Approximate Estimate - tendering and contract estimation

8/3/2019 Approximate Estimate - tendering and contract estimation

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Presented by-Karan Avad

Vinayak KendreRohan Desarda

Apurv VaidyaGaurang Malviya


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Introduction The only safe and secure way of estimating construction

costs is to take out the quantities of works under thedifferent items and multiply these quantities by the

prevailing unit rates as per the DSR issued by the PWD. However, this can be done only when drawing,

specifications and bill of quantities have been preparedand made available to the contractor.

When accurate cost of construction is not yet required anda rough idea is sought at some stage to help decisionmakers decide whether to proceed or not, approximateestimates of construction cost are used.


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Purposes served by Approximate Estimation

To Give a rough idea of the probable expenditure- A rough idea of the probable expenditure has to be

obtained and if this appears feasible, then further detailsmay be considered.

Administrative Approval

In case of government and public works, proper sanctionhas to be obtained for allocating the expenditurerequired for detailed investigations, which is given based

on approximate cost estimating methodValuation and rent fixation

Sometimes it is required to estimate the cost of existingstructure for one or more reasons, in these cases theapproximate methods are adopted


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Methods of Approximate

Estimating Service Unit Method

Square meter of floor area

Cubic meter of the building Rough grouped quantities

Comparison of costs at relative dates


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The service unit method Buildings are constructed to serve a specific purpose.

For example, hospitals are designed to accommodatecertain number of beds. Each bed is then considered asa Service Unit.

Whenever a building is constructed, the Engineer orArchitect keeps record of the place, actual cost,number of service units and year of construction etc.

From this record it is possible to work out per service

unit. This cost is then adjusted to present day considering

inflation and peculiarities of project and multiplied bynumber of units


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Service Unit Method (Total Cost)

Total cost = cost per unit x number of units


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Floor Area Method The floor area of the proposed structure is worked out

and then multiplied by a suitable rate.

This rate of construction per square meter of floor area

is worked out by dividing the known cost ofconstruction of a similar building by the floor area ofthat building

The building must be first measured by its internal

dimensions at each floor level and no deductions aremade for internal walls, ducts, lifts or stair cases.

There are some variations of this method asmentioned in the next slide


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Floor Area method (Variations) One way is to add all the usable f loor areas and exclude

basement and roof

Another way is to use certain rate for each floor,including roof and basement

Using different rate for basement floor, other floorsand roof

Another way is to have the unit rate of the lower floorinclude basement and foundations and that for the topfloor include roof


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Floor area method (Total Cost)

Total cost = cost per square meter x totalproject area.


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The Cube rate method This method is more accurate than the square meter

method because the depth of foundations and the height ofthe structure above the ground level are the additionaldimensions taken into consideration.

In order to use the method, the building volume must befirst assessed

Buildings with distinct types of occupation should havecorresponding volumes assessed separately, for example,car park areas, shopping areas and office areas in a

commercial building This method depends on a number of variables, like

building types, proportion of wall area per floor area,quality of finishes and so on


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Cube rate method (Total Cost)

Total cost = cost per cubic meter x totalproject volume.


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Rough grouped quantities This method aims at overcoming the problems detected in

other single-rate estimating methods, by taking intoaccount variations in plan shape and storey height.

Though, this method was never totally adopted by

construction professionals because it requires much morecalculations than other single-rate methods and becausethe rates needed cannot be directly extracted fromhistorical data.

Basically, the utilisation of the method starts with themeasurement of the building enclosure (comprising floors,external walls and roof areas). Each area is then multipliedby an appropriate weighing factor, thereby resulting the

number of storey enclosure units


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Rough Grouped quantities

(weighting factors) Floor areas, measured from the internal face of

external walls: basements x 3;

Ground floor x 2; first floor x 2.15; second floor x 2,30and add 0,15 for each successive floor.

Roof areas, measured in its plan projection, to theextremities of eaves: roof x 1.

External wall areas, measured on the external face ofthe walls: basement wall area x 2;

Above ground level (without any deduction foropenings x1.


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Rough grouped quantities (Total

Cost)

Total cost = unit cost rate x number ofstorey enclosure units


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Comparison of Costs Method The approximate cost of the proposed structure is

found out by modifying the known cost of similarexisting structure with due consideration to pricefluctuation between the dates of construction of theold and proposed structure.

This method gives best results but it is applicable tostructures which are repetition of similar works.


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Approximate Estimate - tendering and contract estimation