If your glazing bar end caps keep falling off, won’t push all the way in or simply don’t seem to fit, there are a few things worth checking before replacing them.

Push-fit glazing bar end caps are designed to provide a neat finish to the exposed ends of your glazing bars. However, if the cap isn’t sitting correctly, the PVC top cap hasn’t been fully secured or something is obstructing the fitting, you may find that it keeps coming loose.

At The Polycarbonate Store, we supply two ranges of rafter supported glazing bars: Exitex Capex Snapdown and Sunwood (Molan) Snapdown glazing bars. Both use push-fit PVC end caps, although their profiles and fitting requirements differ.

Whether you’re fitting a new polycarbonate roof or trying to secure an existing end cap, this guide covers the most common problems and how to resolve them.

How Do Snapdown Glazing Bar End Caps Work?

Snapdown glazing bars are used to secure polycarbonate sheets onto a supporting timber framework. They’re a popular choice for lean-to roofs, pergolas, carports and other timber-supported roofing projects.

Both Exitex and Sunwood Snapdown glazing bars consist of an aluminium base, rubber gaskets and a PVC top cap.

The aluminium base is secured to the supporting timber rafter, the polycarbonate sheets are positioned onto the gaskets, and the PVC top cap is snapped down to hold everything in place.

A separate PVC end cap is then fitted to the exposed end of the glazing bar, usually at the bottom of the roof towards the gutter.

Unlike screw-fixed glazing bar end caps, Exitex and Sunwood Snapdown end caps are push-fit, using a moulded locating feature to secure them to the glazing bar.

For a more overview explanation of the complete roofing system, take a look at our Polycarbonate Roofing Installation Tips.

Why Do My Glazing Bar End Caps Keep Falling Off?

If your glazing bar end cap won’t stay in place, one of the following could be causing the problem.

1. The End Cap Hasn’t Been Pushed Fully Into Place

One of the most common issues is an end cap that appears to be fitted but hasn’t actually seated properly.

The locating peg or moulded fitting needs to engage with the correct part of the glazing bar. If it hasn’t, the end cap may only be resting against the exposed end. It might stay in place initially but become loose over time.

How to fix it:

• Remove the end cap and check that the locating feature is lined up correctly.
• Try pushing it back into place using firm, even hand pressure. The end cap should sit neatly against the glazing bar without a noticeable gap.
• If it won’t push all the way in, don’t force it. Check for an obstruction or incorrect alignment first.

2. The PVC Top Cap Isn’t Fully Snapped Down

Both Exitex and Sunwood Snapdown glazing bars use a PVC top cap that locks into the aluminium base. If the PVC top cap hasn’t been fully snapped down, particularly at the bottom end of the glazing bar, it may affect how the end cap fits.

How to fix it:

• Check that the PVC top cap is sitting evenly along the aluminium base and that the locking legs are correctly engaged.
• If part of the top cap is sitting higher than the rest, check whether anything is preventing it from locking into position.
• Always press the PVC top cap into place carefully. We don’t recommend using a rubber mallet or hammer, as this can damage the PVC and potentially cause stress fractures.

3. There’s an Obstruction Inside the Glazing Bar

If your glazing bar end cap won’t push all the way in, there may be something obstructing the locating peg. This is particularly worth checking if you’ve cut your glazing bars to length. Small pieces of PVC, aluminium burrs or debris left behind after cutting can prevent the end cap from fitting properly.

How to fix it:

• Remove the end cap and inspect the exposed end of the glazing bar.
• Check for rough cut edges, loose fragments or anything that could interfere with the locating peg.
• Make sure the aluminium base and PVC top cap are correctly aligned.
• If the locating peg appears to be hitting part of the internal glazing bar profile, don’t force it. Check that you’re using the correct end cap and that the glazing bar has been assembled correctly.

4. The End Cap Needs Additional Retention

Sometimes a push-fit end cap can feel loose even when it’s been correctly fitted.

For Exitex Capex Snapdown glazing bars, published fitting guidance recommends applying a small amount of silicone sealant underneath the short upper lip of the end cap before pushing it firmly into position. This helps retain the end cap.

For Sunwood Snapdown glazing bars, check the appropriate fitting instructions before applying silicone or other sealants.

If additional sealant is permitted, make sure it’s compatible with the PVC and polycarbonate roofing materials, and only use a small amount and avoid blocking any drainage paths.

Remember: Silicone should only help secure an end cap that already fits correctly. It shouldn’t be used to compensate for a damaged or incorrectly fitted component.

5. The End Cap Is Damaged or Incorrect

If your end cap has fallen off several times, inspect the locating peg and surrounding PVC.

If the peg is cracked, distorted or broken, the end cap may no longer fit securely.

It’s also important to make sure you’re using the correct replacement end cap.

Although Exitex and Sunwood glazing bars work in a similar way, their end caps aren’t interchangeable as standard.

You can find compatible replacements in our Rafter Supported Glazing Bars & Accessories range.

How to Fit Exitex and Sunwood Snapdown Glazing Bar End Caps

Whether you’re installing a new polycarbonate roof or replacing an end cap that’s come loose, follow these steps to check that everything fits correctly.

Step 1: Check the Glazing Bar Installation

Before fitting the end cap, make sure the aluminium base is securely fixed to the supporting timber rafter.

Check that the rubber gaskets are correctly positioned and that the PVC top cap has been fully snapped down.

The PVC top cap should sit evenly along the glazing bar without any raised or loose sections.

Step 2: Inspect the Exposed End

Check that the aluminium base and PVC top cap are correctly aligned.

If you’ve cut the glazing bar to length, remove any loose fragments or rough edges that could prevent the end cap from fitting.

Step 3: Check the End Cap’s Locating Peg

Inspect the end cap before fitting it.

Make sure the locating peg or moulded fitting isn’t cracked or damaged.

Hold the end cap against the exposed glazing bar and identify where the locating feature is designed to engage.

Step 4: Test Fit the End Cap

Before applying silicone, try fitting the end cap without any sealant.

Line it up carefully and push it into position using firm, even hand pressure.

The end cap should sit neatly against the glazing bar without a significant gap.

If it stops partway, remove it and investigate what’s preventing it from seating correctly.

Step 5: Secure the End Cap

For Exitex Capex Snapdown glazing bars: Apply a small amount of suitable silicone sealant underneath the short upper lip of the end cap, following the published fitting guidance.

For Sunwood Snapdown glazing bars: Follow the appropriate fitting instructions for your product and confirm whether additional sealant is recommended or permitted.

Step 6: Check the Finished Fit

Push the end cap firmly into its final position.

Check that it sits flush against the end of the glazing bar and doesn’t move excessively.

If silicone has been applied, allow it to cure according to the manufacturer’s instructions.

Don’t use a hammer or rubber mallet to force the end cap into place. If it requires excessive force, stop and check the fit.

What If My Glazing Bar End Cap Won’t Push All the Way In?

If your end cap only pushes partway into the glazing bar, don’t assume it just needs more pressure. Start by checking whether the locating peg is entering the correct opening.

If the peg appears to be hitting the aluminium base or PVC locking mechanism, remove the end cap and inspect the profile.

Check that the PVC top cap is fully snapped down, that the end of the glazing bar is free from obstructions and that you’re using the correct end cap.

We wouldn’t recommend cutting off the locating peg, drilling into the glazing bar or permanently gluing the cap into place to overcome a fitting problem.

If you’re still struggling, send our team a photograph of the end cap and the exposed glazing bar profile. We’ll help you identify what could be preventing it from fitting.

Exitex vs Sunwood Glazing Bar End Caps – What’s the Difference?

We supply both Exitex Capex Snapdown and Sunwood Snapdown glazing bars at The Polycarbonate Store.

Although both systems use push-fit PVC end caps, it’s important to use the correct accessories for your glazing bar.

Exitex Capex Snapdown Glazing Bars

Sunwood Snapdown Glazing Bars (Molan)

Frequently Asked Questions

Should glazing bar end caps be glued on?

Exitex and Sunwood Snapdown glazing bar end caps are designed to push into place.

For Exitex, fitting guidance recommends a small amount of silicone underneath the short upper lip to help secure the cap. For Sunwood, check the relevant fitting guidance before applying additional sealant.

We wouldn’t recommend permanently gluing an end cap that doesn’t fit properly.

Can I use silicone to stop my glazing bar end caps falling off?

A small amount of suitable silicone may help retain an end cap where the manufacturer recommends or permits it. However, always check that the end cap is correctly fitted first.

Silicone won’t resolve a damaged locating peg, incorrect alignment or an obstruction inside the glazing bar.

Why does my glazing bar end cap keep popping off?

This could be caused by an incomplete push-fit connection, a PVC top cap that hasn’t been fully snapped down, an obstruction or a damaged end cap.

Check each of these before replacing the cap.

Can I screw my glazing bar end caps into place?

We wouldn’t recommend adding screws unless specifically advised by the manufacturer.

Drilling into the glazing bar could damage the PVC or aluminium profile and interfere with the way the system is designed to work.

Can I use an Exitex end cap on a Sunwood glazing bar?

No, you shouldn’t assume the end caps are interchangeable.

Always select the correct replacement for your glazing bar brand and profile.

Do glazing bar end caps stop water leaks?

Glazing bar end caps provide a neat finish to the exposed ends of the glazing bars, but they’re not the main waterproofing component of a polycarbonate roof.

Correctly fitted rubber gaskets, PVC top caps, sealing tapes and sheet closures all contribute to keeping your roof weather-resistant.

For more information on finishing your polycarbonate sheets correctly, see our Sheet Closure Installation Guide.

Do I need to replace an end cap that’s fallen off?

Not necessarily.

If the end cap is undamaged and the locating peg is intact, it may simply need to be refitted correctly. If the peg is cracked, broken or distorted, replacement is usually the better option.

Need Replacement Glazing Bar End Caps?

If your glazing bar end caps are damaged, missing or no longer fitting securely, we stock end caps for both Exitex and Sunwood Snapdown glazing bars.

Our range includes end caps for different glazing bar profiles and polycarbonate sheet thicknesses, with colour options to match your existing roof.

Browse our Rafter Supported Glazing Bars & Accessories to find the correct replacement.

If you’re unsure which end cap you need, or you’ve tried the steps above and still can’t get it to fit, get in touch with our team.

Send us a photograph of your end cap and the exposed end of your glazing bar, along with the brand and sheet thickness if known. We’ll be happy to help you identify the correct product and advise on the next steps.