Condensation is one of the most common questions we receive about polycarbonate roofing.

A customer may install a brand new twinwall or multiwall polycarbonate roof and then notice droplets, misting or moisture appearing inside the sheets. In some cases, the condensation may disappear during warmer or drier weather; in others, it can be more noticeable first thing in the morning, during colder months or after periods of rain.

The first thing to understand is that condensation within a polycarbonate sheet does not automatically mean the sheet is defective.

Polycarbonate is a cellular material. Twinwall and multiwall sheets contain internal channels which provide insulation and contribute to the sheet’s strength and thermal performance. These channels can also be affected by moisture and changes in temperature.

When warm, moisture-laden air encounters a colder surface or colder air within the sheet channels, water vapour can condense into liquid water. This is a normal physical process and can occur even when a polycarbonate roof has been correctly manufactured and installed.

However, the amount of condensation can be significantly influenced by the way the roof is designed, the environmental conditions, how the sheets have been stored and installed, and how the sheet ends have been sealed.

In this guide, we explain why condensation occurs in polycarbonate sheets, what the manufacturers recommend, how to distinguish normal condensation from potential water ingress, and what you can do to reduce the problem.

What is condensation?

Condensation occurs when water vapour in the air changes from a gas into liquid water. Air always contains a certain amount of moisture. The warmer the air, the greater amount of water vapour it can hold. When that warm, humid air cools sufficiently, it eventually reaches its dew point.

At the dew point, the air can no longer hold all of its moisture as vapour. The excess moisture changes into liquid water, forming droplets on a cooler surface. This is the same process responsible for:

• Water droplets forming on the outside of a cold drink
• Misted bathroom mirrors
• Condensation on windows
• Moisture forming on cold walls
• Morning dew
• Misting inside glazing systems

The same principle applies inside the channels of multiwall polycarbonate sheets.

A simple example

Imagine a roofed structure on a cold night.

Inside the structure, the air may be relatively warm and humid. This can be caused by people, plants, heating, cooking, washing, drying clothes or simply the natural moisture present in the air.

Outside, the temperature falls. The polycarbonate roof becomes colder.

If humid air comes into contact with sufficiently cold surfaces or enters the sheet channels, the moisture can reach its dew point and condense. The result can be visible droplets or misting within the internal channels.

Why does condensation occur inside polycarbonate sheets?

There isn’t usually one single cause. Condensation is affected by a combination of:

1. Temperature difference

The larger the difference between the internal and external temperatures, the greater the potential for condensation.

For example, a conservatory that is warm during the evening but becomes cold overnight can experience significant condensation.

2. Relative humidity

Humidity is particularly important. A structure containing a lot of moisture in the air has a greater potential for condensation than a dry, well-ventilated structure. Common sources of moisture include:

• People breathing
• Plants and soil
• Cooking
• Kettles
• Washing
• Drying clothes
• Hot tubs and swimming pools
• Heating systems
• Damp floors or walls
• Wet building materials
• Rainwater entering an incorrectly sealed structure

A greenhouse can therefore experience considerably more condensation than an open-sided canopy because it contains warm, humid air and vegetation.

3. Cold external temperatures

Cold weather increases the likelihood of condensation because the external face and internal structure of the roof can become colder. This is why customers often notice condensation more during autumn and winter.

4. Poor ventilation

A poorly ventilated structure allows moisture to accumulate. Even if the polycarbonate itself has been installed correctly, high internal humidity can increase the amount of condensation occurring throughout the structure. Good ventilation helps remove humid air and allows moisture to escape.

5. Moisture present during installation

Polycarbonate sheets should be installed clean and dry. If moisture is already present inside the channels when the ends are sealed, that moisture can subsequently condense when temperatures change.

This is particularly important when sheets have been stored outside or exposed to rain before installation. The Polycarbonate Store recommends keeping sheets dry before installation and storing them away from moisture and direct sunlight.

Does condensation mean my polycarbonate sheets are defective?

No. Not necessarily. This is one of the most important points to understand.

Condensation is a physical phenomenon caused by moisture, temperature and humidity. It can occur in correctly manufactured polycarbonate sheets.

The presence of condensation alone is therefore not evidence that the polycarbonate has a manufacturing defect. The manufacturers themselves recognise condensation as something that needs to be managed through correct sheet orientation, end treatment and ventilation.

For example, Brett Martin’s Marlon ST installation guidance specifically states that breather tape is used at the bottom of the sheet to help minimise condensation and that air movement through the breather tape helps equalise vapour pressure inside and outside the sheet. Palram’s guidance similarly requires appropriate sealing of the sheet ends and the use of ventilating breather tape on multiwall products.

Therefore, seeing some moisture inside a multiwall sheet does not by itself establish a product fault.

How the internal channels of polycarbonate work

Twinwall and multiwall polycarbonate are not solid sheets. They contain hollow internal chambers.

For example: Twinwall – Two outer faces connected by internal ribs create a series of hollow channels. Multiwall – Additional internal walls create multiple chambers, increasing the sheet’s rigidity and thermal insulation.

These channels are an important part of the product’s design. They contribute to:

• Thermal insulation
• Rigidity
• Weight reduction
• Light transmission
• Overall sheet performance

However, because the channels are hollow, they must be correctly orientated and appropriately treated at their ends. Any moisture entering the channels needs a route to escape. This is why the manufacturers place particular emphasis on sheet orientation, sealing tape, breather tape and end closures.

Why must the channels run down the slope of the roof?

This is one of the most important installation requirements for multiwall polycarbonate. The internal channels should run in the direction of the roof slope, allowing condensation moisture to drain by gravity.

Palram specifically states that multiwall channels should be vertical when used for siding so that condensation water can drain by gravity. Its SUNLITE technical guidance also specifies that channels should be positioned to facilitate gravity drainage of condensation moisture.

Brett Martin similarly states that Marlon ST sheets must be installed with the ribs running vertically or up-slope and explains that drainage of condensed water vapour is facilitated by installing the sheet with the ribs running in the direction of the slope.

Why is this important?

If the channels run across the roof rather than down the roof:

• Condensation cannot drain correctly
• Moisture can become trapped
• Water can accumulate in the channels
• Dirt and biological growth can become more likely
• The appearance of the sheet can deteriorate

Correct orientation does not necessarily eliminate condensation, but it gives any condensed moisture a route towards the lower edge of the sheet.

What is the difference between aluminium tape and breather tape?

This is an area where we frequently see confusion. The two tapes have different purposes.

Aluminium sealing tape

The solid aluminium or blocking tape is generally applied to the upper end of the sheet. Its purpose is to help prevent:

• Moisture entering from the upper edge
• Dust entering the channels
• Insects entering the channels

It provides a relatively closed seal at the top of the sheet.

Breather tape

Breather tape is applied to the lower end of the sheet. Unlike solid aluminium tape, breather tape is designed to permit controlled air movement.

Brett Martin explains that its breather tape allows air to move freely in and out of the sheet, helping minimise condensation through equalisation of air vapour pressure.

This means the two ends of the sheet are deliberately treated differently.

In simple terms:

Top of sheet → sealed

Bottom of sheet → ventilated

This arrangement helps protect the channels while allowing moisture and air movement to be managed.

Can I use aluminium tape at the bottom of the sheet?

This is a common question, particularly when customers see moisture and assume that the solution is to seal the sheet completely. Generally, you should follow the specific manufacturer’s installation system rather than simply sealing every end with solid tape.

For Marlon ST, Brett Martin specifies aluminium sealing tape at the top and breather tape at the bottom. The breather tape should then be protected with a suitable U-profile/end closure. Palram’s SUNLITE guidance likewise specifies different treatment for the two ends, including ventilating breather tape.

Simply sealing both ends completely can prevent the controlled ventilation and drainage arrangement intended by the manufacturer.

Why do I need a sheet closure if I already have tape?

The tape and the closure perform different functions. A sheet end closure (U-profile, U-channels, sheet end caps) is fitted over the exposed end of the polycarbonate.

It helps:

• Protect the tape
• Protect the open channels
• Reduce the risk of water entering the sheet
• Prevent physical damage to the sheet edge
• Keep insects and debris out
• Provide a finished edge

Brett Martin specifically instructs that the breather tape should be covered with a sheet closure and sealed to the top face of the sheet using a small bead of suitable silicone. The Polycarbonate Store also recommends using sheet closures to protect the exposed ends and provide a weather-resistant finish.

A closure should therefore not be viewed as a replacement for the correct tape. The system works together: Polycarbonate sheet + correct tape + appropriate end closure = correctly finished sheet end.

Can sealing the sheet completely stop condensation?

Not necessarily. In fact, trying to make the sheet completely airtight is not the same thing as controlling condensation. Condensation is primarily driven by temperature, humidity and the dew point.

If humid air is present within a sealed cavity, cooling can still cause that moisture to condense. This is why manufacturers use a controlled approach rather than simply sealing both ends with an impermeable tape. The objective is to:

1. Prevent uncontrolled water, dirt and insects entering.
2. Allow appropriate ventilation of the channels.
3. Provide a drainage route.
4. Prevent moisture becoming trapped unnecessarily.

Why is condensation worse in some buildings than others?

The roof itself may be identical, but the environment underneath it can be completely different. Consider these examples.

Open-sided canopy

• A canopy with open sides has substantial natural ventilation.
• Humidity can disperse quickly.
• Condensation may therefore be relatively limited.

Enclosed conservatory

• A conservatory can trap warm, humid air.
• The greater the humidity and temperature differential, the greater the potential for condensation.

Greenhouse

Greenhouses can have particularly high humidity because of:

• Plants
• Soil
• Watering
• Evaporation
• Warm daytime temperatures
• Cooler nights

Condensation is therefore an inherent consideration when glazing a greenhouse.

Pool enclosure

• An enclosed swimming pool creates a high-humidity environment.
• Even high-performance glazing can experience condensation under these conditions.

Why is condensation worse in winter?

Winter provides almost ideal conditions for condensation. The outside temperature is lower, meaning the roof can become colder. At the same time, the inside of a building may be heated. This creates a substantial temperature differential.

For example: Indoor air: 20°C | Outdoor air: 5°C

The warm internal air contains moisture. When this moisture encounters a sufficiently cold surface, it can reach its dew point and condense. The same principle applies within polycarbonate channels.

This is why customers may notice that a roof which appears completely clear during the summer suddenly develops visible condensation during colder months.

Why is condensation sometimes worse in the morning?

Overnight, temperatures normally fall. The roof therefore cools. Meanwhile, moisture may have accumulated inside the structure. When the temperature reaches a point at which the air can no longer retain all of its water vapour, condensation forms. As the structure warms up again during the morning, the condensation may evaporate.

This can produce a cycle of: Cool night → condensation → warmer morning → evaporation. This is normal behaviour for many glazed structures.

Why does condensation sometimes appear only in certain areas of the sheet?

Condensation does not necessarily occur evenly. It can be influenced by:

• Local temperature differences
• Shade
• Roof orientation
• Structural members
• Glazing bars
• Internal humidity
• Air movement
• Sheet orientation
• The position of the channels
• Localised moisture

This means it is possible for one section of a roof to appear wetter than another even though the same polycarbonate product has been used throughout. For example, a shaded section may remain colder for longer than a section exposed to sunlight.

Why does condensation sometimes appear near the bottom of the sheet?

Because the bottom edge is where moisture can accumulate and drain. If condensation forms inside the channels, gravity will encourage it to move towards the lower edge when the channels are correctly aligned with the roof slope.

This is one reason correct sheet orientation is so important. A small amount of moisture appearing at the lower edge does not necessarily indicate a leak. However, large quantities of water, persistent pooling or evidence of water entering from outside should be investigated.

Is condensation the same as a leak?

No. This distinction is extremely important.

Condensation

Condensation is moisture produced when water vapour changes into liquid water because of temperature conditions. It can occur without any rainwater entering the roof.

Water ingress

Water ingress means external water has entered the roofing system. This could potentially be caused by:

• Damaged sheet
• Incorrectly fitted closure
• Poorly sealed joint
• Incorrect flashing
• Incorrect glazing bar installation
• Failed sealant
• Incorrect roof pitch
• Damaged tape
• Incorrect sheet positioning

The appearance of moisture alone does not tell you which mechanism is responsible. The surrounding circumstances need to be assessed.

How can I tell if it is condensation or a leak?

There are several useful observations.

Condensation is more likely if:

• Moisture appears during cold mornings
• It is worse during winter
• It disappears as the structure warms
• There has been no rainfall
• Moisture is visible inside the channels
• Multiple sheets show similar behaviour
• The structure has high humidity
• The roof is a greenhouse, conservatory or enclosed area

Water ingress may be more likely if:

• Moisture appears immediately after rainfall
• Water is entering from one specific point
• There is evidence of water tracking from a joint
• A closure or flashing is visibly damaged
• One isolated area is affected
• Water is entering the building rather than simply appearing inside the channels
• There is standing water where it should not be

These observations are not a substitute for a professional inspection, but they can help establish whether the issue is environmental condensation or potential water ingress.

Can condensation damage polycarbonate?

Normal condensation does not automatically mean that the polycarbonate is being damaged. However, persistent moisture trapped within the channels is undesirable. This is why manufacturers emphasise correct installation.

Brett Martin states that its recommended tape and ventilation procedures reduce the risk of condensation, water ingress and algae growth within the sheet.

The key objective is therefore not necessarily to promise that condensation will never occur, but to manage moisture correctly and provide a route for it to escape.

Can condensation cause algae or green growth inside the sheet?

It can contribute to an environment in which biological growth becomes possible if moisture, dirt and contaminants are able to enter and remain within the channels. This is another reason why correct end treatment is important.

Brett Martin specifically notes that following its recommended installation procedures reduces the risk of algae growth within the sheet. Once algae or other contaminants become established inside the internal channels, cleaning the inside of a multiwall sheet is extremely difficult because the channels are not designed to be accessed like an ordinary surface.

Prevention is therefore considerably better than attempting to clean the channels later.

Does polycarbonate need ventilation?

The building and the polycarbonate sheet channels are two different considerations.

Building ventilation

A conservatory, greenhouse or enclosed structure benefits from adequate ventilation to control internal humidity. This can include:

• Opening windows
• Roof vents
• Ridge ventilation
• Soffit ventilation
• Louvres
• Mechanical ventilation where appropriate

Sheet channel ventilation

The polycarbonate sheet itself can use breather tape at the appropriate end to allow controlled air movement within the channels. These two forms of ventilation should not be confused. A well-installed sheet can still experience condensation if the building itself has excessive humidity.

Does breather tape let water into the sheet?

Breather tape is designed to allow air movement while restricting the entry of dust and insects. It is not intended to act as an open hole through which rainwater can freely enter. This is why the lower end should be protected with the appropriate sheet closure.

Brett Martin specifically states that the breather tape should be covered by a Sheet Closure and sealed to the top face of the sheet to protect the tape and lower sheet edge from rainwater run-off.

What happens if I don’t use breather tape?

If the sheet channels are completely sealed without following the manufacturer’s recommended ventilation arrangement, moisture can become more difficult to manage.

This does not mean that every sheet without breather tape will immediately develop condensation, but it removes an important part of the manufacturer’s recommended moisture-management system.

For Marlon ST, Brett Martin explicitly recommends breather tape at the bottom of the sheet to minimise condensation.

For SUNLITE, Palram also specifies ventilating breather tape as part of the installation system.

What if I have already installed aluminium tape at both ends?

Do not automatically remove or alter the installation without first checking the manufacturer’s guidance for the exact product and system. Different polycarbonate products and glazing systems can have different installation requirements. If you are experiencing condensation, the first things to establish are:

• Which manufacturer produced the sheet?
• What thickness is it?
• Is it twinwall or multiwall?
• Which direction are the channels running?
• What tape has been used at each end?
• Are the sheet ends protected by closures?
• Is the structure enclosed?
• What is the internal humidity?
• Was the sheet dry when installed?
• Has water entered the channels?
• Is the roof adequately pitched?

These details are much more useful than simply assuming the sheet itself is defective.

What do Palram recommend?

Palram’s SUNLITE guidance places significant emphasis on correct sheet orientation and end treatment.

Palram states that SUNLITE multiwall sheets should be positioned so that the rib channels slope downwards, helping reduce accumulation of dirt and facilitating gravity drainage of condensation moisture.

Palram also specifies appropriate sealing of the sheet ends, including aluminium sealing tape and ventilating breather tape.

For applications where condensation control is particularly important, Palram also manufactures SUNLITE PLUS, a multiwall polycarbonate product with built-in condensation-control technology. Palram describes this as being designed to minimise condensate droplet formation and is particularly suited to applications such as commercial greenhouses, garden centres, covered swimming pools and other humid environments.

This is an important distinction: Standard multiwall polycarbonate can experience condensation. Specialist anti-condensation products can reduce the formation and visual impact of condensate droplets, but they do not change the basic physics of humidity and temperature.

What do Brett Martin recommend?

Brett Martin’s Marlon ST installation guidance is similarly clear. Marlon ST sheets should be installed:

• With the ribs vertical or running up the slope
• With a minimum roof slope of 5°
• With aluminium sealing tape at the top
• With breather tape at the bottom
• With the breather tape protected by a U-profile
• Using compatible materials and sealants

Brett Martin explains that the breather tape allows air movement through the channels and helps minimise condensation by equalising vapour pressure inside and outside the sheet.

Brett Martin also specifically states that allowing air movement through the breather tape does not reduce the insulation performance of the sheet.

This is an important point for customers who worry that ventilating the channels will somehow make the polycarbonate less effective as an insulating material.

Does roof pitch affect condensation?

Roof pitch is primarily important for water drainage, but it can also influence how effectively moisture can drain from the sheet channels.

A steeper roof provides a more effective gravity-driven drainage path. Brett Martin specifies a minimum roof slope of 5° for Marlon ST to allow adequate rainwater run-off. The Polycarbonate Store also recommends adequate roof pitch when designing polycarbonate roofing.

A low-pitched roof can therefore create additional challenges with water management.

Does sheet thickness affect condensation?

Sheet thickness can affect the thermal performance of the roof, but thicker does not simply mean “no condensation”. A thicker multiwall sheet generally contains more material and additional chambers, which can improve thermal insulation. However, condensation is still influenced by:

• Internal humidity
• External temperature
• Internal temperature
• Ventilation
• Dew point
• Sheet orientation
• Installation
• Moisture within the channels

Therefore, upgrading from 10mm to 16mm, for example, should not be presented as a guaranteed solution to condensation. The correct specification depends on the application and required thermal performance.

Can I completely eliminate condensation?

In many applications, no guarantee should be made that condensation will never occur. The realistic objective is to minimise and properly manage condensation. Condensation is ultimately governed by environmental conditions.

Even correctly installed, high-quality polycarbonate can experience condensation where there is sufficient humidity and a suitable temperature differential.

The best approach is therefore to control the factors that can be controlled:

• Control humidity: Improve ventilation and reduce unnecessary sources of moisture.
• Install the sheet correctly: Follow the manufacturer’s installation instructions.
• Orientate the channels correctly: Channels should run vertically or down/up the roof slope as specified by the manufacturer.
• Use the correct tape: Use sealing tape and breather tape in the positions specified by the manufacturer.
• Protect the sheet ends: Use suitable U-profiles/end closures.
• Install when the sheets are dry: Avoid trapping moisture inside the channels.
• Provide adequate drainage: Ensure the roof has an appropriate pitch.

What should I do if my new polycarbonate roof has condensation?

Don’t immediately assume that the sheets are faulty. Start with the installation and environmental conditions.

Check 1: Are the channels running down the roof?

They should run in the direction of the slope.

Check 2: What tape is fitted at each end?

Determine whether the correct sealing and breather tapes have been used.

Check 3: Are the sheet ends protected?

Check that the appropriate end closure/U-profile has been fitted.

Check 4: Was the sheet dry when installed?

Moisture trapped during installation can subsequently condense.

Check 5: Is the building humid?

Consider whether the structure contains plants, heating, people, cooking, washing or other sources of moisture.

Check 6: Is there adequate ventilation?

An enclosed structure with little ventilation will naturally retain more moisture.

Check 7: Is the moisture actually condensation?

Observe whether it appears during cold periods and disappears as the structure warms.

Check 8: Is there evidence of external water ingress?

If moisture appears specifically after rainfall or water is entering the building, the installation should be investigated for potential leakage.

Should I remove the sheets to dry them?

Not necessarily.

Removing polycarbonate sheets can introduce additional risks, particularly if the sheets are damaged, incorrectly reinstalled or subjected to unnecessary handling.

Before dismantling a roof, establish what is causing the moisture. If the issue is normal environmental condensation, removing the sheets may not solve the underlying problem. If moisture has entered the channels because of an installation issue, the appropriate corrective action will depend on the cause.

Where necessary, a competent installer or technical professional should assess the roof.

Can I drill holes into the polycarbonate to let condensation out?

Do not do this as a DIY solution. Drilling additional holes into the sheet can compromise:

• The sheet structure
• Weather resistance
• Thermal performance
• The manufacturer’s intended installation system
• Warranty conditions

The sheet should be installed using the manufacturer’s specified ventilation and drainage arrangement rather than modified afterwards to try to create an alternative ventilation system.

Can I put silicone around everything to stop condensation?

This is also not recommended as a general solution.

Silicone has specific applications within a polycarbonate glazing system, but simply applying large amounts of sealant around the sheet ends will not address the underlying causes of condensation. More importantly, not every sealant is chemically compatible with polycarbonate.

Brett Martin specifically requires the use of low-modulus neutral silicone and warns that unsuitable all-purpose silicone can cause polycarbonate to crack and deteriorate. Palram similarly advises checking chemical compatibility when selecting sealants and other materials for SUNLITE.

Always use a sealant that is specifically confirmed as compatible with the polycarbonate product being installed.

Can condensation occur even if the roof has been installed correctly?

Yes!

Correct installation reduces the risk and helps moisture escape, but it cannot override the environmental conditions surrounding the roof.

For example, an enclosed conservatory at 20°C with high humidity on a cold winter night can still experience condensation even when the polycarbonate has been installed exactly according to the manufacturer’s instructions.

Correct installation is therefore about managing moisture, not promising that moisture can never exist.

Does condensation invalidate my polycarbonate warranty?

The presence of condensation alone does not automatically establish a manufacturing defect. Warranty conditions are product-specific and depend on the manufacturer’s terms, as well as correct storage, handling, installation and use.

Installation that does not comply with the relevant manufacturer’s published recommendations can affect warranty coverage. This is particularly important where there are questions about:

• Incorrect sheet orientation
• Incorrect sealing
• Incorrect glazing systems
• Incompatible sealants
• Incorrect fixing
• Excessive spans
• Incorrect roof pitch
• Damage caused during installation
• Improper storage
• Unauthorised modification

Always check the warranty and installation requirements for the exact product being used.

How should polycarbonate sheets be stored before installation?

Correct storage can help prevent moisture-related problems before installation even begins.

Brett Martin recommends storing Marlon ST sheets flat, preferably indoors, protected from wind, rain and sunlight. The Polycarbonate Store likewise recommends storing sheets in a cool, dry, well-ventilated location and ensuring that the sheets are clean and dry before installation.

Avoid installing sheets that have been exposed to rain or have moisture sitting inside their channels. If a project has been delayed, check the condition of the sheets before installation rather than assuming they remain dry simply because the outer surface looks dry.

What is the best way to reduce condensation in a polycarbonate roof?

There is no single “anti-condensation” fix. The most effective approach is to consider the entire roofing system.

Before installation

• Store sheets correctly.
• Keep sheets dry.
• Check the manufacturer’s installation guide.
• Confirm the correct sheet orientation.
• Plan the correct roof pitch.
• Choose compatible glazing bars and accessories.
• Check the required end treatment.

During installation

• Install sheets with the channels running in the correct direction.
• Apply the correct sealing tape.
• Apply the correct breather tape.
• Fit suitable end closures.
• Use compatible sealants.
• Do not over-tighten fixings.
• Allow for thermal expansion and contraction.
• Keep the sheet channels clean and dry.

Brett Martin specifically highlights thermal movement as an important installation consideration and requires allowance for expansion and contraction in glazing bars, closures and fixing holes.

After installation

• Maintain adequate ventilation.
• Monitor humidity in enclosed structures.
• Keep gutters and drainage routes clear.
• Inspect closures and seals periodically.
• Look for evidence of external water ingress.
• Keep the roof clean.

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Frequently Asked Questions

Is condensation inside polycarbonate normal?

Yes. Some condensation can be a normal consequence of changing temperature and humidity, particularly in enclosed, humid or poorly ventilated structures. It does not automatically indicate a defective sheet.

Why is there water inside my twinwall polycarbonate?

The moisture may be condensation caused by water vapour reaching its dew point, but it could also be caused by external water ingress. The installation and environmental conditions need to be assessed to distinguish between the two.

Why are my polycarbonate sheets wet in the morning?

Overnight cooling can cause moisture in the air to reach its dew point, resulting in condensation. As temperatures rise during the day, the moisture may evaporate.

Does condensation mean my sheets are leaking?

No. Condensation and leakage are different mechanisms. Condensation is created by moisture in the air. A leak involves external water entering the roofing system.

Should I use aluminium tape on both ends?

Follow the manufacturer’s installation instructions for the specific product. Both Palram and Brett Martin specify a combination of sealing and breather tape rather than simply treating both ends identically.

What does breather tape actually do?

It allows controlled air movement through the sheet channels and helps equalise vapour pressure, reducing the risk of moisture becoming trapped. Brett Martin specifically identifies this as a method of minimising condensation.

Does breather tape make the roof less insulated?

Brett Martin states that allowing air movement through the breather tape does not reduce the insulation performance of the sheet.

Can I stop condensation completely?

Not necessarily. The amount of condensation is strongly influenced by environmental temperature and humidity. Correct installation can significantly reduce the risk and help manage moisture, but it cannot eliminate the physical process entirely.

Does a thicker polycarbonate sheet prevent condensation?

Not necessarily. Thickness affects thermal performance, but condensation is also determined by temperature, humidity, ventilation and installation.

Why does my greenhouse have so much condensation?

Greenhouses naturally contain significant amounts of moisture from plants, soil and watering. Warm daytime temperatures followed by cooler nights can create ideal conditions for condensation.

Why is condensation worse in winter?

Cold external temperatures make the roof colder, increasing the likelihood that humid air will reach its dew point.

Can I drill holes in my sheets to release condensation?

No. Do not modify the sheet in this way. Follow the manufacturer’s intended ventilation and drainage system instead.

Can I remove the condensation by heating the roof?

Increasing temperature can cause condensation to evaporate, but this does not remove the underlying moisture from the building. Adequate ventilation is usually more effective for managing humidity.

Can a sheet closure help with condensation?

A correctly fitted closure protects the exposed end of the sheet and helps prevent uncontrolled water, dust and insect ingress. It works alongside the correct sealing/breather tape system rather than replacing it.

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The key takeaway: condensation is about moisture management

Condensation in polycarbonate roofing can look alarming, particularly when it appears inside a brand-new roof. However, condensation does not automatically mean that the polycarbonate sheets are faulty.

Polycarbonate is a thermoplastic glazing material, and twinwall/multiwall products contain internal channels. These channels need to be installed, orientated and finished correctly so that moisture can be managed.

The manufacturers’ guidance is consistent on the key principles:

Palram recommends correct channel orientation, appropriate sealing and ventilating breather tape for SUNLITE multiwall products, with the channel direction allowing condensation moisture to drain by gravity.

Brett Martin recommends installing Marlon ST with the ribs running vertically or up-slope, using aluminium sealing tape at the top and breather tape at the bottom. Brett Martin specifically explains that the breather tape allows air movement and helps minimise condensation by equalising vapour pressure.

The most important thing is therefore to look at the complete roofing system, rather than assuming that visible moisture means the sheet itself has failed.

Correct installation, appropriate end treatment, adequate drainage, sensible ventilation and control of internal humidity all play a role in achieving the best possible performance from a polycarbonate roof.

Need help diagnosing condensation?

If you are experiencing condensation within your polycarbonate roof, don’t immediately assume that the sheets are defective.

Providing clear photographs of the inside and outside of the roof, sheet ends, glazing bars, closures and tape arrangement can also help identify whether the moisture is consistent with normal condensation or whether there may be an installation issue requiring further investigation. Contact Us

The Polycarbonate Store supplies polycarbonate sheets and compatible roofing accessories, but does not undertake installation. For installation-specific issues, the installer should also be consulted and the relevant manufacturer’s technical guidance should always be followed.