When installing corrugated metal roof sheets, ensuring the correct overlap is critical for weatherproofing and long-term performance.
Proper overlaps help stop water ingress, improve structural integrity, and help your roof withstand the elements, especially in areas with heavy rainfall or harsh weather conditions.
This guide will explain the recommended overlap sizes for different types of metal roof sheets and roof pitches.
General Overlap Guidelines for Metal Roof Sheets
The required overlap for metal roofing sheets depends on the pitch (angle) of the roof and the type of sheeting used. We have produced a guide on how to measure the pitch of a roof.
Below are the general recommendations:
- For Roofs with a 10° Pitch: A minimum overlap of 150mm is typically recommended.
- For Roofs with a 5° Pitch: A larger overlap of 300mm is suggested to account for the shallower angle and increased risk of water pooling.
Why Overlap Matters:
Proper overlapping is essential for the effective performance of a metal roof. It ensures that water flows seamlessly down the roof surface, directing it away from the structure and preventing leaks or water ingress that could lead to damage over time.
In addition to enhancing the roof’s waterproofing, proper overlaps contribute to its overall strength and stability.
By creating a tighter seal, overlaps reduce the risk of wind uplift during storms, ensuring that the sheets remain securely in place even in harsh weather conditions.
This added resistance also helps to extend the lifespan of the roofing system, offering long-term protection and peace of mind.
Overlap for Corrugated Roofing Sheets
Corrugated roof sheets require specific attention to overlapping to maintain a weather-tight seal:
- Side Laps: Corrugated sheets should overlap by at least one full corrugation at the edges. This ensures a snug fit and helps prevent water ingress.
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End Laps: For longer runs, sheets should overlap at their ends by 150mm to 300mm, depending on the roof pitch.
A corrugated project in London, supplied by Trade Warehouse.
Tips for Corrugated Roof Overlaps:
- Use mastic lapping tape to seal the overlaps and provide additional waterproofing.
- For areas with heavy rainfall or steep roof pitches, consider increasing the overlap for enhanced protection.
- Ensure the corrugations align properly during installation to avoid gaps or misalignment.
- Consider also using the dripstop membrane to stop your corrugated roof dripping!
Overlap for Tile Form Metal Sheets
Tile effect metal roofing sheets are designed to mimic the look of traditional tiles while offering the benefits of metal roofing.
Correct overlapping is essential to maintain the aesthetic and functional qualities of these sheets:
- Side Overlap: Each sheet should overlap the next by at least one corrugation or gully.
- Installation Direction: Begin installation from right to left, ensuring each sheet laps correctly over the previous one.
- Securing the Overlap: Secure the sheets into position before applying mastic tape and screws for a tight seal.
Additional Tips for Tile Form Sheets:
- Use a wood block and a heavy object (e.g., a mallet) to position the sheets without damaging the surface. Place a soft material between the sheet and the block to prevent scratches.
- Make sure the sheets extend beyond the bottom purlin to direct rainwater into the gutters or away from the building.
Key Considerations for Longer Roofing Projects
For longer roofing spans, like on Dutch barns, metal roof sheets are often supplied in specific lengths to simplify installation.
However, when your project requires sheets longer than the maximum available size, such as 5m for 0.5mm thickness or 7m for 0.7mm thickness, you’ll need to create a two-sheet run:
- Ensure the end lap between the two sheets follows the pitch-specific guidelines (150mm to 300mm).
- Use lapping tape along the overlap to prevent water ingress.
Final Thoughts
The correct overlap for metal roof sheets is crucial for creating a weather-resistant roof.
Whether you’re using corrugated or tile form sheets, following the recommended overlap sizes for your roof’s pitch and using the right sealing techniques will ensure a long-lasting, watertight installation.
Proper planning and careful installation will not only enhance the roof’s performance but also reduce the likelihood of costly repairs in the future.
