How to Fix Corrugated Bitumen Sheets to Timber or OSB (Correct Fixing Pattern Guide)

January 30, 2026

The Step-by-Step Guide to Secure, Long-Lasting Bitumen Roofing

Fixing corrugated bitumen roofing sheets to timber or OSB is straightforward — but ONLY if you follow the correct fixing pattern, spacing and installation technique.
Most leaks in bitumen roofs come from incorrect fixings, not the sheets themselves.

In this guide, you’ll learn exactly how to secure bitumen sheets to:

Timber rafters
Timber battens
Timber frame roofs
OSB or plywood decks

Plus, you’ll see the correct fixing positions, spacing, and the number of fixings needed per sheet.

1. What You’ll Need

✔ Fixings

Use official bitumen roofing fixings (Onduline/Coroline-style), which include:

Colour-matched caps
Rubber sealing washers
Ring shank nails or screw fixings

Avoid standard nails — they WILL leak.

✔ Tools

Hammer or drill/driver
Tape measure
Ladder
Chalk line
Gloves
Marker pen

2. Understanding the Structure You’re Fixing To

Corrugated bitumen sheets can be fixed to either:

A) Timber Battens (Most Common)

Battens typically spaced at:

450mm for sheds
600mm for larger structures

B) Solid Decking (OSB or Plywood)

Sheets lay flat for maximum support.
Fixings go through the crest of the corrugation, not the valley.

C) Timber Rafters (For Pergolas or Open Frames)

Requires purlins/battens across rafters for proper support.

3. The Golden Rules of Bitumen Roof Fixings

Follow these and your roof will last decades:

✔ Rule 1: Always fix on the crest

Never in the valley — this is where water runs.

✔ Rule 2: Use sealing washers

These compress to create a watertight seal.

✔ Rule 3: Don’t overtighten

It can distort the sheet and cause leaks.

✔ Rule 4: Follow correct fixing pattern

Even spacing prevents uplift in strong winds.

✔ Rule 5: Fix through every corrugation at the eaves

This prevents wind lift at the bottom edge.

4. The Correct Fixing Pattern (Essential)

This is the universal fixing pattern for corrugated bitumen sheets.

✔ At the Eaves (Bottom Edge): Fix Every Corrugation

Strengthens the wind-resistant edge
Keeps the sheet flat and stable
Prevents lifting during storms

Example:
A sheet with 10 corrugations = 10 fixings at the eaves

✔ Along Each Side Lap: Fix Every 2nd or 3rd Corrugation

Secure the sheet where it overlaps the next one.

Fix every 2 corrugations for exposed areas
Fix every 3 corrugations for sheltered sites

✔ At Intermediate Battens: Fix Every 2 Corrugations

Fix at every purlin/batten across the slope.

This gives strong anchoring and keeps sheets rigid.

✔ At the Ridge: Fix Every Corrugation

Just like the eaves — the ridge carries uplift loads.

5. How Many Fixings Per Sheet?

On average:

✔ For sheds & small roofs

18–22 fixings per sheet

✔ For larger roofs or exposed locations

25–30 fixings per sheet

Fixings are inexpensive — use more, not fewer.

6. Step-by-Step: How to Fix Bitumen Sheets to Timber or OSB

Step 1 — Prepare the Roof Structure

Ensure battens/OSB are dry and secure
Confirm correct roof pitch: minimum 5°
Snap chalk lines on battens for alignment

Step 2 — Start at the Eaves

Lay your first sheet at the bottom.

Align the sheet so it overhangs 50–70mm
Fix every corrugation across the bottom
Install fixings vertically straight — not at an angle

Step 3 — Install Side Laps

Overlap sheets by:

One corrugation for roofs with 10°+ pitch
Two corrugations for low pitch (5–10°)

Fix through the crest only.

Step 4 — Fix Intermediate Battens

Move upward:

Fix every 2 corrugations across
Follow your chalk line for perfect alignment

Step 5 — Continue Up the Roof Slope

Sheet by sheet:

Maintain consistent overlap
Keep courses straight
Fix regularly to prevent billowing

Step 6 — Fix the Ridge

Install the matching bitumen ridge piece:

Fix every corrugation
Overlap ridge over sheets by at least 125mm
Use sealing washers for every fixing

Step 7 — Seal the Verge (Side Edges)

You can use:

Timber barge boards
Metal verge trims
Bitumen verge pieces

Fix the verge securely to prevent wind uplift.

7. Fixing Bitumen Sheets to OSB (Solid Decking)

This method is used for:

Garden rooms
Converted outbuildings
Heavier-duty roofs

✔ Fixings should still be on the crest

Even on a flat deck.

✔ No battens needed

But ventilation must be considered.

✔ Can use screw fixings for extra pull-out resistance

✔ More fixings recommended

Spacing every 300mm is ideal.

8. Common Fixing Mistakes to Avoid

❌ Fixing through valleys — causes instant leaks
❌ Skipping fixings at the eaves — sheets lift in storms
❌ Not using washers — cap nails alone are not waterproof
❌ Overtightening — distorts the sheet
❌ Incorrect overlap — leads to capillary leaks
❌ Underestimating the number of fixings needed

Avoid these and your roof will be secure for years.