Preliminary Estimate | estimate in construction

Preliminary Estimate | Numericals of Preliminary Estimate

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Preliminary estimate is an estimate to seek out an approximate cost in a short time. It is also known as a rough estimate made in the early stage of design work in any project.

Based on the practical experience of carrying out similar works in the past and their rates, the preliminary estimate is prepared. This estimate is enclosed with a brief report of the project including its necessity, utility and the layout plan.

The preliminary estimate is also prepared for renovation works and demolition works. It can also be carried out in the absence of drawing and specification.

Generally, the preliminary estimate is provided by contractors and builders to the owner. More details provided by owner results in more accuracy of the estimate.

The preliminary estimate is prepared for buildings, roads, irrigation channels, etc.

For Roads: Rate per kilometres is provided based on the thickness, materials and width of the pavement.

For Buildings: Rate per square feet or square meter is provided based on the type of constructions and materials used.

For Irrigation Channels: Rate per km is provided based on the type of channel.

 

Steps in Determining Preliminary Estimate Cost in Buildings  

a. Determine the plinth area of the building. For multi-storeyed building; determine the plinth area of each storey.

b. Calculate the building cost by multiplying the plinth area and rate per square meter.

Building Cost = Plinth Area *  Rate per square meter

c. Determine the cost of services that are based on building cost.

For eg: Cost of electricity is 10 % of building cost and building cost is 20,000 $ then;

Cost of electricity = 0.1 * 200 = 2,000 $

d. Determine Overall Cost by adding building cost and services based on building costs.

Overall cost = Building Cost + Services based on building cost 

e. Determine the cost of services based on the overall cost.

E.g. Cost of sanitation and water supply is 5 % of the overall cost and overall cost is 50,000$ then

Cost of sanitation = 0.05 * 50,000 = 2500 $

f. Always take the cost of contingencies and supervision between 7 to 12 % of the overall cost.

g. Calculate total cost by adding overall cost, services based on overall cost and cost of contingencies and supervision.

Total Cost = Overall cost + Cost of services based on overall cost + Cost of contingencies and supervision

 

Steps in Determining Preliminary Estimate Cost in Roads

a. Determine the length of the road.

b. Select the rate per km based on the thickness, materials and width of the road.

c. Calculate the overall cost by multiplying the length of road and rate per km.

Overall cost = Length of road in km * Rate per km

d. Calculate the cost of supervision and other technical services (like the cost of tests performed ).  Generally, 10 to 30 % of the overall cost is taken for this.

e. Determine total cost by adding overall cost and cost of supervision and technical services.

Total cost = Overall cost + Cost of supervision and technical services

 

Note: Preliminary estimate of irrigation channel is same as an estimate of road. 

 

Advantages of Preliminary Estimate

a. To get surface detail about the approximate cost of construction.

b. It helps the client in choosing the best contractor in terms of economy.

 

Preliminary Estimate Includes

a. Date of Estimate.

b. Approximate cost of construction.

c. Cost of different categories like water supply and sanitation, electricity, contingencies, etc.

d. Some detail (like name, signature, etc)  of preparing person.

 

Numericals of Preliminary Estimate – Buildings

 

1. Prepare a preliminary estimate of a building having plinth area equal to 1600 square meter.

Given that

i. Plinth area rate= $ 200 per m²

ii. Extra for architectural work=  1 ½ % of building cost

iii. For electrical installation= 10% of building cost

iv. For water supply and sanitary installation= 5% of the overall cost


Solution,

i.
1m² rate cost = $ 200

1600m² rate cost = 200×1600 = $ 320,000

∴ Building cost= $ 320,000

 

ii.

Extra for architectural work=  1 ½ % of building cost

= 0.015 * 320000

=  4,800 $

 

iii.
For electrical installation,

= 10 % of 320000

= 0.1 * 320000

= 32,000 $

 

Overall cost = 320000 + 4800 + 32000

= 356,800 $

iv.

For water supply and sanitary installation= 5% of the overall cost

= 0.05 * 356800

= 17,840 $

 

Again,

Note: mostly 10 % of overall cost is assumed for supervision & contingencies 

Contingencies and supervision charge = 10% of 356800

= 35,680 $

 

Total cost = 356,800 $ + 17,840 $ + 35,680 $
= 410,320 $

 

2. Prepare a preliminary estimate of a multistoried office building having carpet area 1600 m². The circulation area is 30% of the building and 10%  is occupied by the wall area. The rate is $ 70 per m². The cost of electricity and sanitary installation is 10% of the building cost. External services are taken as 2% of building cost. Contingences and supervision charge 4% and 5% of overall cost respectively.

Solution,

Let x be the plinth area.

Plinth area = carpet area + circulation area + wall area

x = 1600 + 30% of x + 10% of x

x = 1600 + 0.4x

x – 0.4x = 1600

x = 2666.6 m²

 

Building cost = 70 × 2666.6

=  $ 186,662

 

Cost of electricity and sanitary installation,

= 10% of 186662

= 18,666.2$

 

External services = 2% of building cost

= 0.02* 186662

= 3733.24 $

 

Overall cost= 186662 + 18666.2 + 3733.24

= 209061.44 $

Cost of contingencies and supervision =  9% of 209061.44

=  18815.53 $

 

Total = 209061.44 + 18815.53

= 227876.97 $

 

 

Numericals of Preliminary Estimate – Roads

 

1. Find the preliminary estimate of the road having a length of 10 km. The width of the road is 8 m and the thickness is 0.2 m. The rate per km for the given road is 8,000$.

Solution,

Overall cost = Length of road in km * Cost per km

= 10 * 8000

= 80,000 $

 

Note : Take 10 to 30 % of the overall cost for supervision and technical services

Cost of supervision & technical services  = 20 % of the overall cost

= 0.2 * 80000

= 16,000 $

 

Total Cost = Overall cost + Cost of supervision and technical services

= 80000 + 16000

= 96,000 $

 

Read More: Grades of concrete

Read More: Rise and Fall Method

 

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