Finding the FGL FFL and Natural Ground

Finding the FGL, FFL and the Natural Ground Level

1. Find out the FGL and FFL First.

2. To find the FGL, need to find the highest RL and the lowest RL that the house is located on the property.

So, the find the FGL:

- Highest RL is 12.50; Lowest RL is 10.0.

- 12.50 – 10.0 = 2.50.

This means that there is a fall from the highest part of the house to the lowest part of the house of 2500mm or 2.5 metres.

- 2.50 / 2 = 1.25 (Cut and Fill)

3. So, FGL is:

- 12.50 – 1.25 = 11.25

4. FFL is:

11.25 + 0.3 (thickness of slab) = 11.55

5. To calculate Natural Ground Line:

Rule: If the result is positive then the NGL is below the FGL line, and if is a negative result, then the NGL is above the FGL.

FGL – RL

11.25 – 12.50 = -1.25

This means for the highest part of the house, the natural ground line is above the FGL point by 1250mmm.

For the lowest part of the house,

11.25 – 10.0 = 1.25

This means that the lowest part of the house, the natural ground line is below the FGL point by 1250mm.