Site drainage is covered in Part 2 of the NCC. You can download the NCC free of charge.
3.1.3.3 Surface water drainage
Surface water must be diverted away from Class 1 buildings as follows:
(a)Slab-on-ground — finished ground level adjacent to buildings:
the external finished surface surrounding the slab must be drained to move surface water away from the building and graded to give a slope of not less than (see Figure 3.1.2.2)—
(i)25 mm over the first 1 m from the building in low rainfall intensity areas for surfaces that are reasonably impermeable (such as concrete or clay paving); or
(ii)50 mm over the first 1 m from the building in any other case.
(b)Slab-on-ground — finished slab heights:
the height of the slab-on-ground above external finished surfaces must be not less than (see Figure 3.1.3.2)—
(i)100 mm above the finished ground level in low rainfall intensity areas or sandy, well-drained areas; or
(ii)50 mm above impermeable (paved or concreted areas) that slope away from the building in accordance with (a); or
(iii)150 mm in any other case.
Explanatory information:
The appropriate slab height above finished ground level and the slope of the external finished surface surrounding the slab may vary depending on:
1.The local plumbing requirements; in particular the height of the overflow relief gully relative to drainage fittings and ground level (to work effectively they must be a minimum of 150 mm below the lowest sanitary fixture).
2.The run-off from storms, particularly in areas of high rainfall intensity, and the local topography.
3.The effect of excavation on a cut and fill site.
4.The possibility of flooding.
5.Termite risk management provisions.
Clearances between wall cladding and the finished ground level are provided in 3.5.4.7.
(c)The ground beneath suspended floors must be graded so that the area beneath the building is above the adjacent external finished ground level and surface water is prevented from ponding under the building (see Figure 3.1.3.3).