When screwing corrugated roofing onto the purlins, is it normal to have humpy-profiled stuff between the purlin and the roofing sheet?
I was planning to insert the screws on the ridges of the corrugatons, not the troughs, to minimise leaks. The humpy-profile stuff would prevent the sheet deforming if I over-tightened the roofing screws. Or I could just not over-tighten the screws, which seems simpler.
The project it a wood store for firewood logs.
R.