Expansion and Contraction
With changes in temperature sheets can expand or contract approx 3mm per metre in both directions so allowance must be made for this movement. Ensure the glazing bars you use allow for this and that the bar caps can move with the glazing sheet. Each sheet should be screwed down at one end.
Do remember to oversize the
fixing hole by 3mm. The thermosroof sheets are normally screwed down at the back wall plate
or ridge so that the screws are covered by the flashing. This prevents the
sheet creeping down the glazing bar as it contracts and expands.
Sealing
the Sheet Flutes
The air inside the sheet
flutes must be allowed to expand i.e. the sheet must breathe. The top end of
the sheet is sealed with self-adhesive aluminum tape whilst the bottom (usually
the gutter end) is taped with breather anti-dust tape. Taping is essential to
prevent the ingress of dirt and insects. A sheet closure extrusion is usually
fixed to the bottom of the sheet to protect the breather tape and provide a
neat appearance.
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