Page 38 - Build 151

GOOD DESIGN DETAIL FOR CAVITY CLOSURE WHERE EXTERNAL WALLS ARE SUPPORTED ON CANTILEVERED JOISTS
DESIGN
Cavity closures to cantilevered joists
Drained cavities to external walls need to be constructed correctly to keep wind- driven rain and vermin out and allow drainage and ventilation. One overlooked area is when external walls are supported on cantilevered oor joists.
RIGHT
BY ALIDE ELKINK,
FREELANCE TECHNICAL WRITER, WELLINGTON
DRAINAGE AND VENTILATION is achieved in drained cavities by leaving the bottom of the cavity open and tting a cavity closure to prevent the entry of vermin.
Cavity closures at base of all cavities
Cavity closures are required at the base of all cavities including:
● above window and door heads
● at the base of all walls
● at inter-storey ashed junctions.
ooring cantilevered oor joist
so t framing
top plate metal ashing (optional)
90 × 10 mm trim
They should have 3–5 mm drainage holes or slots to provide an opening area of 1,000 mm2 per metre length of wall.
Walls on cantilevered oor joists
A sometimes overlooked location for cavity closures is at the base of an upper level external wall supported on cantilevered oor joists (see Figure 1).
Although the cantilevered oor joist space must be closed o , the base of the cavity to the
insulation bottom plate
wall above must remain open, so cavity closures should be installed.
Position above bottom of cladding
A drip edge is needed at the base of all walls, above door and window openings and above horizontal ashings that bridge the cavity (E2/AS1 9.1.8.3).
This is done by positioning the cavity closure 10–15 mm above the bottom edge of the cladding.
wall underlay
cavity batten
bevel back weatherboards
cavity closure
10–15 mm minimum drip edge bevel-back weatherboards
batten
Figure 1
Cavity closures to cantilevered oor joists.
insulation wall underlay
so t lining
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