How to Overlap Corrugated PVC Sheets Correctly (Side & End Lap Guide)

January 30, 2026

Get a Watertight, Wind-Resistant PVC Roof Every Time

Overlapping corrugated PVC sheets correctly is essential for creating a watertight, strong and long-lasting roof.
Whether you're roofing a shed, pergola, carport, lean-to or greenhouse, poor overlap is one of the most common causes of leaks — but the solution is simple once you know the correct method.

This guide explains:

How much side overlap PVC sheets need
How pitch affects the overlap size
How to do end overlaps (if required)
Correct overlap direction
Mistakes to avoid

Let’s make sure your PVC roof is installed properly.

1. Why Correct Overlap Matters for PVC Roofing

Proper overlap ensures:

✔ Watertight joints

✔ Wind uplift resistance

✔ Smooth rainwater run-off

✔ Long-term sheet stability

✔ A clean, professional appearance

A PVC roof can last 10–15+ years if overlapped correctly.

2. Side Overlap vs End Overlap — What’s the Difference?

Side Overlap

The horizontal overlap where one sheet covers the next along the corrugations.
This is the most important overlap on a PVC roof.

End Overlap

A vertical overlap where one sheet overlaps another from top to bottom.
Only needed if your sheets aren’t long enough to cover the full slope.

Where possible, use full-length sheets to avoid end laps.

3. How Roof Pitch Determines the Overlap Size

Roof pitch heavily affects how water moves down the sheet.

✔ Roof Pitch 10° or More

Use 1 corrugation side overlap.

Suitable for:

Pergolas
Carports
Apex sheds
Lean-tos with good fall

✔ Roof Pitch 5–10°

Use 2 corrugations side overlap.

Why?

Shallower pitches drain water slower, so extra overlap prevents capillary leaks.

❌ Roof Pitch Below 5°

PVC sheets cannot be used.
Increase the pitch before installing.

4. How to Do the Side Overlap Correctly

Step 1 — Decide the Overlap Direction (Important!)

The overlap must face away from the prevailing wind.

Example:

If wind blows left → right,
Overlap sheets right over left.

This prevents rain being blown under the joint.

Step 2 — Start With a Perfectly Straight First Sheet

Your first sheet must be:

Square
Level
Correctly overhanging the eaves

Any misalignment here will spread across the roof.

Step 3 — Position the Second Sheet

Slide the next sheet over the first, ensuring:

Corrugations line up perfectly
Overlap matches your pitch (1 or 2 corrugations)
Sheets sit naturally without forcing

PVC is flexible — do not bend or twist it to “make it fit”.

Step 4 — Fix the Overlap Securely

Fix side laps:

Every 400–600mm
Through the crest (never the valley)
Using PVC fixings with sealing washers

This prevents uplift and keeps water out.

5. How to Do End Overlaps (Only If Necessary)

End overlaps are less common but must be done correctly.

✔ Minimum end overlap: 150mm (steep roofs)

✔ Recommended end overlap: 200–300mm (shallow roofs)

Rules for end overlaps:

Always place upper sheet over lower sheet
Never fix through both sheets at once
Apply clear PVC-compatible mastic on low pitches
Ensure battens support the end lap area
Fix above the overlap, not in the joint

Never end-overlap PVC sheets if the roof pitch is below 5°.

6. Overlap Coverage Width (Important for Ordering Sheets)

Standard corrugated PVC sheets are ~950mm wide.

After overlap:

✔ 1 corrugation overlap → approx. 900mm coverage

✔ 2 corrugation overlap → approx. 850mm coverage

Use these numbers when calculating:

Total sheets needed
Batten spacing
Ridge or verge trims
Flashing lengths

7. Common Overlap Mistakes (Avoid These!)

❌ Overlapping on the windward side
❌ Less than 1 full corrugation overlap
❌ Misaligned corrugation profiles
❌ Fixing through the valley (causes leaks)
❌ Too little end overlap
❌ No pre-drilled expansion holes
❌ Over-tightening screws (causes cracks)
❌ Using sealant incorrectly or excessively

Correct technique = zero problems.