# Types of Estimate in civil engineering | Which estimate should we use?

The estimate is the process of calculating or computing the various quantity and the expected expenditure to be incurred on a particular work or project. The estimate gives the probable cost of the work. There are different types of estimate described below.

## Types of Estimate

1. Preliminary or approximate estimate
2. Detailed estimate
3. Revised estimate
4. Complete estimate
5. Supplementary estimate
6. Annual repair and maintenance estimate
7. Extension and improvement estimate

#### 1. Approximate estimate

An approximate or preliminary estimate gives the approximate cost of the project. Every owner or Gov. would like to know the approximate cost of the project, before going to further detail of the project.

The preliminary estimate helps to take the financial decision The approximate estimate is prepared from the practical knowledge and cost of similar works. This estimate is prepared to show separately the approximate cost of all-important items of works as cost of land, cost of each building, cost of roads water supply sanitary works, etc.

The estimate is prepared with a brief report explaining the necessity and utility of the project and showing how the cost of separate items has arrived yet. This estimate is prepared for taking administrative approval of the project.

The following are the methods used for the preparation of approximate estimates.

##### a) Plinth area Estimate:

The plinth area of a building means Length x Breadth excluding plinth offsets. The estimates are prepared on the basis of plinth areas of the various buildings proposed to be constructed.

The rates are being arrived at by dividing the total cost of construction by its plinth area. For example, if the total cost of a building i Rs. 2 lakh and its plinth area is 50 sq. m. then plinth area rate=2,00,000/50 = Rs.4000-per sq.m.

Using this rate as the basis of the next construction, the approximate or rough cost of the proposal can be arrived at by multiplying the plinth area of the proposed building with this plinth area rate.

#### Numerical Example

Q) Prepare a preliminary types of estimate for a framed four-storied office building having a carpet area of 300 sq. m, for each floor. Assume area occupied by corridor, verandah, lavatories, staircase, etc, as 25% of built-up area and that occupied by walls and columns as 8.5% of the same.

Given,

(i) Built-up area rate for ground floor (excluding

foundation) = Rs. 1,500/- per sq. m.

(ii) Build-up area rate for 1st. & 2nd. floor = Rs. 1,650/- per

sq.m.

(iii) Build-up area rate for 3rd floor = 1,800/- sq.m

(iv) Extra for foundation = 20% of super-structure cost.

(v) Extra for special Architectural treatment = 1% of Bldg. Cost.

(vi) Extra for water supply and sanitary = 7% of Bldg. cost.

(vii) Extra for Work Charged establishment = 10% of

overall cost.

(ix) Extra for other source = 5% of building cost Built up area i.e., the plinth area = Carpet area + circulation area

Solution:

Built up area i.e., the plinth area = Carpet area + circulation area+ area occupied by walls and columns.

Carpet area= 300 sq m (given): Let P sq m be the plinth area.

or, P = 300 + 25% of plinth area +8.5% of plinth area.

or, P = 300 +0.25x P + 0.085 × P

or, P-0.25P-0.085P = 300 sq m. or, 0.665 P = 300 sq m.

⁂ P = 451.13 sq m.

##### b) Cubical Contents Method:

This method is generally used for multistoried buildings. It is more accurate than the other two methods viz., plinth area method and unit base method. The cost of a structure is calculated approximately as the total cubical contents (Volume of buildings) multiplied by Local Cubic Rate.

The volume of the building is obtained by Length x breadth x depth or height. The length and breadth are measured out to out of walls excluding the plinth offset.

The cost of building= volume of buildings X rate/ unit volume.

Example: Prepare the rough estimate for a proposed commercial complex for a municipal corporation for the following data.

Plinth Area = 500m²/floor

Ht of each storey = 3.5m

No:of storeys = G+2

Cubical content rate = Rs. 1000/m³

Provided for a following as a percentage of structured cost

1. water supply & Sanitary arrangement  -8%
2. Electrification -6%
3. Fluctuation of rates – 5%
4. Contractors profit -10%
5. Supervision & contingencies -3%

Solution:

Cubical content = No.of storeys (Plinth Area x height of each storey)                     = 3(500×3.5) = 5250m³

Structural cost = Cubical content x cubical content rate

= 5250 x 1000 = 52.5 Lakhs

Other provisions:

##### c) Unit Base Method:

According to this method, the cost of the structure is determined by multiplying the total number of units by the unit rate of each item. In case schools and colleges, the unit is considered to be ‘one student and in the case of the hospital, the unit is ‘one bed’.

The unit rate is calculated by dividing the actual expenditure incurred or cost of a similar building in the nearby locality by the number of units.

Example:  To prepare the rough cost estimate of a hostel building that accommodates 150 students. The cost of construction including all provisions is Rs. 15,000/- per student. Determine the total cost of the building.

Solution:

No.of students= 150

Cost of construction including all L.S. provisions = Rs. 15.000/ Total Cost of hostel building = 150 x 15000 = Rs. 22, 50.000/

## 2) Detailed estimate

After getting Administrative approval on a rough cost estimate. detailed estimates are prepared. The estimate is divided into subheads I quantities of various items are calculated individually.

At the end of the detailed quantities, an abstract of cost giving quantities of each item and rate of every item according to the sanctioned schedule of rates shall be attached. In case of non-schedule rates i.e. rates that are not given in the sanctioned schedule of rates, proper analysis of rates shall be attached.

If however the work proposed to be constructed is located in a remote place, the provision for the carriage of the material shall be added in the estimate to avoid any excess over the administratively approved estimate later on.

Detailed specifications & reports should also be attached with the estimate. Technical sanction is given on a detailed estimate.

The detailed estimate shall also provide for the cost of the approach road. water supply, electric installations, and acquisition of land, etc.. so as to call it a comprehensive estimate.

## 3) Revised estimate

When the sanctioned estimate exceeds by 5% either due to the rate being found insufficient or due to some other reasons, a fresh estimate is prepared which is called a Revised Estimate. A comparative statement on the last page of the estimate is attached giving therein the reasons for the increase of cost in the case of each item.

## 4) Complete estimate

This is an estimated cost of all items which are related to the work in addition to the main contractor to the detailed estimate. Most people think that the estimate of structure includes the cost of land, cost of materials, and labor only. But many other direct and indirect costs are also included and are shown below.

## 5) Supplementary estimate

This is a freshly detailed estimate in addition to the original sanctioned estimate prepared when additional works are deemed necessary during the progress of work to supplement the original works. The abstract of cost should show the amount of the original sanctioned estimate as well as the supplementary amount for which sanction is required.

## 6) Annual Repair and Maintenance Estimate

In order to keep buildings, roads, and other projects in perfect condition, annual repairs should be carried out.

1. In case of a building-white washing, oiling and painting of doors and windows, cement plaster repairs (inside & outside), repairs of floors etc. In no case this annual repair amount should increase more than 1½%-2% capital cost of the building.
2. In case of a road-filling patches, maintenance of berms etc

## 7) Extension and Improvement Estimate

If some items are to be extended or improved from the original form and the work cannot be carried out from the annual repair and maintenance fund, then an extension and improvement estimate is to be prepared.

The conditions may be:

1. In case of a building-opening of new doors, change of floors, replastering walls etc.
2. ii. In case of roads-if the whole surface is full of corrugation & patches, then the total surface is to be scarified. The old metal is taken out, consolidation by adding more metal is done and top surface is repainted.

## When and where the above types of estimate are used?

1) Approximate estimate: Approximate estimate is prepared when the project is in the preliminary stage to get the administrative approval of the project. It is prepared where the rough idea of the fund required is necessary before the detailed estimation.

2) Detailed estimation: It is an accurate estimate and consists of detailed particulars for the quantities, rates, and costs of all items involved in a project. It is prepared when the execution of a contract or technical sanction is required.

3) Revised estimate: It is required

• When a sanctioned estimate is likely to exceed by more than 5% either from the rates being found insufficient or from any cause whatsoever except important structural alternations.
• When the expenditure of work exceeds or likely to exceed by more than 10% of administrative approval.
• When material deviations from the original proposal but not due to material deviation if a structural nature.
• When it is found that the sanctioned estimate is more than the actual requirement.

4)   Supplementary estimate

While work is in progress some change or additional works due to material deviation of a structural nature from the design originally approved may be required. Then the supplementary estimate is required.

5) Annual repair and maintenance estimate:

After completion of the project, it is necessary to maintain the structure of work in the same condition. Hence when renewal, replacement, repairs, etc required for an item, annual repair a maintenance estimate is prepared.

6) Extension and improvement estimate:

It is prepared when it is necessary to the extent or improves any item or part of the project.

7) Complete estimate

It is prepared when the cost of all items of work which are related in addition to the main contractor to the detailed estimate is required.