How to Join Polycarbonate Sheet — Installation Guide for Glass-Like Pergola Roofing

DIY enthusiasts often misunderstand the process of joining polycarbonate roofing sheets when covering a pergola. Proper installation is crucial to ensure your pergola is free from water leakage, sagging, and other potential issues.

Installing a glass-like pergola roof can be very easy when you plan the job correctly! Here are the top 8 points you should consider before installing polycarbonate sheets.

1. What slope should a pergola have?
2. Choose the correct plastic roofing sheets — Multiwall & Twinwall polycarbonate or glass-like Solid Polycarbonate sheet?
3. What is the joining method for your polycarbonate roofing sheet?
4. What type of glazing bar to use — plastic joiner or aluminium joiners?
5. How far apart should the rafters be on a pergola?
6. Can you screw your plastic roofing sheets down?
7. Can you join polycarbonate sheets with glue or silicone?
8. How to secure the edge or gable of a polycarbonate roof?

Why Slope is Important for Your Pergola

• Water Drainage: A proper slope allows rainwater to run off the clear roof instead of pooling on top, preventing leaks and structural damage.
• Self-cleaning: A sloped pergola roof makes it easier for leaves, dirt, and debris to slide off, reducing the need for frequent cleaning.
• Improved Aesthetics: A pergola with a sloped glass roof tends to have a more visually appealing appearance.
• A roof without slope and proper support:
  

What Slope Should a Pergola Have?

Polycarbonate roofing suppliers typically recommend a minimum slope of 5 degrees (or 8.8% fall), translating to approximately 88 mm drop for every metre the sheet runs horizontally.

What is the Best Material for My Pergola Roofing?

1. Glass-Like Flat Polycarbonate Roofing

The ExcelitePlas Polycarbonate Solid Locking System requires a 600–800mm rafter distance (centre to centre) and offers glass-like aesthetics, versatility, and easy installation. Featuring a standing-edge and aluminium joining system, it ensures 100% weatherproofing and allows large spans. Available in Clear and Tinted Grey, it's suitable for pergolas, awnings, and patios. Thickness is 4mm, cut to your length.

ExcelitePlas clear solid polycarbonate flat sheets are adaptable for rafters spaced anywhere from 300 to 1000mm apart and can be easily trimmed to fit your specific rafter distance. They can also be installed using ExcelitePlas aluminium H joiners, which provide a sturdy and waterproof solution.

2. Twin-Wall or Multiwall Polycarbonate Roofing

Twin-wall and multi-wall polycarbonate roofing sheets are excellent choices for pergolas, offering several advantages:

• Lightweight and Rigid: Twin-wall sheets are lighter than solid polycarbonate, yet their internal walls provide added rigidity, allowing for larger spans.
• Cost-effective: Reduced material usage makes twin-wall and multi-wall polycarbonate more budget-friendly compared to solid glass-like polycarbonate.
• Improved Insulation: These roofing materials provide better insulation properties, helping to regulate temperature effectively.
  

There are two glazing bar options available for twin-wall sheets:

1. Budget-friendly snap-fix polycarbonate glazing bars — perfect for those with minimal DIY experience.
2. Two-part Aluminium H Joiners:
   • Polycarbonate H joiner — suitable for specific thicknesses.
   • Aluminium H bar — suitable for thicknesses ranging from 2mm to 16mm.

How Far Apart Should the Rafters Be on a Pergola in Australia?

Rafter spacing can range from 450mm to 1000mm, depending on the roofing material you choose. 600–800mm is the recommended rafter distance for glass-like pergola roofing. It is advisable to select the pergola roof system first, then adjust the rafter distance accordingly to accommodate the chosen roof sheets.

Can You Screw Your Plastic Roofing Sheets Down?

When installing polycarbonate corrugated sheets, it's common practice to overlap them at the edges and secure them with oversized screws, allowing for expansion space.

However, when installing glass-like polycarbonate sheets, it's best to avoid penetrating through the sheet to minimise stress points and the risk of cracking. Although drilling holes in polycarbonate sheets is generally safe and less prone to cracking compared to acrylic sheets, it still creates weak points.

In the ExcelitePlas roofing system, we drill holes on the aluminium joiners instead, allowing the polycarbonate panels to expand and contract freely. This approach minimises the risk of cracking and ensures a watertight seal.

Can You Join Polycarbonate Sheets with Glue or Silicone?

While gluing polycarbonate sheets may seem like a simple installation method, it's not recommended due to its limited strength against wind uplift or snow loading. Additionally, polycarbonate sheets undergo expansion and contraction over time, leading to potential water leakage issues.

For a durable and long-lasting roof, installing the sheets using aluminium glazing bars is the preferred approach. If glue is necessary for sealing around the sides or ends of your polycarbonate roofing sheets, ensure you use a compatible LMN silicone sealant (Low Modulus Neutral Cure) for optimal results.

How to Cut Polycarbonate Sheet

How to Secure the Edge or Gable of a Polycarbonate Roof

In general, there are two ways a pergola roof will end on the side: it will either abut another structure like a wall or remain open-sided.

Proper finishing in this area is essential for safeguarding against potential wind uplift, ensuring waterproofing against the wall, and achieving a clean and polished appearance where the edge is visible.

When flashing a polycarbonate roof against a brick wall, options include using flashing tape or metal flashing. Metal flashing can also be used along the edge to provide a tidy finish.

Want to Learn More About Installing Polycarbonate Sheets?

To help make it easier for you, the ExcelitePlas YouTube channel has easy-to-follow installation videos and polycarbonate sheet information.

Our team is also happy to assist. Email sales@exceliteplas.com.au for advice and support, or visit our Dandenong South showroom.