Part 3.2.5 Footing and slab construction

NCC 2019 Volume Two

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Part 3.2.5 Footing and slab construction

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

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

Full masonry

Framed

Articulated full masonry

Framed

Masonry veneer

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

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)

Part 3.4.3; 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 1684.2, AS 1684.3 or AS 1684.4; or

(ii)

Table 3.2.5.2.

(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

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 :

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

the supported floor area; and

the supported roof area (if applicable); and

half the supported wall area in elevation (if applicable).

The width or diameter can be reduced to one half the above footings on rock.

The pad footings must be constructed in concrete except that masonry footings can be used under masonry piers.

Pad footing sizes must also apply to footings supporting roof and floor loads only.

The foundation must provide an allowable bearing pressure of not less than 100 kPa.

The excavation must be backfilled with manually rodded tamped soil, or the footing thickness shall be increased by 50 mm.

Where stump pad footings provide resistance to horizontal or uplift forces, the minimum size of the footing must comply with AS 2870.

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

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 :

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).

A 10% increase in spacings is permitted where the spacing in the other direction is 20% less than that specified.

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.

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.

Alternative reinforcement sizes must comply with AS 2870.

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

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	5.0^{Note 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 :

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).

A 10% increase in spacings is permitted where the spacing in the other direction is 20% less than that specified.

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.

Alternative reinforcement sizes must comply with AS 2870.

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

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 :

All masonry walls must be supported on strip footings.

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.

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).

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.

The measurement of D_f is greater or equal to D plus 75 mm.

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 :

All masonry walls must be supported on strip footings.

The measurement of D_f is greater or equal to D plus 75 mm.

Alternative reinforcing sizes must comply with AS 2870.

Figure 3.2.5.4b Strip footing system for Class M, M-D and H sites

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 :

All masonry walls must be supported on strip footings.

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.

Infill floors must only be used for Class A and S sites.

The measurement of D_f is greater or equal to D plus 75 mm.

Alternative reinforcing sizes must comply with AS 2870.

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	700^{Note 2}	300	3–N16
Class M-D	Articulated full masonry	1100^{Note 2}	400	4–N16

Notes to Table 3.2.5.7b :

All masonry walls must be supported on strip footings.

Infill floors must only be used for Class A and S sites.

The measurement of D_f is greater or equal to D plus 75 mm.

Alternative reinforcing sizes must comply with AS 2870.

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	850^{Note 2}	300	3–N16
Articulated full masonry	1100^{Note 2}	400	4–N16

Notes to Table 3.2.5.7c :

All masonry walls must be supported on strip footings.

Infill floors must only be used for Class A and S sites.

The measurement of D_f is greater or equal to D plus 75 mm.

Alternative reinforcing sizes must comply with AS 2870.

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:

Clad frame
Articulated masonry veneer.
Masonry veneer.
Articulated full masonry.
Full masonry.

Notes to Figure 3.2.5.5 :

Use SL63 when slab length is less than 12 m.
Use SL62 when slab length is less than 18 m.
Use SL72 when slab length is less than 25 m.
Use SL82 when slab length is less than 30 m
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.
Dune sands may require compaction.

Filter

Part 3.2.5 Footing and slab construction

Explanatory information:

3.2.5.1 Footing and slab construction

3.2.5.2 Footings and slabs to extensions to existing buildings

3.2.5.3 Shrinkage control

3.2.5.4 Minimum edge beam dimensions

3.2.5.5 Footings for fireplaces on Class A and S sites

3.2.5.6 Stump footing details