Over half of the mistakes made while constructing a corrugated iron roof can be traced back to incorrect storage or handling. The iron has to be handled and stored correctly because the surface is very easily damaged.
Leave the metal roofing at the manufacturers until you are ready to start installing it. Aim for delivery the day before roofing starts. If the roofing iron arrives before you are able to fix it, you must ensure it is kept bone dry. It is a common mistake to assume that because they are roofing sheets, they can withstand moisture. If the roofing sheets are stacked together and they get wet, they will stain. White rust forms on the coating and it is very difficult to remove. If your roof sheets do get wet, separate each individual sheet. Use bearers to allow airflow around the metal. This will prevent the corrosion.
Gently does it
As for handling, care needs to be taken in order not to damage the paintwork. Sliding sheets across one another will damage them. When separating the roofing sheets, you should lift them cleanly upwards without scratching the one underneath.
Spend more money
Installing a roof can be time consuming and costly. The last thing you need is to have to keep spending money on maintenance. If you scrimp on the cost of fasteners you will forever be replacing loose nails and fixing leaks. Choose good quality roofing screws. These will provide a more secure fixing and last as long as the roofing iron. It’s important not to over tighten the screws. Just tight enough to lightly compress the neoprene washer is sufficient.
If you pre-drill the holes for your roofing screws on the ground, it will be safer and give the roofing a neater appearance. This is only possible if the purlins run parallel to the eaves and the roof is reasonably square.
Using a quality drill bit makes the job easier. The drill bit should be slightly larger than the diameter of the roofing screws. This will prevent stress fractures as the sheets expand and contract.
Take accurate measurements of the purlin centres from the eaves and mark the roofing sheets ready for drilling the screw holes. Don’t forget to add the drop into the gutter to your measurements, usually about 50mm. It’s better to use chalk for marking corrugated roofing iron because pencil may damage the surface.
Cut to the quick
Cutting corrugated iron roofing sheets with a disc cutter makes the job easier and faster. Unfortunately, it also damages the roofing iron beyond repair. Hot particles of steel imbed themselves into the surrounding metal allowing it to corrode. Nibblers will do the job adequately as long as you are careful with the swarf. It’s preferable to cut the sheet with hand shears or best of all power shears. A better finish can be achieved if you make two cuts. The first cut 50mm away from your finished edge allowing you to neatly trim to the line with your second cut.
If you find scratches on your roofing during installation resist the urge to paint it. The paint may well look like a good match from the tin, but after a couple of seasons weathering the patched paintwork will stick out like a sore thumb. Contact the manufacturer and ask for advice on making repairs to their product.
Laying the roofing
Before you start laying the roofing sheets check that the roof is square. If the roof is not square you can still achieve a good finish if you even out the difference, between the two barges. The difference will then be less noticeable as it will be covered by the barge flashing. Run a string line along the eaves, 50mm into the gutter and it will provide you with a straight edge for the roofing sheets.
On completion it’s important to clear the roof of any loose swarf. Tiny particles of iron left on the roof will rust and ruin the surface. A soft brush will do the job or ideally a leaf blower can be used.
A well installed corrugated iron roof will give years of maintenance free service. If you take a little extra care with the preparation and fixing, you will achieve a superior finish.