Corrugated bitumen roof sheets are designed to be easy to install, but small mistakes during fitting can lead to leaks, reduced lifespan, and unnecessary repairs. Many of these issues are avoidable with the right preparation and technique.
In this guide, we highlight the most common mistakes when installing bitumen roof sheets and explain how to avoid them to ensure a strong, weatherproof roof.
Mistake 1: Installing on the Wrong Roof Pitch
One of the most frequent errors is fitting bitumen roofing on a roof with too shallow a pitch.
Why this is a problem:
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Water drains too slowly
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Overlaps can allow backflow
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Increased risk of leaks
Always ensure your roof meets the minimum recommended pitch of 5°.
Mistake 2: Insufficient Sheet Overlaps
Incorrect overlaps are a major cause of water ingress.
Avoid this by:
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Using at least one full corrugation for side overlaps
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Allowing 150–200mm end overlaps depending on pitch
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Positioning overlaps away from prevailing wind
Correct overlaps are essential for waterproofing.
Mistake 3: Fixing Through the Valleys
Fixing through the valleys of the corrugation weakens the sheet and increases the chance of cracking.
Correct method:
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Always fix through the crest of the corrugation
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Use bitumen-specific nails or fixings
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Space fixings evenly across battens
Mistake 4: Overtightening Fixings
Overtightening fixings can:
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Crush the sheet
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Cause stress cracks
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Restrict natural movement
Fixings should be:
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Secure but not forced
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Tight enough to seal, but not distort the sheet
Mistake 5: Skipping Eaves Fillers
Some installers omit eaves fillers to save time or cost.
This leads to:
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Wind-driven rain entering the roof
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Birds and insects nesting
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Debris buildup
Eaves fillers are a small but vital component of a complete roofing system.
Mistake 6: Poor Batten Spacing
Incorrect batten spacing can cause sheets to flex or sag.
Ensure:
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Battens are evenly spaced
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Sheets are fully supported
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Fixings align with timber below
Always follow manufacturer guidance.
Mistake 7: Walking Incorrectly on the Roof
Walking on unsupported areas or valleys can damage the sheets.
Safe practice includes:
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Stepping only on crests
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Walking where battens support the sheet
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Using boards to spread weight
Mistake 8: Installing Sheets Out of Alignment
Starting with a poorly aligned first sheet often results in:
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Crooked rows
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Uneven overlaps
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Untidy roof edges
Take time to square the first sheet properly — it sets the standard for the entire roof.
Mistake 9: Using Incompatible Accessories
Using incorrect or mismatched accessories can compromise waterproofing.
Always use:
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Compatible ridge pieces
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Correct fillers
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Approved fixings
Corrugated bitumen accessory pieces
How to Get Installation Right First Time
To avoid these mistakes:
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Prepare the structure properly
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Use compatible components throughout
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Follow installation best practices
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Take your time with alignment and fixing
Correct installation significantly extends roof lifespan.
Frequently Asked Questions
What is the most common bitumen roofing mistake?
Insufficient overlap and incorrect fixing positions are the most common causes of leaks.
Do mistakes affect roof lifespan?
Yes. Poor installation can drastically reduce how long bitumen roofing lasts.
Can mistakes be fixed later?
Some issues can be repaired, but prevention is far better and more cost-effective.
Are these mistakes common with DIY installations?
They can be, but careful planning and guidance reduce risk significantly.
Is bitumen roofing forgiving to install?
Yes, but only when correct installation principles are followed.
