NCC 2016 Volume Two
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Part 3.2.5 Footing and Slab Construction

Part 3.2.5 Footing and Slab Construction

Explanatory information

Explanatory information:

The footings included in this Part reflect the requirements of AS 2870 and apply to the most common types of soil conditions. If the soil conditions on site are not covered by this Part then additional guidance can be obtained from AS 2870 or the appropriate authority.

These provisions are not meant to prohibit the use of alternative traditional footing methods found through experience to be suitable for local soil conditions (especially those used in stable soils). Such footings may be appropriate, provided they meet the relevant Performance Requirements listed in Section 2.

The diagrams in this Part reflect acceptable footing designs only. They do not provide details for termite management systems such as the correct placement of ant capping and slab edge exposure.

For details on termite management systems, see Part 3.1.3.

3.2.5.1 Footing and slab construction

(a)

Footing and slab construction, including size and placement of reinforcement, must comply with the relevant provisions of this Part and the following details:

(i)

Footings for stumps — the appropriate details in 3.2.5.6 and Table 3.2.5.2.

(ii)

Stiffened raft Class A, S, M, M-D, H and H-D sites — the appropriate details in Figure 3.2.5.3(a) and Figure 3.2.5.3(b).

(iii)

Strip footing systems in Class A, S, M, M-D and H sites — the appropriate details in Figure 3.2.5.4(a) and Figure 3.2.5.4(b).

(iv)

Footing slabs for Class A sites — the appropriate details in Figure 3.2.5.5.

(b)

Footings for single leaf masonry, mixed construction and earth wall masonry must comply with the equivalent footing construction set out in Table 3.2.5.1.

3.2.5.2 Footings and slabs to extensions to existing buildings

(a)

Footings to extensions to Class 1 or 10 buildings may be of similar proportions and details to those used with an existing same Class of building on the same allotment provided—

(i)

masonry and masonry veneer walls are articulated at the junction with the existing building; and

(ii)

the performance of the existing building has been satisfactory, i.e. there has been no significant cracking or movement (see Section 2 of AS 2870 for acceptable footing performance); and

(iii)

there are no unusual moisture conditions on the site.

(b)

Class 10 buildings of clad framed construction may use footing systems appropriate for one class of reactivity less severe than for a house (e.g. site classification M can be reduced to S).

Table 3.2.5.1 EQUIVALENT FOOTING CONSTRUCTION

Actual construction

Equivalent footing construction

(see Figure 3.2.5.2 to 5)
External walls Internal walls
Single leaf masonry
Reinforced Articulated masonry on Class A and S sites; or framed veneer
Reinforced single leaf masonry or reinforced Masonry veneer
Articulated Articulated full masonry
Mixed construction
Full masonry Framed Articulated full masonry
Articulated full masonry Framed Masonry veneer
Earth wall masonry
Infill panels of earth masonry Framed earth masonry veneer
Loadbearing earth masonry earth masonry Articulated full masonry


single leaf masonry

3.2.5.3 Shrinkage control

(a)

Where brittle floor coverings, such as ceramic tiles, are to be used over an area greater than 16 m2, one of the following additional measures must be taken to control the effect of shrinkage cracking—

(i)

the amount of shrinkage reinforcement (steel reinforcement mesh in the slab panel) must be—

(A)

increased to SL92 or equivalent throughout the affected slab area; or

(B)

doubled with an additional sheet of slab mesh throughout the affected slab area; or

(ii)

the bedding system for brittle coverings must be selected on the basis of the expected slab movement and the characteristics of the floor covering (including the use of expansion joints etc.); or

(iii)

the placement of floor covering must be delayed for not less than 3 months after the concrete has been poured.

(b)

At re-entrant or internal corners, two strips, minimum 2 m in length, of 3–L8TM or one strip of 3–L11TM (or 3-N12 bars) must be placed diagonally across the corner in accordance with Figure 3.2.5.1.

Figure 3.2.5.1

REINFORCING AT RE-ENTRANT CORNERS

v2_Fig3251_2005.svg

3.2.5.4 Minimum edge beam dimensions

Except for waffle raft slabs, where the edge rebate is more than 150 mm in depth, the width of the edge beam at the base of the rebate must not be less than 200 mm, except that if R10 or N10 ties at 900 mm spacing (or equivalent) are provided to resist vertical forces, the width of the edge beam at the base of the rebate can be reduced to 150 mm.

3.2.5.5 Footings for fireplaces on Class A and S sites

(a)

Fireplaces must be supported on a pad footing—

(i)

150 mm thick for single storey (one trafficable floor and a wall height not more than 4.2 m) construction; and

(ii)

200 mm thick for 2 storey (two trafficable floors and a wall height not more than 8 m) construction; and

(iii)

reinforced top and bottom with SL72 mesh; and

(iv)

extending 300 mm past the edges of the masonry except for any edge flush with the outer wall.

(b)

The pad footing may form an integral part of the slab.

3.2.5.6 Stump footing details

(a)

Footings for stumps must comply with—

(i)

the provisions of Table 3.2.5.2 for Class A and Class S sites; or

(ii)

the appropriate acceptable construction manual listed in—

(A)

; or

(B)

3.2.0.

(b)

Concrete stumps must—

(i)

be designed in accordance with—

(A)

AS 3600; or

(B)

Table 3.2.5.2 ; and

(ii)

use a minimum 20 MPa concrete as defined in AS 3600.

(c)

Steel stumps must be—

(i)

designed in accordance with—

(A)

AS 4100; or

(B)

Table 3.2.5.2 ; and

(ii)

fully enclosed and sealed with a welded top plate; and

(iii)

encased in concrete sloping away from the stump and finishing not less than 100 mm above finished ground level; and

(iv)

corrosion protected in accordance with Part 3.4.4.

(d)

Timber stumps must be designed in accordance with—

(i)

AS 1684 Parts 2, 3 or 4; or

(e)

Stumps must be braced—

(i)

by a full perimeter masonry base; or

(ii)

for concrete stumps — in accordance with AS 3600; or

(iii)

for steel stumps — in accordance with AS 4100; or

(iv)

for timber stumps — in accordance with AS 1684 Parts 2, 3 or 4.

(f)

Stumps must be embedded into the foundation material not less than 30% of their height above ground level or 450 mm, whichever is the greater.

Table 3.2.5.2 STUMP FOOTING — IN AREAS WITH A DESIGN WIND SPEED OF NOT MORE THAN N2

LENGTH OF STUMP (mm) (including embedded length) CONCRETE STEEL TIMBER
Minimum size (mm) REINFORCEMENT Number of 5 mm (min.) hard drawn wires Minimum size (mm) (SHS = square hollow section) Minimum size (mm)
Less than 1400 100 × 100 or 110 diameter 1 75 × 75 × 2.0 SHS 100 × 100 or 110 diameter
1401–1800 100 × 100 or 110 diameter 2 75 × 75 × 2.0 SHS 100 × 100 or 110 diameter
1801–3000 125 × 125 or 140 diameter 2 75 × 75 × 2.0 SHS 100 × 100 or 110 diameter
Figure 3.2.5.2
PAD FOOTINGS FOR CLAD FRAME, CLASS A AND S SITES
v2_Fig3252_2005.svg
MINIMUM DIMENSIONS OF CIRCULAR AND SQUARE PAD FOOTINGS FOR CLAD FRAME CLASS A AND S SITES
Effective supported areas — m 2 Width of square pad — mm Width of circular pad — mm Thickness (t) — mm Depth — mm
10 400 500 200 400
20 500 600 200 400
30 600 750 250 400

Notes:

  1. The effective area supported by a pad footing is the sum of—
    1. the supported floor area; and
    2. the supported roof area (if applicable); and
    3. half the supported wall area in elevation (if applicable).
  2. The width or diameter can be reduced to one half the above footings on rock.
  3. The pad footings must be constructed in concrete except that masonry footings can be used under masonry piers.
  4. Pad footing sizes must also apply to footings supporting roof and floor loads only.
  5. The foundation must provide an allowable bearing pressure of not less than 100 kPa.
  6. The excavation must be backfilled with manually rodded tamped soil, or the footing thickness shall be increased by 50 mm.
  7. Where stump pad footings provide resistance to horizontal or uplift forces, the minimum size of the footing must comply with AS 2870.
  8. Braced stumps must comply with 3.2.5.6(e).
Figure 3.2.5.3a
FOOTING SLAB AND STIFFENED RAFT SLAB DETAILS FOR CLASS A AND S SITES
v2_Fig3253a_2005.svg
REINFORCEMENT FOR STIFFENED RAFT FOOTINGS Slab Fabric
Site Class Type of Construction Depth (D) mm Bottom reinf. Max. spacing c/l to c/l (m) Slab length <18 m Slab length <25 m Slab length <30 m
Class A Clad Frame 300 3–L8TM - SL72 SL82 SL92
Articulated masonry veneer 300 3–L8TM - SL72 SL82 SL92
Masonry veneer 300 3–L8TM - SL72 SL82 SL92
Articulated full masonry 400 3–L8TM - SL72 SL82 SL92
Full masonry 400 3–L8TM - SL72 SL82 SL92
Class S 300 3–L8TM - SL72 SL82 SL92
veneer 300 3–L8TM - SL72 SL82 SL92
Masonry veneer 300 3–L8TM - SL72 SL82 SL92
Articulated full masonry 400 3–L11TM - SL72 SL82 SL92
Full masonry 450 3–L11TM 5.0Note 2 SL82 SL82 SL92

Notes:

  1. Internal and external edge beams must be arranged to form an integral structural grid (see clauses 5.3.8 and 5.3.9 of AS 2870).
  2. A 10% increase in spacings is permitted where the spacing in the other direction is 20% less than that specified.
  3. Where external beams are wider than 300 mm, an extra bottom bar or equivalent of the same bar size is required for each 100 mm additional width.
  4. Where a reinforced single leaf masonry wall is constructed directly above and structurally connected to a concrete edge beam, the beam may be reduced to 300 mm wide by 300 mm deep and reinforced with 3–L8TM reinforcement.
  5. Alternative reinforcement sizes must comply with AS 2870.
  6. Internal beam details and spacings shall comply with Figure 3.2.5.3(a) or (b). At a re-entrant corner where an external beam continues as an internal beam, the internal beam details shall be continued for a length of 1 m into the external beam.
Figure 3.2.5.3b
FOOTING SLAB AND STIFFENED RAFT SLAB DETAILS FOR CLASS M, M-D, H AND H-D SITES
v2_Fig3253b_2005.svg
REINFORCEMENT FOR STIFFENED RAFT FOOTINGS Slab Mesh
Site Class Type of Construction Depth (D) mm Bottom reinf. Max. spacing c/l to c/l (m) Slab length <18 m Slab length <25 m Slab length <30 m
Class M Clad Frame 300 3–L11TM 6.0Note 2 SL72 SL82 SL92
veneer 400 3–L11TM 6.0Note 2 SL72 SL82 SL92
Masonry veneer 400 3–L11TM 5.0Note 2 SL72 SL82 SL92
Articulated full masonry 500 3–L12TM 4.0 SL82 SL82 SL92
Full masonry 800 3-N16 4.0 SL92 SL92 SL92
Class M-D 400 3–L11TM 5.0Note 2 SL72 SL82 SL92
veneer 400 3–L11TM 4.0 SL72 SL82 SL92
Masonry veneer 500 3–L12TM 4.0 SL82 SL82 SL92
Articulated full masonry 625 3–L12TM 4.0 SL92 SL92 SL92
Full masonry - - - - - -
Class H Clad Frame 400 3–L11TM 5.0Note 2 SL72 SL82 SL92
veneer 500 3–L12TM 4.0 SL82 SL82 SL92
Masonry veneer 700 3–N16 4.0 SL92 SL92 SL92
Articulated full masonry 1000 4–N16 4.0 SL102 SL102 SL102
Full masonry - - - - - -
Class H-D 500 3–L11TM 4.0 SL82 SL82 SL92
veneer 600 3–L12TM 4.0 SL92 SL92 SL92
Masonry veneer - - - - - -
Articulated full masonry 1200 4–N16 4.0 SL102 SL102 SL102
Full masonry - - - - - -

Notes:

  1. Internal and external edge beams must be arranged to form an integral structural grid (see clauses 5.3.8 and 5.3.9 of AS 2870).
  2. A 10% increase in spacings is permitted where the spacing in the other direction is 20% less than that specified.
  3. Where external beams are wider than 300 mm, an extra bottom bar or equivalent of the same bar size is required for each 100 mm additional width.
  4. Where a reinforced single leaf masonry wall is constructed directly above and structurally connected to a concrete edge beam, the beam may be reduced to 300 mm wide by 300 mm deep and reinforced with 3–L8TM reinforcement.
  5. Alternative reinforcement sizes must comply with AS 2870.
  6. Internal beam details and spacings shall comply with Figure 3.2.5.3(b). At a re-entrant corner where an external beam continues as an internal beam, the internal beam details shall be continued for a length of 1 m into the external beam.
Figure 3.2.5.4a
STRIP FOOTING SYSTEMS IN CLASS A AND S SITES
v2_Fig3254a_2005.svg
DIMENSIONS AND REINFORCEMENT FOR STRIP FOOTING SYSTEMS
Site Class Type of Construction D B Reinforcement (top and bottom)
Class A 300 300 3–L8TM
veneer 300 300 3–L8TM
Masonry veneer 300 300 3–L8TM
Articulated full masonry 300 400 4–L8TM
Full masonry 300 400 4–L8TM
Class S 400 300 3–L8TM
veneer 400 300 3–L8TM
Masonry veneer 400 300 3–L8TM
Articulated full masonry 400 400 4–L11TM
Full masonry 500 400 4–L11TM

Notes:

  1. All masonry walls must be supported on strip footings.
  2. Internal strip footings shall be of the same proportions as the external footings and run from external footing to external footing. “Side slip joints” consisting of a double layer of polyethylene shall be provided at the sides of the footing only.
  3. Infill floors may be concrete slabs, brick paving, stone flags or compacted and stabilised earth. For concrete slab infill panels, mesh may be required to control shrinkage in slab panels and around openings or restrained regions. Concrete infill slabs must use a minimum of SL62 mesh to control shrinkage (see also 3.2.5.3).
  4. Where footings are wider than the specified width, an extra bottom bar or equivalent of the same bar size is required for each 100 mm additional width. If strip footings deeper than those required are used, the reinforcement shall be increased to match that specified for the deepened proportions.
  5. The measurement of Df is greater or equal to D plus 75 mm.
  6. Alternative reinforcing sizes must comply with AS 2870.
Figure 3.2.5.4(b)
STRIP FOOTING SYSTEMS IN CLASS M, M-D AND H SITES
v2_Fig3254b_2005.svg
DIMENSIONS AND REINFORCEMENT FOR STRIP FOOTING SYSTEMS
Site Class Type of Construction D B Reinforcement (top and bottom)
Class M 400 300 3–L11TM
veneer 450 300 3–L11TM
Masonry veneer 500 300 3–L12TM
Articulated full masonry 600 400 4–L12TM
Full masonry 900Note 2 400 4–L12TM
Class M-D 500 300 3–L11TM
veneer 550 300 3–L12TM
Masonry veneer 700Note 2 300 3–N16
Articulated full masonry 1100Note 2 400 4-N16
Class H 500 300 3–L11TM
veneer 600 300 3–L12TM
Masonry veneer 850Note 2 300 3–N16
Articulated full masonry 1100Note 2 400 4-N16

Notes:

  1. All masonry walls must be supported on strip footings.
  2. For beams 700 mm or deeper, as specified in the table above, internal footings shall be provided at no more than 6 m centres and at re-entrant corners to continue footings to the opposite external footing. Internal strip footings shall be of the same proportions as the external footings and run from external footing to external footing. “Side slip joints” consisting of a double layer of polyethylene shall be provided at the sides of the footing only.
  3. Infill floors shall only be used for Class A and S sites.
  4. Where footings are wider than the specified width, an extra bottom bar or equivalent of the same bar size is required for each 100 mm additional width. If strip footings deeper than those required are used, the reinforcement shall be increased to match that specified for the deepened proportions.
  5. The measurement of Df is greater or equal to D plus 75 mm.
  6. Alternative reinforcing sizes must comply with AS 2870.
  7. For Class M articulated full masonry and full masonry, internal strip footings must be of the same proportions as the external footing and run from external footing to external footing.
  8. For site Classes M-D and H, a provision shall be made by methods such as an adequate crawl space to allow for future re-levelling due to drying effects.
Figure 3.2.5.5
FOOTING SLABS FOR CLASS A SITES SUITABLE FOR:
  1. CLAD FRAME.
  2. ARTICULATED MASONRY VENEER
  3. MASONRY VENEER
  4. ARTICULATED FULL MASONRY.
  5. FULL MASONRY.
v2_Fig3255_2005.svg
Notes:
  1. Use SL63 when slab length is less than 12 m.
  2. Use SL62 when slab length is less than 18 m.
  3. Use SL72 when slab length is less than 25 m.
  4. Use SL82 when slab length is less than 30 m
  5. In parts of Western Australia (around Perth) and other locations where the site consists of extremely stable sands, and where specified by a professional engineer, the slab thickness may be reduced to 85 mm and reinforced as follows:
    1. Use SL53 when slab length is less than or equal to 12 m.
    2. Use SL63 when slab length is less than or equal to 18 m.
    3. Use SL62 when slab length is less than or equal to 25 m.
  6. Dune sands may require compaction.