Report #: 205

Report Date:

Country: MALAWI

Housing Type:

Housing Sub-Type:

Author(s): Viviana Novelli, Panos Kloukinas, Ignasio Ngoma, Innocent Kafodya, John Macdonald, Katsu Goda

Last Updated:

Regions Where Found: Buildings of this type are the most commonly used in Malawi for both formal and informal settlements. According to the 2008 Census, this building type represents 38.5% of all houses in the country. However, since Malawi is experiencing rapid economic and social changes, including population growth with a high annual rate of about 3%, the percentage mentioned above for this house type has increased considerably.

Summary: Houses made of unreinforced masonry in Malawi are low-rise constructions (typically one-storey and rarely two-storey). A typical storey height is between 2.0m and 2.5m. The plan of the houses has a rectangular shape, and the footprint changes according to the needs and economic resources of the household. A typical footprint is 8mx6m. Houses with greater footprint than typical are generally constructed with better materials and better structural detailing than smaller ones. Bearing walls are single or double skin with a thickness ranging from 100mm to 280mm. The wall thickness varies depending on the size of bricks which are produced locally, with no standard procedure and quality control; the sizes of locally made bricks differ from those of the standardized bricks (220x110x55 or 215×102.5×55 mm). Timber wall plates, to support a roof structure, are used only occasionally on the top of the longest external walls of the houses. The most common mortar adopted for these houses is mud. However, cement is becoming popular, although this material is still considered expensive for the country. Irregular configurations of openings in the wall creates an uneven distribution of load path on spandrels and piers. Lintels on the top of the openings are often not in place. When lintels are implanted, these are made of bamboo/timber planks, masonry bricks, or concrete beams. Concrete lintel bands are used in new houses with masonry bricks and cement mortar. Most houses have pitched or sloped roofs, therefore houses have gables. The gable height is between 0.5m and 1.5m. Gable walls are rarely connected to the roofs, and gable bands are not used to prevent overturning of the gables during an earthquake. Two main roof systems that are adopted for this building type are: light timber truss supporting thatch and timber truss supporting corrugated light metal sheets. These roof systems are classified as light weight structure with a flexible behavior, as they are made of light timber planks and are completely disconnected from t

Length of time practiced: 76-100 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Single dwelling

Typical number of stories: 1

Terrain-Flat: Typically

Terrain-Sloped: Typically

Comments:

Houses of this type have a wide variety in geometry, structural features, mechanical properties, and deficiencies. Although they

Plan Shape: Rectangular, solid

Additional comments on plan shape: Buildings of this construction type have rectangular shapes in plan, with internal walls distributed parallel or orthogonal to the external walls. Re-entrant corners are not considered as irregularity in plan that causes torsion under seismic events, since the observed re-entrant corners are not significantly deeper respect to the plan dimensions in both directions.

Typical plan length (meters): 8

Typical plan width (meters): 6

Typical story height (meters): 2.00-2.50m

Type of Structural System: Masonry: Unreinforced Masonry Walls: Brick masonry in mud/lime mortarMasonry: Unreinforced Masonry Walls: Brick masonry in lime/cement mortar

Additional comments on structural system: External load-bearing walls can be single- or double-skin made of clay bricks with mud or cement mortar. The walls have the function to carry 1) gravity loads: self-weight and light roof, and 2) lateral loads from earthquakes and wind. Past post-earthquake assessments in Malawi and pictures of houses collapsed after Karonga Earthquake in 2009 in section 5.2, have underlined that double-skin walls are generally connected; therefore, houses are highly likely to collapse due to the overturning of at least two adjacent walls. Out-of-plane failure modes of a single wall generally occur in slender single-skin walls subjected to earthquakes.Internal load-bearing walls are mostly single-skin made of clay bricks with mud or cement mortar. The walls have the function to carry 1) gravity loads: self-weight, and 2) lateral loads from earthquakes, if these are connected to the adjacent external walls. Light roof does not sit on internal walls; therefore, the roof weight is only distributed on external walls.

Gravity load-bearing & lateral load-resisting systems: Two building types are applicable to the houses in Malawi 1) unreinforced masonry walls with mud mortar and 2) unreinforced masonry walls with cement mortar. Construction quality can vary significantly within the same type. If built properly (e.g. good connections and good quality materials), buildings with mud mortar can be more resistant than the ones with cement mortar. It is important that both types are considered together in relation to the structural quality detailing of the houses.

Typical wall densities in direction 1: 4-5%

Typical wall densities in direction 2: 5-10%

Additional comments on typical wall densities: No additional comments.

Wall Openings: Openings are mainly distributed on the longest external walls of the houses. The shortest external walls with gables do not always have openings, indeed only big houses have openings on external walls. Openings are evenly spaced and symmetrically distributed. On occasion, they are in a central position or are distributed on only one side of the external walls. The sizes of typical door are width of 800 mm and height of 1800 mm. Windows have different sizes; therefore, dimensions of piers/spandrels can vary within the same wall. Spandrel height can also be very different in the same wall, since openings are not always positioned at the same height. In some cases, spandrels are particularly small (only 300mm). For a typical external wall of 8m, the number of openings is 4 and the percentage of openings with respect to the area of the wall is around 4-5 %.

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Modifications of buildings: New constructions often have a portico made of columns with unreinforced brick masonry or reinforced concrete. Irregularities are observed in the type of materials adopted in the external walls to increase the height of the houses, and to fix damaged walls. Presence of chimneys is also an element of vulnerability, which can be identified in larger houses with better construction detailing and good materials.

Type of Foundation: Shallow Foundation: Wall or column embedded in soil, without footingShallow Foundation: No foundation

Additional comments on foundation: - Houses with fired bricks and mud mortar with a size plan smaller than the typical one (8 m x 6 m) do not have foundations. The walls are built directly on the ground where pegs are placed as anchorages. Houses with larger floor footage have the plinth filled with compacted soil. The plinth walls are usually built directly on the ground. The plinth height of about 300 mm is constructed to prevent damage to the superstructure walls due to water ingress. - Houses with fired bricks and cement mortar often have plinth walls with 1) concrete strip footing with a depth of 230 mm or 2) plinth beams or slab. The inside of the plinth is filled with either compacted soil or crushed or screed surface finish. The plinth height of about 500 mm is constructed to prevent damage to the superstructure walls due to water ingress.

Type of Floor System: No elevated or suspended floor system (single-story building)

Additional comments on floor system: Houses of this class are generally single-storey buildings, and the ground level of this type is made with earth or concrete. In case houses have two storeys, the ground level is made of earth or concrete while the first upper floor is a flexible system made of timber beams.

Type of Roof System: Wooden structure with light roof coveringBamboo, straw, or thatch roof

Additional comments on roof system: Two main roof types for unreinforced masonry brick houses in Malawi are light timber truss-supporting thatch and timber truss-supporting corrugated light metal sheets. Traditionally, roofs were only made of thatching, but corrugated light metal sheets have become the most used roof system in Malawi. The timber truss, made of rafters of 150 mm x 50 mm running orthogonal to the longest external walls, sits directly on the external walls. The lack of pad stones under the purlins/rafters causes severe vertical cracks in the walls indicating an inappropriate distribution of the weight of the roof system. Wall plates are rarely adopted under rafters, and the use of timber ring beams to tie bearing walls is not part of the construction methods adopted for this type of buildings. Both roof types are light horizontal systems, and they are not considered fully rigid along the entire plane and therefore do not act as rigid diaphragms. Furthermore, the roofs are not connected to the bearing walls, therefore they are not providing any restraints against lateral movements of the walls due to winds or earthquakes.

Additional comments section 2:

Infill wall material: No additional comments.

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

Roles of those involved in the design process: A formal design process is not in place. Houses are made by owners/builders using local materials and local construction techniques without proper engineering design. The masons role is to build and advise the owner.

Expertise of those involved in the design process: Not applicable.

Who typically builds this construction type?: OwnerMasonBuilderOther

Roles of those involved in the building process: Houses are made by owners/builders using local materials and local construction techniques without any engineering design. The masons role is to build and advise the owner.

Expertise of those involved in building process: During constructions, there are no interventions by qualified architects and engineers and the building process is not based on licensing or accountability checks. Very little expertise is available and therefore the quality of the houses is generally very poor. Owners/masons involved in the building process do not have any technical knowledge on how houses should be built to be resistant against earthquakes. Their knowledge is based on local experience.

Construction process and phasing: Construction materials are purchased by owners.The houses are built according to the following order -Papering the ground level, where walls will sit-Walls are built using traditional techniques and local materials -Roof is made in place and sits on the wallsTools typically used during the construction: measuring tape, hoes, builders level, strings, trowels, water drums, timber for pegs, and mortar holding points.

Construction issues

Is this construction type address by codes/standards?: Yes

Applicable codes or standards: Standard: MS 791-1:2013 'The structural use of masonry - Part 1: Unreinforced masonry walling'. This standard is specifically for the design of masonry constructions, but this is not generally followed in practice.After the Karonga earthquake in 2009, SAFER HOUSE CONSTRUCTION GUIDELINES have been produced by the Department of Housing and Urban Development within the Ministry of Lands, Housing, and Urban Development to provide practical advice to those involved with the construction of houses.

Process for building code enforcement: Not applicable.

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: Formal or traditional authority provides land allocation for all construction types in formal and informal settlements, and new constructions are registered at the local city council or district commission authority. However, in the informal settlements, since there is not a proper urban planning, and houses are built without or with minimum engineering intervention from an architect or structural engineer in the design and construction process, there is a very little control on the land use and the type of constructions in these settlements (Malawi News Agency, 2016; Food Agriculture and Natural Resources Policy Network, 2006; and Kishindo, 2004).

Typical problems associated with this type of construction: Brick production has contributed to environmental problems including deforestation, decreased soil productivity, lowered ground water levels, and particularly air pollution. Deforestation and high CO2 emissions.

Who typically maintains buildings of this type?: Owner(s)

Additional comments on maintenance and building condition: Houses are often deteriorated due to weathering and externals/internal walls are often damaged by severe cracks indicating partial failures of the houses. Most of the cracks are located under the rafters of the timber roof, underling an inadequate distribution of the load, although roofs are of light weight and flexible. Cracks are also visible on gables, failing for overturning since they are completely disconnected from the roofs. Lack of proper intersection between internal and external walls can be identified by the presence of vertical cracks located on external walls. Severe damage is also caused by settlements. Spoiling and crashing of the masonry bricks are also commonly observed. Interventions to prevent further damage are generally not adopted, and new houses or houses well-kept represent only a minority in the country.

Unit construction cost: Reference year for the following cost: 2018. Since Malawi is experiencing rapid economic and social changes, including population growth, as reported in section 1.3, the costs in this section may change rapidly in the future.The unit rate range per m2 is: K 11,000.00 to K 15,000.00 (US$ 15.00 to US$ 20.00). The costs are based on unit cost of materials and prevailing labour rates as prescribed by the Ministry of Labour.

Labor requirements: Labour requirements-Required time to complete a house depends on the availability of the construction materials and the financial resources of the householder.-One mason with one helper lays 75 bricks per hour. (i.e. 600 bricks per day)-A mason with one helper takes 6 weeks to build a typical house (8 m x 6 m).

Additional comments section 3: No additional comments.

Damage patterns observed in past earthquakes for this construction type: The damage record from past earthquakes is limited. Information related to the damage patterns on this type of constructions is available from the 1989 Salima earthquake (Gupta and Malomo, 1995, Chapola and Gondwe, 2016) and the 2009 Karonga earthquake (United Nations Resident Coordinator, 2009, United States Geological Survey, 2009). During these earthquakes, many of the houses had severe vertical cracks along the side edge of the walls, underlining a lack of connection between facades that visibly collapsed for overturning. Out of plane failure mode was a very common mechanism for these buildings when they were constructed with slender single skin bearing walls. Lack of connections between walls and roof was also the cause of out of plane failure mode of gables. In these constructions, use of gable plates was not part of the construction practice, therefore gables were not restrained and purlins in the roofs were free to push against gable walls causing an arch crack pattern, commonly observed for these house types. In-plane failure modes were common for this type of houses. These failure modes were identified based on the observed crack patterns: 1) X-shape cracks on piers and spandrels, or 2) diagonal cracks involving the failure mode of entire walls. Corner failure modes were also observed for houses with double-skin walls, showing a better capacity and a stronger connection between walls than houses with single skin walls. Typically, houses with a corner failure mode had also a partial/total collapse of roofs.

Additional comments on earthquake damage patterns: No additional comments.

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: These houses are simple rectangular shape constructions. Irregularity in plan or elevation is not a factor affecting the seismic performance, since the houses in question are of single storey. The main seismic vulnerability issues are: 1) poor structural detailing in the connections between (gable) walls and roofs. This causes out of plane failures, the mechanisms to which masonry bearing walls and gables with lack of detailing are mostly vulnerable. 2) Low mechanical properties of local materials. This causes an unpredictable response of the constructions, decreases the capacity of the houses and generates brittle seismic failures. 3) Lack of maintenance. This degrades the seismic capacity and increases the existing structural weakness in buildings. There are also other minor structural vulnerabilities observed for this type of houses, one of those are the re-entrant corners of the longest external walls in bigger houses. However, since the re-corners are never deeper than 1 m, they do not need to be considered as an element of irregularity that significantly impacts the seismic vulnerability. Porticoes are also a common irregularity for these constructions. These are rarely connected to the houses, and in many cases, they are composed by single columns disposed in front the main entrance of the houses to support thatch or corrugated metal sheets extended from the roofs. As these porticoes are generally disconnected from the houses, they do not impact on the building performance. However, they need to be considered as hazard elements, since they can collapse in case of an earthquake. Additional floors are rarely constructed. Occasionally, wall heights are increased using materials with different mechanical properties from the ones used in the initial construction.

Vertical irregularities typically found in this construction type: Re-entrant corner

Horizontal irregularities typically found in this construction type: No irregularities

Seismic deficiency in walls: Walls are made of clay masonry bricks produced locally. Mechanical properties of the local materials are much lower than the standardized ones. Intersecting external walls are generally connected, however they are often built with slender single-skin walls, which decrease the capacity of the building. The walls perform better when they are double skin and built with cement mortar. However, informal houses are mostly built with very weak mud mortar. Walls are disconnected from the roof in most of the houses and there are no elements (i.e. ring beams) tying walls together. Wall plates are occasionally used to support rafters.

Earthquake-resilient features in walls: Connections between external walls are generally good. However, since the deficiencies, (i.e. slenderness of the walls and low mechanical properties of the materials) increase the vulnerability, low seismic performance is expected for these houses.

Seismic deficiency in frames: Not applicable.

Earthquake-resilient features in frame: Not applicable.

Seismic deficiency in roof and floors: The main issue is related to the lack of connection between roof and walls.

Earthquake resilient features in roof and floors: Roofs are flexible systems, consisting of detached timber posts which are rarely connected to the houses. Therefore, if a roof collapses under a lateral load, it might cause injuries, but not necessarily deaths.However, the lack of connections of the roofs to the walls results in inadequate load transfers from the roof to the walls, and high risk for the houses to fail in out of plane.

Seismic deficiency in foundation: Deeper foundations are required.

Earthquake-resilient features in foundation: Not applicable.

Other seismic deficiencies: - Presence of chimneys: Some of the houses have chimneys, but the vast majority in Malawi do not have, since they do not require heating due to moderate-to-high temperatures and the cooking takes place outside the house. These elements should be checked to investigate their structural impact on the houses under a seismic event. - Presence of parapets: These elements are rarely adopted in Malawian houses. They are generally 200 mm of height and are built using the same constructional materials (brick and mortar) adopted in the bearing walls of the houses. These elements are used as additional dead load on the metal sheet roof to prevent uplifting due to wind loads. These elements should be checked to investigate their structural impact on the houses under a seismic event.

Other earthquake-resilient features: Not applicable.

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

Additional comments section 5: The vulnerability rating goes from medium to high. Buildings of Vulnerability Class B cover most of the houses of this building type built in urban and rural areas for informal settlements. These buildings can have double/single-skin walls made of clay bricks and mud/cement mortar. Generally, these houses have the typical plan geometry (8 m x 6 m). These houses have thatch or corrugated metallic sheets supported by a light timber truss. The construction detail varies significantly, therefore factors (e.g. connections, quality material, and maintenance level) impacting the vulnerability can affect the building capacity in a different way, generating a medium class of vulnerability which is between the classes below. Seismic performance of buildings with single-skin walls made of clay bricks and mud mortar is poor and belongs to Class A. Generally, these houses have smaller plan geometry than the typical plan geometry (8 m x 6 m) and are built in rural informal settlements. Most of these houses have thatch or corrugated metallic sheets supported by light timber truss, low quality material, and poor structural detailing (e.g. lack of connection between walls and between walls and roof). For houses with a medium vulnerability in Class C, buildings have double skin walls made of clay bricks and cement mortar. Generally, these houses have bigger plan geometry than the typical plan geometry (8 m x 6 m) and are built in urban formal settlements. Most of these houses have corrugated metallic sheets supported by a timber truss, good quality material, and good structural detailing (e.g. adjacent walls and walls/roof are connected).

Additional comments on seismic strengthening provisions: For buildings of this type, no strengthening interventions are in place. Therefore, the listed interventions above are proposed strategies to improve the building deficiencies.

Has seismic strengthening described in the above table been performed?: Not applicable.

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: Not applicable.

PREPARE project site.

Goda, K., Gibson, E. D., Smith, H. R., Biggs, J., & Hodge, M. (2016). seismic risk assessment of Urban and rural settlements around lake Malawi. Frontiers in Built Environment, 2, 30.

World Population Review

Gupta, H. K., and Malomo, S. (1995). The Malawi earthquake of March 10, 1989: report of field survey. Seismol. Res. Lett. 66, 20-27. doi:10.1785/gssrl.66.1.20

Chapola, L., and Gondwe, J. (2016). Urban development in earthquake prone areas: lessons from 1989 Salima and 2009 Karonga earthquakes. J. Catholic Univ. Malawi 2, 15-26.

United Nations Resident Coordinator. (2009). Malawi: Karonga Earthquake Situ-ation Report No. 3.

UN-Habitat (2010). Malawi: Urban Housing Sector Profile.

National Statistical Office of Malawi (2008). 2008 Population and Housing Census.

States Geological Survey. (2009). Significant Earthquakes of the World

Kishindo, P. (2004). Customary land tenure and the new land policy in Malawi. Journal of Contemporary African Studies, 22(2), 213-225.

Malawi: 'New Land Laws to Empower Chiefs, People 'REPORT from Malawi News AgencyPublished on August 1st 2016Source: AllAfrica.com / Malawi News Agency

Review of land policy in Malawi: Fanrpan policy brief No.3REPORT from Food Agriculture and Natural Resources Policy Network.Published on 30 Jan 2006