Fixing Procedure

Fixing Components


Fasteners should be installed in the quantity, size and fixing intervals as recommended in the Wind Load Table for the class and profile of sheet, for a wind load of up to 1 KPa. Where wind loads exceed 1 KPa enquiries should be referred to the Alsynite Technical Department.

Where installed in conjunction with metal sheets, allowances must be made for the differing expansion rates of the two materials and all holes must be predrilled as specified. Note that unless fasteners are rigidly adhered to the sheets they may be likely to buckle and leak at side laps.


Side Lap Fasteners

Side lap fasteners are necessary to ensure a waterproof lap, and must be located at a maximum 600mm centres. Pre-drilling of the FRP sheet is essential. In certain applications where two FRP sheet are side-lapped, a bulb-type or similar rivet can be used in place of the screw, as differing thermal expansion is not a concern. Ensure that in these situations reference is made to the Alsynite Technical Department. Side-lap fasteners should be installed as per Alsynite's specifications.



All fixing holes must be waterproofed with the use of a sealing washer installed under the head of the fixing screw or rivet. In normal applications a 32mm diameter approved washer will be suitable. The washer should be able to form to the shape of the rib of the profile, It must also be in complete contact around the outside edge of the sheet when the fixing screw is tightened.

A larger washer should be used where necessary to ensure a waterproof seal for unusual profile shapes, or in some cases an irregular sized clearance hole in the FRP sheet.

Note: Do not over-tighten fasteners.


Closure Strips

Also called Eave Fillers, they are used to seal both the top and bottom of various profiles against the entry of water, dust, or vermin at all flashing points and gutters. This is the only recommended method of providing a waterproof seal under normal flashings. Refer to the correct procedure for Parapet Flashing and Eaves Closure located within this section.



Checking the installed sheet

On completion make the following checks:

  • No cracks or damage has occurred from fastening.
  • No damage has occurred from dropped articles.
  • No damage has occurred from accidental foot traffic.
  • Ensure that drill holes are oversize as specified for the sheet length and that fastener being used is the correct size and type.
  • There are no gaps at side or end laps of the Alsynite FRP sheet.
  • Remove all debris from the sheeting.
  • Install signage as required by Building Regulations.


Maintenance of GRP sheeting

While normal rain provides a self washing action, the roof pitch or local environment can allow the accumulation of dust on the inside and outside of the sheeting.

Where accumulation is a problem, hose and broom off the dirt build-up.

In older installations, when light transmission levels can no longer be determined, sheeting can be replaced with a progressive maintenance program.