Types of Estimates
Estimates are prepared at different stages of a project. Here are the main types:
- Preliminary Estimate: Rough estimate prepared during the initial stages of a project. Accuracy: ±10% to ±20%.
- Detailed Estimate: Accurate estimate prepared after detailed drawings and specifications are available. Accuracy: ±5%.
- Quantity Estimate: Focuses on the quantity of materials required.
- Revised Estimate: Prepared when there are changes in the scope of work.
- Supplementary Estimate: Prepared for additional works not included in the original estimate.
Methods of Estimating
Different methods are used for estimating costs in construction projects:
- Unit Cost Method: Cost per unit is calculated and multiplied by the total number of units.
- Square Meter Method: Cost is estimated based on the area of the building.
- Cubic Meter Method: Cost is estimated based on the volume of the building.
- Approximate Quantity Method: Quantities of major items are calculated, and rates are applied.
- Detailed Estimate Method: Involves a detailed breakdown of all items and their costs.
Rate Analysis
Rate analysis is the process of determining the cost of a unit quantity of work. It includes:
- Material Cost: Cost of materials required for the work.
- Labor Cost: Cost of labor involved in the work.
- Equipment Cost: Cost of machinery and tools used.
- Overhead Costs: Includes administrative and other indirect costs.
Specifications
Specifications describe the quality and standards of materials and workmanship. They are essential for:
- Purpose: To define the quality and standards of work.
- Importance: Ensures clarity and avoids disputes during execution.
- Types:
- General Specifications: Broad description of materials and workmanship.
- Detailed Specifications: Detailed description of each item of work.
Valuation
Valuation is the process of determining the present value of a property. It is used for:
- Buying/Selling Property: Helps in determining the fair price.
- Taxation: Used for calculating property taxes.
- Insurance: Determines the insurance value of a property.
- Methods of Valuation:
- Rental Method: Based on the rental income of the property.
- Land and Building Method: Separate valuation of land and building.
- Depreciation Method: Considers the depreciation of the property.
Material Calculations
Detailed calculations for materials like cement, concrete, bricks, and aggregates:
1. Cement Calculation
For 1 m³ of Concrete (M20 Grade):
- Cement: 8 bags (50 kg each)
- Sand: 0.42 m³
- Aggregate: 0.84 m³
For 100 m³ of Concrete:
- Cement: 800 bags
- Sand: 42 m³
- Aggregate: 84 m³
2. Brick Calculation
For 1 m³ of Brickwork:
- Number of Bricks: 500 (standard size: 190 mm × 90 mm × 90 mm)
- Mortar Required: 0.3 m³
For 100 m³ of Brickwork:
- Number of Bricks: 50,000
- Mortar Required: 30 m³
3. Aggregate Calculation
For 1 m³ of Concrete (M20 Grade):
- Coarse Aggregate: 0.84 m³
- Fine Aggregate (Sand): 0.42 m³
For 100 m³ of Concrete:
- Coarse Aggregate: 84 m³
- Fine Aggregate: 42 m³
Formulas
Important formulas used in estimating and costing:
- Plinth Area Method: Cost = Plinth Area × Plinth Area Rate
- Cubic Content Method: Cost = Volume × Cubic Meter Rate
- Depreciation: Depreciation = (Original Cost - Scrap Value) / Useful Life
- Rate Analysis: Total Cost = Material Cost + Labor Cost + Equipment Cost + Overhead Cost