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5.3

Part 5.3 Cavity masonry

Part 5.3 Cavity masonry

(1) Part 5.3 applies subject to the limitations set out in H1D5(2)(c).

(2) Part 5.3 need not be complied with if H1D5(2)(a) or (b) are complied with.

Cavity masonry walls must not be greater than 8.5 m in height when measured above the adjacent finished ground level.

(1) Cavity masonry walls must comply with the relevant provisions of this Part and Parts 5.6 and 5.7, and be constructed as follows:

  1. The height of the wall between lateral supports (floor or ceiling or roof diaphragm) must be not more than 3 m.
  2. Cavity masonry walls subject to wind loads must be supported by masonry cross walls or by steel mullions complying with (3).
  3. Masonry cross walls must be—
    1. not less than 2 m in length; and
    2. at not more than 5.1 m centres where the length of the cavity wall being supported does not contain any opening or control joint; and
    3. not more than 2.5 m from the edge of a control joint in the length of the cavity wall being supported; and
    4. not more than a distance from the edge of an opening in the length of the cavity wall being supported as stated in Table 5.3.3; and
    5. located at both edges of openings of width greater than 2.7 m; and
    6. directly connected to the internal leaf of the cavity wall being supported using—
      1. properly bonded units with at least 90 mm engagement on each side of the interface with the selected bond pattern but not less than every fourth course of masonry; or
      2. medium duty Type A cavity wall ties in aligning mortar bed joints at a vertical spacing of not more than 300 mm; and
    7. connected by a floor or ceiling diaphragm to the wall being supported where floor or ceiling connections are designed in accordance with AS/NZS 4600, AS 1720.1 or AS 3600, as appropriate.

(2) Cavity masonry walls must be constructed of two leaves, with each leaf not less than 90 mm wide.

(3) In cavity masonry construction, a cavity must be provided between the inner and outer masonry leaves as follows:

  1. The cavity must be not less than 35 mm and not more than 75 mm in width, in accordance with 5.7.2.
  2. Except for steel mullions, the minimum cavity width specified in (a) is to be maintained between the outer masonry leaf and any insulation or services located in the cavity.
  3. Where steel mullions are located in a cavity as permitted by (b), a vertical damp-proof course must be placed between the outer masonry leaf and the mullion to prevent moisture penetration.
Table 5.3.3 Spacing of return walls for cavity walls with openings — distance from the edge of an opening (mm)
Wind class Opening width (mm)
900 1500 2100 2700
N3 2100 1800 800 400
N2 3200 2900 2600 2300
N1 2500(Note) 2200(Note) 1900(Note) 800(Note)
Table Notes

The spacing in wind class N1 is smaller than for N2 because 5.6.5 states that for cavity walls in wind class N1, light duty cavity ties are to be used. This results in only relying on one leaf to resist the load instead of sharing it equally as per clause 7.7.3 of AS 3700.

Explanatory information

Steel mullions complying with AS 4773.1 and 4773.2 used to support wind loads may be placed within a cavity. Flat ceiling capable of performing diaphragm action may act as lateral support to walls provided the structure has been specifically designed.

(1) Where internal masonry walls intersect with other internal or external walls they must comply with the relevant provisions of this Part and be—

  1. not less than 75 mm thick; and
  2. either—
    1. bonded at the junctions of the intersecting walls; or
    2. provided with an articulation joint in accordance with 5.6.8.

(2) Where a vertical articulation joint is provided in an internal masonry wall it must be formed in accordance with 5.6.8.

(1) Except where excluded by (2), openings in cavity masonry must be spanned by steel lintels in accordance with 5.6.7.

(2) Openings in cavity masonry not more than 500 mm wide need not be provided with a steel lintel provided the opening is adequately supported.

Explanatory information

An opening of not more than 500 mm is considered to be adequately supported if the masonry bears directly on a timber window head or steel frame.

Damp-proof courses and flashing must be provided in accordance with 5.7.3 and 5.7.4.

Vertical articulation joints are to be installed in accordance with 5.6.8.