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 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 of roof insualtion 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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