NCC 2019 Volume Two
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Part 3.2.2 Preparation
3.2.2.1 Excavation for footings
(a)
Excavation for footings, including thickenings for slabs and pads must be clean cut with vertical sides, wherever possible.
(b)
(c)
Footing excavations must be free of loose earth, tree roots, mud or debris immediately before pouring concrete.
(d)
Topsoil containing grass roots must be removed from the area on which the footing will rest.
(e)
Excavation depths and soil cuts must comply with Part 3.1.1.
State and Territory Variations
State and Territory Variations
3.2.2.1(e) does not apply in New South Wales.
Note: In New South Wales requirements for shoring and adequacy of excavation works are a prescribed condition of development consent. In addition consent authorities can place specific controls on siteworks associated with the construction of a building, by imposing further conditions of development consent. Information addressing siteworks can be found in the Department of Planning and Environment – Act and Regulation note "Health, safety and amenity during construction".
(f)
On loose sand sites or sites subject to wind or water erosion, the depth below finished ground level for footings must be not less than 300 mm.
(g)
Height of finished slab-on-ground must be in accordance with 3.1.3.3(b).
3.2.2.2 Filling under concrete slabs
Filling placed under a slab (except where the slab is suspended) must comply with the following:
(a)
Filling must be either controlled fill or rolled fill as follows:
(i)
Sand used in controlled fill or rolled fill must not contain any gravel size material and achieve a blow count of 7 or more per 300 mm using the test method described in AS 1289.6.3.3.
(ii)
Clay used in controlled fill or rolled fill must be moist during compaction.
(iii)
(A)
Sand fill up to 800 mm deep — well compacted in layers not more than 300 mm deep by vibrating plate or vibrating roller.
(B)
Clay fill up to 400 mm deep — well compacted in layers of not more than 150 mm by a mechanical roller.
(iv)
(A)
Sand fill up to 600 mm deep — compacted in layers of not more than 300 mm by repeated rolling by an excavator or other suitable mechanical equipment.
(B)
Clay fill up to 300 mm deep — compacted in layers of not more than 150 mm by repeated rolling by an excavator or similar machine.
(b)
* * * * *
(c)
A level layer of clean quarry sand must be placed on top of the fill, with a depth of not less than 20 mm.
(d)
A graded stone termite management system complying with Part 3.1.4 may be substituted for the sand required in (c).
3.2.2.3 Foundations for footings and slabs
Footings and slabs, including internal and edge beams, must be founded on soil with an allowable bearing pressure as follows:
(a)
Slab panels, load support panels and internal beams — natural soil with an allowable bearing pressure of not less than 50 kPa or controlled fill or rolled fill compacted in accordance with 3.2.2.2.
(b)
Edge beams connected to the slab — natural soil with an allowable bearing pressure of not less than 50 kPa or controlled fill compacted in accordance with 3.2.2.2(a)(iii) and extending past the perimeter of the building 1 m with a slope ratio not steeper than 2 horizontal to 1 vertical (see Figure 3.2.2.1).
(c)
Pad footings, strip footings and edge beams not connected to the slab, must be—
(i)
founded in natural soil with an allowable bearing pressure of not less than 100 kPa; or
(ii)
for Class A and S sites they may be founded on controlled sand fill in accordance with 3.2.2.2(a).
3.2.2.4 Slab edge support on sloping sites
Footings and slabs installed on the low side of sloping sites must be as follows:
(a)
Slab panels — in accordance with 3.2.2.3(a).
(b)
Edge beams—
(i)
supported by controlled fill in accordance with 3.2.2.3(b) (see Figure 3.2.2.1, Option 1); or
(ii)
supported by deepened edge beams or bulk piers designed in accordance with AS 3600 (see Figure 3.2.2.1, Option 2); or
(iii)
deepened (as per AS 2870) to extend into the natural soil level with a bearing capacity in accordance with 3.2.2.3(b) (see Figure 3.2.2.1, Option 3); or
(iv)
stepped in accordance with AS 2870.
(c)
Edge beams not connected to the slab, pad footings and strip footings — founded in accordance with 3.2.2.3(c).
(d)
Where an excavation (cut) of the natural ground is used it must be in accordance with Part 3.1.1.
Figure 3.2.2.1
Explanatory information:
Explanatory information:
The foundations of a building are critical to its successful performance. As such, the soil must have the strength or bearing capacity to carry the building load with minimum movement.
The bearing capacity of a soil varies considerably and needs to be determined on a site by site basis. For this to occur, the appropriate people need to be consulted. These people may include a qualified engineer or experienced engineering geologist, or it may be determined by a person with appropriate local knowledge. The minimum bearing capacity (soil strength rating) may depend on the site conditions. The soil may be naturally undisturbed or be disturbed by building work or the like. Where soil is disturbed by building work and the like, the bearing capacity can be dramatically altered. This is typically the case for sloping sites where cut and fill procedures are used. In these situations the soil needs to be consolidated, generally via compaction, to achieve the required bearing capacity.
There are a number of alternatives for working on cut and filled sites. These are described in Figure 3.2.2.1.
Option 1 of Figure 3.2.2.1 refers to the controlled fill process which involves the compaction of fill in layers to achieve the bearing capacity described in 3.2.2.3. The depth of fill for each layer is specified to ensure effective compaction. Fill beyond these depths will need to be installed in accordance with the acceptable construction manuals set out in 3.2.0.
Option 2 and 3 of Figure 3.2.2.1 refer to edge beams that extend through the fill into undisturbed soil which provides the 3.2.2.3 required bearing capacity. In this situation the fill is essentially only taking the internal slab loads.
3.2.2.5 Stepped footings
Stepped strip footings must be constructed as follows—
(a)
the base of the footing must be horizontal or have a slope of not more than 1:10; or
(b)
be stepped in accordance with one of the methods shown in Figure 3.2.2.2.
Figure 3.2.2.2 Stepped strip footings
Note to Figure 3.2.2.2: All dimensions in millimetres.
3.2.2.6 Vapour barriers
A vapour barrier must be installed under slab-on-ground construction for all Class 1 buildings and for Class 10 buildings where the slab is continuous with the slab of a Class 1 building as follows—
(a)
Materials
A vapour barrier must be—
(i)
0.2 mm nominal thickness polyethylene film; and
(ii)
medium impact resistant,
determined in accordance with criteria specified in clause 5.3.3.3 of AS 2870; and
(iii)
be branded continuously “AS 2870 Concrete underlay, 0.2 mm Medium impact resistance”.
(b)
Installation
A vapour barrier must be installed as follows—
(i)
lap not less than 200 mm at all joints; and
(ii)
tape or seal with a close fitting sleeve around all service penetrations; and
(iii)
fully seal where punctured (unless for service penetrations) with additional polyethylene film and tape.
(c)
The vapour barrier must be placed beneath the slab so that the bottom surface of the slab is entirely underlaid and extends under edge beams to finish at ground level in accordance with Figure 3.2.2.3.
State and Territory Variations
State and Territory Variations
In New South Wales delete 3.2.2.6 and insert NSW 3.2.2.6 as follows:
NSW 3.2.2.6 Damp-proofing membrane
A damp-proofing membrane must be installed under slab-on-ground construction for all Class 1 buildings and for Class 10 buildings where the slab is continuous with the slab of a Class 1 building as follows—
- Materials
A damp-proofing membrane must be—
- 0.2 mm nominal thickness polyethylene film; and
- high impact resistant, determined in accordance with criteria specified in clause 5.3.3.3 of AS 2870; and
- be branded continuously "AS 2870 Concrete underlay, 0.2 mm High impact resistance".
- Installation
A damp-proofing membrane must be installed as follows—
- lap not less than 200 mm at all joints; and
- tape or seal with a close fitting sleeve around all service penetrations; and
- fully seal where punctured (unless for service penetrations) with additional polyethylene film and tape.
- The damp-proofing membrane must be placed beneath the slab so that the bottom surface of the slab is entirely underlaid and extends under edge beams to finish at ground level in accordance with Figure 3.2.2.3.
Note: A range of polyethylene films can be used, including black film and orange film, provided they satisfy the requirements for high impact resistance in accordance with the criteria specified in clause 5.3.3.3 of AS 2870.
In South Australia delete 3.2.2.6 and insert SA 3.2.2.6 as follows:
SA 3.2.2.6 Damp-proofing membrane
A continuous damp-proofing membrane must be installed under slab-on-ground construction for all Class 1 buildings and for Class 10 buildings where the slab is continuous with the slab of a Class 1 building as follows—
- Materials
A damp-proofing membrane must be—
- 0.2 mm nominal thickness polyethylene film; and
- high impact resistant with resistance to puncturing and moisture penetration,
determined in accordance with criteria specified in clause 5.3.3.3 of AS 2870; and
- be branded continuously “AS 2870 Concrete underlay, 0.2 mm High impact resistance” together with the manufacturer’s or distributor’s name, trade mark or code.
- Installation
A damp-proofing membrane must be installed as follows—
- lap not less than 200 mm at all joints; and
- tape or seal with a close fitting sleeve around all service penetrations; and
- fully seal where punctured (unless for service penetrations) with additional polyethylene film and tape.
- The damp-proofing membrane must be placed beneath the slab so that the bottom surface of the slab is entirely underlaid and extends under edge beams to finish at ground level in accordance with Figure 3.2.2.3.
3.2.2.7 Edge rebates
Edge rebates for slab-on-ground, stiffened raft or waffle raft with masonry cavity or veneer construction must comply with the following:
(a)
The rebate must not be less than 20 mm, except as provided for in (d).
(b)
Exterior masonry must not overhang more than 15 mm past the edge of the slab.
(c)
The edge rebate must be flashed and drained in accordance with Part 3.3.4 and where it cannot be flashed it must be filled with mortar.
(d)
Edge rebates are not required for single leaf masonry.
Explanatory information:
Explanatory information:
See 3.2.5.4 for minimum edge beam details.
Figure 3.2.2.3 Acceptable vapour barrier and damp-proofing membrane location
Note to Figure 3.2.2.3: All dimensions in millimetres.