Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Design and Construction of Stairs
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Design and Construction of Stairs
Download the Lessonotes Mobile Nigeria 2025 app for faster lesson access on Android and iPhone.
Subject: Textile trade
Class: Senior Secondary 3
Term: 2nd Term
Week: 1
Theme: Blocklaying / Bricklaying
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.
This topic introduces students to the fundamental principles, design considerations, and practical construction methods for stairs, an essential structural element in multi-level buildings. Understanding the design and construction of stairs is critical for aspiring artisans and technicians in the blocklaying and general construction industry in Nigeria, ensuring structures are not only functional but also safe, durable, and aesthetically pleasing. The principles learned here are directly applicable to residential, commercial, and public building projects across the country, enhancing students' employability and entrepreneurial prospects.
This section provides a detailed explanation of all important ideas and definitions related to the design and construction of stairs. 2.
1. Definition of Stairs and Their Purpose A stair (or staircase) is a series of steps arranged to connect two or more different floor levels within a building. Its primary purpose is to provide safe and convenient vertical circulation, allowing occupants to move between floors. Stairs also serve as emergency exits and contribute significantly to the aesthetic appeal of a building. 2.
2. Key Terminologies in Stair Construction Understanding these terms is crucial for discussing and designing stairs: Step: Comprises one tread and one riser.
Tread: The horizontal surface of a step upon which one places their foot.
Riser: The vertical portion of a step, connecting one tread to the next.
Going (or Run): The horizontal distance from the face of one riser to the face of the next riser. It determines the depth of the tread.
Rise (Total Rise or Vertical Rise): The total vertical height between two consecutive finished floor levels that the stair needs to span.
Flight: An uninterrupted series of steps between two landings or between a floor and a landing. A stair can consist of one or more flights.
Landing: A level platform provided at the top or bottom of a flight, or between flights, to allow for rest, change of direction, or access to different rooms.
Headroom: The clear vertical distance measured from the line of the nosings to the ceiling, soffit, or any overhead obstruction directly above. Adequate headroom is vital for safety, usually a minimum of 2.0 to 2.2 meters.
Nosing: The projecting edge of a tread beyond the face of the riser below it. It adds to the effective going and helps prevent slipping.
Stringer (or String): The inclined beam or member that supports the ends of the treads and risers. It can be an open string (where treads and risers are visible) or a closed string (where treads and risers are housed within the stringer).
Balustrade: The protective barrier along the open side of a stair, comprising vertical members (balusters) and a top rail (handrail).
Baluster: Vertical posts that support the handrail.
Handrail: The top member of a balustrade, designed to be grasped by hand for support and safety.
Newel Post: A vertical post that supports the handrail at the top, bottom, or an angle/turn of a stair. 2.
3. Types of Stairs Commonly Used in Nigeria The choice of stair type depends on available space, building function, cost, and aesthetic considerations.
1. Straight Flight Stair: Consists of a single straight flight of steps without any change in direction.
Advantages: Simplest to construct, provides direct ascent/descent, suitable for narrow spaces where length is available.
Disadvantages: Requires long linear space, can be monotonous, less safe if very long (no landing for rest).
Nigerian Context: Commonly found in small residential houses, sometimes as secondary access stairs.
2. Quarter Turn Stair: Changes direction by 90 degrees, usually achieved with a square or rectangular landing at the turn.
Advantages: Space-saving compared to a straight flight, provides a resting point.
Disadvantages: Landing might reduce flow if not well designed.
Nigerian Context: Popular in medium-sized homes and offices where a straight run is impractical.
3. Half Turn Stair (Dog-legged Stair): Consists of two flights running in opposite directions, connected by a 180-degree turn via a landing. The flights are usually very close or directly above each other with a small 'dog-leg' space between them.
Advantages: Very common, space-efficient, provides a good landing for rest.
Disadvantages: The space beneath the landing and upper flight might be dark or enclosed.
Nigerian Context: Extremely common in multi-storey residential buildings (duplexes, flats) and small commercial structures.
4. Open Well Stair (Open Newel Stair): Similar to a half-turn stair, but with an open space or 'well' between the flights, providing more light and often a grander appearance.
Advantages: Visually appealing, allows more light penetration, can accommodate lifts or design features in the well.
Disadvantages:* Requires more space than a dog-legged space-efficient, provides a good landing for rest.
Disadvantages: The space beneath the landing and upper flight might be dark or enclosed.
Nigerian Context: Extremely common in multi-storey residential buildings (duplexes, flats) and small commercial structures.
4. Open Well Stair (Open Newel Stair): Similar to a half-turn stair, but with an open space or 'well' between the flights, providing more light and often a grander appearance.
Advantages: Visually appealing, allows more light penetration, can accommodate lifts or design features in the well.
Disadvantages: Requires more space than a dog-legged stair, can be more expensive.
Nigerian Context: Found in larger residential buildings, hotels, and public buildings where aesthetics are a priority.
5. Geometric (Curved/Spiral)
Stair: These stairs are curved in plan, often without newel posts. Spiral stairs are a specific type of geometric stair where steps radiate from a central column.
Advantages: Aesthetically striking, space-saving (especially spiral), creates a focal point.
Disadvantages: Difficult to construct, expensive, can be less comfortable or safe, especially for large items.
Nigerian Context: Used in contemporary designs, luxury homes, and some commercial spaces for architectural flair.
6. Winder Stair: Steps that are wider on one side than the other, used to change direction without a landing.
Advantages: Very space-efficient where a landing is not feasible.
Disadvantages: Less safe, especially for elderly users or carrying items, as the tread width varies. Not recommended for primary stairs.
Nigerian Context: Rarely used for main stairs; sometimes for attic access or secondary service stairs where space is extremely limited. 2.
4. Design Principles and Regulations for Safe and Comfortable Stairs General building regulations and best practices guide stair design to ensure safety, comfort, and accessibility. While specific national codes may vary, the underlying principles are universal.
1. Relationship between Riser (R) and Going (G): This is the most crucial design parameter for comfort.
Rule of Thumb: (2 x Riser) + Going = 550mm to 700mm (or 600mm to 640mm for residential comfort).
Explanation: This formula ensures a comfortable walking rhythm. Too steep (large R, small G) or too shallow (small R, large G) can lead to discomfort or accidents.
Maximum Riser Height: Residential buildings: 220mm (max)
Public buildings: 190mm (max)
Minimum Going: Residential buildings: 220mm (min)
Public buildings: 250mm (min)
Worked Example 1: Calculating Riser and Going A new duplex in Lagos has a floor-to-floor height (total rise) of 3.0 meters (3000mm). The client prefers a comfortable riser height.
Step 1: Determine the number of risers. Assume a preferred comfortable riser height (R) of 180mm (within residential limits). Number of Risers = Total Rise / Preferred Riser Height Number of Risers = 3000mm / 180mm = 16.67 Since the number of risers must be a whole number, we round up or down and adjust the actual riser height. Rounding to 17 risers is usually preferred for smaller adjustment to riser height. Actual Number of Risers = 17 risers. Adjusted Riser Height (R) = Total Rise / Actual Number of Risers Adjusted Riser Height (R) = 3000mm / 17 = 176.47mm (approx. 176.5mm). This is within the 220mm maximum.
Step 2: Determine the number of treads. Number of Treads = Number of Risers - 1 Number of Treads = 17 - 1 = 16 treads.
Step 3: Determine the going (G). Using the formula (2R + G = 600mm to 640mm). Let's aim for 620mm. 2(176.47mm) + G = 620mm 352.94mm + G = 620mm G = 620mm - 352.94mm = 267.06mm (approx. 267mm). This going is within the 220mm minimum for residential and makes for a comfortable stair.
Step 4: Calculate the total going (horizontal length of the stair flight). Total Going = Number of Treads × Going per Tread Total Going = 16 treads × 267mm = 4272mm (4.272 meters).
2. Width of Stair: Residential: Minimum 900mm (for single-family dwellings).
Public/Commercial: Minimum 1200mm (to allow two-way traffic or emergency egress).
Emergency exits: May require wider stairs.
3. Landings: Required for every 12 to 15 risers (typically). Minimum length and width of a landing should be for residential and makes for a comfortable stair.
Step 4: Calculate the total going (horizontal length of the stair flight). Total Going = Number of Treads × Going per Tread Total Going = 16 treads × 267mm = 4272mm (4.272 meters).
2. Width of Stair: Residential: Minimum 900mm (for single-family dwellings).
Public/Commercial: Minimum 1200mm (to allow two-way traffic or emergency egress).
Emergency exits: May require wider stairs.
3. Landings: Required for every 12 to 15 risers (typically). Minimum length and width of a landing should be equal to the width of the stair flight. Essential for safety, rest, and changing direction.
4. Headroom: Minimum 2.0 to 2.2 meters clear headroom is required throughout the entire length of the stair, measured vertically from the nosing line to any overhead obstruction. This is vital for tall individuals and for carrying items.
5. Handrails and Balustrades: Required for stairs with more than two risers, particularly on the open sides of flights and landings.
Handrail height: 900mm to 1000mm from the nosing line. Balusters should be spaced such that a 100mm sphere cannot pass through (to prevent children from falling through). Handrails must be graspable and continuous where possible.
6. Lighting: Stairs must be adequately lit, both naturally and artificially, to ensure safe use at all times.
7. Fire Resistance: In public buildings, stairs are often designed as fire-protected escape routes, requiring fire-resistant materials and enclosures.
8. Non-slip Surfaces: Treads should have non-slip finishes or strips to prevent accidents. 2.
5. Construction Process of Stairs (Reinforced Concrete Stair as a common Blocklaying/Bricklaying task) The construction of a reinforced concrete stair often involves blocklayers who are skilled in formwork construction and concrete placement.
Phase 1: Planning and Setting Out
1. Site Inspection & Measurements: Verify the floor-to-floor height and available space.
2. Detailed Design: Finalize the number of risers, treads, going, and overall dimensions based on the design principles and structural engineer's drawings.
3. Setting Out: Accurately mark the stairwell opening, the starting and ending points of the stair flight, stringer lines, and landing positions on the floor slab and walls using chalk lines, measuring tapes, and plumb bobs.
Phase 2: Formwork Erection This is a critical stage that determines the final shape and accuracy of the stair. Blocklayers often construct this formwork.
1. Support System: Erect sturdy vertical props (adjustable steel props or timber posts) to support the entire formwork structure. These must rest on solid ground or a structurally adequate slab below.
2. Soffit Formwork: Construct the inclined bottom formwork (soffit) of the stair slab. This is typically made from timber planks or plywood supported by bearers and joists, which are in turn supported by the vertical props. The soffit must be smooth and accurately angled.
3. Side Formwork (Stringers): Erect formwork for the sides of the stair (the stringers) to contain the concrete laterally. These must be plumb and accurately define the width of the stair.
4. Riser Formwork: This is the most intricate part. Individual riser boards (timber or plywood) are cut to the exact riser height and length and securely fixed between the stringer forms. They must be perfectly vertical and parallel to each other, maintaining the calculated going distance. These boards are usually slightly chamfered at the bottom edge to allow for easy removal after concrete sets.
5. Landing Formwork: Construct horizontal formwork for any landings, ensuring they are level and supported adequately.
6. Bracing and Support: Ensure all formwork is adequately braced and supported to withstand the weight and pressure of wet concrete. Check all dimensions, levels, and plumbness before reinforcement placement.
Phase 3: Reinforcement Placement
1. Cut and Bend Rebars: Steel reinforcement bars (rebars) are cut and bent according to the structural engineer's drawings. This usually includes main bars running along the soffit (bottom) of the stair slab, distribution bars perpendicular to the main bars, and additional bars at landings and connections to floor slabs.
2. Positioning: Place the rebars within the formwork, ensuring correct spacing and adequate concrete cover (typically 20-25mm from the formwork surface) using plastic or concrete spacers (chairs).
3. Tying: Tie the rebars together and plumbness before reinforcement placement.
Phase 3: Reinforcement Placement
1. Cut and Bend Rebars: Steel reinforcement bars (rebars) are cut and bent according to the structural engineer's drawings. This usually includes main bars running along the soffit (bottom) of the stair slab, distribution bars perpendicular to the main bars, and additional bars at landings and connections to floor slabs.
2. Positioning: Place the rebars within the formwork, ensuring correct spacing and adequate concrete cover (typically 20-25mm from the formwork surface) using plastic or concrete spacers (chairs).
3. Tying: Tie the rebars together securely with binding wire to maintain their position during concrete pouring.
4. Shear Links: Install shear links (stirrups) at critical points, especially where the stair slab connects to landings or floor beams, to resist shear forces.
Phase 4: Concrete Pouring and Curing
1. Mixing and Transport: Prepare or order concrete of the specified mix ratio. Transport it carefully to the stair location.
2. Pouring: Pour the concrete starting from the bottom of the flight, working upwards. This helps to compact the concrete properly and reduce segregation.
3. Compaction: Vibrate the concrete thoroughly using a poker vibrator to remove air voids and ensure proper compaction around the reinforcement. Hand tamping and rodding are also used, especially in smaller, tighter areas.
4. Screeding and Finishing: Level and smooth the treads and landings immediately after pouring using a wooden float or steel trowel. Ensure correct slopes for drainage on landings if exposed to weather.
5. Curing: Protect the fresh concrete from rapid drying for at least 7 days (or longer depending on mix design and weather) by covering with polythene sheets, hessian sacks, or by regularly wetting the surface. This is crucial for achieving the designed concrete strength and preventing cracks.
Phase 5: Formwork Removal and Finishing
1. Formwork Removal: Carefully remove the formwork once the concrete has gained sufficient strength (typically 3-7 days for risers and sides, 14-21 days for soffit and props, depending on the concrete strength and support system).
2. Repairs: Carry out any necessary minor repairs or patching of concrete surfaces.
3. Finishing: Apply desired finishes to the treads and risers (e.g., screed, tiles, marble, granite, timber). Install balustrades, handrails, and newel posts according to design.
Note on Block-Built Stairs: In some simpler constructions, especially for external stairs or those in non-load bearing situations, steps can be built up using sandcrete blocks, filled with lean concrete or rubble, and then screeded. This method is less common for main internal stairs due to structural limitations but can be economical for garden steps or simple risers over a concrete ramp. The principles of going, riser, and overall dimensions remain the same.
Understanding the design and construction of stairs has numerous direct applications and integrations within the Nigerian context: Safety and Accessibility in Public Spaces: Application: Knowledge of comfortable riser-going ratios, minimum widths, and handrail requirements directly informs the construction of safe stairs in schools, hospitals, markets, and government buildings across Nigeria. Poorly designed stairs are a common cause of accidents. Skilled artisans can contribute to reducing these incidents by adhering to standards, benefiting the entire community, especially the elderly and children.
Integration: Students can be tasked with evaluating stair designs in their local communities (e.g., their school, local market, or clinic) and proposing improvements based on learned principles, fostering a sense of civic responsibility and practical problem-solving. Entrepreneurship and Employment in the Construction Industry: Application: The ability to accurately design and construct stairs is a highly valued skill for blocklayers, masons, and general building contractors in Nigeria's booming construction sector. This knowledge opens doors to employment opportunities in residential and commercial building projects, from simple bungalows to multi-storey complexes in cities like Lagos, Abuja, and Port Harcourt. Artisans proficient in bespoke stair construction (e.g., using concrete, timber, or steel for modern designs) can set up their own businesses, creating jobs and contributing to the local economy.
Integration: The lesson can integrate discussions on career pathways in construction, highlighting the demand for skilled stair constructors. Students can research local construction companies or artisans specializing in stair work to understand market demands and pricing. Sustainable Building Practices and Cost Optimization: Application: Efficient stair design reduces material waste (e.g., optimizing concrete and reinforcement usage) and construction time, leading to cost savings, which is crucial in Nigerian construction projects where budgets are often tight. Choosing appropriate stair types for specific spaces can minimize overall building footprint and material requirements. Using locally sourced materials for finishes (e.g., local hardwood for handrails, local tiles for treads) also supports the local economy and reduces carbon footprint.
Integration: Students can be challenged to design a stair for a given scenario using locally available and sustainable materials, considering cost-effectiveness and environmental impact. This connects the technical knowledge to broader economic and environmental principles relevant to Nigeria's development goals.