Common Polycarbonate Roofing Problems

A leaking polycarbonate roof is one of the most common problems reported by homeowners, but the cause is not always obvious. Water can travel along roofing components before appearing inside, meaning the visible drip is not necessarily where the water is entering.

Before replacing sheets or applying sealant, it is important to inspect the complete roofing system.

Common causes of leaks include:

• Loose or damaged wall flashing allowing water behind the roof edge.

• Side flashing that has moved, allowing wind-driven rain underneath.

• Glazing bars that are not correctly seated or have damaged seals.

• Loose fixing buttons or damaged sealing washers.

• Missing or damaged foil tape and breather tape.

• Blocked gutters causing water to overflow beneath the roof edge.

• Insufficient roof pitch preventing water from draining efficiently.

The best approach is to inspect each possible entry point methodically rather than assuming the polycarbonate sheet itself has failed.

Condensation is another common concern with multiwall polycarbonate roofing, but it is important to understand that some condensation is completely normal.

Multiwall sheets are designed with internal air chambers, and when warm, moisture-rich air meets a colder surface, condensation can naturally form inside these flutes.

The problem usually occurs when moisture cannot drain away correctly or when the sheet has not been prepared or installed correctly.

Common causes of excessive condensation include:

• Missing or incorrectly fitted breather tape.

• Blocked or damaged sheet end closures.

• Poor ventilation beneath the roof.

• Incorrect roof pitch preventing moisture drainage.

• Dirt or insects entering the internal sheet flutes.

• Incorrect sheet orientation.

A correctly installed polycarbonate roof should allow condensation to escape naturally through the lower breather tape while preventing contamination from entering the sheet.

Over time, polycarbonate sheets can become dirty, marked or appear cloudy due to exposure to the outdoor environment. In many cases, this is a maintenance issue rather than a sign that the sheets need replacing.

Common causes include:

• Dirt, dust and airborne pollution building up on the surface.

• Leaves and organic debris collecting around roof edges.

• Algae or moss growth in damp or shaded locations.

• Incorrect cleaning methods causing surface marks.

• Dirt entering inside the sheet flutes due to damaged sealing components.

Before considering replacement, the sheets should be cleaned using the correct methods. Polycarbonate should only be cleaned with gentle equipment such as clean water, mild detergent and a soft cloth or brush.

Never use abrasive pads, solvents, bleach or pressure washers, as these can damage the surface and reduce the lifespan of the sheets.

If cloudiness appears to be inside the sheet rather than on the outside surface, the issue may relate to damaged sealing tapes or moisture entering the internal chambers.

Polycarbonate sheets are designed to withstand normal outdoor conditions, but they can become damaged through impact, incorrect installation or long-term exposure to extreme conditions.

Damage does not always mean the entire roof needs replacing. The first step is to assess the type and severity of the problem.

Common causes of damaged polycarbonate sheets include:

• Falling branches or debris causing impact damage.

• Cracks caused by excessive stress around fixings.

• Sheets becoming distorted due to restricted thermal movement.

• Damage caused by incorrect cleaning methods.

• Age-related deterioration after many years of exposure.

A damaged sheet should be inspected carefully to determine whether it can remain in service or whether replacement is required. Small surface marks may only affect appearance, while cracks, splits or damaged edges can affect the weather resistance of the roof.

When replacing a damaged sheet, it is important to identify and correct the original cause of the damage. Simply fitting a new panel without addressing installation issues may result in the same problem occurring again.

Over time, movement from temperature changes, weather exposure and normal ageing can cause some roofing components to loosen or deteriorate.

Loose components do not always cause an immediate leak, but they can reduce the weather resistance of the roofing system and allow problems to develop if left untreated.

Common issues include:

• Fixing buttons becoming loose or damaged.

• Rubber sealing washers deteriorating.

• Glazing bar caps lifting or becoming displaced.

• Flashings moving away from the roof or wall.

• End closures becoming damaged or missing.

During an inspection, check that all components remain securely positioned and that there are no visible gaps where water could enter.

If a component has become loose, avoid simply tightening everything excessively. Polycarbonate sheets need to expand and contract naturally, and over-tightening fixings can place unnecessary stress on the sheets.

Where components have failed, replacing the individual part is often enough to restore the roof without replacing the complete system.

Drainage problems are one of the most overlooked causes of issues with polycarbonate roofs. A roof can be correctly installed, but blocked gutters or restricted drainage can still allow water to build up and find its way into areas where it should not.

Leaves, moss, dirt and other debris can collect inside gutters and around the lower edge of the roof. Over time, this can prevent rainwater from flowing away correctly and cause overflowing during heavy rainfall.

Common drainage-related problems include:

• Gutters filled with leaves or organic debris.

• Blocked downpipes preventing water from escaping.

• Water overflowing back beneath the roof edge.

• Debris preventing water from reaching the gutter correctly.

• Poor drainage around the roof perimeter.

During your inspection, check that water can move freely from the polycarbonate sheets into the gutter system and away from the building.

Keeping gutters and drainage channels clear is one of the simplest maintenance tasks you can carry out and can prevent many avoidable roofing problems.

When a problem appears with a polycarbonate roof, the best approach is to inspect the system methodically rather than replacing components straight away.

Use this checklist to help identify where to look first:

Water Leak

☐ Check wall flashing and side flashing.

☐ Inspect glazing bars and seals.

☐ Check fixing buttons and washers.

☐ Inspect sheet end closures and sealing tapes.

☐ Confirm gutters and drainage are clear.

Condensation

☐ Check that breather tape is fitted correctly.

☐ Check end closures are installed.

☐ Inspect ventilation beneath the roof.

☐ Confirm the roof has sufficient fall.

Dirty or Cloudy Sheets

☐ Clean the sheet surface using approved methods.

☐ Check whether cloudiness is on the surface or inside the flutes.

☐ Inspect sealing tapes if dirt is visible inside the sheet.

Damaged Sheets

☐ Check whether damage affects the strength or weather resistance.

☐ Identify what caused the damage.

☐ Confirm the replacement sheet matches the original.

Loose Components

☐ Check glazing bar caps.

☐ Inspect fixings and sealing washers.

☐ Check flashings and trims.

☐ Replace damaged components where necessary.

Taking a structured approach will usually identify the cause of the problem and prevent unnecessary replacement of parts that are still working correctly.