INSPECTION OF ROOF CEILING SPACE
AS STATED WITHIN THE VICTORIAN BUILDING AUTHORITY
COMMON ROOFING TERMS
The following are the requirements for the building practice, design, and specification of roof framing
TYPES OF ROOFS
Are either coupled or non-couples
The roof pitch in a coupled roof construction shall be not less than 10 degrees and ceiling joists and collar joists
shall be fixed to opposing pairs or rafters.
Rafters are to be continuous in length from the ridge to the wall plate or shall be lapped or spliced at their
support points. Rafters may be supported under purlins.
For a coupled roof with no roof struts, provided with nominal fixing only the maximum distance between
external walls shall not exceed 6000 mm for sheet roofs or 4000 mm for tile roofs, except where the roof
connections and members are designed in accordance with AS 1720.1
A non-coupled roof has rafters supported off walls, ridge beams and/or intermediate beams. It may have
ceilings in the same plane as the roof. Rafters, ridge and intermediate beams may be exposed internally.
The design of a timber roof truss is normally in accordance with engineering principles and AS 1720.1. The
wind design criteria is to be consistent with that used in AS 1684.4 – 2006 “Light timber frame code”.
Ceilings may be fixed to the underside of ceiling joists, rafters or purlins or the bottom chord of trusses with or
Where ceiling battens are used, the size and fixings shall be appropriate for the mass of the
ceiling material used, to provide a flat finish to the ceiling.
Ceiling joists generally are spaced to supported ceiling linings and for coupled roofs, they are in single lengths
or can be spliced and at the same spacings and in the same direction as the main rafters so they may be fixed
to and act as ties between the feet of pairs of the opposite rafter
SPLICES AND JOINTS IN COUPLED ROOFS
Where splices in ceiling joists are necessary, they shall be made only at points of support. Splices shall be buttjointed with fish plates of minimum length six times the joist depth. Fish plates shall be a minimum of 19 mm
thick by the full depth of the ceiling joist. Alternatively, the ceiling joists may be lapped for a distance
equivalent to at least three times their depth.
Lapped ceiling joists, or both ends of the butted ceiling joists to fishplates shall be secured with at least hand
driven nails, or 8/3.05 mm diameter machine-driven nails, or with an M12 bolt.
Engineered nail plated joists shall be spliced and supported in accordance with the manufacturer’s
Hanging beams generally, support ceiling joists and the attached ceiling material only. Hanging beams are
usually at right angles to ceiling joists and are located directly above them. Hanging beams are generally, are
generally held in a vertical position at both ends to an available rafter, gable end struts or by means of angle
strutting from internal walls.
Under purlins generally, are single lengths where possible are in straight runs and generally, at right angles to
the direction of the rafters.
PROPS AND/OR STRUTS
Struts and/or props are members that support under purlins, ridge boards and hip and valley gutters. Struts,
generally are supported by walls, strutting beams or combined strutting or hanging beams. Struts are not
normally supported on hanging or counter beams.
Struts are normally either vertical or perpendicular to the rafters or at an angle not exceeding 30 degrees to
They are birds mouthed or halved to under purlins or if not birds mouthed a 30 X 0.8 galvanized
the iron strap is passed over the under purlin and nailed to each side of the strut with 4/30 X 2.8 diameter nails
and to the under purlin with 2/30 X 2.8 diameter nails each side in addition to at least 2 skew nails.
Collar ties are provided to all coupled roofs.
Where the rafter span is such as to require support from under purlins, collar ties are generally fitted to
opposing common rafters at a point immediately above the under purlins. Where under purlins are not
required, the collar ties are fitted to opposing rafters at a height above the top plate not greater than two-thirds of the rise of the roof.
Collar ties are generally fitted to every second pair of common rafters or at 1200 mm maximum spacings,
whichever is the lesser.
Collar ties are fixed to rafters with one M10 bolt for ties greater than 4.2 meters long
or minimum 2/75 hand-driven nails or 3/75 X 3.05 mm diameter machine-driven nails forties up to 4,2 meters
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