Cutting box section roofing ?

[Rob Graham]

My daughter's partner has bought some second hand box section steel roofing for a shed he's building. He asked me how to cut it !!

What's the answer please

Rob

[Tim Watts]

Would a jigsaw work?

[harry]

The answer is, if possible, don't. Let the sheets overlap. It's cut with sheers/guillotine. This "wipes" the galvanising over the cut edge and stops corrosion. I've tried painting the cut edges in the past but doesn't last long.

You can cut it with an angle grinder but the cut edges soon rust and the plastic finish starts to bubble up. Also the stuff tends to "nip" the grinder and is quite dangerous; wear goggles/gloves. Cut from both side, ie turn the sheet over and cut the high bits.

If you can arrange it, put any edges you've cut out of the weather (eg under the crest or under the adjoining sheet).

The sheets are secured with screws with sealing washers in the valleys. These must go in at right angles for the seals to work. If they don't, you get roof leaks and corrosion. There are different ones for wood and metal.

[John Jackson]

Yes, but it would be quite slow.

[Adrian]

ANGLE GRINDER!

When you say "box section" - do you mean box section, or do you mean square section profile? Is it just single-skin?

The pros use a nibbler - air-powered ones are FAR cheaper than electric.

[Muddymike]

Attacking from top and bottom with those very thin cutting disks. Watch out they are easy to break.

Mike

[Tim Lamb]

In message , Rob Graham writes

Harry is mostly correct!!

A 9" angle grinder will cut very easily but the heat lifts the plastic/paint protection and the steel soon rusts.

Some professionals installing a barn here used a nibbler but I didn't notice whether the jaws were anvil type or shear.

Much of my recently installed roofing is box section sandwich with up to

75mm of PIR foam between two metal sheets.

The solution here was a *rage demolition saw* with a circular blade designed for cutting thin section metal. The saw has a compartment for trapping metal swarf but eye protection is vital. The saw shoe is long enough to span the corrugations but making up a wooden saw guide will help.

[Brian-Gaff]

Whatever it is, use ear defenders when doing it. Brian

[Dave Plowman (News)]

Of course if you want a nice square cut, a chop saw with the correct blade might be easier. The common small angle grinder has a limited cutting depth in a mounting frame. And not really seen one for a 9" type.

I've got an mains electric nibbler - Hitachi - which cost a fortune used. Very nice tool, though.

Air powered ones need a decent air supply, which may not be practical for everyone.

[Rob Graham]

Many thanks for all your answers, guys.I'll pass them on.

[newshound]

The first question is "how thick is it". If it is the serious industrial thickness stuff used for large barns and the like, the answers given are OK. If it is the really flimsy stuff, 0.5 or 0.7 mm which is all you need for small domestic work, provided it is adequately supported and fixed down, it cuts easily with tin snips.

You can cut the 0.5 mm with a good kitchen scissors.

[Tim Lamb]

Ummm... It isn't the thickness but the shape that causes the problem. Perhaps cut to within 5mm with angle grinder and tidy up with snips? A narrow strip should bend out of the way.

[Kevin]

I used an air nibbler for plain box profile sheets. For the sandwich stuff (steel-foam-steel), I used a reciprocating saw, cutting from the inside, almost flat, surface.

Kevin

[Tim Lamb]

Usually, when cutting the *sandwich* you are trying to create a lap or drip.

There is a problem where the foam is exposed at the eaves. Without the top sheet extending beyond the foam fill, rain water dribbles down the face and may soak in. Sheets supplied *cut to length* by the manufacturer arrive with this lap ready formed. They also supply a 1m wide foam *fill* strip to close off the gaps at the ridge.

Attaching suitable gutters is a further problem: when the gutter bracket mounts are too far from the drip point. I have overcome this by attaching a suitably angled gutter board to the roof itself.