Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Estimating and Costing of Construction Jobs
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Estimating and Costing of Construction Jobs
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Block laying, Brick laying & Concrete Works
Class: Senior Secondary 3
Term: 2nd Term
Week: 3
Theme: Entrepreneurship In Building Trades
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
Students should beable to:Illustrate with aid of sketchesof a simple on ebedroom selfcontainedbuilding with working. specificationand estimatecost of materials.
toilet, with good quality locks and hinges.
Windows: Aluminium sliding windows with mosquito nets.
Finishes: Internal and external walls to be rendered with cement sand mortar (1:4) and painted with emulsion paint. Floor finished with ceramic tiles.
Plumbing: PVC pipes for water supply and waste. Water closet (WC), wash hand basin, kitchen sink. Septic tank and soak away system.
Electrical: Surface conduit wiring, standard light points, socket outlets, fan points. Distribution board (DB). 2.
5. Quantity Take-off This is the process of measuring the quantities of each item of work from the drawings and specifications.
General Rules: Measure in logical order (e.g., excavation, foundation, blockwork, concrete, roofing, finishes). Use appropriate units (m3 for excavation/concrete, m2 for blockwork/plastering/painting/flooring/roofing, m for skirting/cornice, number for doors/windows/sanitary fittings). Apply deductions for openings (doors, windows) where relevant (e.g., for plastering, painting). For blockwork, deductions are usually made for openings larger than 1.0 m2. 2.
6. Pricing and Bill of Quantities (BoQ)
Pricing: Once quantities are determined, obtain current unit rates for materials from local suppliers and market surveys. Labour rates are based on prevailing wages.
Bill of Quantities (BoQ): A detailed document listing all items of work with their measured quantities, unit rates, and total costs. It serves as the basis for tendering and contract administration. For this lesson, a simplified materials cost schedule will be developed. 2.
7. Step-by-Step Process for Estimating Material Costs for a Simple Building
1. Understand the Project Scope: Carefully study the sketch and specifications of the one-bedroom self-contained building.
2. Break Down the Building into Work Items: Divide the construction into measurable parts (e.g., Foundation (excavation, concrete), Blockwork, Concrete Slab, Roofing, Doors, Windows, Finishes).
3. Perform Quantity Take-off for Each Work Item: Example 1: Foundation Excavation: Measure the total length of all strip foundations from the plan (perimeter of the building + any internal load-bearing walls). Multiply by width and depth of the trench (e.g., Length x 0.45m x 0.90m = Volume in m3).
Example 2: Foundation Concrete: Use the same length as excavation. Multiply by width and depth of concrete (e.g., Length x 0.45m x 0.30m = Volume in m3).
Material Calculation for Concrete (Mix 1:3:6): For 1m3 of 1:3:6 concrete, approximately: Cement: 5 bags Sand: 0.45 m3 Gravel: 0.90 m3 (
Note: These are approximations; exact quantities depend on bulking factors and specific mix designs. For SS3, these approximations are acceptable.)
Example 3: Blockwork (150mm thick): Calculate the total linear length of 150mm walls. Multiply by the height of the walls (e.g., from top of foundation to wall plate level, deducting window/door heights). This gives the area in m
2. Number of blocks per m2: For 150mm blocks (450x150x225mm), approximately 9 blocks per m2 (allowing for mortar joints). Material Calculation for Blockwork Mortar (1:6 Cement:Sand): For 100 blocks, approximately 1 bag of cement and 0.1 m3 of sand.
Example 4: Roofing: Calculate the plan area of the roof. For a simple gable roof, typically multiply the plan area by a factor (e.g., 1.2 to 1.3) to account for pitch and overhangs. Alternatively, measure rafter length and roof width. * Material Calculation: Number of sheets (based on length and width of sheets, allowing for overlaps), timber for trusses (measured in lengths of specific sizes, e.g., 50x75mm, 50x100mm).
4. Obtain Unit Prices: Research current market prices for cement, sand, gravel, blocks, steel, timber, roofing sheets, doors, windows, paint, etc., in Naira. (Provide assumed rates if market research is not feasible for the students).
5. Calculate Total Material Cost for Each Item: Multiply quantity by unit price.
6. Summarise Costs: Compile all material costs into a comprehensive schedule. --- This section explains the core concepts and methodologies for estimating and costing construction jobs, focusing on practical application. 2.
1. Estimating Definition: Estimating in construction is the process of predicting the probable cost of a project before its commencement. It involves calculating the quantities of materials, labour, plant, and other resources required, and then applying current unit prices to these quantities.
Purpose: To determine the financial feasibility of a project, assist in budgeting, secure financing, evaluate bids, and control costs during construction.
Types of Estimates: Preliminary Estimate (Approximate Estimate): Prepared at the initial stage of a project when detailed drawings are not available. It uses methods like area method, cubic content method, or unit rate method based on similar past projects. Useful for feasibility studies.
Detailed Estimate: Prepared when complete working drawings and specifications are available. It involves a precise calculation of quantities for each item of work, applying current market rates. This is the focus for this lesson. 2.
2. Costing Definition: Costing refers to the actual determination and analysis of expenses incurred in undertaking a construction project or a specific item of work. While estimating predicts future costs, costing accounts for actual expenditures.
Purpose: To monitor project expenditure against the estimate, analyse profitability, and provide data for future estimates. 2.
3. Components of an Estimate A comprehensive estimate typically includes:
1. Material Costs: Cost of all raw materials (e.g., cement, sand, gravel, blocks, steel, timber, roofing sheets, paints, plumbing fittings, electrical cables). This is calculated by multiplying the quantity of each material by its unit market price.
2. Labour Costs: Wages paid to skilled and unskilled workers. This can be calculated based on daily rates, task rates, or rates per unit of work (e.g., per square metre of blockwork).
3. Plant and Equipment Costs: Costs associated with machinery and tools, including hire charges, fuel, maintenance, and depreciation. For small projects, this might involve basic tools; for larger ones, excavators, concrete mixers, etc.
4. Overhead Costs: Indirect costs not directly attributable to a specific work item but essential for the project. Examples include site supervision salaries, administrative expenses, permits, insurance, transportation, temporary facilities (site office, store), water, and electricity. Usually calculated as a percentage of material and labour costs or as a lump sum.
5. Profit: A percentage added to the total cost to ensure the contractor makes a gain from the project. This varies depending on market conditions, project risk, and contractor's policy (typically 10-25%). 2.
4. Working Drawings and Specifications Working Drawings: These are graphical representations (e.g., floor plans, elevations, sections) that show the dimensions, layout, and construction details of a building. They are essential for accurate quantity take-off. For a simple one-bedroom self-contained building, a basic floor plan showing room dimensions, wall thicknesses, door and window positions is sufficient.
Specifications: A written document that describes the quality of materials, workmanship, and methods to be used in construction. It complements the drawings by providing detailed instructions for each work item. Example for a One-Bedroom Self-Contained Building: Foundation: Strip foundation, 900mm deep, 450mm wide.
Concrete mix 1:3:6 (cement:sand:gravel). Hardcore layer 150mm thick, well compacted.
Walls: 150mm thick sandcrete blocks for external walls, 100mm thick sandcrete blocks for internal walls. Well cured.
Floor: Ground floor finished with 50mm thick cement screed on 150mm thick concrete slab (mix 1:2:4), over 200mm laterite filling and 250micron polythene sheet damp proof membrane.
Roof: Timber roof truss, treated hardwood, rafters @ 600mm centres. Long span aluminium roofing sheets, gauge 0.55mm, with necessary accessories.
Doors: Panel doors (e.g., flush doors) for entrance and toilet, with good quality locks and hinges.
Windows: Aluminium sliding windows with mosquito nets.
Finishes: Internal and external walls to be rendered with cement sand mortar (1:4) and painted with emulsion paint. Floor finished with ceramic tiles.
Plumbing: PVC pipes for water supply and waste. Water closet (WC), wash hand basin, kitchen sink. Septic tank and soak away system. * Electrical: Surface conduit wiring, standard light points, socket outlets, fan points. Distribution board (DB). 2.
5. Quantity Take-off This is the process of measuring the quantities of each item of This section outlines practical activities for both the teacher and students, suitable for a Nigerian classroom setting. 3.
1. Teacher Activities Introduction (10 minutes): Introduce the topic: Estimating and Costing.
Engage students with a real-life scenario: "Imagine a client wants to build a small shop. How do we tell them how much it will cost before we even start?" Briefly explain the importance of accurate estimation in preventing losses and ensuring project success.
Concept Explanation (20 minutes): Define "Estimating" and "Costing," differentiating between them. Discuss the key components of an estimate (materials, labour, plant, overheads, profit), emphasising material costs for this lesson. Explain the role of working drawings and specifications using simple examples relevant to a building. Illustrating the One-Bedroom Self-Contained Building (20 minutes): On the whiteboard or using a prepared chart, sketch a basic floor plan of a one-bedroom self-contained building.
Keep it simple: living room, bedroom, kitchen, toilet/bathroom. Label the rooms, dimensions, and indicate wall thicknesses (e.g., 150mm external, 100mm internal).
Activity: Guide students in identifying different parts of the building from the sketch (e.g., foundation, walls, doors, windows, roof).
Developing Specifications (20 minutes): Using the sketched building, lead a discussion to generate a basic working specification.
Activity: Ask students to suggest materials and finishes for different parts (e.g., "What kind of blocks for the wall?", "What type of roofing sheet?"). Consolidate their suggestions into a clear, concise specification list on the board (refer to Section 2.4). Demonstrating Quantity Take-off and Costing (30 minutes): Focus on one or two major items: Foundation concrete and blockwork.
Foundation Concrete: Demonstrate calculating the total length of the foundation from the sketch. Explain how to calculate the volume of concrete required (Length x Width x Depth). Provide approximate material quantities for 1m3 of 1:3:6 concrete (cement, sand, gravel). Provide realistic unit costs (e.g., Cement: N5,000/bag; Sand: N10,000/m3; Gravel: N15,000/m3). Show the step-by-step calculation for the total cost of foundation concrete materials.
Blockwork: Demonstrate calculating the total area of external 150mm block walls (Length x Height, deducting major openings). Explain the number of blocks per m2 (approx. 9 blocks for 150mm blocks). Show calculation for total blocks. Provide approximate material quantities for mortar (cement, sand per 100 blocks). Provide realistic unit costs (e.g., 150mm block: N450/block). Show the step-by-step calculation for the total cost of blockwork materials.
Wrap-up and Q&A (10 minutes): Summarise the key steps in estimating material costs. Address student questions and clarify any misunderstandings. 3.
2. Student Activities Participation: Actively participate in discussions, ask questions, and contribute ideas for specifications.
Sketch Interpretation: Identify different building elements and dimensions from the teacher's sketch.
Specification Development: In groups or individually, list down basic specifications for key building components.
Quantity Take-off Practice: Practice calculating quantities for specific items based on the teacher's demonstration and provided dimensions.
Costing Practice: Apply given unit rates to calculated quantities to determine material costs.
Note Taking: Take detailed notes on definitions, processes, and example calculations. --- This section provides scaffolded practice questions for students, along with detailed solutions, to reinforce understanding. Assume the following realistic unit costs for practice: Cement: N5,000 per bag Sharp Sand: N10,000 per m3 Gravel (Granite): N15,000 per m3 150mm Sandcrete Block: N450 per block 100mm Sandcrete Block: N350 per block Long Span Aluminium Roofing Sheet (0.55mm gauge): N4,000 per linear metre (approx. N2,500/m2 effective area)
Question 1: Sketch and Basic Specification Draw a simple, labelled floor plan sketch of a one-bedroom self-contained building with the following approximate dimensions: Living Room (3.5m x 3.0m), Bedroom (3.0m x 3.0m), Kitchen (2.0m x 1.5m), Toilet/Bathroom (1.5m x 1.2m). Assume external walls are 150mm thick and internal walls are 100mm thick. Then, list basic working specifications for: a) Foundation, b) External Walls, c) Roofing.
Solution 1: a)
Floor Plan Sketch: (Teacher to draw on board or provide handout. Example description below for teacher reference) A rectangular shape overall. Divide into rooms as specified. Show door openings (e.g., 900mm wide for main entrance and living/bedroom, 750mm for kitchen/toilet). Show window openings (e.g., 1200mm wide for living/bedroom, 900mm for kitchen/toilet). Label rooms and indicate dimensions. Indicate wall thicknesses. ``` +-------------------------------------------------+ | | | EXTERNAL 150mm WALL | | +---------------------+ +------------------+ | | | LIVING ROOM | | BEDROOM | | | | (3.5m x 3.0m) | | (3.0m x 3.0m) | | | | |--D--| | | | | | +------------------+ | | | | | 100mm Int. Wall | | | +-----W---------------+--+-----+-------------+ | | | KITCHEN | | TOILET/BATH | | | | (2.0m x 1.5m) |--D--| (1.5m x 1.2m) | | | +---------------------+ +-----+-------------+ | | | +-------------------------------------------------+ (
Note: 'W' for window, 'D' for door. Dimensions are internal. Actual drawing would be to scale with clear wall lines) ``` b)
Basic Working Specifications: Foundation: Strip foundation, 900mm deep x 450mm wide.
Concrete mix 1:3:
6. External Walls: 150mm thick sandcrete blocks.
Roofing: Timber roof truss, treated softwood. Long span aluminium roofing sheets (0.55mm gauge).
Question 2: Quantity Take-off for Foundation Concrete (for Question 1 sketch) Using the sketch description from Question 1, calculate the total volume of concrete (mix 1:3:6) required for the strip foundation. Assume the foundation concrete is 450mm wide and 300mm deep. (For simplicity, assume only external walls have foundations for this exercise).
Solution 2:
1. Determine External Perimeter: Length of building = 3.5m (LR) + 0.15m (wall) + 3.0m (BR) + 0.15m (wall) = 6.8m (approx. assuming shared internal 100mm wall in the middle is not founded externally). Width of building = 3.0m (LR/BR) + 0.15m (wall) = 3.15m (approx. assuming kitchen/toilet project out at one end). Alternatively, measure each section: Top/Bottom long walls: (3.5 + 3.0 + 0.15(wall between BR & K/T) + 0.1(wall between LR & K/T)) 2 + 0.15(wall) = ~6.8m + 6.8m = 13.6m Side walls: (3.0 + 1.5 + 1.2 + 0.1(wall)) 2 = 5.8m 2 = 11.6m (this is getting too complex for SS3 without a clear diagram. Let's simplify the perimeter based on the overall dimensions). Let's assume the overall dimensions for the entire building footprint based on the room sizes are roughly: Overall Length = (3.5m + 3.0m) + 0.15m (ext. wall) + 0.1m (int. wall) + 0.15m (ext. wall) = 6.9m Overall Width = (3.0m) + 0.15m (ext. wall) + 0.1m (int. wall) + 0.15m (ext. wall) = 3.4m Revised simplified perimeter calculation (assuming a simple rectangle enclosing all rooms): Living Room (3.5m x 3.0m) Bedroom (3.0m x 3.0m) Kitchen (2.0m x 1.5m) Toilet/Bathroom (1.5m x 1.2m) Let's assume overall external dimensions including 150mm external walls: Length = 3.5 + 0.15 (wall) + 3.0 + 0.1 (internal wall) + 0.15 (wall) = 6.9m. Width = 3.0 + 0.15 (wall) + 0.1 (internal wall) + 1.5 + 0.15 (wall) = 4.9m.
External Perimeter (P): 2 (Overall Length + Overall Width) P = 2 (6.9m + 4.9m) = 2 11.8m = 23.6m Internal Load-Bearing Walls: (e.g., wall separating living room/bedroom from
This topic has profound real-life relevance in Nigeria, impacting various aspects of community, economy, and individual lives.
Entrepreneurship and Job Creation: Many Nigerians engage in building projects, from personal homes to small businesses. The ability to accurately estimate and cost jobs allows individuals to start and manage their own construction businesses, offering services as contractors, material suppliers, or independent estimators. This directly contributes to job creation and economic empowerment at the local level. For example, a student can learn to prepare a cost estimate for building a community toilet block or a small church hall, securing contracts and managing the project effectively. Informed Decision-Making and Consumer Protection: For ordinary Nigerians, understanding estimating and costing empowers them to make informed decisions when embarking on personal building projects. They can critically evaluate quotes from contractors, understand where their money is going, and avoid being overcharged or exploited. This knowledge can also help them budget realistically for their dream homes or business premises, preventing project abandonment due to financial mismanagement.
Resource Management and Waste Reduction: Accurate estimation leads to efficient procurement of materials, reducing waste and over-ordering which are common issues in construction. This not only saves money but also promotes sustainable practices by optimising resource use. For instance, knowing the exact number of blocks and bags of cement needed for a specific wall reduces material wastage often seen on Nigerian construction sites. ---