Box profile sheets should be laid left to right from the eaves to the ridge, if overlapping the sheets length ways a 300mm overlap should be allowed. Typical purlin spaces are between 600mm (for 0.5mm gauge) and 1200mm (for 0.7mm gauge) centres.
Sheets must be overlapped as shown below with the ‘unfinished’ end on top. This is to stop the capillary action drawing water from the pan into your roof space.
If fixing into timber, 32mm timber Tek fixings should be used and are fixed through the pan. Do not over tighten the fixings. The fixings should only be tightened until the washer starts to bulge. The Tek fixings are self cutting and sealing, however if you have not used them before it might be advisable to drill a small pilot hole first.
It is advised to put extra fixings (2 per pan as shown) at the edges to ensure any strong winds don’t lift off the sheets, 1 fixing per pan, at each purling, should be sufficient for the rest of the sheets unless you live in a very windy area.
22mm stitch screws should also be used to pinch the overlaps together, this is recommended on roofs with a shallow pitch, it is also recommended to use a Butyl sealant tape on all overlaps for shallow pitch roofs.
Foam fillers should be used at the ridge and eaves to stop any small birds or insects getting into the roof space. If you are using anti-condensation lined sheets you should leave the ridge and eaves open to allow air circulation, essential for evaporating condensation held in the liner.
In box profile, fixing the sheets should be done at every valley in accordance to the British standard, corrugated should be fixed through the top of the corrugation.