Fundamentals of Estimating and Costing

 Estimate:

An estimate is the anticipated or probable cost of a work.  Usually it is prepared before the execution of construction work.

Estimating:

The process of working out the probable cost of a work is called estimating. Estimating include taking out quantities and abstracting. So in other words the process of calculating the quantities and costs of the various items in connection with work required for satisfactory completion of work is also called as estimating.

Purposes of Estimating:-

i. To know the approximate cost of proposed work.

ii. To obtain administrative approval and technical sanction.

iii. To know the requirement of tools, plants and equipment.

iv. To fix up the completion period.

v. To draw up a construction schedule and programme.

vi. To invite tender for execution of work.

vii. To keep control over expenditure during construction.

Costing:

Costing is the process of determining actual cost of work before the execution of work.

 

Purpose of Costing:-

i. To arrange the finance for proposed work.

ii. To know the probable cost of project before the execution.

iii. For valuation of existing property

iv. To know the cost of various items, well in advance, to be constructed

Types of Estimate:

There are two types of estimates:

1. Approximate Estimate

2. Detailed Estimate

 

Different Types of Approximate Estimate:

i. Plinth area method

ii. Cubical content method

iii. Service unit method

iv. Typical bay method

v. Approximate quantity method

 

Different Types of Detailed Estimate:

i. Revised estimate

ii. Supplementary estimate

iii. Revised and supplementary estimate

iv. Repair and maintenance estimate

v. Renovation estimate

 

Detailed Estimate:

Detailed estimate is an accurate estimate and consisting of working out quantities of each item of works and working the cost. The dimensions – length, breadth and height of each item are taken out correctly from drawing and quantities of each item are calculated and abstracting is done. 

Detailed estimate is prepared in two stages:

1. Details of Measurements and Calculation of Quantities.

2. Abstract of Estimated Cost.

 

Types of Detailed Estimate:

1. Revised Estimate.

2. Supplementary Estimate

3. Revised & Supplementary Estimate.

4. Repair & Maintenance Estimate.

5. Renovation Estimate.

1. Revised Estimate:

It is a detailed estimate for the revised quantities and rates of items of works originally provided in the estimate prepared and submitted for fresh technical sanction.

Revised estimate is prepared under following circumstances:

1.When the original sanctioned estimate is likely to exceed by more than 5%.

2.When the expenditure on a work exceeds or likely to exceeds by more than 10% of the administrative approval.

3.When there are material deviation from original proposal but not due to material deviation of a structural nature.

4.When sanctioned estimate is found more than actual requirement.

2. Supplementary Estimate:

It is prepared when additional work is required to supplement original work. It is also required when further development is necessary during the progress of work.This is the fresh estimate of the additional work.

 

Supplementary estimate is prepared under following circumstances:

1.During the execution of project, certain new items or additional works crop up to supplement the original project. Under such circumstances, it becomes necessary to prepare supplementary estimate.

2.Supplementary estimate is prepared for covering the estimate of sub-work of a project, which is considered necessary for full development of project.

3.Sometimes changes due to material deviation of a structural nature from the original approved design are necessary when the work is in progress. Then for all such items supplementary estimate is prepared.

 

Difference between Revised Estimate and Supplementary Estimate:

Sr. No.	Revised Estimate	Supplementary Estimate
01	It is prepared when original sanctioned estimate exceeds more than 5 %	It is prepared when additional work is required to supplement the original work.
02	It is prepared when there is material deviation from original proposal	It is prepared when some items are excluded or additional items are incharged in work.
03	Abstract sheet is not required	Separate abstract sheet is required
04	Revision or addition of drawing is not necessary	Revision or addition of drawing required.

 

 

3. Revised and Supplementary Estimate:

When the work is practically abandoned and estimated cost of remaining work is less than 95% of original work, or less than 90% of the original sanctioned estimate or when there is material deviation and changes in design, then the amount of original estimate is revised by the competent authority. A supplementary and revised estimate is prepared and fresh technical sanction of the competent authority is obtained.

 

4. Repair & Maintenance Estimate:

When work is over it is necessary to maintain the structure in proper condition. For this purpose an estimate is prepared is called Repair & Maintenance Estimate. For annual repair of building 1 to 1.5 % of original construction cost of whole building is provided.

 

5. Renovation estimate:

It is a type of estimate prepared for renovation of buildings, bunglow, flat and row houses. eg. If flooring has to be changed, internal walls to be added or removed, dado has to be changed, WC or bath fittings has to be changed etc. renovation estimate is to be prepared. While preparing a renovation estimate a list of items to be completed to renew the structure is prepared. Then quantity of items of works that needed to be completed is calculated. For calculation of quantities of items of work measurements are taken at site of work.