How to Install Polycarbonate Side Flashings
Polycarbonate side flashings provide a neat, professional finish to the exposed edges of a polycarbonate roof while helping to protect the sheet edges from the weather. They are fitted to the outermost sheets on both sides of the roof, improving the appearance of the installation and helping to direct rainwater away from the roof structure.
This guide is written specifically for PolycarbonateX PVC side flashings used with rafter-supported polycarbonate roofing systems. Our side flashing has a unique F-shaped profile that fully encloses the exposed edge of the polycarbonate sheet while extending down the roof verge to create a clean, weather-resistant finish.
In this guide, we'll explain how PolycarbonateX side flashings work, how to fit them correctly and the most common installation mistakes to avoid, helping you achieve a professional-looking roof that's built to last.
Before You Begin
Before fitting your PolycarbonateX side flashings, make sure the roof structure has been completed and the outer polycarbonate sheets have already been installed within the glazing bar system. The side flashings are one of the final components to be fitted and provide a neat, weather-resistant finish to both exposed edges of the roof.
This guide is written specifically for PolycarbonateX white PVC side flashings designed for rafter-supported polycarbonate roofing systems. Unlike a simple edge trim, our side flashing has an engineered F-shaped profile that completely encloses the exposed edge of the polycarbonate sheet while returning vertically down the roof verge to create a clean fascia.
Before starting, check that you have the correct side flashings for your chosen sheet thickness and roof length. The flashing should match the thickness of your polycarbonate sheets so it fits securely over the sheet edge.
It's also worth checking that the outer glazing bars and polycarbonate sheets are fully aligned before fitting the side flashings. Any adjustments are much easier to make now than once the roof edge has been completed.
Understanding the F-Shaped Side Flashing Profile
Before fitting the side flashing, it's helpful to understand how the profile works and why it has been designed this way.
Unlike a simple L-shaped edge trim, the PolycarbonateX side flashing has a cross-section shaped like a capital letter "F". Each part of the profile has a specific purpose.
The two horizontal sections of the profile are the same length and form a continuous channel that the edge of the polycarbonate sheet slides into. This fully encloses the exposed edge of the sheet, protecting it from accidental knocks while creating a neat, finished appearance.
The longer vertical section of the profile extends down the outside edge of the roof, covering the roof verge to form a clean fascia. This gives the roof a much more professional appearance while helping to direct rainwater away from the exposed edge of the roof structure.
Because the side flashing fully surrounds the sheet edge, it also helps conceal the open edge of the polycarbonate sheet and any visible tapes or end details when viewed from the side.
When correctly installed, the side flashing becomes an integral part of the roofing system, improving both the appearance and weather resistance of the completed roof.
Step 1 – Fit the Side Flashing
Once the polycarbonate sheets, glazing bars and roof structure have been fully installed and aligned, you're ready to fit the PolycarbonateX side flashings.
Starting at one end of the roof, position the side flashing so that the open channel of the F-shaped profile aligns with the exposed edge of the outer polycarbonate sheet.
Carefully slide the side flashing along the full length of the sheet, ensuring the sheet enters evenly between the two horizontal sections of the profile. The flashing should move smoothly into position without needing excessive force.
As the flashing is fitted, the two equal-length horizontal sections fully enclose the edge of the polycarbonate sheet, while the longer vertical section naturally returns down the outside of the roof verge to form a neat fascia.
Check that the flashing remains fully engaged along the entire length of the sheet. The edge of the polycarbonate should sit neatly inside the profile without twisting or leaving any visible gaps.
Once correctly fitted, the side flashing should provide a clean, continuous finish from one end of the roof to the other, protecting the exposed sheet edge while giving the roof a professional appearance.
Step 2 – Check the Finished Installation
Before finishing the installation, take a few minutes to inspect both side flashings from the top, side and front of the roof. A correctly fitted side flashing should run perfectly straight from one end of the roof to the other, creating a clean, continuous edge.
Check that the edge of the polycarbonate sheet is fully enclosed inside the F-shaped profile along its entire length. The sheet should remain completely inside the channel formed by the two horizontal sections of the flashing, with no exposed sheet edge visible.
Next, inspect the vertical face of the side flashing. It should sit neatly down the outside of the roof verge, creating an even fascia that follows the line of the roof. There should be no twists, bows or gaps between the flashing and the roof edge.
Finally, stand back and view the roof from the front. Both side flashings should mirror each other, creating a symmetrical finish that frames the roofing system and gives the installation a neat, professional appearance.
If any part of the flashing has not seated correctly, remove it carefully and refit it rather than forcing it into place. Taking a few extra minutes now will ensure your roof looks its best and performs as intended for many years.
Common Side Flashing Installation Mistakes
Although PolycarbonateX side flashings are simple to install, fitting them correctly is important to achieve a neat, weather-resistant finish. Here are the most common mistakes we see and how to avoid them.
Installing the Flashing Before the Roof Is Aligned
The side flashings should be one of the final components to be fitted. Always make sure the glazing bars, polycarbonate sheets and roof structure are correctly aligned before installing the flashings.
Using the Wrong Flashing for the Sheet Thickness
Side flashings are designed to suit specific polycarbonate sheet thicknesses. Always check that the flashing matches your sheets before installation to ensure a secure fit.
Not Fully Engaging the Sheet Inside the Profile
The edge of the polycarbonate sheet should be fully enclosed within the F-shaped profile along its entire length. If the sheet is only partially inserted, the flashing won't provide the intended finish or protection.
Twisting the Flashing During Installation
When sliding the flashing onto the sheet, keep it straight and supported along its full length. Twisting the profile can make it difficult to fit correctly and affect the finished appearance of the roof.
Forcing the Flashing Into Position
The side flashing should slide smoothly over the edge of the sheet. If excessive force is required, stop and check the alignment rather than forcing the profile into place, as this may damage the flashing or the sheet edge.
Frequently asked questions
What does a side flashing do?
A side flashing provides a neat, professional finish to the exposed edges of a polycarbonate roof. It protects the edge of the sheet while helping to improve the overall appearance of the roofing system.
Why is the PolycarbonateX side flashing F-shaped?
The F-shaped profile fully encloses the edge of the polycarbonate sheet while the longer vertical section returns down the roof verge to create a clean fascia. This provides a much neater finish than a simple edge trim.
Do I need a side flashing on both sides of the roof?
Yes. A side flashing should normally be fitted to both outer edges of a rafter-supported polycarbonate roof to provide a consistent appearance and protect both exposed sheet edges.
Do side flashings support the roofing sheets?
No. The roofing sheets are structurally supported by the glazing bars and timber rafters. The side flashings are a finishing profile that protects the sheet edge and completes the appearance of the roof.
Can I cut a side flashing to length?
Yes. If required, PVC side flashings can be cut to suit the finished roof length using suitable cutting tools. Always ensure the cut is clean and square before installation.
Can I fit the side flashings after the roof has been completed?
Yes. Side flashings are designed to be one of the final components fitted, once the roofing sheets and glazing bars have been installed and correctly aligned.
Do I need silicone with a side flashing?
No. PolycarbonateX side flashings are designed to fit mechanically over the edge of the sheet and do not normally require silicone as part of the installation.
How do I know if the flashing is fitted correctly?
A correctly installed side flashing will fully enclose the edge of the polycarbonate sheet, run straight along the roof and sit neatly down the outside verge, creating a clean, continuous finish.
Need More Help?
Still unsure which sheet thickness is right for your project? Our UK team can help you check your requirements, calculate the materials you need or visualise how your finished roof could look.