corners it is essential that the seals meet and do not leave a gap under the four way lap. See diagram A. The sealant should be soft enough not to interfere with the fit of the sheet and sufficiently elastic to fill uneven gaps. The sealant should be stable over a wide range of temperatures, water resistant and adhere to the metal surfaces.Generally a single sealer strip can be used at side laps and a double line of strip at end laps. The sealant should also be compatible with filler block materials and at least 12mm wide to ensure that it is not cut through by the fixings.B. Barrier Tape
When using dissimilar materials in roofing and cladding it is necessary to use barrier tape to prevent galvanic corrosion or electrolytic reaction. Barrier tape should be applied to the supporting structure before the sheets are fixed and should have a thickness of at least 0.12mm. Most barrier tapes are self adhesive and to ensure good adhesion it may be necessary to dry the purlin flanges. The tape should be approximately 10mm wider than the flange so as to overlap each side by some 5mm and should be overlapped at joints to ensure continuity of protection. See diagram B.
C. Filler Blocks
Profiled foam filler blocks are available for profiled sheets to provide a seal between the profiled sheets and the flashings. E.P.D.M. is the most common material used in foam fillers and reference should be made to the manufacturers’ recommendations in repect of resilience to temperature changes, fire resistance etc.
It is important to order the correct filler block, i.e., large rib or small rib to match either the outer or the inner skin of the profile.
Sequence of Laying
The direction of laying the sheets should be such that the exposed side laps face away from the prevailing wind. Wherever possible it is preferable to use single lengths of sheeting from ground to eaves or from eaves to ridge. Where end laps are necessary, the sequence of laying the sheets is as shown in the diagram.
Frequent checks should be made on the width of roof covered which should be a multiple of the cover width of the sheet and that work is not running off square. Sheets must be correctly aligned with each other.
When fixing curves at eaves and ridge it is necessary to ensure that the walls and roof slopes are fixed simultaneously. Because the curves are more rigid they will not easily allow for fixing tolerances and it is not advisable to fix the roof or wall sheeting and then fix the eaves and ridge curves. The sequence of laying is as shown in the digram.
Upon installtion of each section of the roof all debris should be removed, e.g., swarf, rivet mandrels, nails, screws etc., to ensure that they do not cause stains and corrosion. Likewise cement and mortar dropping will leave permanent stains. Marks from oil or grease should be removed by washing with a mild detergent and all plastic film when applied should be stripped from the sheets immediately, otherwise after exposure to ultra-violet the film will be more difficult to remove and may leave sticky deposits on the sheet which collect dirt.