The Complete Guide to Finishing Corrugated Bitumen Roofs Properly

Sealing the verges (side edges) and ridge (top edge) of a corrugated bitumen roof is essential for keeping your roof watertight, wind-resistant and long-lasting.
Most leaks and uplift problems don’t come from the sheets — they come from poor ridge or verge installation.

Whether you're roofing a shed, garage, pergola, lean-to or garden building, this guide explains exactly how to seal the ridge and verges correctly, what fixings to use, and mistakes to avoid.

1. Why Proper Ridge & Verge Sealing Matters

✔ Stops wind uplift

Unsealed edges act like a wind sail and can lift sheets in storms.

✔ Prevents rainfall blowing under sheets

Especially important on exposed sites.

✔ Keeps out debris, insects and birds

Prevents nesting between sheets and timber.

✔ Improves waterproofing

Most leaks occur at sheet joins, not in the middle.

✔ Creates a clean, professional finish

Neat edges = a long-lasting, better-looking roof.

2. What You Need for Sealing Ridges & Verges

✔ Matching Bitumen Ridge Pieces

Available in:

• Black

• Green

• Red

• Brown

✔ Bitumen Verge Trims / Barge Boards

Used to secure the outer sheet edge.

✔ Fixings (with caps & rubber washers)

Essential for a watertight seal.

✔ Tools

• Hammer or drill/driver

• Tape measure

• Marker or chalk

• Gloves

• Ladder

3. How to Seal the Ridge (Top of Roof)

The ridge is the highest point of the roof and the area most exposed to wind and driving rain.

Step 1 — Overlap the Sheets Correctly

Your bitumen sheets should:

• Meet evenly along the ridge

• Overlap the ridge by at least 125–150mm

• Have fixings on the top corrugation line

If sheets are uneven, trim before adding your ridge.

Step 2 — Lay the Ridge Centre Line

Place the ridge so that:

• The centre sits exactly over the ridge line

• One side of the ridge overlaps each slope evenly

• It follows the angle of the roof naturally

Most bitumen ridge pieces are flexible to match your roof pitch.

Step 3 — Fix the Ridge at Every Corrugation

This is essential to prevent wind uplift.

✔ Fix through every crest of the corrugation
✔ Fix both sides of the ridge
✔ Use fixings with rubber sealing washers
✔ Ensure caps are closed to protect the fixing head

For maximum strength, start by fixing at the:

• Centre

• Two ends

• Then work along the ridge line evenly

Step 4 — Overlap Ridge Pieces

If you need multiple ridge pieces:

• Overlap by 150–200mm

• Fix through both layers

• Ensure the overlap faces away from the prevailing wind

This prevents driving rain from flowing under the lap.

4. How to Seal the Verges (Side Edges)

Verge sealing prevents wind-driven rain and stops the outer sheet lifting or curling.

Option 1 — Using Bitumen Verge Pieces (Recommended)

Step 1 — Position the Verge Trim

• Place the verge so it covers the sheet edge

• Ensure it sits on top of the corrugation

• Keep it straight along the roofline

Step 2 — Fix Through Every Corrugation

Just like the eaves, verge edges take the brunt of wind uplift.

✔ Fix every corrugation
✔ Use sealed fixings
✔ Do not overtighten
✔ Ensure the trim is flush with the sheet

Step 3 — Overlap Multiple Ver g e Pieces

If your roof is long:

• Overlap verge trims by 150mm

• Fix through both layers

• Ensure smooth alignment

Option 2 — Using Timber Barge Boards (Traditional Method)

If you prefer timber finishing:

• Fix timber barge board along the roofside

• Sheets rest against it securely

• Fix through every corrugation into the timber

• Paint or weatherproof timber for longevity

This creates a classic shed-style finish.

5. Tips for a Windproof, Long-Lasting Finish

✔ Fix every corrugation on both the ridge and verge

This prevents gaps and uplift.

✔ Check sheet alignment before fixing the ridge

A crooked line will cause sealing gaps.

✔ Always fix on the crest, never the valley

The valley is where rain flows.

✔ Use more fixings on exposed roofs

High-wind areas need tighter fixing patterns.

✔ Keep overlaps facing away from the wind

This prevents capillary leaks.

6. Common Ridge & Verge Mistakes to Avoid

❌ Fixing in the valleys
❌ Using too few fixings
❌ Leaving the verge edge floating
❌ Incorrect ridge overlap direction
❌ Overtightening fixings (crushes bitumen)
❌ Not sealing the top corrugation line
❌ Letting ridge pieces overlap too little (<100mm)
❌ Not using sealing washers

Avoid these and your roof will perform flawlessly.

7. Frequently Asked Questions

1. Do I need a ridge piece on every bitumen roof?

Yes — unless you have a single-slope lean-to roof.

2. How much should ridge pieces overlap?

150–200mm for maximum weather protection.

3. Can I use screws instead of nails?

Yes — screws provide stronger pull-out resistance.

4. Should verges be fixed on every corrugation?

Yes — this protects against wind uplift.

5. How do I make verges look neat?

Use matching verge trims or straight timber barge boards.

Buy Ridges, Verges & Bitumen Roofing Accessories

At bitumenroofing.co.uk, we supply:

• Bitumen ridge pieces

• Bitumen verge trims

• Corrugated bitumen sheets

• Colour-matched fixings

• Eaves fillers

• Everything for a watertight roof

• Fast UK delivery

• Cheap prices

• Unbeatable service

👉 Shop Bitumen Ridge Pieces
👉 Shop Verge Trims
👉 Shop Corrugated Bitumen Sheets