Lesson Notes By Weeks and Term v5 - Grade 10

Lesson Video

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Performance objectives

• Define setting out and foundations.
• Explain the 3-4-5 method for setting out.
• Identify types of shallow foundations.
• Describe how to construct a strip foundation.
• Calculate concrete volume for a foundation.

Lesson summary

Setting out and foundations are the crucial first steps in any construction project.

Think about it: without accurate setting out, your house wouldn't be square, your walls wouldn't be straight, and your doors wouldn't fit! Similarly, a poorly designed or constructed foundation will lead to cracking walls, sinking floors, and ultimately, structural failure. In a country like South Africa, where affordable housing is a significant need, understanding these basic construction processes is vital, not only for aspiring builders but also for informed citizens who might want to build their own homes or oversee construction projects.

Lesson notes

2.1 Setting Out: The Blueprint on the Ground Setting out is the process of transferring the building plan from paper onto the ground. It essentially marks the exact position and dimensions of the building before any excavation or construction begins. Accuracy is paramount because errors at this stage will cascade throughout the entire project, leading to costly rework and structural problems. It’s like drawing the outline for a painting; if the outline is wrong, the entire painting will be flawed. Why is setting out so important?

Accuracy: Ensures the building is square, level, and meets the design specifications.

Cost Savings: Prevents errors that lead to material wastage and rework.

Structural Integrity: Ensures the building is stable and safe.

Compliance: Adheres to building regulations and permits. 2.2 The 3-4-5 Method (Pythagorean Theorem) The 3-4-5 method is a simple and reliable technique for creating a perfect right angle (90 degrees).

It's based on the Pythagorean theorem: a² + b² = c². In a right-angled triangle, the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.

How it works: Measure 3 meters (or any multiple of 3) along one line (e.g., the proposed front of the building). Mark this point. Measure 4 meters (or the same multiple of 4) along the adjacent line, starting from the same corner. Mark this point. Measure the distance between the two marked points. If the angle is a perfect right angle, this distance will be 5 meters (or the same multiple of 5). Adjust the angle until the distance is exactly 5 meters. You now have a perfect 90-degree angle.

Worked example

Let's say you want to set out a right angle using the 3-4-5 method.

You measure 6 meters (2 x 3) along one line and mark the point.

You measure 8 meters (2 x 4) along the adjacent line from the same starting point and mark the point.

The distance between the two marked points should be 10 meters (2 x 5). If it's not, adjust the angle until it is.

2.3 Profile Boards (Batter Boards)

Profile boards are wooden frames erected a short distance away from the building lines. They provide a stable reference point for marking the building's dimensions and levels. Wires or strings are stretched between the profile boards to indicate the exact position of the building walls, even after excavation has commenced.

Construction of Profile Boards:

They typically consist of two upright posts driven into the ground, with a horizontal crossbar nailed across them.

They are erected far enough away from the excavation to avoid being disturbed during construction (usually 1-2 meters).

Pegs or nails are driven into the crossbars to mark the exact position of the building lines.