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The Ultimate Guide to Polycarbonate Roofing Sheets for DIYers

  • Writer: The Plastics Shed
    The Plastics Shed
  • May 8
  • 3 min read

Introduction

Planning a new roof for your conservatory, carport, pergola, or greenhouse? Our polycarbonate roofing sheets are the ideal solution – lightweight, strong, and cut to your exact size. This ultimate DIY guide from The Plastics Shed covers everything: what polycarbonate sheets are, how to choose the right thickness and colour, installation tips, and the accessories you'll need for a professional result.


What Are Polycarbonate Roofing Sheets?

Polycarbonate is a tough, transparent plastic known for its impact resistance and UV protection. Our multiwall sheets (including twinwall and triplewall) feature internal chambers that offer excellent thermal insulation and rigidity, making them ideal for roofing. These sheets are not solid polycarbonate — which is a single solid layer like glass — but structured sheets designed specifically for roofing and glazing applications. While multiwall sheets are strong and durable, they are not classified as "virtually unbreakable" like solid polycarbonate, and should be supported and installed correctly.


Why Choose Polycarbonate?

  • Tough and Weather-Resistant: Engineered to handle wind, rain, and impacts better than glass of equivalent weight.

  • Lightweight: Easy to handle and install without specialist tools

  • UV-Protected: Coated to prevent yellowing and brittleness

  • Energy Efficient: Excellent insulation properties thanks to the multiwall design

  • Cut to Size: Reduces waste, removes the hassle of cutting, and ensures a perfect fit for your project

Why let us cut it for you? Cutting polycarbonate yourself can be tricky. It requires a fine-tooth saw, safe clamping, proper taping, and blowing out all the swarf to prevent moisture buildup inside the sheet's chambers. You’ll also need to buy foil and breather tape. When you order from us, we take care of all that – giving you clean, professionally trimmed, ready-to-install panels with no mess or margin for error.

Choosing the Right Thickness

Each thickness of polycarbonate sheet has different uses. Here’s a quick breakdown:

  • 4mm / 6mm Twinwall: Ideal for greenhouses, cold frames, and cloches. Great glass alternative.

  • 10mm Twinwall: Good for budget canopies or lean-tos. Light-duty use only.

  • 16mm Triplewall: A popular all-rounder. Great for carports, sheds, and patio covers.

  • 25mm Multiwall: Higher insulation. Use for conservatories and year-round rooms.

  • 35mm Multiwall: Maximum insulation and rigidity. Ideal for orangeries or enclosed pool houses.





Colour Options Explained

  • Clear: Maximum light. Good for greenhouses and bright indoor areas.

  • Opal: Diffused light. Reduces glare and heat. Excellent for patios and schools.

  • Bronze: Tinted for shade. Great for south-facing carports or pergolas.

  • Solarguard: Reflects solar heat. Blocks up to 50% of heat with minimal light transmission – perfect for very sunny spots.


Installation Basics

Installing polycarbonate roofing is DIY-friendly when done with the right guidance and accessories. Here are the core steps:

  1. Frame Support: Ensure rafters or bars are spaced correctly for your sheet thickness.

  2. Allow Expansion: Deduct around 20mm from the measured width to allow for thermal movement.

  3. Use Glazing Bars: Secure the sheets between aluminium or PVC glazing bars.

  4. Seal the Ends: Apply breather tape to the bottom edge and solid foil tape to the top. Use U-profiles to cap them off.

  5. Slope: Maintain a fall of at least 5 degrees to allow water runoff.

  6. Fixings: If needed, use buttons with neoprene washers for direct fixing (not usually required with glazing bars).

Note: Always install with the UV-coated side facing out.


Accessories You Might Need

We stock a full range of matching accessories to complete your build:

  • Glazing Bars: Connect sheets and provide a watertight seal

  • Wall Plates & Eaves Beams: Support the top and bottom of a lean-to roof

  • F-Sections & U-Profiles: Finish open sheet edges

  • Vent & Foil Tapes: Seal the ends to prevent dirt and condensation

  • Fixing Buttons: For additional fixing if required

  • Silicone & Sealants: For edge sealing and flashing


Tools & Tips for DIYers

  • Leave the protective film on until the end of the installation

  • Clean using soapy water – never use abrasives

  • Always check spans and loads if in a high wind/snow area

⚠️ Reminder: We strongly recommend using our cut-to-size service. It ensures your panels are accurately trimmed, cleanly edged, and installation-ready — no swarf, no taping, no risk.

Ready to Build?

Use our Cut-to-Size Calculator on this page to instantly price your polycarbonate sheets. Simply choose your sheet type, thickness, and dimensions – we’ll do the rest.

For help with choosing accessories, visit our Polycarbonate Accessories section, or browse all Glazing Bars, Wall Plates, and Sheet Closures. If you’re unsure what you need, call us on 01922 254100 – we’re always happy to help.


Don’t miss our full guide: How to Install Polycarbonate Roofing Sheets – with diagrams, spacing charts, and expert tips.




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