What is an Estimate and its advantage and disadvantage

 


Estimating

Estimating is a crucial part of civil engineering that involves predicting the costs, materials, labour, and time required for a construction project.

 Proper estimation ensures efficient resource allocation, project feasibility, and financial planning. In India, estimates follow standards and guidelines provided by the Bureau of Indian Standards (BIS) .

What is an Estimate?

An estimate is the approximate calculation of the cost of a construction project, including materials, labour, equipment, and overhead expenses. The accuracy of an estimate depends on project details, market rates, and construction methods.

The primary objectives of estimation are:

·        Determining project feasibility

·        Budget allocation

·        Resource planning

·        Avoiding cost overruns

Types of Estimates in Civil Engineering

1. Preliminary Estimate (Rough Cost Estimate)

·        Used in the initial stages of a project to assess its feasibility.

·        Based on past projects, per square metre rates, or lump sum values.

·        Commonly used for government approvals, budget allocation, and large-scale planning.

·        Example: If a municipal corporation wants to build a new hospital, a rough cost estimate is prepared based on similar hospitals previously constructed.

2. Detailed Estimate

·        Provides an in-depth calculation of materials, labour, equipment, and contingencies.

·        Prepared using item-wise analysis as per the Schedule of Rates (SOR).

·        Includes quantities, unit rates, and total cost breakdown.

·        Required for tendering, contractor payments, and financial approvals.

·        Example: A bridge construction project will have a detailed estimate specifying the quantity of cement, steel, and other materials required, with respective costs.

 

3. Quantity Estimate (Material Estimate)

·        Focuses on material requirements for procurement planning.

·        Ensures timely availability of resources.

·        Commonly used in large infrastructure projects.

·        Example: In road construction, a quantity estimate will detail how much bitumen, aggregates, and concrete will be needed for each kilometre.

4. Revised Estimate

·        Prepared when the original estimate is exceeded by more than 5% due to changes in design or material costs.

·        Requires approval from the concerned authorities.

·        Example: If the cost of steel rises significantly during the execution of a high-rise building, a revised estimate will be needed to accommodate the price hike.

5. Supplementary Estimate

·        Additional estimate prepared for extra work beyond the original project scope.

·        Ensures smooth execution of unforeseen modifications.

·        Example: If an additional parking lot is to be added to an existing commercial complex, a supplementary estimate will be created for the extra cost.

6. Plinth Area Estimate

·        Based on the built-up area of a structure multiplied by the construction rate per square metre.

·        Used for quick cost approximation.

·        Example: A residential building with a plinth area of 200 square metres and a per-square-metre construction cost of ₹15,000 will have an estimated cost of ₹30 lakhs.

7. Cube Rate Estimate

·        Uses the volume of the structure (length × width × height) multiplied by a standard rate per cubic metre.

·        Suitable for multi-storey buildings.

·        Example: A commercial tower with a total volume of 10,000 cubic metres and a construction rate of ₹5,000 per cubic metre will be estimated at ₹5 crore.

8. Annual Repair and Maintenance Estimate

·        Prepared for regular upkeep of infrastructure.

·        Includes costs for minor repairs, repainting, and restoration works.

·        Example: For a government office building, an annual repair estimate might include ₹2 lakhs for plumbing, ₹3 lakhs for electrical work, and ₹5 lakhs for painting.

IS Codes and IRC Guidelines for Estimation

The following standards govern estimation in India:

·        IS 1200: Method of Measurement of Building Works

·        IS 7272: Guide for Preparation of Project Estimates

·        IRC 84: Guidelines for Estimation of Road Works

·        CPWD Manual for Works Estimation

Applications of Estimates

·        Government Infrastructure Projects: Roads, bridges, and buildings.

·        Private Construction: Residential and commercial properties.

·        Industrial Projects: Factories, warehouses, and plants.

·        Renovation & Repair Works: Restoring old structures.

Advantages of Estimation

·        Ensures Financial Planning: Prevents budget overruns.

·        Aids in Tendering: Helps contractors bid competitively.

·        Reduces Material Wastage: Ensures efficient resource use.

·        Minimises Delays: Prevents cost escalations.

Disadvantages of Estimation

·        Inaccuracy Due to Market Fluctuations: Prices of materials and labour change frequently.

·        Errors in Calculation: Small miscalculations can lead to huge cost variations.

·        Time-Consuming Process: Requires thorough analysis and approvals.

 

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