NCC 2019 Volume Two
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 3.2.5.3a and Figure 3.2.5.3b.

(iii)

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

(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

External walls

Internal walls

(see Figure 3.2.5.2 to Figure 3.2.5.5 )

Single leaf masonry

Single leaf masonry

Single leaf masonry

Reinforced single leaf masonry

Articulated masonry on Class A and S sites; or framed

Articulated masonry veneer

Reinforced single leaf masonry

Articulated masonry or reinforced single leaf masonry

Masonry veneer

Articulated single leaf masonry

Articulated masonry

Articulated full masonry

Mixed construction

Mixed construction

Mixed construction

Full masonry

Framed

Articulated full masonry

Articulated full masonry

Framed

Masonry veneer

Earth wall masonry

Earth wall masonry

Earth wall masonry

Infill panels of earth masonry

Framed earth masonry

Articulated masonry veneer

Loadbearing earth masonry

loadbearing earth masonry

Articulated full 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)
(B)
(b)

Concrete stumps must—

(i)

be designed in accordance with—

(A)

AS 3600; or

(B)
(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)
(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 1684.2, AS 1684.3 or AS 1684.4; 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 1684.2, AS 1684.3 or AS 1684.4.

(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

Stump footing material

Length of stump (including embedded length)

1400 mm or less

Length of stump (including embedded length)

1401–1800 mm

Length of stump (including embedded length)

1801–3000 mm

Concrete

Minimum size: 100 mm × 100 mm or 110 mm diameter

Reinforcement:

Minimum number of 5 mm hard drawn wires: 1

Minimum size: 100 mm × 100 mm or 110 mm diameter

Reinforcement:

Minimum number of 5 mm hard drawn wires: 2

Minimum size: 125 mm × 125 mm or 140 mm diameter

Reinforcement:

Minimum number of 5 mm hard drawn wires: 2

Steel

Minimum size: 75 mm × 75 mm × 2.0 mm SHS

Minimum size: 75 mm × 75 mm × 2.0 mm SHS

Minimum size: 75 mm × 75 mm × 2.0 mm SHS

Timber

Minimum size: 100 mm × 100 mm or 110 mm diameter

Minimum size: 100 mm × 100 mm or 110 mm diameter

Minimum size: 100 mm × 100 mm or 110 mm diameter

Note to Table 3.2.5.2: SHS = square hollow section.

Figure 3.2.5.2 Pad footings for clad frame, Class A and S sites
v2_Fig3252_2005.svg
Table 3.2.5.3 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 to Table 3.2.5.3 :

1.

The effective area supported by a pad footing is the sum of—

a.

the supported floor area; and

b.

the supported roof area (if applicable); and

c.

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
Table 3.2.5.4a Reinforcement for stiffened raft footings for Class A sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l

Slab fabric where slab length <18 m

Slab fabric where slab length <25 m

Slab fabric where slab length <30 m

Clad frame

300

3-L8TM

N/A

SL72

SL82

SL92

Articulated masonry veneer

300

3-L8TM

N/A

SL72

SL82

SL92

Masonry veneer

300

3-L8TM

N/A

SL72

SL82

SL92

Articulated full masonry

400

3-L8TM

N/A

SL72

SL82

SL92

Full masonry

400

3-L8TM

N/A

SL72

SL82

SL92

Table 3.2.5.4b Reinforcement for stiffened raft footings for Class S sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l

Slab fabric where slab length <18 m

Slab fabric where slab length <25 m

Slab fabric where slab length <30 m

Clad frame

300

3-L8TM

N/A

SL72

SL82

SL92

Articulated masonry veneer

300

3-L8TM

N/A

SL72

SL82

SL92

Masonry veneer

300

3-L11TM

N/A

SL72

SL82

SL92

Articulated full masonry

400

3-L11TM

N/A

SL72

SL82

SL92

Full masonry

450

3-L11TM

5.0 (m) Note 2

SL82

SL82

SL92

Notes to Tables 3.2.5.4a to 3.2.5.4b :

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 must comply with Figure 3.2.5.3a or Figure 3.2.5.3b. At a re-entrant corner where an external beam continues as an internal beam, the internal beam details must 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
Table 3.2.5.5a Reinforcement for stiffened raft footings for Class M sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l (m)

Slab mesh where slab length <18 m

Slab mesh where slab length <25 m

Slab mesh where slab length <30 m

Clad frame

300

3-L11TM

6.0 Note 2

SL72

SL82

SL92

Articulated masonry veneer

400

3-L11TM

6.0 Note 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

Table 3.2.5.5b Reinforcement for stiffened raft footings for Class M-D sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l (m)

Slab mesh where slab length <18 m

Slab mesh where slab length <25 m

Slab mesh where slab length <30 m

Clad frame

400

3-L11TM

5.0 Note 2

SL72

SL82

SL92

Articulated masonry 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

N/A

N/A

N/A

N/A

N/A

N/A

Table 3.2.5.5c Reinforcement for stiffened raft footings for Class H sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l (m)

Slab mesh where slab length <18 m

Slab mesh where slab length <25 m

Slab mesh where slab length <30 m

Clad frame

400

3-L11TM

5.0 Note 2

SL72

SL82

SL92

Articulated full masonry

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

N/A

N/A

N/A

N/A

N/A

N/A

Table 3.2.5.5d Reinforcement for stiffened raft footings for Class H-D sites

Type of construction

Depth (D) (mm)

Bottom reinf.

Max. spacing c/l to c/l (m)

Slab mesh where slab length <18 m

Slab mesh where slab length <25 m

Slab mesh where slab length <30 m

Clad frame

500

3-L11TM

4.0

SL82

SL82

SL92

Articulated masonry veneer

600

3-L12TM

4.0

SL92

SL92

SL92

Masonry veneer

N/A

N/A

N/A

N/A

N/A

N/A

Articulated full masonry

1200

4-N16

4.0

SL102

SL102

SL102

Full masonry

N/A

N/A

N/A

N/A

N/A

N/A

Notes to Table 3.2.5.5a to 3.2.5.5d :

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 must comply with Figure 3.2.5.3b. At a re-entrant corner where an external beam continues as an internal beam, the internal beam details must be continued for a length of 1 m into the external beam.

Figure 3.2.5.4a Strip footing systems for Class A and S sites
v2_Fig3254a_2005.svg
Table 3.2.5.6a Dimensions and reinforcement for strip footing systems for Class A sites

Type of construction

D (mm)

B (mm)

Reinforcement (top and bottom)

Clad frame

300

300

3–L8TM

Articulated masonry veneer

300

300

3–L8TM

Masonry veneer

300

300

3–L8TM

Articulated full masonry

300

400

4–L8TM

Full masonry

300

400

4–L8TM

Notes to Table 3.2.5.6a :

1.

All masonry walls must be supported on strip footings.

2.

Internal strip footings must 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 must 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 must 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.

Table 3.2.5.6b Dimensions and reinforcement for strip footing systems for Class S sites

Type of construction

D (mm)

B (mm)

Reinforcement (top and bottom)

Clad frame

400

300

3–L8TM

Articulated masonry 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 Table 3.2.5.6b :

1.

All masonry walls must be supported on strip footings.

2.

Internal strip footings must 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 must 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 must 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 3.2.5.4b Strip footing system for Class M, M-D and H sites
v2_Fig3254b_2005.svg
Table 3.2.5.7a Dimensions and reinforcement for strip footing systems for Class M sites

Site Class

Type of construction

D (mm)

B (mm)

Reinforcement (top and bottom)

Class M

Clad frame

400

300

3–L11TM

Class M

Articulated masonry veneer

450

300

3–L11TM

Class M

Masonry veneer

500

300

3–L12TM

Class M

Articulated full masonry

600

400

4–L12TM

Class M

Full masonry

900 Note 2

400

4–L12TM

Notes to Table 3.2.5.7a :

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 must 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 must 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 must be provided at the sides of the footing only.

3.

Infill floors must 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 must 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.

Table 3.2.5.7b Dimensions and reinforcement for strip footing systems for Class M-D sites

Site Class

Type of construction

D (mm)

B (mm)

Reinforcement (top and bottom)

Class M-D

Clad frame

500

300

3–L11TM

Class M-D

Articulated masonry veneer

550

300

3–L12TM

Class M-D

Masonry veneer

700Note 2

300

3–N16

Class M-D

Articulated full masonry

1100Note 2

400

4–N16

Notes to Table 3.2.5.7b :

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 must 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 must 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 must be provided at the sides of the footing only.

3.

Infill floors must 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 must 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 site Classes M-D and H, a provision must be made by methods such as an adequate crawl space to allow for future re-levelling due to drying effects.

Table 3.2.5.7c Dimensions and reinforcement for strip footing systems for Class H sites

Type of construction

D (mm)

B (mm)

Reinforcement (top and bottom)

Clad frame

500

300

3–L11TM

Articulated masonry veneer

600

300

3–L12TM

Masonry veneer

850Note 2

300

3–N16

Articulated full masonry

1100Note 2

400

4–N16

Notes to Table 3.2.5.7c :

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 must 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 must 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 must be provided at the sides of the footing only.

3.

Infill floors must 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 must 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 site Classes M-D and H, a provision must 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 to Figure 3.2.5.5 :

  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.