Polycarbonate Roofing Accessories Explained: Glazing Bars, Tapes & Fixings
Polycarbonate Roofing Accessories: What Do You Need?
When installing a multiwall polycarbonate roof, the sheets are only one part of the system.
A complete roof can also require glazing bars, sealing tapes, sheet end closures, fixings and flashings, depending on the design of the structure.
Each component performs a different job. Some are fundamental to almost every installation, while others are only required in particular roof configurations.
This guide explains the main polycarbonate roofing accessories, what they do and when you may need them.
Polycarbonate Roofing Accessories at a Glance
The main components used with multiwall polycarbonate roofing are:
| Component | What it does | When is it needed? |
|---|---|---|
| Glazing bars | Join adjacent sheets and secure them to rafters | Between adjoining sheets |
| Sealing tape kit | Protects the open sheet flutes while allowing moisture management | At the open ends of multiwall sheets |
| Sheet end closures | Protect and finish the sheet ends | At exposed sheet ends |
| Fixing buttons | Provide additional through-sheet support where required | Depends on roof design |
| Side flashing | Finishes/weatherproofs an outside roof edge | Depends on outside-edge design |
| Wall flashing | Weatherproofs the junction with a wall | Roofs meeting a wall |
| Glazing-bar end caps | Finish the exposed ends of glazing bars | Where glazing bars terminate visibly |
The exact quantities depend on your roof dimensions and layout.
1. PVC Top Cap & Aluminium Base Glazing Bars
Glazing bars are used where adjacent polycarbonate sheets meet.
The PolycarbonateX PVC Top Cap & Aluminium Base Glazing Bar combines an aluminium base with a PVC snap-fit top cap.
The aluminium base is fixed to the supporting rafter, with the edges of adjacent polycarbonate sheets positioned within the glazing system.
The PVC top cap then fits over the base to secure and weatherproof the joint.
What Do Glazing Bars Do?
Glazing bars help:
- Secure adjacent sheets
- Support the sheet edges
- Create a weather-resistant joint
- Maintain the correct relationship between sheets and rafters
- Accommodate the roofing system's required fitting clearance
- Produce a neat finished joint
They are an important part of the roof rather than simply a cosmetic trim.
Where Are Glazing Bars Installed?
A glazing bar normally sits directly above a supporting rafter.
Where two sheets meet, their adjacent edges are held within the glazing bar.
For example, if a roof uses approximately 980mm-wide sheets with 1000mm rafter centres, the glazing system occupies the area around the rafter while providing the appropriate fitting arrangement for the sheets.
See our Rafter Spacing Guide for a more detailed explanation.
What Length Glazing Bars Are Available?
PolycarbonateX glazing bars are available in:
- 3m
- 4m
- 6m
The required length generally relates to the projection of the roof.
Choose a bar long enough for the required installation rather than attempting to create unnecessary joints along the roof slope.
2. Do I Need Glazing Bars on the Outside Edges?
Not every roof uses exactly the same outside-edge arrangement.
Glazing bars can be used on the outside edges to create a consistent glazing system around the roof, but some installations may instead use an appropriate side-edge detail.
This is why the number of glazing bars isn't always simply:
number of sheets + one
The correct quantity depends on how the two outside edges of the roof are being finished.
If you're planning the complete roof rather than buying individual components, use the PolycarbonateX Roof Kit Calculator to determine the appropriate arrangement.
Choosing glazing bars and fixings for metal frames
3. Polycarbonate Sealing Tape Kit
Multiwall polycarbonate contains open internal channels, commonly called flutes.
These need to be treated correctly at the high and low ends of the sheet.
PolycarbonateX supplies the required tapes together as a sealing tape kit covering up to 10 metres.
The kit provides two different types of tape because the two ends of the sheet perform different functions.
Foil/Sealing Tape — Upper Edge
Foil or sealing tape is fitted to the upper end of the sheet.
Its purpose is to help prevent:
- Rainwater entering the flutes
- Dirt entering the chambers
- Insects entering through the upper end
- External contamination entering the sheet
Breather Tape — Lower Edge
Breather tape is fitted to the lower or gutter end of the sheet.
It helps protect the channels from insects and contamination while allowing moisture management at the lower end.
The two tapes shouldn't be reversed.
The basic rule is:
Top of sheet → foil/sealing tape
Bottom of sheet → breather tape
See our Condensation in Polycarbonate Sheets Guide for a detailed explanation of why the two ends are treated differently.
How Much Sealing Tape Do I Need?
Each PolycarbonateX sealing tape kit covers up to 10 metres.
When calculating your roof, consider the total width of the sheet ends that need treating.
Rather than calculating separate rolls of foil tape and breather tape, the PolycarbonateX system uses the combined kit.
The Roof Kit Calculator automatically accounts for the required sealing tape kits when calculating a complete roof.
4. Sheet End Closures
Sheet end closures are fitted over the ends of multiwall polycarbonate sheets after the appropriate tapes have been applied.
PolycarbonateX sheet end closures are supplied in 2.1m lengths.
What Do End Closures Do?
They help:
- Protect the taped sheet edge
- Finish the exposed ends neatly
- Protect the open flute area
- Form part of the lower-edge finishing detail
The end closure shouldn't be confused with sealing or breather tape.
Tape treats the open flutes.
The end closure protects and finishes the sheet edge.
Both perform different jobs.
5. Fixing Buttons
Fixing buttons are purpose-designed through-sheet fixings that can provide additional support where required by the roof design.
They shouldn't be treated as a replacement for glazing bars at sheet joints.
What Do Fixing Buttons Do?
Fixing buttons can:
- Provide additional sheet restraint
- Support the sheet between glazing bars where appropriate
- Spread the fixing load over a larger area than a standard screw head
Because polycarbonate expands and contracts as its temperature changes, through-sheet fixings must be installed correctly.
The fixing arrangement needs to accommodate the normal thermal movement of the sheet rather than unnecessarily restricting it.
See our Polycarbonate Expansion & Contraction Guide for more information.
6. Side Flashing
Side flashing is used to finish and weatherproof an exposed outside edge of the roof where the particular design requires it.
It can provide a neat transition along the side of a polycarbonate roof and help protect the edge detail from weather.
Whether you require side flashing depends on how the outside sheets and supporting structure have been designed.
This is why outside-edge planning should be done before ordering the sheet widths.
7. Wall Flashing
A lean-to, veranda or canopy attached to an existing building needs an appropriate weatherproof detail where the roof meets the wall.
PolycarbonateX supplies 225mm wall flashing tape for this purpose.
What Does Wall Flashing Do?
Wall flashing helps prevent rainwater travelling behind the upper edge of the roofing system at the wall junction.
It's commonly required for:
- Lean-to roofs
- Attached pergolas
- Verandas
- Canopies
- Other roofs terminating against a wall
A freestanding roof with no wall junction wouldn't normally require wall flashing for this purpose.
8. Glazing-Bar End Caps
Glazing-bar end caps fit to the exposed ends of the glazing bars.
Their main purposes are to:
- Provide a neat finished appearance
- Protect the exposed end of the glazing-bar system
- Complete the installation detail
Don't confuse glazing-bar end caps with sheet end closures.
They are different components:
Glazing-bar end cap → finishes the glazing bar
Sheet end closure → finishes the polycarbonate sheet
This distinction is particularly useful when ordering replacement parts.
What Accessories Do I Need for a Pergola?
A typical polycarbonate pergola roof may require:
- Multiwall polycarbonate sheets
- PVC top cap & aluminium base glazing bars
- Sealing tape kit
- Sheet end closures
- Appropriate fixings
- Fixing buttons where required
- Side flashing depending on the outside-edge arrangement
- Glazing-bar end caps
If the pergola is attached to a wall, wall flashing may also be required.
A completely freestanding pergola doesn't need wall flashing unless its particular design creates a wall junction elsewhere.
What Accessories Do I Need for a Lean-To Roof?
A typical lean-to installation may include:
- Multiwall polycarbonate sheets
- Glazing bars
- Sealing tape kit
- Sheet end closures
- Appropriate fixings
- Fixing buttons where required
- Side-edge finishing components
- Wall flashing
- Glazing-bar end caps
Because a lean-to normally terminates against an existing building, the wall junction is particularly important.
See our Best Polycarbonate Sheets for Lean-To Roofs Guide for more information about planning the complete roof.
Do Accessories Need to Match the Sheet Thickness?
Some components must be compatible with the selected polycarbonate thickness.
For example, the glazing system and sheet end closures need to be suitable for the sheet they're being used with.
Don't assume that an accessory intended for one sheet thickness will automatically fit another.
PolycarbonateX supplies multiwall roofing in 10mm, 16mm and 25mm, so select compatible components for the chosen sheet.
Can I Mix Different Polycarbonate Roofing Systems?
It's generally better to use components known to be compatible with one another.
Different manufacturers and systems can vary in:
- Dimensions
- Profiles
- Gaskets
- Fitting methods
- Tolerances
- Sheet engagement
A component that looks similar isn't necessarily interchangeable.
If you're replacing a single part on an existing roof, identify the existing system before assuming a new component will fit.
What Order Should the Components Be Installed?
The precise installation sequence depends on the roof, but broadly the process involves:
- Prepare and check the supporting structure.
- Confirm rafter centres and roof pitch.
- Prepare the polycarbonate sheets.
- Apply foil/sealing tape to the upper sheet ends.
- Apply breather tape to the lower sheet ends.
- Fit the appropriate sheet end closures.
- Install the glazing system and sheets according to the required layout.
- Install any required fixing buttons.
- Complete the outside-edge details.
- Weatherproof the wall junction where required.
- Fit finishing components such as glazing-bar end caps.
Always follow the installation requirements for the particular components you're using.
Common Accessory Mistakes
Several installation problems can be avoided by understanding what each accessory actually does.
Using the Same Tape at Both Ends
The upper and lower sheet ends have different requirements.
Use foil/sealing tape at the top and breather tape at the bottom.
Confusing End Closures with Glazing-Bar End Caps
These are completely different parts.
One finishes the sheet; the other finishes the glazing bar.
Buying Bars Before Planning the Sheet Layout
The number of glazing bars depends on the sheet arrangement and outside-edge design.
Plan the complete roof first.
Forgetting Thermal Expansion
Polycarbonate changes dimensions as its temperature changes.
The roofing system needs to accommodate this normal movement.
Treating Accessories as Optional Finishing Pieces
Some accessories are primarily finishing components, but others perform important weatherproofing, support or moisture-management functions.
Don't budget for the sheets alone and assume everything else is cosmetic.
What Do I Need for a Complete Polycarbonate Roof?
A complete roofing system needs to be considered as a whole.
The exact components depend on:
- Roof width
- Roof projection
- Sheet thickness
- Sheet width
- Number of sheets
- Rafter centres
- Outside-edge arrangement
- Whether the roof meets a wall
- Supporting structure
See our Complete Polycarbonate Roof Kit Guide for a full explanation of how these components work together.
Use the PolycarbonateX Roof Kit Calculator
If you're planning a complete roof, the easiest way to determine the required sheets and accessories is to use the PolycarbonateX Roof Kit Calculator.
Rather than calculating every component independently, the calculator uses the roof configuration to determine the appropriate materials and quantities.
This can help avoid two common problems:
Missing an essential component and having to place another order.
or
Ordering accessories you don't actually need.
Conclusion
A multiwall polycarbonate roof is a complete system rather than simply a collection of sheets.
The main accessories each have a specific purpose:
Glazing bars join and secure adjacent sheets.
Foil/sealing and breather tapes treat the upper and lower sheet flutes.
Sheet end closures protect and finish the sheet edges.
Fixing buttons provide additional support where required.
Side flashing finishes appropriate outside-edge details.
Wall flashing weatherproofs roofs where they meet a wall.
Glazing-bar end caps finish the exposed ends of the glazing bars.
Planning these components alongside the sheet layout is considerably easier than trying to add them after the roof has already been designed.
