Quantity surveying & Costing (CE-503 (C)) - Unit 1 Short Notes

UNIT 1: FUNDAMENTALS OF ESTIMATION, COSTING AND VALUATION

1.1 Introduction to Estimation

Purpose and Importance:

• Purpose: To ascertain the probable cost of construction before commencement, enabling financial planning, budget control, and sanctioning.

• Importance:

  • Provides basis for tender and contract agreements.

  • Helps in securing loans/financial assistance.

  • Enables comparison of design alternatives.

  • Acts as a control document during execution.

Types of Estimates (Hierarchy of Accuracy & Detail):

[!TIP] Exam Focus: Distinguish between Revised (excess over sanctioned estimate) and Supplementary (new/additional items) estimates with examples (e.g., foundation change vs. adding a new room).

1.2 Preparation of Detailed Estimates

Data Required:

1. Drawings: Plans, elevations, sections, detailed drawings.

2. Specifications: Detailed description of materials, workmanship, standards.

3. Rates: Current Schedule of Rates (CSR) or prevailing market rates.

4. Bye-laws & Standards: Local building regulations, IS codes.

Step-by-Step Procedure:

1. Take-off Quantities: Measure dimensions from drawings for each item (e.g., length, breadth, depth).

2. Calculate Net Quantities: Apply deduction rules (see 1.3).

3. Abstract Quantities: Group similar items (e.g., all brickwork) and sum net quantities.

4. Apply Rates: Multiply abstract quantities by respective unit rates.

5. Calculate Total Cost: Sum costs of all items.

6. Add Contingencies & Overheads: Include petty supervision, contingencies, etc.

7. Prepare Abstract Sheet: Final summarized cost statement.

Factors to be Considered:

• Site conditions (soil, accessibility, water table).

• Material availability & transportation.

• Labor skill & productivity.

• Seasonal impacts (monsoon, winter).

• Proper measurement units (IS 1200).

• Wastage allowances (material, labor).

[!TIP] Common Pitfall: Forgetting to apply deduction rules for openings (doors, windows) in masonry/plastering, leading to overestimation.

Example: Rough Estimate for Commercial Complex (Plinth Area Method) Given: Plinth Area = 500 m²/floor, No. of storeys = G+2 (3 floors), Total Plinth Area = 1500 m².

Plinth Area Rate = Rs. 3500/m² (assumed for structure).

Additional percentages: WSS 8%, Electrification 6%, Fluctuation 5%, Profit 10%, Petty Sup. & Cont. 3%.

Calculation:

1. Structured Cost = Total Plinth Area × Rate = 1500 × 3500 = Rs. 52,50,000

2. Add for Services & Contingencies:

   • WSS: 8% of 52,50,000 = 4,20,000

   • Electrification: 6% = 3,15,000

   • Fluctuation: 5% = 2,62,500

   • Profit: 10% = 5,25,000

   • Petty Sup. & Cont.: 3% = 1,57,500

3. Total Estimated Cost = 52,50,000 + (4,20,000+3,15,000+2,62,500+5,25,000+1,57,500)

   = 52,50,000 + 16,80,000 = Rs. 69,30,000

Alternatively, using Cubical Content:

Total Volume = Plinth Area × Height per storey × No. of storeys = 500 × 3.5 × 3 = 5250 m³.

Rate = Rs. 1000/m³ → Structured Cost = 52,50,000 (same as above if rate adjusted).

1.3 Estimation Methods and Techniques

A. Building Estimation: Long Wall & Short Wall Method

• Principle: Walls along the longitudinal direction are "long walls"; those perpendicular are "short walls." Their lengths vary with each course due to footing steps.

• Procedure:

  1. Find center line lengths of walls from plan.

  2. For each footing/section, calculate individual long/short wall lengths using:

  • Long Wall Length = Center Line Length + (½ × Width of Footing on one side) + (½ × Width of Footing on other side) for that level.

  • Short Wall Length = Center Line Length - (½ × Width of Footing on one side) - (½ × Width of Footing on other side).

  3. Multiply by respective breadth/height and sum.

Example: For a single room 5m × 4m (external dimensions), wall thickness 0.3m.

• Center Line Length (Long Wall) = 5m, (Short Wall) = 4m.

• If footing width at foundation = 0.6m, then:

  • Long Wall at foundation = 5 + (0.6/2) + (0.6/2) = 5.6m.

  • Short Wall at foundation = 4 - 0.3 - 0.3 = 3.4m.

[!TIP] Exam Tip: This method is essential for masonry quantity in foundations/plinth where wall lengths change due to footing offsets.

B. Earthwork Calculation for Roads

• Mid-Sectional Area Method:

  • Area at midpoint of two sections is used.

  • Volume between two sections = Average Area × Distance.

$$ \text{Volume} = \left( \frac{A_1 + A_2}{2} \right) \times d $$

where \(A_1, A_2\) are cross-sectional areas at chainages.

• Mean Sectional Area Method (for long embankments/cuttings):

  • Calculate area at both ends of a length.

  • Mean Area = \( \frac{A_1 + A_2}{2} \)

  • Volume = Mean Area × Distance between sections.

  • For Embankment/Cutting with Slopes:

    • Cross-sectional area depends on side slopes.

    • Embankment: \( A = (B + Z \cdot H) \cdot H \)

      where \(B\) = top width, \(H\) = height, \(Z\) = slope (horizontal:vertical).

    • Cutting: \( A = (B + Z \cdot H) \cdot H \) (same formula, but \(H\) is depth of cutting).

Example (from Jun 2025):

Length = 0.5 km = 500 m, Top width \(B\) = 4 m, Depth \(H\) = 2 m, Slope \(Z\) = 1.5:1.

Assuming uniform cross-section:

\( A = (4 + 1.5 \times 2) \times 2 = (4 + 3) \times 2 = 14 \, \text{m}^2 \)

Volume = \( 14 \times 500 = 7000 \, \text{m}^3 \).

C. Material Statements

• For M20 Grade Concrete (1:1.5:3 by volume, but often 1:2:4 by volume for RCC):

  • Note: IS 10262:2019 uses design mix, but for site estimates, nominal mix ratios are used.

  • For 1 m³ of R.C.C. (1:2:4):

    • Total parts = 1+2+4 = 7.

    • Cement = \( \frac{1}{7} \) m³ = 0.1428 m³ → Bags (50kg/bag, density 1440 kg/m³) = \( \frac{0.1428 \times 1440}{50} \) ≈ 4.11 bags.

    • Sand = \( \frac{2}{7} \) m³ = 0.2857 m³.

    • Aggregate = \( \frac{4}{7} \) m³ = 0.5714 m³.

  • Add 5-10% wastage for bulkage (sand) and wastage.

D. Deduction Rules (IS 1200)

• In Masonry Work:

  • No deduction for opening ≤ 0.1 m².

  • For openings > 0.1 m²:

    • Deduct area of opening only (not extra for lintels, sills) if opening area ≤ 0.5 m².

    • Deduct area of opening + area of lintel/sill (if specified) if opening area > 0.5 m².

    • For rectangular openings, deduct full area; for arched, deduct area up to springing line + ½ of arch area.

• In Plastering/Painting:

  • Deduct area of opening if opening area > 0.5 m².

  • No deduction for openings ≤ 0.5 m².

  • No addition for jambs, reveals, soffits.

[!TIP] Common Error: Confusing rules for masonry (deduct lintel area only for large openings) vs. plastering (deduct only opening area for large openings).

E. Quantity Take-off for Specific Items

1. Earthwork in Excavation (Foundation): Measure net volume after deducting for column/pedestal pits if specified.

2. Lime Concrete in Foundation: Area × Thickness (usually 150-300 mm).

3. Brickwork:

   • Foundation/Plinth: Use long wall/short wall method with step lengths.

   • Superstructure: Use center line method (if no footing steps) or individual wall lengths.

4. Damp Proof Course (DPC): Length × Breadth (usually 2.5 cm thick).

5. Drainage: Pipes (length), manholes (nos.), chambers (volume).

6. Electrification: Points (nos.), wiring (length), sub-station (volume).

7. Culvert: Components (abutments, wing walls, bed, slab/pipe) – measure individually.

1.4 Rate Analysis and Costing Principles

Definition & Objectives:

• Definition: Determining the rate per unit of work by breaking down costs of materials, labor, equipment, overheads, and profit.

• Objectives:

  • To fix fair rates for items of work.

  • To control costs during execution.

  • To compare contractor bids.

  • To prepare detailed estimates.

Factors Affecting Rate Analysis:

1. Material Costs: Purchase price + transportation + taxes + wastage (typically 5-10% for bricks/sand, 2-5% for cement).

2. Labor Costs: Skilled/unskilled wages, task work rates, overtime, welfare.

3. Equipment & Tools: Depreciation, hire charges, fuel, maintenance.

4. Overhead Charges: Site establishment, supervision, utilities, insurance (usually 5-10% of total).

5. Contractor's Profit: Risk factor, competition, project size (usually 10-15%).

6. Fluctuation of Rates: Market volatility of materials/labor.

Principle of Units:

• Follow IS 1200 for standard units:

  • m, m², m³ for length, area, volume.

  • kg, quintal, tonne for weight.

  • no., each for countable items (doors, windows).

  • running meter (rm) for pipes, wires.

Preparation of Rate Analysis: Example for Lime Concrete (1:2:6 with brick ballast) Assume 1 m³ of lime concrete in foundation.