How to Install Polycarbonate Sheet (with Snap Down Glazing Bars)

Polycarbonate sheet is one of the most popular roofing solutions for homeowners for one main reason; it is easy to fit on a wide range of roof types! When you are looking for a clear roof that’s easy to handle then polycarbonate roofing sheets could be the best option for you.

Twinwall and Multiwall Polycarbonate sheets offer a lightweight roofing option that’s simple to install. If you’re an experienced DIYer there is no need to worry about hiring tradesmen when fitting polycarbonate sheets! The most popular way of installing polycarbonate roofing is with a PVC Snap down glazing bar system. PVC Glazing bars offer a good level of strength and durability at a budget level that’s achievable for most households.

At this point, it’s worth noting that if you are looking for the best way to fix polycarbonate sheets then you should consider an aluminium glazing bar range. Although there is a greater upfront cost, they outlast PVC bars and can prove more cost-effective long term. However, for a basic pergola or lean roof, you can’t go wrong using a snap fix glazing bar system!

This ‘How to’ guide covers everything you need to know about how to fit a polycarbonate roof with a PVC glazing bar system.

If you are looking to install Solid Polycarbonate roofing or glass then please read our How to Install Glazing bars guide.

Tool required to install polycarbonate sheets:

  • Fine/medium tooth saw (Hack, circular or hand saw)
  • Drill
  • Timber Screws
  • Rubber Mallet
  • Appropriate PPE

How to Install Polycarbonate Roofing Sheets - Steps:

  1. Always wear the appropriate PPE equipment. Safety Glasses are recommended when cutting the glazing bars to length.
  2. Before starting installation ensure you have installed the Endstop bar, or drip trim, to the ends of your polycarbonate sheets. View this video guide to learn How to Install End Stop Bar.
  3. Check the length of your glazing bars base bars against your rafters. 
  4. Trim to length using a fine tooth saw. Remember to allow approximately 40mm extra to overhang over your eaves. This ensures water drains off into the gutter
  5. Optional step - Predrill the PVC base bars with pilot holes. This makes screwing down the glazing bars easier once you are up at roof height!
  6. Place the first base bars on the top of your rafters. It is easiest to start at one end.
  7. Line the Base bars up with the rafter and allow for an expansion gap of approximately 2mm between the polycarbonate sheets and Snap down glazing bars
  8. Select suitable screws for your rafters. If you have timber rafters then use standard exterior timber screws.
  9. Screw down the first two base bars starting with your first rafter (gable or wall). Please note: if starting with a wall bar ensure the base bar is approximately 9mm away from the wall to give space for the top cap.
  10. Ensure you have screws at the top and bottom of the PVC glazing bars. Then screw down in between at 200-300mm intervals
  11. Place the first polycarbonate sheet onto the roof
  12. Peel back the protective film a little on the polycarbonate sheeting to allow for the glazing bar top caps
  13. Place the Snapa top caps on top of the base bars to check the length and trim if required. Ensure the bottom gutter end of the top cap is flush with the front face of the Endstop bar so that the Bar End Cap will fit properly. Approximately the top cap should be 7mm beyond the base bar.
  14. Starting at one end, slowly push click the Snapa top cap down until you hear a “Click”
  15. Use a rubber mallet to gently tap the polycarbonate glazing bar top cap fully into place
  16. Screw the Snapa Bar End Cap Onto the end of the glazing bar using the small screw and screw cap provided. If pent or freestanding roof using Bar End Caps both ends.
  17. Snap the small cap into place to create a neat finish on your roof!
  18. For the outer rafters use a Gable Bar if it is an open edge or Wall bar is against a side abutting wall.
  19. Finally, if a Lean-to roof, then seal along the back with a Top Wall Flashing to complete!

Common Polycarbonate Roofing Sheet Installation questions:

Polycarbonate Sheet Installation Diagram

Below are two installation diagrams for polycarbonate sheets showing the key components for each area of the roof. One diagram shows a typical lean-to roof as you might see used on a pergola and the other an Apex Roof which is often used on gazebos.

Polycarbonate Sheet Lean To Project
Polycarbonate Sheet Apex Project


Which way up do polycarbonate sheets go?

Polycarbonate sheets only have one UV protected side so it is important that when installing them that side faces outwards towards the sun. If installed upside down there is a discolouring and brittleness risk.

The quick way to tell which side is UV Protected is to look at the protective sheet film. The UV protected side will have branded tape, e.g. Axiome®, on it and will say “UV Protection this side”. If the film has been removed it can be harder to tell so best checked before installing.

Solid Polycarbonate Sheets are UV protected on two sides so no need to worry about which side faces up when you are installing them.

How can I find polycarbonate roofers installers near me?

Installing polycarbonate roofing is an easy job so any competent roofer, joiner, builder or general tradesman should be able to assist you. The easiest way to find a local polycarbonate roof installer is to use a Trade Recommendation site and contact those with the best reviews. A good sign is if they have had previous experience building a lean-to or similar.

The best way to find an installer for your polycarbonate sheeting is via recommendation! If you see a roof your friend or neighbour has, that has been constructed well, then speak to them for contact details.

How to join polycarbonate sheets end to end?

Polycarbonate sheets can be joined end to end using a horizontal glazing bar or H section. It is only recommended to join sheets end to end where you have an extra long or deep roof (usually 5 metres plus) as a single length sheet is always best for waterproofing.

How to seal polycarbonate sheets?

The best way to seal polycarbonate sheets is to use an End Stop Bar. An End Stop Bar is an F Shape profile that caps off the end of your sheets and provides a drip into the gutter. You can also add an extra layer of protection by using Anti Dust Tape.

Sealing polycarbonate sheets is essential to the waterproofing and lifespan of your roof. Learn how to install End Stop Bar and How to Install polycarbonate sheet tape with our How2 Videos below:

How to Install End Stop Bar
How to Seal Polycarbonate Sheets with Tape

What expansion gap should be left between the polycarbonate sheets and glazing bars?

Leave approximately a 2mm gap between the edge of the polycarbonate sheet and the glazing bar internal wall to allow for any expansion.

Looking for polycarbonate roofing installation guides?

For full polycarbonate roofing installation instructions then please check out our step-by-step guides on the links below:

Polycarbonate roofing sheet installation instructions
Snap down glazing bars installation instructions
Rafter aluminium glazing bar installation instructions
Self supporting glazing bars installation instructions

Would you like further help with your Polycarbonate Sheet Project?

Simply jump on our Live Chat or via email where our Teams will provide you with all the advice and support you require for your project.

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