Corrugated roofing is the covering of choice for buildings where shedding water quickly matters more than how the roof looks: garages, workshops, stables, farm buildings and the back half of a great many industrial estates. It is quick to fit, cheap per square metre and unforgiving of a badly formed edge, which is where nearly all of its problems begin.
The profiles, and what each is for
Traditional corrugated sheet has a rolling sinusoidal profile and is the pattern most people picture. Box profile has flat pans and square upstands, sheds water faster and spans further between purlins, which is why it has taken over most new work. Tile effect profile is box profile pressed to look like a tiled roof from the ground, used where an outbuilding needs to look domestic. All three are the same job to fit, and the depth of the profile decides how far apart the purlins can be.
The asbestos question comes first
Corrugated sheeting on a building put up before the year 2000 is very often asbestos cement rather than metal. It is not a hazard while it is whole and undisturbed, and the guidance is clear that cutting, drilling and breaking it is what releases fibres. That makes identification the first job, not the last: it changes who can remove it, how it must be handled and where it can go, and no legitimate contractor will price it as ordinary waste.
Fixing, laps and the edges that fail
Sheets are screwed through the crown of the profile with a washered fastener into the purlin below, and the two things that go wrong are both at the joints. Side laps that are too shallow for the pitch let wind drive water sideways under the sheet. End laps without sealant do the same at every horizontal joint. At the perimeter, the barge, eaves and ridge flashings are what stop wind lifting the leading sheet, and a roof that has lost a sheet in a gale nearly always lost the flashing first.
Questions people ask about corrugated roofing
What pitch does a corrugated roof need?
It depends on the profile and the lap, and manufacturers publish a minimum for each. Shallower pitches need deeper laps and sealed joints, which is why an old sheet reused on a flatter roof leaks even though nothing about it has changed.
Can corrugated sheets be laid over an old roof?
On an outbuilding with sound purlins it is common, and it is only sensible where somebody has established that what is underneath is sound and, on a pre-2000 building, what it is made of.
How long does a corrugated metal roof last?
The coated face outlasts the cut edges and the fixings, so the practical life is usually set by when the fasteners and the sheet ends start to corrode. Re-fixing and cut edge treatment are the maintenance that extends it.