The following section sets out requirements for the installation
of plastic roof and wall cladding sheets in a roof or wall structure.
All fixing done to AS 1562-3-2006.
General Provisions
Inspection
Prior to installation, the installer shall inspect the rafter
and batten spacing in roofs, and the stud and noggin spacing in
walls, to establish that their layout will provide the required
laps and any specified overhangs, e.g. eaves.
Cutting of sheets
Cutting and cut edge finishing shall be carried out as recommended
by the manufacturer/supplier or by other means to achieve a cut
with minimal damage to the sheet.
Supports at hips and valleys
Hip and valley trimmers shall be provided and shall be fixed flush
with the top face of purlins and spanning between them. They shall
run parallel to the edge of the sheeting, and shall be placed
so as to permit the fastening of the sheeting or of hip ridging.
End laps
A minimum of 200 mm overlap shall be provided at all ends (including
those with dissimilar materials) and such lap shall be supported
with a rafter, batten, stud, or noggin (dwang).
All sheets, when fastened, shall have full bearing on rafters,
battens, studs or noggins (dwangs) and their ends shall extend
not less that 50 mm beyond the point of fastening.
At all end laps between plastic and dissimilar material sheeting,
two lines of compressive foam strip or of flexible sealant shall
be placed across the full width of the lap approximately 150 mm
apart with one line 25 mm from the end of the plastic sheeting.
NOTES:
- The compressive foam strip should be light in colour for
PVC and preferably be of the type impregnated with a weather-resistant
viscous fluid.
- Some sealants are not compatible with certain types of plastic
materials and can lead to stress and cracking if incorrectly
used. The manufacturer’s instructions should be followed
carefully.
Side laps at inserts
Each individual plastic building sheet shall overlap and be supported
by adjacent roof or wall cladding in accordance with eh manufacturer’s
installation instructions.
At the overlapping joint between plastic sheeting and adjacent
sheeting additional side-lap fasteners may be required in accordance
with the manufacturer’s instructions. In these cases the
fasteners shall bond the plastic sheeting and the adjacent sheeting
together, and appropriate allowances shall be made for the differential
expansion rates of the materials and with the provision of a suitable
sealing washer at each fixing point.
Projections through sheeting
Where any projections such as pipes, ducts, chimneys and the like
pass through sheeting, they shall be adequately insulated and
flashed. For roofs, such projections shall pass through the pan
of pan type sheets or through the crest of the corrugation or
corrugated sheets. Where this is not possible because of the position
or size of the projection, ribs or corrugations shall be cut away
as required, provided that such cut ribs or corrugations are adequately
flashed and that, where necessary, all cut sections of the sheeting
are supported by additional roof framing. In such cases, all cutting
and flashing shall be arranged so that adequate provision is made
for drainage of all pans or corrugations.
Fastening procedure
Wherever possible, plastic sheeting shall be fastened concurrently
with the other materials. Normal sheet installation shall be followed,
and the sheets shall be installed using fasteners that are strong
enough to securely fasten the sheet. All fasteners shall be provided
with adequate sealing. All fasteners shall be tightened to provide
a weatherproof seal without deformation or damage to the sheet
profile. The number of fasteners shall be in accordance with the
sheet manufacturer’s instructions.
Unless otherwise specified, side lap fasteners shall be provided
at joins with other more rigid sheeting material in accordance
with the sheet manufacturer’s instructions.
Fastener types
Nails and pop-rivets shall not be used to secure plastic roof
and wall cladding sheets. The following types of fasteners may
be used:
(a) Hook bolts and nuts.
(b) Cranked hook bolts and nuts.
(ac) Square-bend L-hook bolts and nuts.
(d) Square-bend U-bolts and nuts.
(e) Round-bend U-bolts and nuts.
(f) J-bolts and nuts.
(g) Self-tapping screws.
(h) Roofing bolts, nuts and clips.
(i) Cone-head roofing screws.
(j) Toggle fasteners.
(k) Compression fasteners.
(l) TEK fasteners.
NOTE:
Nails and pop-rivets may be used for uPVC wall cladding boards
when used in accordance with the manufacturer’s instructions
Fastener holes
In roofing applications, holes shall be drilled through the crest
of any profiles except where valley fasteners are specified for
the installations. For walls, fastening may be through the crest
or valley of the profile.
All holes for fasteners shall be pre-drilled in exact positions
to suit supporting members, i.e., on the centre-line of timber
or metal supports, or, if normal hook bolts are used, as close
as possible to the edge of the supports.
NOTE: It is usual for such holes to be drilled
with the sheet in position. Stack drilling methods should not
be used. Holes are drilled oversize to accommodate thermal expansion.
The coefficient of linear expansion of plastic roof and wall cladding
materials may be taken as follows:
(a) uPVC …………………………………………………… 7
x 10-5 per 1°C.
(b) GRP …………………………………………………… 2.5
x 10-5 per 1°C.
(ac) Polycarbonate …………………………………… 7
x 10-5 per 1°C.
Washers
All washers shall be of a type that will compress to provide a
weatherproof seal over the fixing hole and of a type that will
support the sheeting during actual wind load conditions.
NOTE: Some washers are not compatible with certain
types of plastic materials and can lead to stress cracking if
incorrectly used. The manufacturer’s instructions should
be adhered to.
Sealing at flashings on roofs
Plastic roof sheeting is not easily reshaped after manufacture
and will require special weather seals to be provided at all flashing
and capping points. Typically a foam closure strip matching the
profile of the plastic sheeting should be provided to seal the
corrugations or pans of the profile under each flashing. The foam
closure should be bonded to the pans or valleys of the plastic
sheeting with a flexible waterproof sealant and should be continuous
over the entire width of the plastic sheeting. Ideally it should
be fitted at least 100 mm behind the turn down of the flashing.
NOTE: Some sealants are not compatible with certain types of plastic
materials and can lead to stress cracking if incorrectly used.
The manufacturer’s instructions should be adhered to.
Unsupported overhang
The maximum unsupported overhang allowable for GRP, PVC and polycarbonate
shall be in accordance with the provision of the following Table:
TABLE OF MAXIMUM ALLOWABLE OVERHANG
| Sheet type
|
Maximum
unsupported overhang |
| GRP |
150 mm |
| PVC |
50 mm |
Polycarbonate
|
50 mm |
Where wire safety mesh is incorporated under plastic roofing
sheeting and where the safety mesh passes over the supporting
member (purlin, batten or the like) directly under the plastic
sheeting, a compressive foam strip of minimum 6mm thickness or
solid strip of minimum 1 mm thickness shall be provided between
the plastic sheeting and the safety mesh. The protective strip
of material shall be the full width of the face of the supporting
member and extend at least 25 mm past both edges of the plastic
roof sheeting (or safety mesh).
NOTE: The compressive foam strip should be light
in colour for PVC and preferably be of the type impregnated with
a weather-resistant viscous fluid.
When plastic roof sheeting is supported at both edges of each
sheet by the adjacent roofing, safety mesh shall be the full width
of the opening between the two adjacent roof sheets. Where the
plastic sheeting is not supported at the edges, the safety mesh
shall extend a minimum of 600mm past the unsupported edge of the
plastic sheet.
Fixing Details
FGW Fibrelite sheeting shall be installed in accordance with
Australian Standards 1562.3, 2006 design and installation of sheet
roof and wall cladding Part 3: Plastic combined with FGW fixing
instructions.
Fixing of fibreglass GRP for roof applications; each ridge to
be fastened at both ends and every second ridge at intermediate
purlins. Predrill clearance holes 3-4mm above fixing screw diameter
to allow for thermal expansion.
Sheeting shall be installed using the correct recommended fastening
screws to suit the cladding together with a 32mm weather washer
to avoid water penetration. The fixing screws should not be over
tightened to the extent that the sheeting could buckle.
Lapping of sheets should be a minimum of 300mm and sealed with
2 continuous beads of suitable non setting sealant across the
full width of the sheet.
Safety mesh should be used under fibreglass roofing in conjunction
with purlin tape (75mm x 5mm) or a 65mm wide fibreglass protection
strip should be installed over the safety mesh to avoid fracturing
of the underside of the sheeting.
Span Chart
