Lesson Notes By Weeks and Term v4 - SHS 2
SUBSTRUCTURE AND SUPERSTRUCTURE
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
SUBSTRUCTURE AND SUPERSTRUCTURE
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Applied Technology
Class: SHS 2
Term: 1st Term
Week: 17
Grade code: 2.3.2.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 2.3.2.CS.1
Indicator code: 2.3.2.LI.2
Theme: BUILDING CONSTRUCTION TECHNOLOGY
Subtheme: SUBSTRUCTURE AND SUPERSTRUCTURE
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 lesson introduces the fundamental process of "Setting Out" in building construction. Before any foundation is dug or a single block is laid, the exact position and outline of the building must be transferred from the architectural drawings onto the actual piece of land. This process is called setting out. It is the critical first step in building the substructure (the part of the building below the ground, like the foundation). In Ghana, we see new buildings going up in our towns and villages every day. A well-set-out building stands strong and straight, while a poorly set-out one can lead to cracks, structural failure, or even disputes with neighbours over land boundaries.
A. Context: Substructure and Superstructure Before we learn to set out, let's remember what we are building. A building is divided into two main parts: Substructure: This is the part of the building that is below the ground level. Its main job is to transfer the load of the entire building safely to the soil. It includes the foundations. Superstructure: This is the part of the building that is above the ground level. It is the part we see and use every day, including the walls, floors, columns, beams, and roof.
Setting out is the very first practical step in constructing the substructure. B. What is Setting Out? Setting out is the process of transferring the dimensions and position of a proposed building from the architectural drawings (the plan) to the actual ground on the construction site.
Think of it this way: An architect draws the house on paper. The mason or site engineer uses setting out to "draw" the same house, at full size, on the ground using pegs and strings. This outline on the ground shows exactly where to dig the trenches for the foundation.
The lines established during setting out represent the centre-lines or the faces of the foundation trenches and walls. C. Why is Setting Out so Important? (Reasons for Setting Out) Setting out is not just about making lines on the ground; it is a critical step for several reasons: Accuracy: It ensures the building has the correct size, shape, and angles as designed by the architect. Without it, rooms could be smaller than planned, and walls might not be straight. Positioning: It ensures the building is placed correctly on the plot of land, respecting the required distances (setbacks) from roads, other buildings, and property boundaries. This helps prevent land disputes with neighbours or the local assembly. Orientation: It helps to position the building correctly in relation to the sun, wind, and views, as intended in the design. For example, ensuring windows face a certain direction for good ventilation. Structural Integrity: It guarantees that all corners are true right angles (90°). If the corners are not square, the loads from the superstructure will not be distributed correctly into the foundation, which can lead to structural weaknesses and cracks over time. Foundation Guide: The lines from setting out provide a clear and exact guide for the workers who will excavate the foundation trenches. This prevents wastage of labour and materials from digging in the wrong place or at the wrong size. D. Tools for Setting Out To perform setting out correctly, you need a set of specific tools: Measuring Tape (Steel): For measuring distances accurately. A 30m or 50m tape is common. Pegs (Wooden or Steel): Sharpened stakes driven into the ground to mark corners and important points. Builder's Lines (String/Nylon Cord): Stretched tightly between pegs or profile boards to mark the straight lines of the walls. Hammer or Mallet: For driving pegs into the ground. Profile Boards: These are simple horizontal boards nailed to two upright posts, set up outside the corners of the building outline. The lines are tied to nails on these boards, so the lines can be removed for digging and replaced in the exact same spot later. Builder's Square: A large L-shaped tool made of steel or wood, used to check or set out perfect 90° angles (right angles). Spirit Level: To ensure the profile boards are set perfectly level (horizontal). E. Methods of Setting Out The most important part of setting out is establishing the corners accurately, especially the first right angle (90°). From this first corner, the rest of the building can be laid out. Method 1: The 3-4-5 Method (Using Pythagoras' Theorem) This is the most common and accurate method used by masons in Ghana and worldwide. It is based on a mathematical principle called Pythagoras' Theorem (a² + b² = c²). A triangle with sides in the ratio 3:4:5 will always have a perfect right angle (90°) between the two shorter sides (3 and 4).