book chapter boq

7/29/2019 Book Chapter BOQ

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205

Chptr 9

Bii i

IntroductIonBuilding production is the organization and managementof the plans, equipment, materials and labour involvedin the construction of a building, while at the sametime complying with all codes, rules and contractualstipulations. The procedure should be designed to runefficiently to keep costs low and to allow returns on the

investment to be realized as early as possible.While many topics included in this chapter, such

as standardization, organization of building workscarried out by a contractor, tendering, contracting,inspection and control and progress charts, may havelimited relevance for small-scale building projects onAfrican farms, it is felt that an engineer will needsome knowledge of these topics when tackling workinvolving the construction of communal and centralfacilities for agricultural production and services andmedium- to large-scale rural buildings.

The costs of rural buildings such as animal housing

and stores for produce can be expected to be repaid interms of increased production, improved animal health,reduced storage losses, increased quality of produceand more efficient work performance. Other buildingssuch as dwellings are expected to be worth their costsmainly in terms of the standard of space, environment,convenience, construction and appearance they provide.

The term costs in this context means costs overthe whole life of the building, including operating andmaintenance costs, as well as an annual portion of theinitial cost of construction. It also includes the costsof building materials and construction labour, and feespaid to consultants, architects and legal advisors, aswell as interest on capital and any loss of productionincurred during the construction phase.

Building planning is thus concerned with economicbuilding rather than with cheap building, i.e. withproviding the required standard of facilities at thelowest cost. It should be noted that costs include notonly cash payments but also the value of materials andwork provided by the farmer and the family, becausethese are resources that could have been used foralternative activities at the farm to generate income orproduce food.

Most methods for construction costing and

economic feasibility studies assume that resourcesemployed for the construction, as well as the benefitsof the finished structure, can be valued in a convenientmonetary unit. Subsistence farmers are part of the

monetary economy to only a limited extent, so itis difficult to put a fair price on material and worksupplied by them for construction at their farms, or tocorrectly value the benefits of the structure.

There is a national interest in the efficient use of theresources invested in buildings. Governments expresstheir minimum demands in the form of building

regulations, codes and laws.A farmer employing an engineer to design a building,

a contractor to construct it and suppliers to delivermaterials will expect delivery of work and goods tothe standard and price stipulated in the agreement. Forlater reference it is common to formalize the agreementin a contract that makes reference to drawingsand specifications for the structure and to generalspecifications. Inspections and controls are carried outto ensure compliance with the agreement.

the BuIldIng productIon process

The building production process begins when thefarmer starts to seriously consider investing in astructure and ends only when the finished building isin use. The process is divided into stages that follow inlogical sequence. Each stage is terminated by a decision.Table 9.1 gives an outline plan of work for the buildingproduction process.

In small projects where the farmer performs virtuallyall tasks involved, it may not be necessary to followthe chart in detail. Nevertheless the same proceduralbasics and logical order should be followed. Duringthe initial planning stages, the costs are low comparedwith the importance of the tasks involved. The highcosts involved in correcting errors once site operationsand construction are under way can be avoided if timeis spent working out a good, functional design that istechnically and economically sound.

Methods of constructIonThe methods of constructing rural buildings referto the way in which units and components of thebuilding structure are produced and assembled. Themanner of organizing this process differs from regionto region and depends on the level of technology andthe materials available. The operations involved in the

construction of rural buildings of traditional designsare familiar to most rural people in Africa, and smallbuildings on farms are usually constructed by thefarmers and their families.


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206 Rural structures in the tropics: design and development

Table 9.1

t bii i

s sb tk b p i i r k dii b

brifing Incption Invstigt diffrnttrntivs for

invstmnts nddvopmnt of th frmnow nd in th futur.atrntivs to finnc thinvstmnt. Suitiity ofconditions for diffrntntrpriss

Cint, gricuturconomist, vrious

spciists s rquirdfor tchnic rifing

Invstmnt pn

Dvopmnt pn

Choic of invstmnttrntiv. appoint

frm uiding nginr

Fsiiity Crry out studis ofusr rquirmnts, sitconditions, rquirmntsfrom uthoritis,function nd tchnicrquirmnts nd cost

Cint, frm uidingnginr, vriousspciists s rquirdfor tchnic rifing

Fsi, trntivsts of functionnd tchnicrquirmnts withindiction of thircost

Choic of functionnd tchnicrquirmnts

Sktchpnsat. a

Outinproposs

Dvop rif furthr.Roughy sktch trntivsfor th gnr pproch

to yout, functionpnning, dsign ndconstruction. approchuthoritis

Cint, frm uidingnginr, vriousspciists s rquird to

dvop th rif

atrntiv roughsktchs for gnroutins with

indiction of thircost

Choic of gnroutin

Schmdsign

Compt th rif.Compt th functionpnning of th yout.Priminry constructiondsign nd costccution. Otin outindcision from uthoritis

Cint

Frm uiding nginr

atrntiv outinproposs forconstruction dsignwith indiction ofcost. Compt rifnd function yout

Choic of constructiondsign. Priminrydcision to producth uiding

Sktchpnsat. b

Stndrddrwings

Dvop nd comptth rif. Coct drwingsfrom ri sourcs.Study th drwings ndvut thm rgrdingth function ndtchnic rquirmnts

Cint

Frm uiding nginr

atrntiv stndrdyouts

Choic of drwing st.Priminry dcision toproduc th uiding

brif shoud not modifid ftr this point

Fin dsign Dtidsign

Fu dsign of vry prtnd componnt of thuiding. Compt costchcking of dsigns. Findcisions from uthoritis

Frm uiding nginr.assistnc fromspciist nginrsmight rquird inrg nd compxprojcts

Compt st ofdrwings, tchnicspcifictions,function instructionsnd n ccurt coststimt

Fin dcision toproduc th uiding

any furthr chng in oction, siz, shp or cost ftr this point wi rsut in ortiv work

Workingdrwings

Productioninformtion

Prprtion of finproduction informtion i..drwings, schdus ndspcifictions rgrdingproduction mthods nd

ssmy nd insttioninstructions. Prpr tim schdu for thproduction of th uiding

Frm uidings nginr.assistnc from spciist might rquird in rg ndcompx projcts

Productioninformtion. Timschdu

Dtid dcision tocrry out work

Purchs bis ofquntitis

Prprtion of i ofquntitis nd tndrdocumnts

Frm uiding nginr(somtims spciistssistnc rquird)

bi of quntitis

Tndr documnts

Sct prsons ndfirms to invitd fortndring

Tndrction

evut nd comprtndrs nd quottionsftr hving put costs toxcptions nd dditionsin th tndrs ndquottions. Drw up ndsign contrcts

Cint

Frm uiding nginr

Contrctor

Contrct withcontrctor ndsuppirs

Sct contrctor ndsuppirs. Contrctormy contrctsucontrctors


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207Chapter 9 Building production

However, where new methods of construction,materials or layouts have been adopted, as well aswhere there is an increase in the size of the project, theassistance of trained artisans will usually be required.Self-help projects for the construction of communalfacilities such as village stores must be accompanied bya training programme for the people involved. Wheremost of the construction is done by employed buildingworkers, three different contemporary building methodscan be distinguished traditional; post traditional andsystem building.

The traditional method of constructing farmbuildings is increasingly being replaced by post-traditional methods and, to some extent, by system-building methods. This rapid adoption stems from themarketing of modern building products by the materialsmanufacturing industry. The change has also beenpromoted by a rapid rise in population, which has led toa scarcity of traditional materials such as thatch.

tii biiIn traditional buildings, the forms of constructionhave been developed by the traditional building trades,

particularly walling, roofing, plastering, carpentry andjoinery. This method is a process of combining manysmall units. Most of the fabrication and assembly takesplace at the site and usually at the position that thecompleted structure is to be located.

Within each tribal culture, traditional buildingsresult in structures that are similar but differ slightly,depending on the specific requirements and site.Owing to the limited range of materials and forms ofconstruction used, the craftsmen are familiar with thecontent and order of operations in their own trade andknow their relationship to operations in other trades sowell that they carry it out with a minimum of detailedinformation.

The traditional craft-based building method isflexible and able to accommodate variations in marketdemand for the work of craftsmen more readily andinexpensively than methods based on highly mechanizedfactory production. This is because production is carried

out by the craftsmen and there is little investmentin equipment, especially mechanical equipment, andfactory buildings. However, the proportion of skilledlabour required at the site is fairly high.

s sb tk b p i i r k dii b

Sitoprtions

Projctpnning

Hir our, provid toos,prpr ccss rod to sit,

put up tmporry storsnd shds, cr th sit,prpr stockpi rsnd st out th uiding

Contrctor Sit prprd forctu construction

ctivitis

Oprtionson sit

Construction ctivitis.Divry of mtris.Tchnic contros ndinspctions. Sit mtings,ccounts nd conomiccontro

Contrctor

Frm uiding nginr

Cint

Finishd uiding Dcision ontrntivs, whnoprtions do notor cnnot procdccording to th pns

Comption Tchnic inspction oncomption. Corrction ofrrors, dfcts nd short-comings. Fin tchnicinspction

Contrctor

Cint

Frm uiding nginr

Compt uiding

Rsponsiiity for thuiding trnsfrrdto cint

accptnc of thquity of th workcrrid out y thcontrctor

Post-construction

entryintosrvic

Study instructionsnd rn how tooprt quipmntnd insttions inth uiding. Dvopsmoothy runningproduction work routins

Cint

Frm workrs

effctiv gricuturproduction invovingth uiding

Gurnt Invstigt nd inspcthiddn dfcts, rrorsnd shortcomings s thyshow. Inspction t thnd of th gurntpriod. action formsurs s rquirdfoowing th ovinspctions. Ccut fininvstmnt cost

Contrctor

Cint

Frm uiding nginr

Frm workrs

buiding withouthiddn dfcts ndshortcomings

accptnc of workt th gurntinspction.Rsponsiiity fordfcts

Fdck anys tchnic ndfunction prformncof th projct. anys

jo rcords from sitoprtions. anys costs

Frm uiding nginr

Contrctor

Cint

Rcommndtions forth dsign of simirfutur projcts

Table 9.1 (continued)

t bii i


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p-ii biiThe post-traditional or conventional method of buildingmixes traditional and new forms of construction,involving both the old crafts and newly developed

techniques based on new materials. To some extenttraditional building has always been in a state of change,but the introduction of Portland cement and mild steelhas made it feasible to construct large and complexbuildings, and this has led to the need to organize theconstruction process efficiently.

The amount of on-site fabrication has been reducedby the introduction of prefabricated, factory-producedcomponents, especially in the field of joinery andcarpentry (windows, doors, cupboards, roof trusses,etc.). Reinforced concrete and preformed steel lendthemselves to off-site fabrication of parts, followedby their assembly on site. Post-traditional building

differs from traditional building mainly in terms of thescale of the work carried out and the use of expensivemachinery for many operations.

The use of prefabricated, standardized componentsreduces the amount of skilled labour, but at the sametime reduces the freedom of the designer in meetingvarying design requirements. The scale of operationmakes it necessary to pay greater attention to planningand organization of the work to ensure that materialand labour are available in a continuous flow, thatthe mechanical equipment is used efficiently, and thatthe construction can proceed smoothly. It is therefore

necessary to consider production operations during thedesign stage.

sm biiSystem building is a method under which most of thebuildings component parts are factory-produced andsite-assembled. The main advantages of system buildingare the possibilities for efficient factory productionof large numbers of similar building elements and thereduced period of time necessary for assembly at thesite. A disadvantage of this method is the high level ofaccuracy required for setting out and for foundationwork because the nature of the components and theprinciples of the system are such that mistakes aredifficult to correct during the assembly process.

The components (e.g. wall, floor, ceiling and roofelements) are usually related to a specific buildingtype, such as houses, schools or warehouses, or toa restricted range of types. The design of buildingsproduced by this method is inflexible and limits thepossibility of adjusting to specific requirements at acertain site or to a local building tradition. The buildingcomponents may, for example, be produced for onlyspecific dimensional measurements. For example, ifprefabricated wall elements are 3.6 metres long, then

the building length must be a multiple of 3.6 metres.Components of one system will not ordinarily fit

with components of other systems, a situation referredto as a closed system. On the other hand, an open

system allows each component to be interchangedand assembled with components produced by othermanufacturers. In order to keep the variety withinacceptable limits for mass production, such a system

must operate within a framework of standardization ofthe main controlling dimensions, e.g. floor-to-ceilingheight of wall elements.

prefaBrIcatIonPrefabrication is the manufacture of buildingcomponents either on-site (but not in situ) or off-sitein a factory. The use of prefabricated components canreduce the need for skilled labour at the site, simplifyconstruction by reducing the number of separateoperations, and facilitate continuity in the remainingoperations. However, prefabrication is not necessarilytime-saving or economical in the overall construction

project. For example, the use of prefabricated lintelsmay save formwork and result in continuity in thebricklaying work, but could be uneconomical if a liftingcrane is required at the site to place them, when it is notrequired for any other purpose on the job.

o-i biiOn-site prefabrication may be an advantage where anumber of identical components such as roof-trusses,doors, windows, gates and partitions are required.Once a jig, mould or prototype has been made by askilled craftsman, a number of identical components

can be produced by less-skilled labour, e.g. the farmercould do this job when there is time available duringthe off-season. Prefabrication of such items as roof-trusses also makes for more convenient and effectiveproduction than construction in situ.

It is advantageous to prefabricate some concretecomponents. Components for elevated positions requiresimpler formwork if cast on (or in) the ground so thatthe soil can be used to support the formwork. Althoughprefabrication eliminates the waiting time for concretecomponents to harden sufficiently for subsequenton-site operations to continue, the weight and size ofconcrete parts may make prefabrication impractical.

Local production by farmers of adobe bricks,burnt bricks, soil blocks, etc. is not normally referredto as prefabrication, although similar planning andorganization are required for the production of theseunits as for the production of prefabricated buildingcomponents.

o-i biiFactory production of components requires capitalinvestment in machinery and premises, a high degreeof work organization, standardization and a steadydemand for the products. Building components that

can be produced economically in a factory essentiallyfall into three categories:

1. Those that have a high degree of standardizationand are in great demand, making mass production,


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utilizing the greater efficiency of modern factoryproduction, feasible, e.g. bricks, blocks, pipes,windows, doors and building hardware.

2. Those that incorporate materials or finishes that

are exclusively or more efficiently produced usingfactory-based techniques, e.g. metal components,plastic items, galvanized items and baked-paintfinishes.

3. Those that make use of new factory-basedtechniques and machines, e.g. laminated-woodbeams, pre-stressed concrete beams and insulatedsandwich panels.

Factory production is relatively inflexible becauselarge runs of any one component are essential foreconomical operation. The mere transfer of a simpleoperation from a site to a factory will not in itself

reduce costs; on the contrary, it may increase them.This is particularly true for components for ruralbuildings because the demand for them originatesfrom a large number of scattered construction projects,resulting in high transportation and distribution costs.Therefore many factory-made components used inrural buildings will have been designed primarily forother purposes.

dIMensIonal coordInatIonand standardIzatIonIn order to limit variety in the size of similar components,to facilitate their assembly at the site and to make

them interchangeable between different manufacturers,building components are manufactured in standardizeddimensions based on an accepted system of dimensionalcoordination. Such preferred dimensions are given instandards, together with specifications for minimumtechnical performance requirements.

As the experience gained in factory production ofcomponents increases, the technique will be appliedto components of increasing size and complexity (e.g.wholly finished wall elements) and this will increasethe need for dimensional coordination. One system ofdimensional coordination uses the international basicbuilding module of 100 millimetres. The reference

system establishes a three-dimensional grid of basicmodules, or very often multimodules of 300 millimetres,into which the components fit.

The modular grid does not give the size of thecomponent but does allow space for it. In order for thecomponent to fit correctly, it will always be slightlysmaller than the space allowed for it. The system mustallow for some inaccuracy in the manufacturing process

Figur 9.1 gi 3M mim b 200 mm -bi m (a). Bii

m ii m (B), x m (c), i (d) (e)

m i i mi 3M mim.

A AC C C

AA B B BB

B

E

C

C

D

200 12 x 3 m = 12 x 300 = 3 600 200 300 300

300

300

200

8x3m=

8x300=2400

200


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and changes in size owing to changing temperature andmoisture conditions.

This is expressed as a tolerance in size. For example,a window that is allowed a basic size of 1 200 mm for itswidth is produced with a working size of 1 190 mm anda manufacturing tolerance of 5 mm, which is expressedas 1 190 5 mm. The actual dimension of a windowdelivered to the site would be somewhere between1 185 mm and 1 195 mm. The joint would be designedto take these deviations into account.

Modular-size concrete blocks are 290 mm long andmodular format bricks are 190 90 40 or 90 mmactual size to allow for 10 mm mortar joints and plaster.The actual size of openings will then be 1 220 mm. Inthis process the designer has a responsibility to specifytolerances that can be achieved with available craftsmen

and factories.It will be easier to fit factory-produced window and

door casements, which are made to standard modularsizes, if these sizes are also used when bricks and blocks

are manufactured locally. The common brick size of215 102.5 65 mm allows for laying four courses to300 mm vertically and four brick lengths to 900 mmhorizontally, if 10 mm joints are used.

BuIldIng legIslatIonIn urban areas, government authorities issue buildingregulations to ensure the safety, security and welfareof those who use the buildings and to make maximumuse of the scarce resources available for buildingconstruction. Typically, building regulations coversubjects such as building materials, structural integrity,fire precautions, thermal and acoustic insulation,ventilation, window openings and stairways, as well asdrainage and sewage disposal. Building regulations maystate minimum functional requirements, such as room

height and space, for specific types of rooms.Additional legislation applicable to buildings may be

found in the public health act and public roads act. Thebuilding regulations and other legislation are statutory,

Figur 9.1 rii bi i, k i, mi ji ik (Note that tolerance

and joint thickness are not to scale.)

ITEM

Basic space allowed forthe building component

Minimum joint thicknesses

Maximum size of thebuilding component

Minimum size of thebuilding component

Minimum size

Work size and tolerance

Maximum size

Wall opening

Manufacturing tolerance

Minimum joint thicknesses

EXAMPLE

Modular grid lines

4 x 3 m = 1 200 mm

2 x 25 mm = 5 mm

1 200 mm - 5 mm = 1 195 mm

1 200 mm - 15 mm = 1 185 mm

1 185 mm

1 190 5 mm

1 195 mm

1 205 5 mm

1 195 mm - 1 185 mm = 10 mm

2 x 75 mm = 15 mm


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i.e. they must be followed as far as they apply. Thelocal authority ensures that the legislation is compliedwith through its building inspector, health inspector,etc. However, the authorities will sometimes issue

guidelines for building, in addition to the regulations.These are mere recommendations and the designer maydiverge from them if there are good reasons.

Building regulations do not normally apply tobuildings outside urban areas, but there may be instanceswhere other legislation is applicable, for example,where a farmer wants to connect to a main water supplyor a main sewer or to run a drain under a public road.Therefore it is wise to contact the local authoritiesabout any new building proposal or major alterationto an existing building. If local authority approval isnecessary, copies of drawings and specifications willhave to be submitted for its advice and approval.

constructIon costIngThroughout the building production process, costswill have a major influence when choosing betweenalternative designs. An excessively high cost may evencause the whole project to be abandoned. In the initialstages, when rough sketches are evaluated, generalguideline costs based on building area or volumemay be sufficient. In the final design stage, when thefarmer has to decide whether or not to proceed withconstruction, a more detailed cost estimate based on asimplified bill of quantities is usually prepared.

A contractor will need the most accurate costestimate based on a bill of quantities, as the quotationshould be low enough to be competitive but stillgenerate a profit. On large projects, the bill of quantitiesis also used to determine interim payments for workthat has been completed.

Qi iThe objective of quantity surveying is to provide anaccurate bill of quantities, which is a list of the amountsof all materials and labour necessary to complete aconstruction project. In the simplified version, suppliedby the designer with the final design documents, thelabour requirement is not detailed. Sufficient accuracyfor the purposes of this bill can be obtained byincluding labour as a lump sum, or as the numberof hours or days of work, or as a percentage of thebuilding material cost.

A bill of quantities for a standard drawing oftenexcludes such operations as site clearance, excavationand fill, and external works, because such quantitiesmay vary greatly from one site to another and cantherefore be difficult to assess accurately at the time thedrawing is completed. Indeed, the bill for a standarddrawing may be a mere list of materials, perhaps with a

rough estimate of labour added.To avoid mistakes or the omission of any item,

sophisticated methods have been developed for quantitysurveying of large-scale projects. As rural buildings are

normally smaller and far less complex, a simplifiedprocedure will be adequate. Many rules of thumb orconversions have been developed to take into accountsuch factors as cutting waste, differences between

nominal and actual sizes, and breakages.

Taking-offThe objective of taking-off is to produce a detailed listof all materials and work. The quantities are assessed onthe basis of detailed project drawings and specificationsand listed, as far as possible, in the order that buildingconstruction will proceed. The first items are siteclearing, excavation and foundations and final items arefinishings and external works.

The dimensions of each item are obtained from thedrawings and then the quantity is calculated in the unitsin which the item is customarily sold or priced. For

example, excavation or fill, concrete, mortar and waterwould be in cubic metres, aggregates in cubic metresor tonnes, cement and lime in numbers of bags, andmany things such as bricks and blocks, windows anddoors, building boards and roofing sheets in numbersof units. Sawn timber is listed as the number of pieces ofa specific size or, where that is unnecessary, total linearor volume quantities. Round timber is listed as thenumber of units of a specific cross-section and length.

A particular item that occurs in several places ina building can be noted each time it occurs or thenumber of units can be totalled in one place. One way

of ensuring completeness is to tick off each item on thedrawing as it is listed.

Assessment of labourDetailed labour requirements to complete the type ofconstruction commonly used in farm buildings may bedifficult to find in published sources. This is becausethe contractors, who have the best knowledge of suchdata, use them as a means to compete for tenders. Also,most construction companies involved in rural buildingare too small to employ a quantity surveyor who couldcollect the data. Data published by quantity surveyorsor building contractors associations tend to emphasizeurban types of construction.

Rough estimates of the labour requirement neededby the designer of rural structures must be obtainedthrough experience and by analysing a number ofprojects similar to the one at hand. Where the farmerand the farm labourers construct a building, it is to beexpected that the labour requirement will be higherthan when skilled construction workers are used.However, farm labour is available without any extracash payment and there may be few alternative uses forit during the off-season.

Bill of quantitiesThe items for a bill of quantities are normally groupedtogether under headings for either the main operations(excavation, foundations, walling, flooring, roof


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structure, roofing, finishing and external works) or thetrades involved (earthwork, masonry, concrete work,

carpentry and painting). Work normally carried outby subcontractors (wiring, plumbing, installation ofequipment and furnishing) is listed separately.

The total quantity of each material or volume istransferred from the taking-off sheets to the appropriateheading in the bill of quantities and, while doing so,a percentage allowance for waste and breakage isnormally added. The percentage added will depend onthe type of material or volume but is often taken to bebetween 5 percent and 15 percent.

To keep a record of the items, they should be tickedoff on the taking-off sheets as they are transferred tothe bill of quantities. Labour may be listed under eachoperation or trade but, in the simplified bill, it is givenas a lump sum at the end.

Example:Prepare a bill of quantities for the poultry houseillustrated in Figure 9.2. Start with taking-off.

Footing and foundation for poles, concrete 1:3:6Footing, end walls 2 5.8 0 4 0.2 0.93 mFooting, side walls 2 7.6 0.3 0.15 0.68 mFoundation for poles 4 0.3 0.3 0.6 0.22 mWaste and spill 10% 0.18 m

2.01 m

The amount of ingredients can be calculated using thefigures in Table 5.13.

FloorBase layer of gravel 8.4 5.0 0.15 6.30 m

Sand for blinding 8.4 5.0 0.02 0.84 mConcrete (5% waste) 8.4 5.0 0.08 1.05 3.53 m

BricksArea of sidewalls,(0.6 + 0.2) (2.4 + 2.8 + 2.4) 2 12.16 mminus door opening 0.6 1.00 0.6 m

11.56 m

Number of standard bricks(0.215 + 0.010) (0.065 + 0.010) = 0.017 m per brick11.56 1/0.017 = 680 bricks

Area of gable walls 0.40 (2.0 + 0.4) 4 3.84 m5.0 (2.25 + 0.4) 2 26.50 m5.0 0.5 1.34 2 6.70 m

37.04 m

Number of standard bricks(0.1025 + 0.010) (0.065 + 0.010) = 0.0084 m/brick,37.04 1/0.0084 = 4 410 bricks

Number of bricks, 680 + 4 410 5 090Waste and breakage 15% 765Total number of bricks 5 855

Figur 9.2 Mi i

A

A

B B

ELEVATION

ELEVATION

PLAN

END VIEW

SECTION B-B

SECTION A-A

Door and frame

Foundation for pole300 x 300 x 600 mmconcrete mix 1:3:6

145 mm brickwall, plastered andwhitewashed on both sides

260 mm brickwall, plastered andwhitewashed on both sides

400 2 400 2 800

8 400

5

000

2

000

600

50

2 400 400

Purlin 50 mm gumpole

Corr galv steel sheet

Roof truss

Beam 100 mmgumpole

Pole 100 mmgumpole

80 mm concrete floormix 1:3:6

Frame for chicken wiresawn timber 50 x 50 mm

400

300

400

200


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Mortar, composition 1:1:6Sidewalls 11.56 m 0.025 0.29 mEnd-walls 37.04 m 0.051 1.89 mWaste and spill 15% 0.32 m

2.50 m

Plaster, cement plaster 1:5Plaster thickness 10 mm(11.56 + 37.04) 2 0.01 0.97 mWaste and spill 15% 0.15 m

1.12 m

The amount of cement and sand for the mortar andplaster can be calculated using the values in Table 5.17.

Wooden postsGum-poles 3.0 m, diameter 100 mm 4 pieces

Wood preservative 2 litres

TrussesGum-poles 4.0 m, diameter 100 mm 4 piecesBolts 110 mm long, diameter 8 mm 10 piecesBolts 200 mm long, diameter 8 mm 2 pieces

PurlinsGum-poles 3.0 m, diameter 50 mm 18 pieces

RoofingCorrugated steel sheets are laid in two rows on each

side and the covering width is 533 mm per sheet. Thelength of the roof is 9 metres.

9 000/533 = 16.9

i.e. 17 sheets are required per row, or a total of 68.

Roofing nails6 nails per m 68 m = 408. As each kilogram of nailsholds about 97, the requirement will be 4.5 kilograms.

Netting wallFrame, timber 50 50 mm , including 10% waste 51.8 mChicken wire 1 800 mm wide 16.0 m

DoorCasement, timber 75 75 mm, including 10% waste 5.5m

timber 25 100 mm 2.0 mDoor frame, timber 25 100 mm 7.7 m

subtotal timber 25 100 mm 9.7 m

10% waste 1.0 mTotal timber 25 100 mm 10.7 m

NailsStaples for fixing the chicken wire 1 kgWire nails 75 mm 1 kgWire nails 100 mm 1 kg

WhitewashWhitewash is required for 97 m

When all requirements are calculated, the amounts are

included in the bill of quantities as follows:

Table 9.2

Bi qii ( fi 9.2)

Im dii ui Q. r t

1. Foundtion, 2.01 m concrt, mix 1:3:6 (10 prcnt wst)

Cmnt 50 kg 9.0

Rivr snd (0.88 m) tonn 1.3

Crushd ston (1.8 m) tonn 2.9

2. Foor, grv (6.3 m) tonn 10.1

Snd (0.84 m) tonn 1.23.53 m concrt, mix 1:3:6 (5 prcnt wst)

Cmnt 50 kg 14.0

Rivr snd (1.6 m) tonn 2.3

Crushd ston (3.2 m) tonn 5.0

3. bricks (215 102.5 65 mm) numr 5 910

4. Mortr, 2.5 m, mix 1:1:6 (15 prcnt wst)

Cmnt 50 kg 13.0

lim kg 250.0

buiding snd (2.8 m) tonn 4.0

5. Pstr, 1.13 m, mix 1:5 (15 prcnt wst)

Cmnt 50 kg 7.0

buiding snd (1.3 m) tonn 1.8

6. Posts, gum-pos (3.0 m f 100 mm) numr 4

Wood prsrvtiv itrs 2.0


10/20


ciAs mentioned in the introduction to this section, it isnecessary to continuously assess the building costs fora proposed structure throughout the planning stagesof the building production process. Three levels ofaccuracy can be distinguished: general guidance cost,specific guidance cost and accurate costing.

In addition, costing is carried out during constructionto ascertain how the project is progressing from afinancial point of view and to determine any interimpayments to the contractor.

In the post-construction stage, the actual cost ofthe project should be calculated so that a record can beproduced that will enable future building work to beaccurately costed.

Unfortunately this is often neglected by designersand builders of rural structures.

General guidance costIn this case rough estimates, simply giving the scaleof costs, are derived by experience and analysis of anumber of other similar projects. For example, if the

Im dii ui Q. r t

7. Roof structur, gum-pos (4.0m f 100 mm) numr 4

Gum-pos (3.0m f 50 mm) numr 18

bots (110 mm f 8 mm) numr 10

bots (200 mm f 8 mm) numr 2

8. Roofing, corrugtd gvnizd iron shts

(CS 8/76 2.0 m, 0.018 mm) numr 68

Roofing nis kg 4.5

9. Ntting w

Swn timr (grd 3) 50 50 mm running mtr 51.8

Chickn wir, width 1 800 mm, mtr 16.0

10. Door, swn timr (grd 2)

75 75 mm running mtr 5.5

Swn timr (grd 2)

25 100 mm running mtr 10.7

Hings numr 2

ltch numr 1

11. Nis, stps kg 1.0

Wir nis 75 mm kg 1.0

Wir nis 100 mm kg 1.0

12. Whitwsh (97 m)

lim kg 50.0

Snd kg 10.0

Cmnt

13. Furnishings, fd troughs numr 4

Drinkrs numr 4

TOTal MaTeRIal COST

14. Trnsport cost for mtri

15. erthworks, xcvtion to v m

Rmov top soi m

excvtion for foundtion m

16. Construction mn-dys

17. extrn works

18. Contingncis

19. Suprvision nd contrctors ovrhd costs

TOTal COST

Table 9.2 (continued)

Bi qii ( fi 9.2)


11/20


costs of a number of grain stores are assessed and ineach case compared with the capacity of each storein tonnes, then a rough cost for grain stores can beestimated in terms of cost per tonne stored.

Hence an estimate can be given for a proposednew grain store if the capacity is known. Similarly, abuilding for dairy animals can be estimated if an averagecost per cow is known from a number of different units.

Furthermore, for particular types of construction,it is possible to obtain average figures in terms of floorarea. This type of estimate is based on a number ofprojects, some of which may not be directly comparable.

Specific guidance costsBy comparing similar projects, it may be possible toobtain reasonably accurate estimates before takingtime to design the building and work out the bill of

quantities. In this case, the costs of other buildingsshould be assessed in three components:

1. Established costs: costs that either have a fixedvalue or a uniform-unit value regardless of the sizeof the building. Examples are windows and doors.

2. Variable costs: costs that vary with the size of thebuilding. As the length of a building grows, itstotal cost will grow but, at the same time, the unitcost may decrease so that even though a buildingis 50 percent longer the cost increase may be only40 percent.

3. Additional costs: costs such as fees for consultants,

architects, lawyers and accountants. Interest,insurance, fitting costs and losses should also beincluded.

Therefore, if a number of similar buildings areanalysed, good estimates of each of these types of costsmay be obtained and reliable specific guidance costs canbe determined.

Accurate costingThis is done in conjunction with the bill of quantities.An accurate total cost of a job can be derived from therate column in the final bill of quantities, together withthe cost rate for each item. This requires each individualitem of material, volume or labour to be costed.

However, for convenience and to facilitate thecalculation of a quotation, many building contractorsderive a cost per quantity of common types ofconstruction. For example, a cost per square metre ofconcrete block wall will include the cost of the blocks, thelabour to mix mortar, the cost of mortar materials and thelabour required to lay the blocks. It may even incorporatea factor taking into consideration the average requirementof window and door openings and scaffolding.

However, costing with this degree of detail requiresconsiderable information that can only be gained

from experience and data that have been collectedand analysed over a number of building projects. Theunit costs will have to be reviewed continuously or becorrected with an index for building costs.

econoMIc feasIBIlItyIn addition to the actual cost of constructing a building,which must be considered in relation to the financialcapacity of the farmer, the total annual cost of the

building should be determined. When the annual costis then compared with the expected increase in incomeor the saving in storage costs, it forms the basisfor deciding whether or not the new building is aworthwhile investment, i.e. it determines the economicfeasibility of the building.

To derive the true annual cost of a building, anumber of factors must be considered. These includethe estimated life of the building, annual repairs andmaintenance, interest on the investment, insurance and,in some countries, real estate taxes. With the possibleexception of repairs and maintenance, these are fixedcosts that occur whether or not the building is used.

Consequently it is important to plan carefully both theuse of the building and the construction.

The building may be considered as a production cost,and the potential income from the enterprise housed init must be sufficient to justify the cost of building. Itshould be stressed, however, that there may well bereasons other than economic ones for constructing abuilding. For instance, a dwelling cannot be justified interms of profitability alone as aspects such as amenityand welfare considerations may outweigh other factors.

Bii i (ii i)

Physical lifeAll building components have a limited life. After a time,materials will deteriorate to a point where they can nolonger fulfil their function. While repair, replacementand maintenance can extend the life, eventually theoverall deterioration becomes excessive.

The life span of a building is influenced by its designand construction. In general, more costly materialssuch as steel and concrete are likely to last longer thantimber and other organic materials. The physical life ofrural buildings may range from two to five years for thesimplest structures and as much as fifty years or morefor substantial ones. An average figure is between 10and 20 years.

Economic lifeAlthough a building may last for many years, it maycease to be economically sound at an earlier time for anyof several reasons. It may be that the design has becomeobsolete and is not suitable for new mechanization; orperhaps it is too small because the farm has grown;or a new enterprise requires a new layout or interiorpartitions, but supports simply cannot be moved toaccommodate the new requirements. General purpose

buildings will therefore have a longer economic lifethan those built for a specific enterprise.


12/20


Write-off lifeIt is impractical to expect any enterprise to pay thefull cost of a new building in the year immediatelyfollowing construction. Therefore the capital cost of the

building is allocated or depreciated over several years.The number of years is determined by the write-off life,that is to say, the number of years over which it seemsfeasible to spread the original cost, but never fewer thanthe duration of a loan. In addition, the write-off lifemust not exceed the estimated physical or economic lifeto avoid being in possession of a useless building forwhich the original cost has not yet been fully paid.

As economic conditions change rapidly, the riskof a large investment is reduced considerably if thedepreciation can take place over a relatively shortwrite-off period. Ten years is considered short, 15 to 20years medium, and 20 to 30 years a long period. This

means that a building that is still physically sound andeconomically practical after the depreciation has beencompleted can be considered an economic bonus forthe farm.

For cost estimation, depreciation is usually calculatedon a straight-line basis, that is to say, equal annualamounts over the write-off life. The annual straight-linedepreciation cost is the original cost of the buildingdivided by the years of write-off life. There are a numberof alternative methods for assessing depreciation, mostof which result in higher costs in the early years anddecreasing costs over the life of the building.

IThe cost of the money used to construct a buildingmust be considered, whether the financing is by meansof a loan or by cash at hand. If money is borrowed,the interest cost is obvious. However, if farmers investtheir own money, they are foregoing interest incomefrom a bank or the possibility of other investments.Consequently, interest is still a real expense and shouldbe included as an annual building cost.

The interest rate used is either the rate actually beingpaid or the prevailing rate for mortgage loans in thearea. The interest charge is assessed during the yearsof depreciation and, during that period, the amountinvested (principal) is gradually written off, from thefull cost at the start to zero at the end.

Therefore the annual interest charge is usuallybased on the rate, multiplied by the average investment(original cost divided by two, or the original cost andhalf the rate). It should be pointed out that both a long-term mortgage with equal monthly payments (interestplus principal) and compound bank interest will resultin higher interest costs.

ri mi

Although all buildings will require some maintenance,the cost will vary with the type of building, the climateand environment, the materials used in constructionand the use of the building. Although the cost for

repairs and maintenance will vary from one year to thenext and generally increase with the age of the building,it is common practice to assume a uniform annualallowance throughout the life of the building.

It is typical to allow between 1 percent and3 percent of the initial construction cost for repairs andmaintenance. While this is true in a monetary economy,it may not apply in a subsistence economy.

I xIf an owner carries insurance on buildings to coverthe risk of fire and other hazards, then the cost of thatinsurance is included as an obvious annual cost. On theother hand, if farmers choose not to take out insurance,they are in reality carrying the risk themselves andshould still include an annual charge for insurance.Insurance will ordinarily range between 0.5 percent and

1 percent of the original cost.In countries where an annual real estate tax is levied,

the taxes must also be included as an annual buildingcost. Taxes will range from zero, where there are none,up to 1 or 2 percent of the original cost of the building.

a The five principal components of the annual cost of abuilding have been discussed in some detail. A varietyof situations produce a rather wide range in the annualcost figures. The greatest variation occurs in the write-off period. This is influenced by the life of a loan,

the life of the building and, in some cases, simply thearbitrary decision of the farmer.

In the following examples, all the low-range valuesare combined, as are all the high-range values. Itshould be pointed out, however, that they may occurin any combination. A high depreciation cost and lowmaintenance or low interest is perfectly possible.

l Mim hi

Dprcition 3.5 (29 yrs) 6.25 (16 yrs) 10 (10 yrs)

Intrst* 3 5 7

Mintnncnd rpirs

1 2 3

Txs 0 1 2

Insurnc 0.5 0.75 1

Tot nnucost s prcntgof th origincost

8% 15% 23%

*Not: Th intrst rt is hvd, s ordinriy intrst is sd

on th vrg vu or on-hf of th origin cost.

Having determined a write-off life and thecorresponding depreciation percentage, as well asprevailing values for the other costs, the total percentageis multiplied by the original cost of the building to


13/20


obtain the annual cost. Next an estimate is made ofthe net income from the enterprise to be housed andthe result compared with the annual building cost.The income should more than cover the building cost,

allowing for a reasonable profit.It should be noted that an existing building alreadyhas annual costs and that it is the increased cost of areplacement building that is compared with an increasedincome. If the plan is for an entirely new building tohouse a new enterprise, then the totalannual buildingcost is compared with the total net income from theenterprise.

c mThe annual cost for a building, as illustrated in theprevious section, includes the capital cost in the formof depreciation as well as the carrying cost or interest.

If the farmer is fortunate enough to be able to payall or most of the original cost of the building, thena comparison of annual building costs with incomeindicates the length of the period over which the farmercan expect to recover the investment. However, if thebuilding project has to be financed largely by a loan,then cash flow and the ability to repay both capital andinterest charges must be considered.

Any grantor of a loan will usually demand thatrepayments start immediately but, owing to theproblems commonly experienced by farmers in startingup production in a new building, the earnings at this

stage may be lower than expected. In the case of animalhousing, the capital needed to purchase animals, feedand equipment is often larger than anticipated. Theresult may be insufficient cash during the first few yearsafter the building has been constructed.

Even where a careful analysis has shown theenterprise to be profitable, that is to say, it has shownthe expected average annual cost to be lower than theexpected average income, the combined interest andprincipal payments on a long-term loan are likely toexceed the estimated average annual costs.

This makes it important to determine not onlywhether the cost of a new building can be justified, butalso whether the necessary cash flow can be generatedto cover both interest and capital repayments. Whilethis is more of a business-management problem thana farm-structures problem, it is no less important to afarmer contemplating a new building.

organIzatIon for constructIonof sMall BuIldIngsIn the case of farm structures, the future proprietor the farmer is normally much more directly involvedin any repair or construction process than would bethe case with a building in an urban area. Although the

farmer may appoint an advisor to help with planningand design, employ a contractor or local craftsmen andtake out a loan to finance the construction, the familysparticipation at all stages will normally be of great

importance and serve to reduce the amount of cashnecessary for the project.

Depending upon the level of self-involvement bythe farmer, the family and any farm labour, and the

way in which the construction is administered, fourforms of organization can be distinguished: personalmanagement; divided contract; general contract andturnkey contract.

fm iiPersonal management is a very common form oforganization for repair work and construction of small-to medium-size rural buildings. The work is carried outby the employer (the farmer and the family), with theassistance of farm labourers and temporarily employedcraftsmen. The employer may simply administer thework or participate in the construction work.

Figur 9.3 p mm

A divided contract implies that the employerengages different contractors for the constructionwork and for installation and fitting work. This formof organization differs from personal managementmainly in that the building construction work iscarried out on a contract.

Self-involvement by the farmer can be arrangedeither by excluding some operations from the contract,such as earthwork and external work, or by givingthe farmer some form of employee status with thecontractor. The latter is more easily arranged whena running-account payment system is used for thecontract (see section entitled Forms of payment).

Building materials may be purchased by either theemployer or the contractor. The contractor for thebuilding construction work may be appointed to act asa coordinator for the various contracts.

Bu

ildingworkers

Supplie

rs

Insta

llat

ion

con

tra

ctors

Consultants

Builder

Construction work

Materials Workand

materials

DrawingsSpecifications

Bills of quantitiesCost estimates


14/20


Figur 9.4 dii

A general contract implies that the employer engagesone contractor to carry out all the building constructionoperations. The contractor may in turn engagesubcontractors to carry out work, such as fittings andinstallations, which the contractor lacks the skills orcapacity to undertake. This form is uncommon for farmbuilding construction, except for large projects.

A turnkey contract differs from the general contractin that the planning and design of the building is alsoincluded in the building contract. This form is veryrare for rural building construction, except perhapsfor completely prefabricated buildings in which themanufacturer serves as the contractor for erection.

Figur 9.5 g

Bu

ildingcontractor(s)

Insta

ll.contr.

Supplie

rs

Consultants

Builder

Construction work

Materials Workand

materials



Generalcontracto

r

Supp

li

ers

Insta

ll.contractors

Consultants

Builder

Construction work

Materials

Workand

materials



Figur 9.6 tk

fm mThe contract or agreement between an employer anda contractor may state that the payments for thecontracted work will be made at a fixed price, withor without instalments for work completed, or ona cost-plus basis up to a ceiling figure, or with arunning account for cost of materials purchased, plus

an agreement on labour costs.A fixed price is common for general and turnkey

contracts, and is often used for divided contracts.The advantage of a fixed price to the employer isthat the cost of the construction is known at anearly stage. However, the contractor will requirecomprehensive documentation in the form of drawingsand specifications to be able to give a quotation for afixed-price contract.

Incomplete documentation will cause problemsand frequent negotiations to decide on details andvariations, usually involving additional expenditure.Therefore a running account is frequently used in caseswhere the documentation is insufficient or where it isdifficult to make a satisfactory description of the workbeforehand, as with repair and maintenance work. If aceiling is placed on the running account, the employerwill be guaranteed a maximum cost and will benefit,compared with a fixed price contract, should the workbe less costly than the stated maximum.

tenderIngThe objective of tendering is to obtain proposalsfor construction work from different contractorsand quotations for building materials from different

suppliers. Competition between suppliers to submit themost favourable offer should result in a less expensivebuilding for the farmer.

Turn

-keycontractor

Supp

li

ers

Insta

ll.contractors

Consultants

Builder

Construction work

Materials

Workandmaterials




15/20


t When the farmer has decided to proceed with theproposed structure, the farmer and the advisors willprepare the tender documents, which usually comprise

a letter of instructions, the necessary drawings andspecifications and perhaps a bill of quantities, and willsend them to various contractors and suppliers.

A contractor, or an estimator, will cost all buildingmaterials, volumes and labour and, after adding anallowance for supervision, overheads, insurance,contingencies and profit, will prepare a tender that issent to the prospective employer in a sealed envelope.

During preparation of the tender, the contractor willvisit the proposed building site to consider possibledifficulties, in particular: access to the site and theneed for temporary roads; storage of materials; type ofground; arrangements for siting any temporary office

or welfare buildings; availability of labour in the area;arrangements for protecting the works against theftand vandalism. The contractor may also request fullerwritten documentation from the employer and, wheresubcontractors are to be employed, obtain tenders fortheir work.

A supplier of building materials or equipment willrequire less documentation and usually will not have tovisit the site in order to prepare a quotation. The offermay or may not include transport to the site.

When the reply period specified in the tenderinstruction has expired, all the sealed envelopes

containing the offers from the contractors and suppliersare opened. The contractors/suppliers may be invitedto attend the opening of bids and be given names,prices and other relevant information contained in theoffers. After careful evaluation of the offers, the mostfavourable, which will not necessarily be the cheapest,is accepted and a contract is prepared.

M iOpen tendering: The prospective employer advertisesin the press, giving brief details of the work, andissues an open invitation to contractors to apply forthe necessary documents. The advertisement shouldstate that the employer is free to select any or none ofthe bids that may be tendered. Tenderers are normallyrequired to submit references and to pay a deposit forthe documents, which will be returned on receipt of aserious tender. Open tendering is uncommon for ruralconstruction work.

Selective tendering: Competitive tenders areobtained by drawing up a list of three to five seriouscontractors or suppliers in the area and inviting themto submit quotations. Normally the farmer and theadvisor will know of a sufficient number of contractorswho have the skill and experience to construct farm

buildings and are also known for their integrity. Hencethe lowest tender can usually be accepted.

Negotiated contracts are obtained by contacting oneor two contractors or suppliers who have been found

satisfactory in the past. The price for carrying out thework or delivering the material is negotiated until anagreement is reached. Negotiated contracts are alsocommonly used where the magnitude of the contract is

not known at first, such as repair work, excavation inunknown ground, or where the tender documents areinsufficient.

In such cases, the negotiation will normally aim atestablishing reasonable task rates for a contract, witha running account. With a fixed contract, a contractorwould have to safeguard against the unexpected and alarge allowance for unforeseen expenditure would leadto a high contract price.

ei Quotations submitted to the prospective employer arelikely to contain reservations, exceptions, additions and

other conditions for the work or delivery of materials.A contractor may also suggest an alternative design orbuilding method. If the letter of instructions for tenderstates that all such divergences from the tender documentsshould be priced separately, it will be quite simple torecalculate the tenders so that they are comparable. Inother cases they will have to be costed by the employer.

The letter of instruction will normally ask thecontractor to submit references from similar projectsconstructed in the past. For large projects, a bankreference and a performance bond are advisable. Theseshould be examined to establish the contractors practical

and financial ability to undertake the proposed work.

contractsA contract is a legal document signed by both partiesbefore witnesses. The essence of a contract forconstruction work is the promise of a contractor toerect the building as shown on the drawings, and inaccordance with the detailed specifications, in return fora specified amount of money known as the contract sum.A variety of standard forms are available for buildingconstruction contracts, but it would be desirable todevelop a standard contract form specifically applicableto rural building construction.

If a bill of quantities is included in the documentsattached to the contract, the employer will be responsiblefor any errors of measurement or shortcomings thatoccur in the bill. However, the selected contractor canbe asked to check the bill and accept responsibility forit as being final. In the case of contracts without a billof quantities, the bill is prepared by the contractor andany errors are then his responsibility.

A standard contract form may include the followinginformation, but each clause in it should be studiedprior to signing, and any clause that fails to meet thespecific requirements of the project should be modified

or deleted:1. Names and addresses of employer and contractor.2. List of all attached documents, i.e. drawings,

specifications and bill of quantities.


16/20


3. Amount of the contract sum.4. Starting date and completion date.5. Weekly penalty to be paid should the contractor

fail to complete the work on time. (Not always

included.)6. Directions for the employer to make a fair andreasonable extension of time for completionshould the work be delayed through any causebeyond the contractors control.

7. Directions for the contractor to comply with allapplicable rules and regulations issued by localauthorities.

8. Directions for the contractor to arrange regularsite meetings between the contractor and theemployer and to keep a diary detailing progressof the work. (Not always applicable.)

9. Directions for the contractor to obtain the

employers approval before any work is executedthat diverges from the drawings or specifications,in particular where the variations involveadditional expenditure.

10. Reference to a list of any building materials andequipment that will be supplied by the employer.

11. The extent of the contractors responsibility forany liability, loss or claim arising during theexecution of the contract work, whether forpersonal injury or loss or damage to property.

12. Insurance requirements for the contractor.13. Statement requiring the contractor to pay, at his

own expense, for any defects or faults arisingfrom materials or workmanship that are not inaccordance with the drawings and specifications.

14. Statement requiring the contractor to pay, at hisown expense, for any hidden defects or faultsthat may appear during a specified guaranteeperiod, usually 3 to 12 months, after the contractwork has been completed.

15. Payment schedule, describing the percentage ofthe contract price to be paid on completion ofeach step.

16. Guarantee amount: normally about 10 percent ofthe contract sum is withheld until the guaranteeperiod has expired or all defects are corrected,whichever is later.

17. Procedure for resolving disputes between thecontractor and employer, e.g. that they shall bereferred to arbitration for a binding decision.

18. The signatures of the contractor, the employerand witnesses.

specIfIcatIonsThe specifications document supplements the drawings.The drawings should describe the geometry, locationand relationships of the building elements to one

another. The specifications set out quality standards formaterials, components and workmanship that cannotbe written on the drawings.

For example, if the drawing states that concreteType 1 should be used for a floor, the specifications mayset out a mixing ratio, quality standards for aggregateand water, compaction and curing practices, and quality

standards for joints and finish.Minimum requirements for capacity and reliabilityof equipment, as well as calculations relating todesign, insulation, ventilation, etc., may be included asappendices. While in small projects, which are typicalof numerous rural structures, many of the specificationsmay be included on the drawings, in large-scale projectsthe specifications may run to scores of pages.

g iiiAs much of the information in the specificationswill be similar from one project to another, it canbe generalized to apply to most buildings. In many

countries, the building industry or government agencieshave therefore developed a General specification forbuilding works. This normally covers the majority ofmaterials, types of construction, fittings, furnishings,etc. for the types of buildings and other structuresbuilt in urban areas. While some of the informationincluded may also apply to rural structures, in generala list of specifications will need to be developed for theparticular structure.

The advantages of using a general specification arethat all parties are expected to have access to a copyand that they are familiar with the quality standards

required in the various sections. Any planner/designerpreparing specifications for a building may refer to thesection numbers in the general specification withoutrepeating the text of those sections. In addition,particular specifications that supplement, amplify oramend the provisions of the general specification willbe required for each specific project.

To avoid confusion arising from discrepanciesbetween the various building documents, the drawingsnormally prevail over the general specification,particular specifications override both drawings andthe general specification and building code regulationsoverride all other documentation.

Occasionally, when the government is the employeror when buildings are financed with government loansor subsidies, the general specification is consideredstatutory, but in all other cases its provisions can beused and amended as and when required.

progress chartA progress chart is a schedule, used to coordinate thesequence and timing of the operations in a buildingproduction process. It helps to ensure a timely supplyof manpower, materials, equipment, machinery andsubcontracted services by providing information on

which dates and in which quantities they will berequired, so that they can be ordered in good time. Itcan also be used to monitor the progress of the workand ensure compliance with the schedule.


17/20


The chart is often divided into three parts: The first part is produced by the farmer or

an advisor and covers all work up to the timesite operations start. It includes the sketches,

any applications to authorities, final workingdrawings, tendering and ordering. The second part is normally produced by the

contractor and includes all site improvements andconstruction operations (see Figure 9.7).

The third part covers the start-up of productionin the building and is developed by the farmerand advisors.

The preparation of a progress chart starts withlisting all operations and their expected duration andidentifying operations that must follow each other insequence.

In the second step, a chart is developed showing theinput of labour, machinery and equipment for various

operations until the completion date is met. Whiledoing this, it will be noticed that there is a sequence ofoperations called critical operations that must followeach other in a specific order and together determine

the total time required to carry out the work.In the third step, the requirements in terms ofresources, in particular labour, and to a lesser extentmachinery, are adjusted so that a fairly uniformworkforce can be maintained. This is done by amendingthe timing and sequence of operations that can takeplace partly or wholly at the same time as the criticaloperations.

The fourth step consists of monitoring the work,in particular the critical operations, and revising theprogress chart as problems or delays arise, e.g. delayedreplies from authorities, contractors or suppliers;delayed delivery of materials and subcontracted

services; delays in site operations owing to prolongedbad weather.

Figur 9.7 p

ACTIVITYWeek no.

Site clearing

Setting out

Remove top soil

Excavation for foundation

Footing

Foundation wallPlace main post

1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

2

3

4

5

6

7

Rafters and purlins8

Roofing9

Filling for floor slab10

Formwork for floor slab11

Casting floor slab12

Walls13

Partitions14

Feed troughs15

Doors and windows16

Guttering17

Backfill to foundation18

Furnishing19

Wiring20

Finishes21

Excavation - urine tank22

Construction - urine tank23

Access road24

Making good and finishes25

Work complete

Order placed for material Subcontractor contracted Prefabrication at site


18/20


InspectIon and controlWhenever a building is constructed, it is likely thatfaults and defects will occur as a result of such factorsas deficiencies in the building materials, negligence

by workmen and mistakes in the drawings andspecifications. Occasionally a contractor may betempted to increase the profit by knowingly producinginferior work. To avoid this as far as possible,the employer or a person experienced in buildingconstruction (appointed by the employer) should actas an inspector during site operations. Control isnormally carried out continuously as the constructionwork proceeds. In addition, more formal inspectionsare required upon completion of a contract and at theend of any guarantee period to determine whether thecontracted payment should be made.

The duties of the inspector include the following:

1. To ensure that the contractor complies withthe drawings, specifications and contractualprovisions for the project.

2. To ensure that the project progresses accordingto schedule.

3. To inspect and control all materials deliveredto the site and to reject any that fail to meet thespecified quality.

4. To reject work that does not comply with thecontractual quality and to stop work whencontinuation would result in substandard work.

5. On behalf of the employer, to interpret drawings,

specifications and contractual provisions, andto act on the employers behalf concerningvariations.

safety at BuIldIng sItesAccidents may be caused by falling objects, falls resultingfrom unstable scaffolding or ladders or inadequateguard rails. Unguarded machinery, hazardous materials,carelessly maintained electrical wiring and equipmentcan also result in injury. Excessive haste may contributeto accidents and to wasteful, poor-quality work.

Most accidents can be avoided and safety standardsimproved considerably with little or no expense if thefollowing basic safety precautions at the building siteare observed:

1. Storing materials and tools in an organized fashion,with none left scattered around the building site.

2. Ensuring that tools, machinery and equipmentare well maintained, with all guards coveringmoving parts in place.

3. Maintaining a clean and tidy building site withthe removal of all waste, particularly scrap timberwith protruding nails.

4. Making sure that all operators have been carefullyinstructed in the use of machinery and the

handling of hazardous materials.5. Insisting that all workers wear suitable clothing

and protective gear, such as hard hats, hard-toeshoes and safety glasses.

6. Using properly designed, supported and bracedscaffolds, ladders and platforms.

7. Establishing and enforcing rules as to wherepeople can work while elevated members are

being installed.8. Making sure that all temporary wiring andelectrical equipment is well maintained andgrounded, and is properly used.

9. Having a good safety programme and makingworkers aware of hazards and how to avoidaccidents.

10. Maintaining suitable first-aid equipment andsupplies, and making sure workers know how touse them, to minimize the effects of any accidentsthat do happen.

BuIldIng MaIntenance

Buildings deteriorate as a result of age, weathering anduse. This necessitates maintenance and repair to ensurethat the building retains its appearance and remains ina serviceable condition. Cleaning, repainting, reroofingand replacing or repairing broken parts, such as windowpanes and roof tiles, help to maintain the original valueof the building.

Maintenance costs can be kept down by usingmaterials that are suitable for the climatic conditions andwith which local builders are accustomed to working.Furthermore, the building should be simple in detail,have easily replaceable parts and be free of unnecessarily

complex or sensitive technical installations.The fabric of a building should be thoroughly

inspected once or twice a year to assess the performanceof the different elements of the building. The inspectionwill result in a list of repair and maintenance jobs thatshould be carried out promptly, because insufficientor delayed measures will accelerate deterioration.Although maintenance work is usually carried out bythe farmer, in the case of large repairs it may be carriedout by hired building workers or a contractor. Whena contractor is engaged, payment is often made on thebasis of time and materials used according to an agreedschedule of prices.

revIew QuestIons1. Define building production.2. When does the building production process

begin?3. Briefly describe the various types of prefabrication.4. Outline the role of a quantity surveyor in the

building production process.5. Describe the terms take-off and bill of

quantities.6. Briefly describe the building costing process for

rural structures.

7. Differentiate between the physical life and theeconomic life of a building.

8. Briefly describe the tendering process in buildingproduction.


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9. Outline the three types of tendering that are usedin building construction.

10. Describe the progress chart as used in buildingproduction.

11. Explain the role of inspection and control inbuilding production.12. Describe some of the safety standards that should

be observed on a building site.13. Why is it necessary to maintain a building?

further readIngChapell, D. & Willis, A. 2010. The architect in practice.

10th edition. Oxford, Wiley Blackwell.Fullerton, R.L. 1978. Building construction in warm

climates. Part 2.Oxford, Oxford University Press.Harrison, L.G, III & Lstiburek, J.W. 2009.ASHRAEguide for buildings in hot and humid climates. 2ndedition. ASHRAE.

Miles, D. & Sygga, P. 1987. Building maintenance:a management manual. Revised edition. ITDGPublishing.

Miles, D. 1978. Accounting and bookkeeping for thesmall building contractor, Practical Action.

Miles, D. 1979.Financial planning for the small buildingcontractor. Practical Action.

Miles, D. 1980. The small building contractor and theclient. Practical Action.

Osbourn, D. & Greeno, R. 2007. Introduction tobuilding. 4th edition. London, Pearson Education,Prentice Hall.

Seeley, I.H. & Winfield, R. 1998. Building quantitiesexplained (building and surveying). 5th edition.Palgrave Macmillan.

Willis, A.J. & Willis, C.J. 1980. Practice and procedurefor the quantity surveyor. 8th edition. London,Granada Publishing Ltd.


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