General

Reflective foil laminate is recommended as sarking because of its insulating and weatherproofing properties. Its use is advised with long run rafters and low roof pitches at all times.

Sarking reflective foil insulation material should be a double sided, anti-glare type with flammability index of a maximum of 5 in accordance with AS 1903-1976 Reflective Foil Laminate and should be fixed in accordance with AS 1904-1976.

Support

Anti-ponding boards should be installed to support sarking at eaves with roof pitches below 20 to ensure that any water collected by the sarking will be discharged into the eaves gutter. Refer AS 1904-1976.

Laying

Sarking material should overlap not less than 150mm and be festooned over rafters allowing a sag of not less than 25mm and not more than 65mm except at the eaves.

At the ridge line sarking shall be terminated 50mm from the fascia approximately 50mm (or sufficient to allow effective run off into the gutter) and be securely fixed to top edge of fascia.

Protection Against Membrane Flexing

Where local wind activity is likely to cause extensive flexing (flapping) of the sarking membrane, a polyurethane security pad shall be installed in a staggered pattern under each second row of battens between each pair of rafters.

End Laps

End laps shall overlap by one full rafter spacing.

Hot Flues

Sarking should be cut back from hot flue surfaces to leave a clear space of 50mm.

Penetrations

The membrane shall be turned up and sealed to divert water around the projection.

No Gutters (where applicable)

Where a tilting batten is used in place of a fascia board and there is no gutter, the sarking material shall be neatly cut back to the outside edge of the tilting batten.

Rafter Centres & Sarking Support

Where rafter centres exceed 600mm, up to 900mm AS 1736-1975 advises that the sarking membrane should be supported by wire mesh or be otherwise adequately reinforced. Where the rafter centres exceed 900mm this recommendation becomes a requirement of the Standard.

Valley

At valleys, sarking should be held in place by fixing valley battens parallel to the valley gutter. The sarking should overlap the valley by no more than 25mm - refer Roof Finishes Section.

Batten Set Out

1. First setout nail to be fixed from front edge of fascia.

(a) when using 38 x 25 battens - 312mm
(b) when using 50 x 25 battens - 300mm

Note: With double undercheck files - underchecks should straddle from edge of fascia or bellcast batten.

2. Top setout nail to be fixed from edge of ridge board.

(a) when using 38 x 25 battens - 50mm
(b) when using 50 x 25 battens - 62mm

3. Measure distance between bottom and top setout nails.

4. Refer this measurement on ready reckoner to find Batten gauge.

Example - Rafter length 7.14m
100mm Lap Batten gauge 0.310mm Adjustable Courses 23
75mm Lap Batten gauge 0.340mm Adjustable Courses 21

Fixing Systems

Systems for fixing battens to rafters, and tiles to battens, shall comply with the loading requirements of Clause 1.4.1 of AS 2050-1989. The following additional requirements apply:

(a) Fixing for tiles to battens and for battens to steel frames shall be non-ferrous, stainless steel or steel with an appropriate corrosion-resistant coating.

(b) Clout nails shall comply with AS 2334, have a minimum diameter of 2.8mm, and be of a length such that the nail will penetrate not less than 15mm into the batten.

(c) Self-drilling screws shall comply with AS 3566.

Notes:

1. Attention is drawn to the risk of corrosion resulting from unfavourable galvanic relationships in fixing metallic substrate, particularly in areas where corrosive situations may be encountered, e.g. close to the sea.

2. The specification for the fixing of the batten to the rafter or truss is dependent on the design wind velocity as nominated by the designer or builder.