The Complete Guide to Sealing Multiwall Polycarbonate Roofing Sheets

Correctly sealing the ends of multiwall polycarbonate sheets is one of the most important steps in any roofing installation. This simple process prevents condensation, algae growth, debris build-up, insects, and water ingress inside the flutes — ensuring your roof stays clear, clean and long-lasting.

In this guide, you’ll learn exactly how to fit breather tape, aluminium foil tape, and end closures the right way for a professional, durable finish.

1. Why Proper Taping & End Closures Matter

Multiwall polycarbonate sheets contain internal flutes that run the full length of the panel. These hollow chambers must be protected to prevent long-term problems.

✔ What happens if sheet ends are not sealed correctly?

• Condensation builds up

• Green algae forms in the flutes

• Dust and insects enter

• Flutes stain and discolour

• Sheets look dirty from the inside

• Lifespan is significantly reduced

Correct taping is essential for:

• Clean appearance

• Proper drainage

• Weather protection

• Long-term performance

2. What Each Tape Does (Top vs Bottom)

Polycarbonate sheets have a top end (ridge end) and a bottom end (gutter end). Each must be treated differently.

Bottom Edge — Breather Tape

Breather tape:

• Allows moisture to escape

• Stops insects entering

• Prevents dust from entering

• Reduces condensation build-up

• Keeps flutes clean

It is perforated, meaning it breathes — essential for the sheet’s drainage system.

Top Edge — Solid Aluminium Tape

Aluminium tape:

• Fully seals the top

• Prevents water ingress

• Blocks insects and debris

• Protects the inside of the flutes

It is non-breathable and creates a strong, weather-tight barrier.

3. End Closures: The Final Protective Layer

End closures clip over the taped ends to:

• Protect the tape

• Improve weather resistance

• Stop UV degradation of tape

• Prevent wind-driven rain from pushing under the tape

• Create a clean finish

Most end closures include drainage slots at the bottom to complement breather tape.

4. Tools & Materials You Will Need

Tools

• Scissors or sharp knife

• Roller or firm hand pressure

• Tape measure

• Rubber mallet

Materials

• Breather tape

• Aluminium tape

• End closures (correct thickness)

• Multiwall polycarbonate sheets

All available at polycarbonatex.co.uk.

5. Step-by-Step: How to Fit Breather Tape (Bottom End)

This is the most important part of the condensation control system.

Step 1 — Clean the Sheet Edge

Use a dry cloth to remove:

• Dust

• Swarf (plastic dust)

• Debris

The edge must be clean and dry.

Step 2 — Apply the Breather Tape

1. Start at one end.

2. Apply the tape straight and evenly.

3. Press firmly as you go.

4. Tape must cover the entire width of the sheet.

Step 3 — Fold Tape Over the Edges

Fold 20–25mm around each side to seal the corners.

Step 4 — Press the Tape Down Firmly

Use:

• A roller

• Hard thumb pressure

Ensure there are no air gaps.

Step 5 — Fit the End Closure

1. Slide the end closure onto the taped edge.

2. Ensure the drainage slots are at the bottom.

3. Tap gently with a rubber mallet until secure.

Your bottom edge is now sealed, breathable, and fully protected.

6. Step-by-Step: How to Fit Aluminium Tape (Top End)

Step 1 — Clean the Sheet Edge

Again, ensure no dust or swarf is present.

Step 2 — Apply Aluminium Tape

1. Stick right along the edge

2. Keep the tape straight

3. Avoid wrinkles

4. Cover the entire width

Step 3 — Fold the Tape Over the Sides

Fold 20–25mm onto each side of the sheet.

This ensures a strong weather-tight seal.

Step 4 — Press Down Firmly

Use a roller for maximum adhesion.

Step 5 — Fit the End Closure

Once applied:

1. Push the end closure onto the taped end

2. Tap gently to secure

3. Ensure it sits flush and straight

7. Common Mistakes to Avoid

❌ Using the wrong tape on the wrong end

• Top end = aluminium

• Bottom end = breather

❌ Not cleaning the sheet first
Debris weakens adhesion.

❌ Skipping the end closure
Tape alone will fail over time.

❌ Trapping moisture inside flutes
Always clean swarf and avoid wet cleaning.

❌ Using clear adhesive tape
Never use household tapes — they fail rapidly.

8. Frequently Asked Questions

1. Do I need tape AND end closures?

Yes — tape protects the flutes, end closures protect the tape and improve weather resistance.

2. Which direction should the flutes run?

Always downhill, from top to bottom.

3. Can I leave the flutes unsealed temporarily?

No — even a short period can let dust or insects in.

4. What if moisture appears inside after taping?

It usually means:

• Wrong tape used

• Poor adhesion

• No end closure

• Flutes cleaned with water

5. Does tape need replacing?

Aluminium lasts for years.
Breather tape may need replacing during reroofing.