World Housing Encyclopedia Report

Country: Malawi

Housing Type: Rural mud wall building (nyumba yo mata OR ndiwula)

Contributors:Mauro SassuIgnasio Ngoma

Primary Reviewer:Manuel A. Lopez M.

Created on: 6/5/2002Last Modified: 7/2/2003

This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions, and recommendations expressed herein are those

of the various participants, and do not necessarily reflect the views of the Earthquake EngineeringResearch Institute, the International Association for Earthquake Engineering, the Engineering Information

Foundation, John A. Martin & Associates, Inc. or the participants' organizations.

Table of Contents

General Information............................................................................................1Architectural Features........................................................................................ 2Socio-Economic Issues...................................................................................... 3Structural Features............................................................................................. 5Evaluation of Seismic Performance and Seismic Vulnerability.......................... 9Earthquake Damage Patterns............................................................................ 11Building Materials and Construction Process..................................................... 12Construction Economics.....................................................................................14Insurance............................................................................................................15Seismic Strengthening Technologies................................................................. 16References......................................................................................................... 17Contributors........................................................................................................ 18Figures................................................................................................................19

1 General Information

1.1 CountryMalawi

1.3 Housing TypeRural mud wall building (nyumba yo mata ORndiwula)

1.4 SummaryThis housing construction type is used only forresidential purposes. The building techniqueconsists of timber poles as the core or base witha mud smear (plaster) applied on both sides.The plan is circular (only one floor) and the roofis formed by grass thatch supported on timberpoles and cross members. The circular shape ofthe plan and the light weight of the roof,combined with the wood skeleton or frame,ensure a good seismic response. The seismicvulnerability is increased by poor connections ofthe wood skeleton and by progressive damageof the natural components.

FIGURE 1: Typical "nyumba yo mata"Buildings

1.5 Typical Period of Practice for Buildings of This Construction TypeHow long has thisconstruction been practiced< 25 years< 50 years< 75 years< 100 years< 200 years X> 200 years

Is this construction still being practiced? Yes NoX

1.6 Region(s) Where UsedAll the three regions of Malawi (Northern, Central and Southern region) representing about 5% of theentire housing stock.

1.7 Urban vs. Rural ConstructionWhere is this construction commonly found?In urban areasIn rural areas XIn suburban areasBoth in rural and urban areas

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2 Architectural Features

2.1 OpeningsWindows are not provided in this type of circular housing and there is only one door with a typical sizerange of (1.50 - 1.70 m) height X (0.60 - 0.80 m) wide. The diameter of the round plan is estimated atabout 3 - 4 m. In some cases an additional external ring of about 0.50 m is constructed to keep domesticanimals and for extra storage space.

2.2 SitingYes No

Is this type of construction typically found on flat terrain? XIs this type of construction typically found on sloped terrain? (hilly areas) XIs it typical for buildings of this type to have common walls with adjacentbuildings?

X

The typical separation distance between buildings is 3 meters

2.3 Building ConfigurationMainly circular shape.

2.4 Building FunctionWhat is the main function for buildings of this type?Single family house XMultiple housing unitsMixed use (commercial ground floor, residential above)Other (explain below)

2.5 Means of EscapeNone.

2.6 Modification of BuildingsPeriodic restoration of the roof (three-five years) and re-smearing with mud on internal and externalsurfaces.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyGenerally a single family occupies a single dwelling

3.2 Number of Housing Units in a Building1 units in each building.

3.3 Average Number of Inhabitants in a BuildingHow many inhabitants reside in a typical building of thisconstruction type?

During the day / businesshours

During the evening / night

< 5 X X5 to 10 X10-20> 20Other

3.4 Number of Bathrooms or Latrines per Housing UnitNumber of Bathrooms: 1Number of Latrines: 1

Additional Comments: external single latrine and small shelter for bathing are used per housing unit.

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor X /Poor X /Middle Class /Rich /

Additional Comments: These houses are communal built and haven't been priced. 50% (very poor - lessthan 50US$/per year) - 50% (poor - less than 100US$/per year). It is difficult to estimate. (From the webpage -CIA-The world factbook- the GPD per capita is USD900.00, 2000 est.)http://www.odci.gov/cia/publications/factbook/geos/mi.html#Econ

3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner FinancedPersonal SavingsInformal Network: friends and relatives XSmall lending institutions/microfinance institutionsCommercial banks / mortagesInvestment poolsCombination (explain)Government-owned housingOther

3.7 Ownership

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Type of Ownership/OccupancyRentOwn outright XOwn with Debt (mortgage or other)Units owned individually (condominium)Owned by group or poolLong-term leaseOther

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4 Structural Features

4.1 Lateral Load-Resisting SystemTimber poles form the inner skeleton of the building. Timber vertical elements, of about 5-7 cm diameter(butt end) with a spacing of approximately 1.5 cm, provide the circular transverse section of the structure;horizontal wooden elements (half part of an element with a diameter of 2-3 cm) connect the vertical onesby way of bark strings. The mud layers give transverse stiffness to the wooden skeleton, completing theconnection.

4.2 Gravity Load-Bearing StructureThe roof and the mud smear vertical loads are directly supported by the wooden structure.

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4.3 Type of Structural SystemMaterial Type of

Load-BearingStructure

# Subtypes

Masonry Stone masonrywalls

1 Rubble stone (field stone) in mud/lime mortar or withoutmortar (usually with timber roof)

2 Massive stone masonry (in lime or cement mortar)Earthen walls 3 Mud walls X

4 Mud walls with horizontal wood elements5 Adobe block or brick walls6 Rammed earth/Pise construction

Unreinforced brickmasonry walls

7 Unreinforced brick masonry in mud or lime mortar8 Unreinforced brick masonry in mud or lime mortar with

vertical posts9 Unreinforced brick masonry in cement or lime mortar

(various floor/roof systems)Confined masonry 10 Confined brick/block masonry with concrete posts/tie

columns and beamsConcrete blockmasonry walls

11 Unreinforced in lime or cement mortar (various floor/roofsystems)

12 Reinforced in cement mortar (various floor/roof systems)13 Large concrete block walls with concrete floors and roofs

Concrete Moment resistingframe

14 Designed for gravity loads only (predating seismic codes i.e.no seismic features)

15 Designed with seismic features (various ages)16 Frame with unreinforced masonry infill walls17 Flat slab structure18 Precast frame structure19 Frame with concrete shear walls-dual system20 Precast prestressed frame with shear walls

Shear wall structure 21 Walls cast in-situ22 Precast wall panel structure

Steel Moment resistingframe

23 With brick masonry partitions24 With cast in-situ concrete walls25 With lightweight partitions

Braced frame 26 Concentric27 Eccentric

Timber Load-bearingtimber frame

28 Thatch29 Post and beam frame30 Walls with bamboo/reed mesh and post (wattle and daub) X31 Wooden frame (with or without infill)32 Stud wall frame with plywood/gypsum board sheathing33 Wooden panel or log construction

Various Seismic protectionsystems

34 Building protected with base isolation devices or seismicdampers

Other 35

Additional Comments: Wattle and daub may not fully cover/describe the structural timber elements wherewooden poles are used instead of bamboo/reeds mesh.

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4.4 Type of FoundationType Description

Shallow Foundation Wall or column embedded in soil, without footing XRubble stone (fieldstone) isolated footingRubble stone (fieldstone) strip footingReinforced concrete isolated footingReinforced concrete strip footingMat foundationNo foundation

Deep Foundation Reinforced concrete bearing pilesReinforced concrete skin friction pilesSteel bearing pilesWood pilesSteel skin friction pilesCast in place concrete piersCaissons

Other

Additional Comments: The back-fill is tamped (compacted) after all vertical members are placed.

4.5 Type of Floor/Roof SystemMaterial Description of floor/roof system Floor Roof

Masonry VaultedComposite masonry and concrete joist

StructuralConcrete

Solid slabs (cast in place or precast)Cast in place waffle slabsCast in place flat slabsPrecast joist systemPrecast hollow core slabsPrecast beams with concrete toppingPost-tensioned slabs

Steel Composite steel deck with concrete slabTimber Rammed earth with ballast and concrete or plaster finishing X

Wood planks or beams with ballast and concrete or plaster finishingThatched roof supported on wood purlins XWood single roofWood planks or beams that support clay tilesWood planks or beams that support slate, metal asbestos-cement or plasticcorrugated sheets or tilesWood plank, plywood or manufactured wood panels on joists supported bybeams or walls

Other

Additional Comments: Roof and floor are considered to be flexible diaphragms.

4.6 Typical Plan DimensionsAdditional Comments: 3 - 4 m in diameter i.e. circular plan

4.7 Typical Number of Stories1

4.8 Typical Story Height2 meters

Additional Comments: The height is generally less than two meters.

4.9 Typical Span

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4 meters

Additional Comments: The plan is mainly of circular shape with diameter 3-4 m. There is a principal beambearing the main central post which supports all the purlin members carrying the thatched roof.

4.10 Typical Wall Density10 - 13%

4.11 General Applicability of Answers to Questions in Section 4This is traditional building type.

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5 Evaluation of Seismic Performance and Seismic Vulnerability

5.1 Structural and Architectural Features: Seismic ResistanceStructural/ArchitecturalFeature

Statement True False N/A

Lateral load path The structure contains a complete load path for seismic force effects fromany horizontal direction that serves to transfer inertial forces form thebuilding to the foundation.

X

Buildingconfiguration

The building is regular with regards to both the plan and the elevation. X

Roof construction The roof diaphragm is considered to be rigid and it is expected that the roofstructure will maintain its integrity, i.e.. shape and form, during anearthquake of intensity expected in this area.

X

Floor construction The floor diaphragm(s) are considered to be rigid and it is expected that thefloor structure(s) will maintain its integrity, during an earthquake of intensityexpected in this area.

X

Foundationperformance

There is no evidence of excessive foundation movement (e.g. settlement)that would affect the integrity or performance of the structure in anearthquake.

X

Wall and framestructures-redundancy

The number of lines of walls or frames in each principal direction is greaterthan or equal to 2.

X

Wall proportions Height-to-thickness ratio of the shear walls at each floor level is: 1) Lessthan 25 (concrete walls); 2)Less than 30 (reinforced masonry walls); 3)Less than 13 (unreinforced masonry walls).

X

Foundation- wallconnection

Vertical load-bearing elements (columns, walls) are attached to thefoundations; concrete columns and walls are doweled into the foundation.

X

Wall-roofconnections

Exterior walls are anchored for out-of-plane seismic effects at eachdiaphragm level with metal anchors or straps.

X

Wall openings The total width of door and window openings in a wall is: 1) for brickmasonry construction in cement mortar: less than 1/2 of the distancebetween the adjacent cross walls; 2) for adobe masonry, stone masonryand brick masonry in mud mortar: less than 1/3 of the distance between theadjacent cross walls; 3) for precast concrete wall structures: less than 3/4 ofthe length of a perimeter wall.

X

Quality of buildingmaterials

Quality of building materials is considered to be adequate per requirementsof national codes and standards (an estimate).

X

Quality ofworkmanship

Quality of workmanship (based on visual inspection of few typical buildings)is considered to be good (per local construction standards).

X

Maintenance Buildings of this type are generally well maintained and there are no visiblesigns of deterioration of building elements (concrete, steel, timber).

X

Other

5.2 Seismic FeaturesStructural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall No structural bond between mud and

timber coreWell tied vertical and horizontalmembers light structure

None

Frame (columns,beams)

N/A N/A N/A

Roof and floors Wall/roof connection weak. Floor is non-structural - it is made of rammed earth.

Roof with strong mesh structure. None

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5.3 Seismic Vulnerability RatingVulnerability

High (Very PoorSeismicPerformance)

Medium Low (ExcellentSeismicPerformace)

A B C D E FSeismic

Vulnerability Class0

0 - probable value< - lower bound> - upper bound

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6 Earthquake Damage Patterns

6.1 Past Earthquakes Reported To Affect This ConstructionYear Earthquake Epicenter Richter magnitude(M) Maximum Intensity (Indicate

Scale e.g. MMI, MSK)1989 Salima 6 MMI VIII1967 Thambani in Mwanza 5.41966 Mwanza 5.31957 Champira 5 MMI IIIV

Additional Comments: In 1973 another earthquake hit Livingstonia measuring 5.1 on the Richtermagnitude. The 1989 Salima earthquake was the worst in Malawi. It is reported that 9 people lost theirlives and over 50,000 people were left homeless. Rural mud wall buildings performed reasonably well.Geologists forecast more intense earthquakes in Malawi.

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7 Building Materials and Construction Process

7.1 Description of Building MaterialsStructural Element Building Material Characteristic Strength Mix Proportions/ Dimensions CommentsWalls Timber/mud N/A N/A Not able to

measureFoundations N/A - - Not able to

measureFrame Timber N/A N/A Not able to

measureRoof Timber N/A N/A N/AFloor Rammed earth N/A N/A

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?Builder lives in this construction type. It is communally built

7.3 Construction ProcessThis type of construction is completed by a group/communally. Timber poles are cut to the same length2.5 m, holes (0.3 m depth) to receive the poles dug in the ground, poles are placed in the holes but notfirmly back filled, the horizontal members are tied to the poles, and the embedded poles are firmly fixed inthe ground ensuring that the poles are vertical. The mud is now placed/smeared on both sides of the polewalls. The tools used are axe, hoe and buckets.As regards the roof, a central pole (0.2 - 0.3 m diameter) is placed at centre (embedded 0.3 m in theground) to receive pitched/sloping members (0.06 - 0.07 m diameter) acting as rafters spanning to circularwalls. These receive horizontal members 0.03 m diameter acting as purlins placed at 0.3 m centres topand bottom and tied by bark strings. The pitch is not less than 20 degrees. The grass depth is about0.025 m forming a thatch. The grass is supported on the timber skeleton by three rows of timber placed atthe eaves level, mid-way and top tied by bark strings.Poles 0.15 m diameter and spaced 0.6 m apart support eaves projections. These poles are placed about0.7 m from the wall forming a verandah or khonde. The verandah/khonde is raised 0.15 m above groundlevel to protect wall from surface or rain water.

7.4 Design/Construction ExpertiseThe level of expertise is good as it is a practice communally executed which ensures all the necessaryskills and knowledge.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

7.6 Role of Engineers and ArchitectsNo role at all.

7.7 Building Permits and Development Control RulesYes No

Building permits are required XInformal construction XConstruction authorized per development control rules X

7.8 Phasing of Construction

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Yes NoConstruction takes place over time (incrementally) XBuilding originally designed for its final constructed size X

7.9 Building MaintenanceWho typically maintains buildings of this type?BuilderOwner(s) XRenter(s)No oneOther

7.10 Process for Building Code EnforcementNone

7.11 Typical Problems Associated with this Type of ConstructionLow comfort; no facilities; necessity of periodic rebuilding of the roof.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)Not possible to estimate because of communal nature of construction.

8.2 Labor Requirements (estimate)In general, 7 to 10 days (can take longer if done by single person) are required to complete theconstruction. This includes the cutting of timber poles, digging of holes, placing of poles in the holes,tieing the horizontal members (connecting the vertical poles with transverse thin wooden branches),smearing/application of mud on both sides of poles wall, roofing, and flooring.

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9 Insurance

9.1 Insurance IssuesYes No

Earthquake insurance for this construction type is typically available XInsurance premium discounts or higher coverages are available for seismicallystrengthened buildings or new buildings built to incorporate seismically resistantfeatures

X

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?

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10 Seismic Strengthening Technologies

10.1 Description of Seismic Strengthening ProvisionsType of intervention Structural Deficiency Description of seismic strengthening provision usedRetrofit(Strengthening)

Wall/roof connection is weak Periodic rebuilding of the roofMud not properly connected with timbercore

Periodic re-plastering of the surfaces

Floor is not structural Possible relative settlements

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Yes

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?The work prevents environmental damages, including damage from earthquakes

10.4 Was the construction inspected in the same manner as new construction?Yes

10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?The owner

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?N/A: the damaged buildings has been rebuilt

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11 ReferencesChapola, L. S. (1991) " Seismicity and Source Mechanisms of the Malawi Rift and Adjacent Areas, from1900 to 1990. (for the course of seismology 1990-1991 at International Institute of Seismology andEarthquake Engineering, Building Research Institute, Tsukuba, Japan.

Gupta, H. K. (1992) " The Malawi Earthquake of March 10, 1989: A Report of Macroseismic SurveyTectonophy 209, No. 1-4, 165-166

Chapola, L. S. (1993) " An Estimation of Earthquake Hazards and Risks in Malawi" Geological SurveysDepartment, P.O. Box 27, Zomba.

Chapola, L. S. (1994) " Seismicity and Tectonics of Malawi" (for National Atlas of Malawi), GeologicalSurvey Department, P.O. Box 27, Zomba.

Chapola, L. S. (1997) " State of Stress in East and Southern Africa and Seismic Hazard Analysis ofMalawi" M. Sc. Thesis. (Institute of Solid Earth Physics, University of Bergen, Norway)

Malawi Government (1999) "National Housing Policy"

Kamwanja, G. A. (1988) "Low Cost Building Materials in Malawi" Ph. D. Thesis. University of Malawi.

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12 ContributorsName Mauro Sassu Ignasio NgomaTitle Associate Professor Senior LecturerAffiliation Department of Structural Engineering,

University of PisaUniversity of Malawi

Address Via Diotisalvi 2 The Polytechnic, P/B 303,City PisaZipcode 56126 Blantyre 3.Country Italy MalawiPhone 39 050 835715 265-670411Fax 39 050 554597 265-670578Email m.sassu@ing.unipi.it ingoma@poly.sdnp.org.mwWebpage

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13 Figures

FIGURE 1: Typical "nyumba yo mata" Buildings

FIGURE 2: Key Load-Bearing Elements

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FIGURE 3: Plan of a Typical Building

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FIGURE 4: Critical Structural Details

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