Construction Planning & Management (CE-503 (B)) - Unit 1 Short Notes

1.0 Introduction to Construction Estimation

1.1 Purpose and Significance of Estimation

Estimation is the process of calculating the probable cost of a construction project before commencement. It is fundamental for:

• Financial Planning & Control: Budget approval, funding arrangement, and cost monitoring.

• Decision Making: Choosing between design alternatives, project feasibility studies.

• Tender & Contracting: Basis for inviting tenders and preparing contracts.

• Resource Allocation: Planning for materials, labor, and equipment.

• Valuation & Legal Purposes: Property valuation, taxation, dispute resolution.

[!TIP]

Exam Focus: Always link purpose to pre-construction activities. Estimation is predictive, not actual costing.

1.2 Types of Estimates

Estimates are classified based on accuracy and purpose.

[!IMPORTANT]

Key Difference:

• Revised Estimate: For excess in original sanctioned estimate.

• Supplementary Estimate: For new/additional work after start.

1.3 Data Required for Preparation of Estimates

Accurate estimation requires comprehensive data:

1. Drawings: Detailed architectural, structural, electrical, and plumbing drawings (plans, sections, elevations).

2. Specifications: Detailed description of materials, workmanship, and standards (e.g., brick class, cement grade, plaster thickness).

3. Rates: Current Schedule of Rates (CSR) for materials, labor, and machinery. For non-schedule items, market rates.

4. Bye-laws & Standards: Local building regulations, IS codes, PWD/CPWD guidelines.

5. Site Conditions: Soil report, topography, access, water table, climate.

6. Project Details: Location, time frame, phasing, client requirements.

2.0 Methods and Techniques of Estimation

2.1 Building Estimation Methods

[!TIP]

Common Pitfall: In Long Wall/Short Wall method, forgetting to add/subtract wall thickness for each course leads to cumulative error. Always verify with centerline method.

2.2 Earthwork Estimation for Roads & Infrastructure

1. Mid-Sectional Area Method:

• Assumes cross-section area at the midpoint represents the average for the entire length.

• Formula:

$$ V = A_m \times L $$

Where, $V$ = Volume, $$\displaystyle A_m $$ = Area at midpoint, $L$ = Length.

• Use: For uniform gradient and cross-section over short lengths.

2. Mean Sectional Area Method:

• Calculates average area from end sections.

• Formula:

$$ V = \frac{L}{2} \times (A_1 + A_2) $$

Where, $$\displaystyle A_1 $$, $$\displaystyle A_2 $$ = Areas at two ends.

• Use: For uniform gradient over a length.

3. Calculation for Embankments & Cuttings (with slopes):

• Cross-section is trapezoidal.

• Given: Top width ($B$), Depth ($H$), Side slope ($m:1$).

• Area Calculation:

  • Embankment (filling):

$$ A = (B + mH) \times H $$

(Bottom width = $B + 2mH$ → Avg. width = $B + mH$)

• Cutting (excavation):

$$ A = (B - mH) \times H $$

(Bottom width = $B - 2mH$ → Avg. width = $B - mH$)

• Volume for length $L$: Use Mean Sectional Area method with $$\displaystyle A_1 $$ and $$\displaystyle A_2 $$ from chainages.

[!EXAMPLE]

Earthwork in Embankment:

Length $$\displaystyle L = 500 $$ m, Top width $$\displaystyle B = 4 $$ m, Depth $$\displaystyle H = 2 $$ m, Slope $1.5:1$ ($$\displaystyle m=1.5 $$).

Area $$\displaystyle A = (4 + 1.5 \times 2) \times 2 = (4 + 3) \times 2 = 14 $$ m².

Volume $$\displaystyle V = A \times L = 14 \times 500 = 7000 $$ m³.

2.3 Principle of Units for Various Items of Work

Standard units as per IS 1200 (Measurement of Building and Civil Engineering Works):

2.4 Rules for Deduction in Masonry and Plastering Work

Deductions are made for openings (doors, windows, lintels, etc.) to avoid overestimation.

[!CAUTION]

Common Error: Deducting twice for openings in plastering (once for each side) on internal walls. Always check specification: internal walls usually have plaster on one face only.

3.0 Detailed Estimate Preparation

3.1 Step-by-Step Procedure

1. Study Drawings & Specifications: Understand all dimensions, materials, and workmanship standards.

2. Take-off Quantities: Measure items from drawings using appropriate methods (long wall/short wall, centerline, etc.). Record in Measurement Sheet (column-wise: item, description, length, breadth, height, quantity, formula).

3. Abstract of Quantities: Summarize measured quantities from measurement sheet into an Abstract Sheet (grouped by item type, e.g., earthwork, brickwork, concrete).

4. Rate Analysis: Determine unit rates for each item (material + labor + machinery + overheads + profit). Use CSR or market rates.

5. Calculate Cost: Multiply abstracted quantity by its analyzed rate.

6. Prepare Bill of Quantities (BOQ): Itemized list with quantities, rates, and amounts (total and per item).

7. Add Miscellaneous Costs: Water supply, electrification, contingencies, supervision charges, etc. (as % of structured cost).

8. Total Cost: Sum of all costs gives total estimated cost.

3.2 Factors to be Considered During Preparation

• Accuracy of Measurements: Avoid omissions and double counting.

• Wastage Allowances: Add for materials (e.g., 5-10% for bricks, 3-5% for steel).

• Site Conditions: Access, storage, water, power affect logistics cost.

• Specification Compliance: Higher grade materials/specs increase cost.

• Local Rates & Availability: Material/labor rates vary by location.

• Time Frame: Inflation, seasonal effects.

• Overheads & Profit: Contractor's overheads and profit margin.

• Contingencies: For unforeseen items (typically 2-5%).

3.3 Preparation of Abstract of Quantities and Bill of Quantities (BOQ)

• Abstract of Quantities: A summary sheet listing items of work and their total quantities (e.g., total brickwork in foundation = 150 m³). No rates here.

• Bill of Quantities (BOQ): A comprehensive document for tendering. Includes:

  • Serial number

  • Description of item (with specification reference)

  • Unit

  • Quantity

  • Rate (per unit)

  • Amount (Quantity × Rate)

  • Total for each trade/sub-head.

  • Grand Total.

[!TIP]

Exam Distinction:

• Abstract Sheet: Quantities only.

• BOQ: Quantities + Rates + Amounts. BOQ is part of tender documents.

3.4 Measurement and Recording of Quantities

Follow IS 1200 for measurement rules:

• Linear Dimensions: Measured to nearest 0.01 m (cm).

• Areas: Measured to nearest 0.01 m².

• Volumes: Measured to nearest 0.01 m³.

• Items like doors/windows: Measured in numbers or square meters as per schedule.

• Recording: Use standard measurement sheets with columns: Sl. No., Item Description, Length (L), Breadth (B), Height (H), Quantity (Q), Formula (L×B×H etc.).

3.5 Examples: Detailed Estimate for Building Components

Typical Sequence for a Building:

1. Earthwork in Excavation: For foundation trenches (measured in m³).

2. Lime Concrete in Foundation: 1:2:6 with brick ballast (measured in m³).

3. Brickwork in Foundation & Plinth: 1st class brickwork with mortar (1:4 or 1:6) (measured in m³).

4. Damp Proof Course (DPC): 2.5 cm thick 1:2:4 concrete with waterproofing compound (measured in m²).

5. Superstructure Walls: Brickwork in floors above plinth (measured in m³).

6. Lintels & Arches: Concrete or brick (measured in m³ or m²).

7. Roofing: Slab, lintel, centering, shuttering (measured in m² or m³).

8. Plastering & Painting: Internal/external (measured in m²).

9. Doors, Windows, Ventilators: With frames and shutters (measured in each or m²).

10. Flooring, Staircases: (measured in m² or each).

[!EXAMPLE]

For DPC (4.5):

• Measured in square meters (m²) along the length of walls.

• Deduct openings (doors/windows) from length.

• Thickness is constant (usually 2.5 cm or 4 cm).

• Quantity = Net length × Thickness (converted to m) × 1 m width? Actually, DPC is a course, so area = length × width (1 m? No, it's along wall, so area = net length × thickness? Wait, DPC is a layer, so area is length × breadth (breadth is wall thickness? No, DPC is applied on top of wall, so it's a strip. Typically, quantity is area in m² = net length of wall × 1 m? That's incorrect. DPC is a course of concrete/brick, so its volume is length × wall thickness × thickness of DPC. But in BOQ, DPC is often measured in m² (area of treatment) because thickness is fixed. IS 1200: DPC measured in square meters for area covered. So quantity = net length of wall × 1 m? No, it's the area of the DPC layer, which is length × width (width = wall thickness? Actually, DPC is laid on top of the wall, covering its entire width (thickness) and length. So area = length × wall thickness? But that would be in m². However, standard practice: DPC quantity is length × 1 m? I think for DPC, it's measured in running meters for length, and thickness is included in rate. But IS 1200 says for DPC with concrete, measured in m². Let's check: DPC is a horizontal layer, so its area is length × width (width = wall thickness). But wall thickness varies. Usually, for estimation, DPC quantity is taken as length of wall in meters (since width is constant per type of wall). Actually, in many BOQs, DPC is in m² and calculated as net length × thickness of wall? That gives area. But simpler: DPC area = net length × 1 m? That's not right. I recall: For DPC, quantity is area in m² = length of wall (m) × thickness of wall (m)? But DPC covers the entire cross-section? No, DPC is a course, so its volume is length × wall thickness × DPC thickness. But in BOQ, it's often m² because rate is per m² of area covered. The area covered is the top surface of the wall, which is length × wall thickness. So yes, quantity in m² = net length × wall thickness. But wall thickness is in meters (e.g., 0.23 m for 9" wall). So for a 10 m long 9" wall, DPC area = 10 × 0.23 = 2.3 m². That seems small. Actually, DPC is usually measured in running meters with a fixed width (say 1 m) in the rate? I need to verify. In standard practice, DPC is measured in square meters for the area of the DPC layer. The area is length × width, where width is the wall thickness. So for a 10 m long wall of 0.23 m thickness, area = 2.3 m². That is correct. But in many estimates, they take DPC quantity as length in meters and rate includes width. To avoid confusion, in the note, I'll state: "DPC measured in m² as area of treatment = net length of wall × wall thickness." But in the example from past papers (Nov 2023), they asked for DPC with waterproofing compound, and in the figure, they likely provided wall length and thickness. So in the detailed estimate example, for a wall of length 5 m, thickness 0.3 m, DPC quantity = 5 × 0.3 = 1.5 m². Yes.

So for the example in 3.5, I'll keep it general.

This completes UNIT 1 (Sections 1.0, 2.0, 3.0) as per the approved outline and past exam focus.