How to get 90° on Layout of Building ? What is 3-4-5 Rule in Layout of any civil structure ?

The 3-4-5 rule is the most common and standard rule in overall civil engineering to find out right angle in layout, we Civil Engineers have various codes to ensure the principles to ensure the safety and stability of civil structures, the 3-4-5 Rule is very handy and it is the trick that applies as Pythagorean theorem to create right angles during layout of building or during construction process. This rule is particularly useful in the early stage when we cast or setup foundation for our building or structures where right angle is must and is crucial because if a structure is not in right angle then the structure will not look good and the load distribution will also be affected in the building.

This 3-4-5 Rule work in simple triangular ratio, this mathematical relationship allow us to quickly check the corner of a square by using tape measure.

What is 3-4-5 rule ?

According to Pythagoras theorem in a right-angle triangle, the square of the hypotenuse side is equal to the sum of squares of the other two sides, We will use this method to get right angle in any layout of building / civil structure .

Right angle ion building layout is important due to

  1. Elevation Look
  2. Equal load Distribution
  3. Provide Level and Surface

According to Pythagoras Theorem : C2=A2+ B2

Where A,B & C are the sides of the right angle triangle.

Lets Suppose : AB = 3m, BC = 4m Then Side AC will be 5m

Let’s Calculate the Side

 AC2=AB2+ BC2

AC = √AB2+ BC2

AC = √32+ 42

AC = √9 + 16

AC = √25 = 5m

Use in Construction/ in Layout

Material Needed

  1. Measuring Tape
  2. Chalk Power/ POP
  3. 2 Person
  4. Calculator
  5. String / Wire
  6. Rods / ranging Rods

Let’s Suppose we have a plot / Wall of known Length [ABCD] and we have to measure right angle for layout

Let’s consider a Wall/ Plot ABCD, having four walls/ Side AB, BC, CD, & DA.

Step 01:

Measure 3m on AB and Mark with any pugs or with temporary benchmark, mark it as E .

Step 02:

Measure 4m on BC and mark with temporary benchmark, mark it as F

Step 03 :

Measure and adjust the sides of AB & BC until we get the length of EF as 5m.

Repeat these steps from all the sides of plot /wall, you will get all corner as right angle.

We can use this methods in

  1. Residential buildings,
  2. Underground tanks,
  3. Outhouses,
  4. All Layout , etc.

The unit may vary from meter / feet but the process will be same in all the method.

by the help of this 3-4-5 rule you can easily check the layout of a building or a structure without any advanced equipment’s like : Total Station, Dumpy Level, Level Station etc. just you need to have a measuring tape and 2 person and thread and pugs.