Installing steel roofing might seem straightforward, but even seasoned tradespeople can slip up when it comes to the finer details. Whether you’re working on a new build or a refurbishment, avoiding these common mistakes can save time, money, and call-backs. Here’s what to watch out for when installing steel roofing sheets.
1. Skipping the Prep Work
Before you lift a sheet, make sure you’ve got the right gear. Your basic kit should include:
Tape measure, straight edge, spirit level, pencil, string line, sealant and gun, drill with magnetic socket, tin snips, nibbler, (optional) jigsaw with fine-tooth blade.
Avoid using a standard circular saw — unless it’s fitted with a cold-cut blade specifically rated for steel. Otherwise, the heat build-up can damage protective coatings.
Rushing into installation without these tools will slow you down and risk poor finish quality.
2. Ignoring Minimum Pitch and Spans
Steel sheeting must be laid at a minimum pitch of 4 degrees. Note: this applies to uninsulated single-skin systems. For insulated or composite roofing, always check the manufacturer’s minimum pitch guidance. Also remember: 0.5mm thick box profile sheets can span a maximum of 1500mm between supports.
This assumes standard purlin centres and loading conditions, and may vary depending on the profile and project requirements.
3. Laying in the Wrong Direction
Steel sheets should always be laid away from prevailing winds. If you get this wrong, wind-driven rain will find its way under laps — no matter how well sealed they are.
4. Not Squaring the First Sheet Correctly
Your first sheet must be squared to the eaves, not the verge. Misalign this and every sheet after it will be off — a nightmare for aesthetics, water run-off, and flashing installation.
5. Incorrect Lap Details
Here’s a big one:
- Lay the purlin bearer leg under the underlap, not the overlap.
- Apply a continuous run of 5mm x 6mm lap-seal mastic along the crown of the underlapping sheet before positioning the overlap.
- Use 4 main fixing screws across the width of each sheet at every support, through the valley, not the crown.
Valley fixing is preferred for weatherproofing. In structural applications, crown fixing may be used if required — always follow system-specific recommendations. - 22mm stitcher screws should secure the side laps, evenly spaced.
6. Forgetting to Cap and Seal Properly
Drill screws should be tight — but not overtightened — and always finish with colour-coded caps to protect against corrosion and improve finish. Neglecting this step can shorten the lifespan of your steel roofing system.
7. Incorrect Flashing Installation
When fitting barge and ridge flashings, follow these steps:
- Run lap-seal mastic along the crowns where flashings will sit.
- If barge flashings don’t reach the second crown, use a slip flashing.
- Work from the bottom up, overlapping each barge by at least 150mm.
- Fix through the crown at 400mm centres with stitcher screws.
- At the ridge, install foam fillers that match the sheet profile, with Butyl sealant applied using consistent pressure on both sides of the ridge line. Overlap ridge flashings against prevailing winds and fix into every crown.
Avoid the Call-Backs
Steel roofing is a robust, long-lasting solution — but only if it’s installed right. Avoiding these common mistakes helps ensure better performance, cleaner finishes, and fewer problems down the line.
Need high-quality steel sheets or flashings that are made to last? Southern Sheeting stocks a wide range of steel roofing products that work as hard as you do.
