Most pitched roofs covered with
tiles rely upon the ability to easily nail or screw components such as
gutter brackets, snow guards, telephone cables, television aerials, soffit
boards, over fascia ventilation systems and interlocking tile eaves clips
to a structural or semi structural piece of the roof. A fascia board,
whilst not as structurally important in a roof as a rafter or a purlin,
should be considered as a semi structural member. If timber fascia boards
are replaced with another material, such as UPVC, there can be
compatibility problems.
Fixings
UPVC fascia boards can cope with heavy components, such as overhead
telephone cables, when they are fixed through the material and into the
roof structure behind. Light weight components can be fixed into the rigid
UPVC outer skin to give an acceptable fixing. Where tensile loads such as
wind forces on interlocking eaves tile clips are fixed into the top edge
of the fascia board where there is no rigid plastic skin, the foam core is
likely to be inadequate.
Foam core
The open foam core on the top edge of the fascia board
provides less resistance to nail or screw pull-out than with softwood,
even with the best high-density foam. To my knowledge no UPVC fascia board
manufacturer provides pull out tables for nails and screws into their
products to allow designers to decide if the resistance is adequate, or to
compare it with the nail or screw pullout resistances quoted in BS 5268.
Grill fixing
Where 9mm thick fascia board is used to over clad existing timber
fascia boards, some over fascia ventilation grills, designed to lip over
the front edge of the fascia and nail into the middle of a 19mm timber
fascia, may be compromised.
With a 9mm thick UPVC section the nail
fixing designed to pass into the centre of
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