Urban: 35%. Rural: 20%.
Wall Openings Rural: Houses have four walls, two of which have openings. Openings are less than or equal to 30% of the wall area. The other two walls generally do not have openings.Urban: There is a number of openings in these houses. The amount of openings can be as high as 50%.
Is it typical for buildings of this type to have common walls with adjacent buildings? No
Modifications of buildings There is no modification from the original structure.
Type of Foundation Shallow Foundation: Rubble stone, fieldstone strip footing
Additional comments on foundation
Type of Floor System No elevated or suspended floor system (single-story building)
Additional comments on floor system
Type of Roof System Wooden structure with light roof coveringWooden beams or trusses with heavy roof coveringBamboo, straw, or thatch roof
Additional comments on roof system Timber: thatched roof supported on wood purlins; wood planks or beams that support slate, metal, asbestos-cement or plastic corrugated sheets or tiles; wood planks or beams supporting natural stones slatesRoof system can be considered as flexible diaphragm.
Additional comments section 2 Adobehouses have independent walls between each other, however spacing between those walls is scarce in most cases.

 

Building Materials and Construction Process

 

 

Description of Building Materials


Structural Element Building Material (s)Comment (s)
Wall/Frame Adobe Brick0.25 kg/cm2(Shear) 13:4:3 (sand:lime:clay)400mmX200mmX150mm
Foundations Mortar1:2 (soil: straw)
Floors WoodTiles
Roof WoodTiles
Other

Design Process


Who is involved with the design process? Owner
Roles of those involved in the design process Generally, neither engineers nor architects have a role in the design, or construction of this housing type.
Expertise of those involved in the design process

Construction Process


Who typically builds this construction type? OwnerMasonBuilder
Roles of those involved in the building process The builder typically lives in this construction type.
Expertise of those involved in building process There is some experience to build this construction type; however, the work force is not trained.
Construction process and phasing First of all, the builder hydrates the adobe mixture, composed of 65% sand, 20% lime and 15% clay. The water volume could be 1/3 of the whole mixture volume. Bricks are made by placing this mixture into molds measuring 40cmX20cmX15cm. After 3 days, the bricks are removed from the molds and dried for four weeks. Meanwhile, the site where the structure will be erected is leveled. Once this step is complete, excavation for the foundation begins. The width of the excavation is one and a half times the width of the wall. Both stone and mortar are placed into the hole; this will be the foundation. After the foundation is finished, the walls begin to be erected up to 2.5 m. It has to be noted that maximum height per construction day must be 1m to avoid crushing of the walls due to its own weight. When walls reach 2.5 m, approximately, the roof is built. Wood purlins are place on top of walls spaced 20 cm between purlins. Later tiles or steel sheets are placed. The construction of this type of housing takes place in a singlephase. Typically, the building is originally designed for its final constructed size.
Construction issues

Building Codes and Standards


Is this construction type address by codes/standards? Yes
Applicable codes or standards There is a Adobe Building Law, dated in 1946. Later, adobe housing construction practices were addressed in an appendix by El Salvadors 1994 Building Code, in "Norma para la Contruccion de Viviendas", where it gives recommendations about building better adobe housing without imposing enforcement. Then, by 2014, the Vice Secretary of Housing (Viceministerio de vivienda y desarrollo urbano) has issued a group of technical norms, as a complement of the Adobe building law; such norms were developed after a 8 research year project finaced by JICA named "Taishin" (http://taishin.wsiefusion.net/inicio) and can be found at http://osartec.gob.sv/index.php/rts/viewdownload/4-inventario-rts/402-urbanismo-y-construccion-en-lo-relativo-al-uso-del-sistema-constructivo-de-adobe-para-vivienda-de-un-nivel.
Process for building code enforcement N/A

Building Permits and Development Control Rules


Are building permits required? Yes
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 The biggest problem of this type of construction is water due to weathering. Adobe has be protected against water.In addition, it has low resistance against seismic excitation, because of its very high mass-to-strength ratio.
Who typically maintains buildings of this type? Owner(s)No one
Additional comments on maintenance and building condition

Construction Economics


Unit construction cost Rural: US$ 15 /m2 Urban: US$ 30 /m2.
Labor requirements Rural: A month to build the bricks and 1.5 months to construct the house, using two people for the whole process.
Additional comments section 3

 

Socio-Economic Issues

 

 

Patterns of occupancy One family typically occupies one house.
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 5-10
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 Ratio of housing unit price to annual income: 1:1 or betterThe prices are expressed in US$. Ecomomic Level: For Very Poor Class the Housing Unit Price unit is 350 and theAnnual Income is 1000. For Poor Class the Housing Unit Price unit is 700 and the Annual Income is 2500. ForMiddle Class the Housing Unit Price unit is 12000 and the Annual Income is 20000.
Typical Source of Financing Informal network: friends or relatives
Additional comments on financing
Type of Ownership RentOwn outrightOther
Additional comments on ownership Urban: Typically own outright. Rural: The landowners give a space to peasants to build their houses and to work the land. The peasants give part of their harvest to the landowner as rent.
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

 

Earthquakes

 

 

Past Earthquakes in the country which affected buildings of this type


YearEarthquake Epicenter Richter Magnitude Maximum Intensity
1936San Vicente
1951Jucuapa/ Chinameca
1965San Salvador
1982Pacific Ocean
1986San Salvador
2001Pacific Ocean
2001San Vicente
6.1VII-VIII (SIEBERG)
6(MSK) VIII
6(MMI) VIII
7.2(MMI) VII
5.4(MMI) VII
7.7(MMI) VIII
6.5(MMI) VII

Past Earthquakes


Damage patterns observed in past earthquakes for this construction type El Salvador had two big EQ at the beginning of 2001. The first one was on 13 January 2001 with ITS epicenter located in the Pacific Ocean and with magnitude Mw=7.7, with a maximum estimated intensity of VIII (MMI). The second one happened on 13 February 2001 with epicenter at San Juan Tepezontes and Mw=6.5; the estimated intensity was VIII in some places, however in many of the affected areas its intensity was VII (MMI). One of the most important features of these two EQ is that they destroyed adobe housing in many places throughout El Salvador.
Additional comments on earthquake damage patterns Wall: Damages due flexural and shear effects.Roof and floor: Total and partial collapse of the roof due to material degradation and loss of support from walls.

Structural and Architectural Features for Seismic Resistance


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.
Structural/Architectural Feature Statement Seismic Resistance
Lateral load pathThe structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation.FALSE
Building Configuration-VerticalThe building is regular with regards to the elevation. (Specify in 5.4.1)TRUE
Building Configuration-HorizontalThe building is regular with regards to the plan. (Specify in 5.4.2)TRUE
Roof ConstructionThe roof diaphragm is considered to be rigid and it is expected that the roof structure will maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area.FALSE
Floor ConstructionThe floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) will maintain its integrity during an earthquake of intensity expected in this area.N/A
Foundation PerformanceThere is no evidence of excessive foundation movement (e.g. settlement) that would affect the integrity or performance of the structure in an earthquake. TRUE
Wall and Frame Structures-RedundancyThe number of lines of walls or frames in each principal direction is greater than or equal to 2.TRUE
Wall ProportionsHeight-to-thickness ratio of the shear walls at each floor level is: Less than 25 (concrete walls); Less than 30 (reinforced masonry walls); Less than 13 (unreinforced masonry walls);TRUE
Foundation-Wall ConnectionVertical load-bearing elements (columns, walls) are attached to the foundations; concrete columns and walls are doweled into the foundation.FALSE
Wall-Roof ConnectionsExterior walls are anchored for out-of-plane seismic effects at each diaphragm level with metal anchors or straps. FALSE
Wall OpeningsTRUE
Quality of Building MaterialsQuality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). FALSE
Quality of WorkmanshipQuality of workmanship (based on visual inspection of a few typical buildings) is considered to be good (per local construction standards).FALSE
MaintenanceBuildings of this type are generally well maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber).FALSE

Additional comments on structural and architectural features for seismic resistance Wall openings are most true in the rural and may be false in urban.
Vertical irregularities typically found in this construction type Other
Horizontal irregularities typically found in this construction type Other
Seismic deficiency in walls There is a lack of dependable joints among walls, especially at the top of walls. This causes adjacent walls to open up during an earthquake.
Earthquake-resilient features in walls
Seismic deficiency in frames
Earthquake-resilient features in frame
Seismic deficiency in roof and floors There is inadequate vertical and horizontal load transfer mechanism from roof to walls.
Earthquake resilient features in roof and floors
Seismic deficiency in foundation
Earthquake-resilient features in foundation

Seismic Vulnerability Rating


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

High vulnerabilty Medium vulnerabilityLow vulnerability
ABCDEF
Seismic vulnerability class o -|

Additional comments section 5 Wall: Damages due flexural and shear effects.Roof and floor: Total and partial collapse of the roof due to material degradation and loss of support from walls.

Retrofit Information

 

 

Description of Seismic Strengthening Provisions


Structural Deficiency Seismic Strengthening
Walls: There is lack of dependable joints among walls, especially at the top of walls. This causes adjacent walls to open up during an earthquake. Collar Beam or Lintel Band: This feature ties the walls together.Buttresses: This feature helps to retain the integral action of walls and facilitate the connection of collar beams with each other.Vertical and Horizontal Reinforcement using bamboo: This features tries to provide reinforcement similar to that for concrete structures. Adobe bricks have to be molded appropriately to use this kind of strengthening technique.
Roof: Very heavy elements. Sheets of metal: Use this feature instead of clay tiles.

Additional comments on seismic strengthening provisions As mentioned above, after the 2001 Eq's, the Japanese International Cooperation Agency JICA financed the TAISHIN a research program oriented to improve the seismic performance of four building practices, Abode, masonry using soil-cement bricks, masonry using concrete blocks and masonry using concrete panel blocks, systems used in low income dwellings. Extensive research was conducted and a great deal of information was obtained. The following web site can be checked to get more data: http://taishin.wsiefusion.net/inicio
Has seismic strengthening described in the above table been performed? Yes, it has. However, It is not widely used. It has been done as a test in some rural communities.
Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? It was done as a test.
Was the construction inspected in the same manner as new construction? No, it was not. These houses did have supervision.
Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? An ONG.
What has been the performance of retrofitted buildings of this type in subsequent earthquakes? Very good, nothing happened to them. However, they are located in an area that was not as affected by the recent earthquakes.
Additional comments section 6

 

References

-Alvarez G., S de J. Informe tcnico sobre aspectos sismologicos del terremoto en El Salvador del 19 de junio de 1982. Dpto. De Sismologia, Centro de Investigaciones Geotcnicas, San Salvador, 1982.


- Ambraseys, N.N., Bommer, J.J, Buforn, E, Udias, A., The earthquake sequence of May 1951 at Jucuapa, El Salvador, Journal of Seismology (in press) 2000, pag 1-17, Netherlands.


Harlow, D.H., White, R.A., Rymer, M.J., Alvarez, S., The San Salvador Earthquake of 10 octuber 1986 and its historical context, Bulletin of the Seismological Society of America, Vol 83, #4, pp1143-1154, August 1993.


- Lara G., M.A. The El Salvador earthquake of June 19, 1982. EERI Newsletter, vol. 17, no. 1, 87-96, 1983.


Levin, S.B. The Salvador earthquakes of December, 1936. Bulletin of the Seismological Society of America, vol. 27, 377-407, 1937.


Norma Especial para Diseno y Construccion de Viviendas. Reglamento para la Seguridad Estructural de las Construcciones. Ministerio de Obras Publicas. San Salvador. 1994.


Rosenblueth, E, Prince, J. El temblor del San Salvador, 3 de mayo de 1965: Ingenieria Sismica, Primer Congreso Nacional de Ingenieria Sismica, Guadalajara, 1965.


Ministerio de Obras Publicas (MOP), 2014,"Mejoramiento de la tecnologia para la construccion y sistema de difusion de la vivienda social sismo-resistente" TAISHIN. http://taishin.wsiefusion.net/


Ministerio de Obras Publicas (MOP), 2014, "Urbanismo y construccion en lo relativo al uso del sistema constructivo de adobe para viviendas de un nivel RTS 91.02.01:14", 17p. http://osartec.gob.sv/index.php/rts?limitstart=0&order=date&dir=desc


TAISHIN, 2008, "Adobe sismo-resistente, resultados de investigacion", Mejoramiento de la tecnologia para la construccion y sistema de difusion de la vivienda social sismo-resistente, Proyecto de cooperacion tcnica. 127 p.


Authors




Name Title Affiliation Location Email
Manuel A. Lopez Engineer UES Universidad de El Salvador. Final 25 Av. Norte. San Salvador lopeman@sal.gbm.net
Julian Bommer Doctor Imperial College Department of Civil and Environmental Engineering. Imperial College of Science. South Kensington, London j.bommer@ic.ac.uk
Gilda Benavidez Architect Escuela de Ingenieria Civil, Universidad de El Salvador Final 25 Av. Norte. San Salvador proyecto1@navegante.com.sv

Reviewers


Name Title Affiliation Location Email
Sergio Alcocer Director of Research Circuito Escolar Cuidad Universitaria, Institute of Engineering, UNAM Mexico DF 4510, MEXICO salcocerm@iingen.unam.mx