Types of Estimate in Estimating and Costing
Syllabus: Types of Estimate (4 Hours)
3. Types of Estimate (4 hours)
3.1 Approximate estimate, purpose and methods
3.2 Detailed estimate
3.3 Revised estimate
3.4 Supplementary estimate
3.5 Complete estimate
3.6 Splitting of cost of building, road, water supply and sanitary works into sub-heads
3.7 Detail estimation formats (Summary of cost, detail quantity estimate, analysis of rate, abstract of cost and bill of quantities)
Types of Estimate Notes
The following types of estimates are used in civil engineering projects to assess financial feasibility, arrange administrative sanction, invite tenders, and execute construction works:
- Preliminary or Approximate Estimate
- Detailed Estimate
- Revised Estimate
- Supplementary Estimate
- Annual Repair or Annual Maintenance Estimate
- Extension and Improvement Estimate
- Complete Estimate
- Split-up of Cost of Building Works
1. Preliminary or Approximate Estimate
An approximate estimate is carried out to get an approximate cost in a very short time and gives a rough idea of the probable outlay for a proposed project. It is prepared in the preliminary stages to check feasibility and obtain administrative approval.
a) Per Unit Basis Method
In this method, the total estimated cost is determined by multiplying the total number of units required by the prevailing rate per unit from similar past projects.
- Building Projects: Per unit basis / capacity basis
- Hospital Building: Per bed
- Water Tanks & Reservoirs: Per litre / per gallon
- Road Construction: Per kilometre (km)
- Bridge Work: Per metre of span
- School Building: Per classroom / per student
- Cinema Hall / Auditorium: Per seat
b) Plinth Area Basis Method
This method is primarily used for building projects. The preliminary cost is calculated by multiplying the plinth area of the building by the current plinth area rate in the locality.
Key Percentage Guidelines:
- Circulation Area: Corridors, staircases, lifts, verandahs $\rightarrow$ $30\%$ to $45\%$ of plinth area.
- Wall Area: Outer & inner walls $\rightarrow$ $10\%$ to $20\%$ of plinth area.
- Work Up to DPC: Cost $\approx 18\%$ of total building cost.
- Wood Work (Doors & Windows): Cost $\approx 16\%$ of total building cost.
Given Dimensions:
- Living room = $4\text{ m} \times 6\text{ m} = 24\text{ m}^2$
- Bedroom = $3\text{ m} \times 8\text{ m} = 24\text{ m}^2$
- Kitchen = $3\text{ m} \times 3\text{ m} = 9\text{ m}^2$
- Store = $2\text{ m} \times 3\text{ m} = 6\text{ m}^2$
- Toilet = $2\text{ m} \times 4\text{ m} = 8\text{ m}^2$
$$\text{Total Carpet Area} = 24 + 24 + 9 + 6 + 8 = 71\text{ m}^2$$
Assuming circulation area $= 30\%$ of plinth area ($0.30x$) and wall area $= 10\%$ of plinth area ($0.10x$), where $x$ is the total plinth area:
$$x = 71 + 0.30x + 0.10x \implies 0.60x = 71 \implies x \approx 118.33\text{ m}^2 \quad (\approx 118\text{ m}^2)$$ $$\text{Estimated Cost} = 118\text{ m}^2 \times \text{Rs } 10,000/\text{m}^2 = \mathbf{\text{Rs } 11,80,000}$$c) Cube Rate Basis Estimate
In this method, the cost is calculated based on the total cubical content (volume) of the building. It takes into account not only the plan area but also the height of the building, making it more accurate than the simple plinth area method.
d) Approximate Quantity Estimate
- It is more accurate than the per unit, plinth area, or cube rate methods.
- Approximate total quantities for major structural items of work (e.g., excavation, masonry walling, RCC slabs/columns, plastering, painting) are worked out from basic layouts.
- These approximate quantities are multiplied by their respective rates to obtain the estimated cost for each major component.
2. Detailed Estimate
A detailed estimate is the most accurate method of estimation. In this approach, every individual item of work is measured and calculated meticulously using full-dimensioned working drawings (length, breadth, and height/depth) recorded in a Detail Measurement Sheet. The cost of each item is then computed using an Abstract Cost Sheet.
Core Components / Formats:
a) Detail Measurement and Calculation Sheet:
| S.N. | Description of Item | No. | L (m) | B (m) | H/D (m) | Quantity |
|---|---|---|---|---|---|---|
| 1. | Earthwork in excavation in foundation | 2 | 10.00 | 1.00 | 0.90 | $18.00\text{ m}^3$ |
b) Abstract of Estimate Cost Sheet:
| S.N. | Description of Work | Quantity | Unit | Rate (Rs.) | Amount (Rs.) |
|---|---|---|---|---|---|
| 1. | Earthwork in excavation | 18.00 | $\text{m}^3$ | 400.00 | 7,200.00 |
Accompanying Documents of a Detailed Estimate:
- Report: Brief background, structural suitability, necessity, and design philosophy.
- Specifications: General specifications (quality of materials) and Detailed specifications (workmanship and proportions).
- Drawings: Architectural plans, structural sections, elevations, site plan, and layout plans.
- Design Calculations & Charts: Structural design computations, hydraulic calculations, load estimates.
- Particulars of Rates & Analysis of Rates: Justification of rates applied for material and labor.
3. Revised Estimate
A revised estimate is a detailed estimate prepared for revised quantities and rates of items of work originally provided in the original sanctioned estimate, without material deviations of structural nature from the originally approved design.
Conditions for Preparing a Revised Estimate:
- When the original detailed estimate is likely to exceed or market prices increase/decrease by more than 5% of the original estimate.
- When the total expenditure on an item of work is likely to exceed by more than 10% of the administrative approval.
- When there are material deviations from the original proposal during execution.
- When the original structural design is modified significantly.
4. Supplementary Estimate
A supplementary estimate is a fresh detailed estimate prepared when additional items of work or additions are required to supplement the original works during progress.
- The abstract must show the amount of the original estimate alongside the additional amount requested for the supplementary items.
- It is prepared whenever extra items or structural extensions need to be added to ongoing project works.
5. Annual Repair or Annual Maintenance Estimate
An Annual Repair (A.R.) or Annual Maintenance (A.M.) estimate is a detailed estimate prepared annually to keep a structure or public work in proper order, safe, and operable condition.
- Building Works: White washing, colour washing, painting of doors and windows, plaster repairs, and minor plumbing fixes.
- Road Works: Patch-hole repairs, maintenance of retaining walls, gabion structures, side drains, clearing culverts and bridges.
- Cost Allocation: The total estimated cost of maintenance is generally taken as 1.5% to 2% of the initial capital cost of the structure.
6. Extension and Improvement Estimate
- Extension Estimate: Prepared when additional floors (e.g., adding a second storey) or new structural wings are added to an existing building.
- Improvement Estimate: Prepared when existing room dimensions, layout arrangements, or structural finishes are modernized or altered in size.
7. Complete Estimate
A Complete Estimate encompasses all costs related to the main project from inception to completion, beyond the basic physical construction contract.
Inclusions in a Complete Estimate:
- Cost of land (actual acquisition price, compensation).
- Cost of legal expenses, registration, and title verification.
- Cost of main construction (materials, labor, plant, supervision).
- Engineering fees (a) Architectural design, survey & estimate preparation (b) Site supervision charges.
- Permits/fees for temporary water, power, and utility connections during construction.
- Transportation and administrative expenses incurred by owner/client.
- Contingencies and unforeseen charges.
8. Split-up of Cost of Building and Civil Works
Building Works Split-up (Load Bearing Structure)
| S.N. | Cost Items | Percentage of Whole Cost |
|---|---|---|
| 1. | Earthwork in Excavation & Filling | $1\%$ of whole cost |
| 2. | P.C.C. in Foundation | $5\%$ of whole cost |
| 3. | Damp Proof Course (D.P.C.) | $1\%$ of whole cost |
| 4. | Brick Work | $34\%$ of whole cost |
| 5. | Roofing Work | $20\%$ of whole cost |
| 6. | Flooring Work | $6\%$ of whole cost |
| 7. | Wood Work (Doors & Windows) | $16\%$ of whole cost |
| 8. | Plaster & Pointing Work | $10\%$ of whole cost |
| 9. | White Washing, Colour Washing & Painting | $2\%$ of whole cost |
| 10. | Miscellaneous Work | $5\%$ of whole cost |
| TOTAL = | 100% (Load Bearing) | |
General Cost Ratio Rules:
- Cost of Materials: $65\%$ to $70\%$ of total building cost.
- Cost of Labour: $30\%$ to $35\%$ of total building cost.
- Cost of Foundation & Plinth: $10\%$ to $15\%$ of total cost.
- Cost of Superstructure: $85\%$ to $90\%$ of total cost.
- Cost of Second Storey: $85\%$ to $90\%$ of ground floor cost.
Cost Breakdown for Road Works:
| Road Structural Component | Percentage Share |
|---|---|
| Earthwork Embankment / Cutting | $14\%$ |
| Soling Coat with Stone Aggregate | $22\%$ |
| Wearing Coat with Stone Aggregate | $25\%$ |
| Bituminous Surfacing / Carpet | $19\%$ |
| Other Works (Drainage, Culverts, Signage) | $20\%$ |
Building Service Percentages:
- Water Supply & Sanitation Work: $\approx 10\%$ of building cost.
- Electrical Installation: $\approx 8\%$ of building cost.
Solved Numerical Examples
Problem Statement: Prepare a preliminary estimate of a building project with a total plinth area of all buildings of $1500\text{ m}^2$. Given the following particulars:
- Plinth area rate = Rs $950$ per $\text{m}^2$
- Extra for special Architectural treatment = $1.5\%$ of building cost
- Extra for water supply & sanitary installation = $5\%$ of building cost
- Extra for Electrical installations = $14\%$ of building cost
- Extra for services = $6\%$ of building cost
- Contingencies = $3\%$ of overall total cost
- Supervision charges = $8\%$ of overall total cost
Solution:
1. Cost of building = $1500\text{ m}^2 \times \text{Rs } 950/\text{m}^2 = \mathbf{\text{Rs } 14,25,000.00}$
2. Special Architectural treatment ($1.5\%$ of Rs $14,25,000$) = $\text{Rs } 21,375.00$
3. Water supply & sanitary installation ($5\%$ of Rs $14,25,000$) = $\text{Rs } 71,250.00$
4. Internal Electrical installations ($14\%$ of Rs $14,25,000$) = $\text{Rs } 1,99,500.00$
5. Other services ($6\%$ of Rs $14,25,000$) = $\text{Rs } 85,500.00$
Sub-total Building & Services Cost (TC) = $14,25,000 + 21,375 + 71,250 + 1,99,500 + 85,500 = \mathbf{\text{Rs } 18,02,625.00}$
6. Contingencies ($3\%$ of TC) = $0.03 \times 18,02,625 = \text{Rs } 54,078.75$
7. Supervision charges ($8\%$ of TC) = $0.08 \times 18,02,625 = \text{Rs } 1,44,210.00$
Grand Total Estimated Cost = $18,02,625 + 54,078.75 + 1,44,210 = \mathbf{\text{Rs } 20,00,913.75}$
Problem Statement: Prepare a preliminary estimate for a framed four-storied office building having a carpet area of $300\text{ m}^2$ for each floor. Assume area occupied by corridors, verandahs, staircase etc. as $25\%$ of built-up area and that occupied by walls & columns as $8.5\%$ of the same. Given data:
- Built area rate for Ground Floor (excluding foundation) = Rs $1,500/\text{m}^2$
- Built area rate for 1st & 2nd floor = Rs $1,650/\text{m}^2$
- Built area rate for 3rd floor = Rs $1,800/\text{m}^2$
- Extra for foundation = $20\%$ of superstructure cost
- Extra for special Architectural treatment = $1\%$ of building cost
- Extra for W/S & Sanitary = $7\%$ of building cost
- Extra for Electrical installation = $8\%$ of building cost
- Extra for other services = $5\%$ of building cost
- Extra for Contingencies = $4\%$ of overall cost
- Extra for Work Charge Establishment = $10\%$ of overall cost
Solution:
Let $x$ be the built-up area or plinth area per floor.
$$x = \text{Carpet Area} + \text{Circulation Area} + \text{Wall/Column Area}$$ $$x = 300 + 0.25x + 0.085x \implies x(1 – 0.335) = 300 \implies 0.665x = 300$$ $$x = 451.13\text{ m}^2 \quad (\text{Plinth area per floor})$$Superstructure Cost Breakdown:
- Ground Floor Cost = $451.13\text{ m}^2 \times \text{Rs } 1,500 = \text{Rs } 6,76,695.00$
- 1st & 2nd Floor Cost = $2 \times 451.13\text{ m}^2 \times \text{Rs } 1,650 = \text{Rs } 14,88,729.00$
- 3rd Floor Cost = $451.13\text{ m}^2 \times \text{Rs } 1,800 = \text{Rs } 8,12,034.00$
Total Cost of Superstructure = $6,76,695 + 14,88,729 + 8,12,034 = \mathbf{\text{Rs } 29,77,458.00}$
Extra for Foundation ($20\%$ of superstructure) = $0.20 \times 29,77,458 = \text{Rs } 5,95,491.60$
Total Building Cost = $29,77,458 + 5,95,491.60 = \mathbf{\text{Rs } 35,72,949.60}$
Additions on Building Cost:
- Architectural treatment ($1\%$) = $\text{Rs } 35,729.50$
- W/S & Sanitary ($7\%$) = $\text{Rs } 2,50,106.47$
- Electrical installation ($8\%$) = $\text{Rs } 2,85,835.97$ ($\approx \text{Rs } 2,85,836.00$)
- Other services ($5\%$) = $\text{Rs } 1,78,647.48$
Overall Cost / Sub-total = $35,72,949.60 + 35,729.50 + 2,50,106.47 + 2,85,836.00 + 1,78,647.48 = \mathbf{\text{Rs } 43,23,269.05}$
Final Additions:
- Contingencies ($4\%$ of overall cost) = $0.04 \times 43,23,269.05 = \text{Rs } 1,72,930.76$
- Work Charged Establishment ($10\%$ of overall cost) = $0.10 \times 43,23,269.05 = \text{Rs } 4,32,326.91$
Grand Total Estimated Cost = $43,23,269.05 + 1,72,930.76 + 4,32,326.91 = \mathbf{\text{Rs } 49,28,526.72} \quad (\approx \mathbf{\text{Rs } 49,28,526.00})$
Problem Statement: Prepare a preliminary estimate of a school building for 800 students in order to assess the amount of fund based on the following particulars:
- Carpet area required per student = $1.2\text{ m}^2$
- Area of corridors, verandah & lavatories etc. = $20\%$ of plinth area
- Area of walls = $15\%$ of plinth area
- Consider plinth area rate = Rs $14,000/\text{m}^2$
- Cost of Water Supply = $5\%$ of building cost
- Cost of Sanitation = $7\%$ of building cost
- Cost of Electrification = $12\%$ of building cost
- Cost of approach road & boundary wall = $3\%$ of building cost
- Contingency & Work Charged Establishment = $5\%$ & $2.5\%$ of total cost respectively
Solution:
$$\text{Total Carpet Area} = 800 \times 1.2\text{ m}^2 = 960\text{ m}^2$$
Let $x$ be the plinth area of the building:
$$x = \text{Carpet Area} + 0.20x + 0.15x \implies x(1 – 0.35) = 960 \implies 0.65x = 960$$ $$x = 1476.923\text{ m}^2 \quad (\approx 1476.92\text{ m}^2)$$$$\text{Cost of Building} = 1476.92\text{ m}^2 \times \text{Rs } 14,000 = \mathbf{\text{Rs } 2,06,76,880.00}$$
Sub-head Services & Site Works:
- Water Supply ($5\%$ of building cost) = $0.05 \times 2,06,76,880 = \text{Rs } 10,33,844.00$
- Sanitation ($7\%$ of building cost) = $0.07 \times 2,06,76,880 = \text{Rs } 14,47,381.60$
- Electrification ($12\%$ of building cost) = $0.12 \times 2,06,76,880 = \text{Rs } 24,81,225.60$
- Approach road & boundary wall ($3\%$ of building cost) = $0.03 \times 2,06,76,880 = \text{Rs } 6,20,306.40$
Total Cost (TC) = $2,06,76,880 + 10,33,844 + 14,47,381.60 + 24,81,225.60 + 6,20,306.40 = \mathbf{\text{Rs } 2,62,59,637.60}$
Final Contingencies & Work Charged Establishment:
- Contingencies ($5\%$ of TC) = $0.05 \times 2,62,59,637.60 = \text{Rs } 13,12,981.88$
- Work Charged Establishment ($2.5\%$ of TC) = $0.025 \times 2,62,59,637.60 = \text{Rs } 6,56,490.94$
Grand Total Estimated Cost = $2,62,59,637.60 + 13,12,981.88 + 6,56,490.94 = \mathbf{\text{Rs } 2,82,29,110.42}$
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