Installation
Oil canning can occur in fixed cladding, even though it does not fit accurately, when fixings are too far apart or when fixings are overdriven. It can also result from an uneven substrate, irregular bearing on the purlins or by the structural framing being out of line.
Thermal expansion can also increase oil canning. Longitudinal expansion should be accommodated by using sliding clips allowing movement. See Expansion Clips. Transverse expansion is usually accommodated in the upstand of the profile, but this can only happen if adjacent pans are not in contact at the base. Wide perimeter flashings must be designed to allow for independent movement of the flashing and the cladding.
A convex curve in the roof structure can cause canning as it puts the pan of the profile under compression. Sometimes this curve is inadvertent. Concave roof cladding and flashings give rise to oil-canning because the pans are in compression. There are limitations on curved radii to avoid oil canning. See Curved Roofs.
Commercially designed truss sections and rafters may have camber induced in their manufacture, anticipating deflection under load. The degree of curve that may be accommodated by any profile is largely determined by the width of the pan and is, also, affected by the material thickness and grade.
- Log in to post comments