A polycarbonate roof is one of the best ways to create a bright, usable outdoor space for a pergola, lean-to roof, veranda or carport. However, one of the most common concerns homeowners have is heat build-up during warmer weather.

If your outdoor area feels too hot in direct sunlight, you may be wondering whether there’s a way to reduce the temperature without replacing the entire roof.

The good news is that there are several highly effective ways to reduce heat under a polycarbonate roof — and in many cases, small changes can make a noticeable difference.

In this guide, we’ll explain what causes heat build-up, which types of polycarbonate perform best in sunny conditions, and the most effective ways to keep your covered outdoor space cooler and more comfortable.

Helpful Links

Cut-to-size polycarbonate sheets
https://polycarbonatex.co.uk/products/cut-to-size-multiwall-polycarbonate-sheet

Multiwall accessories
https://polycarbonatex.co.uk/collections/multiwall-accessories

Delivery information
https://polycarbonatex.co.uk/pages/delivery-policy

Why Does a Polycarbonate Roof Get Hot?

Polycarbonate sheets allow natural light to pass through the roof, which is one of the reasons they are so popular for pergolas and patio covers. However, sunlight also carries heat energy.

When sunlight passes through the sheets, heat can build beneath the structure — particularly during:

• Direct afternoon sun
• Hot summer days
• Low-airflow areas
• South-facing gardens

The amount of heat build-up depends on several factors, including sheet colour, thickness, ventilation and roof design.

Importantly, not all polycarbonate roofs perform the same. A properly designed system can remain surprisingly comfortable, even during warmer weather.

The Biggest Factors That Affect Heat Build-Up

Before looking at solutions, it’s important to understand what causes some roofs to feel hotter than others.

1. Sheet Colour

This has one of the biggest impacts on temperature.

Clear Polycarbonate Sheets

Clear sheets allow the maximum amount of sunlight through. This creates a bright and open feel, but it also allows more solar heat into the covered area.

Best for:

• Maximum daylight
• Bright patios
• Shaded gardens

Opal Polycarbonate Sheets

Opal sheets diffuse sunlight rather than allowing direct glare through the roof.

This helps:

• Reduce harsh sunlight
• Create softer light
• Lower heat build-up slightly

Opal is often the most popular all-round option for pergolas and seating areas.

Bronze Polycarbonate Sheets

Bronze sheets reduce both glare and solar heat gain more effectively than clear sheets.

They are ideal for:

• South-facing gardens
• Very sunny locations
• Areas where shade is preferred

Comparison Table: Which Colour Reduces Heat Best?

2. Sheet Thickness

Thicker multiwall sheets provide better insulation and can help reduce heat transfer.

10mm Polycarbonate

A good standard option for most pergolas and lean-to roofs.

16mm Polycarbonate

Provides:

• Better insulation
• Reduced heat transfer
• Less glare
• Improved comfort

For larger roofs or sun-exposed areas, 16mm sheets are often worth the upgrade.

3. Ventilation Around the Structure

One of the biggest mistakes people make is focusing only on the roof itself.

Even the best roofing material will feel warm if air cannot circulate properly.

Poor airflow traps hot air underneath the structure, creating a greenhouse effect.

Ways to Improve Ventilation

• Keep pergola sides open
• Avoid fully enclosing the structure
• Leave space for airflow at the roof edges
• Use fans in enclosed spaces

Good airflow can dramatically improve comfort levels.

4. Roof Orientation

The direction your roof faces affects how much sunlight it receives throughout the day.

South-Facing Roofs

Receive the highest sun exposure and usually experience the most heat build-up.

North-Facing Roofs

Typically remain cooler and receive softer light.

If your roof faces south or west, bronze or opal sheets are often the better choice.

Best Ways to Reduce Heat Under a Polycarbonate Roof

Now let’s look at the most effective solutions.

Choose the Right Sheet Colour

This is usually the single most effective upgrade.

For hot gardens or direct sunlight:

👉 Bronze polycarbonate usually performs best.

For balanced performance:

👉 Opal is often ideal.

Upgrade to Thicker Sheets

Thicker sheets improve:

• Insulation
• Rigidity
• Noise reduction
• Overall comfort

For many homeowners, upgrading from 10mm to 16mm creates a noticeable difference.

Ensure Proper Roof Height

Very low pergola roofs can trap heat more easily.

A slightly higher roofline helps:

• Improve airflow
• Reduce trapped hot air
• Create a more open feel

Add Shading Around the Area

Additional shading can make a huge difference.

Examples include:

• Side screens
• Outdoor blinds
• Climbing plants
• Garden screening

This reduces direct sunlight entering from the sides.

Avoid Fully Enclosed Designs

Fully enclosed structures tend to trap warm air.

If possible:

• Keep at least one side open
• Improve cross-ventilation

Use Cut-to-Size Sheets for Better Performance

Correctly sized sheets help ensure:

• Proper installation
• Correct expansion gaps
• Better roof performance overall

Order here:
https://polycarbonatex.co.uk/products/cut-to-size-multiwall-polycarbonate-sheet

Common Mistakes That Increase Heat Build-Up

Choosing Clear Sheets for Full Sun

This is extremely common.

Many people prioritise brightness without considering heat levels.

Using Thin Sheets on Large Roofs

Thin sheets offer less insulation and can make spaces feel hotter.

Poor Ventilation

Even high-quality roofing will feel uncomfortable if airflow is restricted.

Installing the Roof Too Low

Lower roofs trap warm air more easily.

Frequently Asked Questions

Do polycarbonate sheets make pergolas too hot?

Not necessarily. The right sheet colour, thickness and ventilation setup can keep the space comfortable even in warmer weather.

Which polycarbonate colour is coolest?

Bronze polycarbonate generally reduces heat and glare the most.

Do thicker sheets reduce heat?

Yes. Thicker multiwall sheets provide better insulation and can help reduce heat transfer.

Is opal or clear polycarbonate better for patios?

Opal is usually preferred for patios because it diffuses sunlight and creates a softer, more comfortable space.

Accessories for Better Roof Performance

A complete roofing system includes:

• Glazing bars
• Sealing tapes
• End closures
• Fixings

Browse accessories here:
https://polycarbonatex.co.uk/collections/multiwall-accessories

Delivery Information

Check delivery details here:
https://polycarbonatex.co.uk/pages/delivery-policy

Conclusion

Heat build-up under a polycarbonate roof is influenced by several factors, including sheet colour, thickness, roof design and ventilation. Fortunately, there are many effective ways to create a cooler and more comfortable outdoor space.

For most homeowners, choosing opal or bronze multiwall polycarbonate sheets, improving airflow and using the correct sheet thickness will provide the best balance of light, comfort and long-term performance.

By selecting the right materials from the start, you can enjoy a bright outdoor area without excessive heat during warmer months.