Choosing the correct roof pitch is essential when installing corrugated bitumen roof sheets. An insufficient slope can lead to poor water runoff, leaks, and reduced roof lifespan.
So, what roof pitch is required for corrugated bitumen roofing?
In this guide, we explain minimum pitch requirements, why pitch matters, and how to ensure your roof performs properly.
What Is Roof Pitch?
Roof pitch refers to the angle or slope of a roof, usually measured in degrees. It determines how effectively water drains from the surface.
The lower the pitch:
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The slower water drains
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The greater the reliance on overlaps and sealing
Minimum Roof Pitch for Corrugated Bitumen Roofing
For most corrugated bitumen roof sheets, the minimum recommended roof pitch is 5°.
At or above this pitch:
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Rainwater drains effectively
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Overlaps remain watertight
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Long-term performance is maintained
Corrugated bitumen roof sheets
What Happens If the Roof Pitch Is Too Low?
Installing bitumen roofing below the recommended pitch can cause:
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Water pooling
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Backflow under overlaps
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Increased risk of leaks
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Reduced sheet lifespan
In very shallow roof applications, alternative roofing systems may be more suitable.
Overlap Requirements at Low Pitches
If your roof pitch is close to the minimum:
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Increase end overlaps (up to 200mm)
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Ensure side overlaps are at least one full corrugation
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Use eaves fillers and ridge fillers to reduce wind-driven rain
Roof Pitch for Common Bitumen Roofing Applications
Sheds & Garden Buildings
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Typically 5°–10°
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Ideal for standard corrugated bitumen sheets
Garages & Workshops
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Often 7°–15°
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Provides excellent drainage and durability
Lean-to Roofs
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Usually steeper pitches
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Performs very well with bitumen roofing
Can You Use Corrugated Bitumen Roofing on Flat Roofs?
No. Corrugated bitumen roof sheets are not designed for flat roofs.
Flat roofs require:
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Felt systems
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EPDM rubber
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GRP fibreglass roofing
Using bitumen sheets on a flat roof will almost certainly lead to water ingress.
How to Check Your Roof Pitch
Simple ways to measure roof pitch include:
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Using a digital angle finder
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Measuring rise over run
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Using a smartphone angle app
Always measure before purchasing materials.
Why Roof Pitch Matters for Longevity
Correct pitch:
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Improves water runoff
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Reduces stress on fixings
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Prevents premature wear
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Helps maintain waterproof integrity
This directly affects how long your roof lasts.
How long do corrugated bitumen roof sheets last?
Installation Tips for Low-Pitch Roofs
If your roof is close to the minimum pitch:
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Ensure fixings are correctly spaced
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Avoid overtightening
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Use compatible accessories throughout
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Install ridge pieces carefully on pitched roofs
Corrugated bitumen ridge pieces
Frequently Asked Questions
What is the minimum roof pitch for bitumen roofing?
Most corrugated bitumen roofing requires a minimum pitch of 5°.
Can bitumen roofing be installed on a flat roof?
No. Bitumen sheets are not suitable for flat roofs.
Does roof pitch affect waterproofing?
Yes. Lower pitches require more precise installation and greater overlaps.
Is a steeper pitch better?
A steeper pitch improves water runoff and generally increases roof lifespan.
Do accessories matter more on low-pitch roofs?
Yes. Eaves fillers, ridge pieces, and correct overlaps become even more important.
