Optimizing Flat Roof Performance: A Guide to Effective Air & Moisture Management

Yorke Gilmore


Yorke Gilmore - Flat Roofing Specialist


Flat roofs have many benefits, including taking up less space and not using as many materials. However, they still need to be maintained to prevent problems from occurring.  

In today’s blog, we’re going to be talking about how air and moisture can affect flat roofs and what must be done to ensure flat roof longevity.


Importance of Air & Moisture Management

During the winter months, there is a higher possibility that moisture will form in flat roofs. This is because the cold outside air is coming into contact with the warm air inside the building.  

If this happens and there is no plan in place to deal with the condensation, the roof can suffer from major damage. The timber that’s used to support the roof can potentially rot, leading to the building becoming extremely unsafe.  

To ensure no building gets to this stage, extra care must be taken when insulating a flat roof. By creating an airtight structure that’s well insulated, moisture build-up can be reduced, mitigating the chance of significant problems.


Key Components of Flat Roofing Systems

The three key components of a flat roofing system are the roof membrane, the insulation inside and the roof deck.

Roof Membrane

Roof membranes can be made in various ways:  

Built-Up Roofing: This system uses multiple different layers of materials. They are often alternated with layers of bitumen-coated fibreglass.  

Single-Ply Membranes: As the name suggests, this is just one layer of roofing material. EPDM is one example, which is a synthetic rubber membrane that is extremely durable with very high weather resistance. TPO and PVC are also commonly used. These are made from thermoplastic and provide great energy efficiency.  

Modified Bitumen: This uses both built-up roofing and single-ply membrane to provide a hybrid system. Typically, it uses asphalt and modifiers to give greater flexibility and strength.  


Insulation is a crucial part of a flat roofing system. Good insulation prevents heat from escaping during colder months and entering during warmer months, leading to reduced energy consumption and lower utility bills.   Insulation also helps with condensation control. It maintains a consistent temperature across the roofing structure, reducing mould and moisture.

Roof deck

The roof deck is the very top of the flat roof. Common roof deck materials include:  

Plywood: This is a very cost-effective option and also looks great.  

Concrete: This is most commonly used in industrial buildings due to its high durability and fire resistance.  

Metal: This is another common one, known for its structural strength.


Vapour Barriers

Vapour barriers are a sheet of material that acts as a barrier, stopping moisture from getting into the flat roof and negatively impacting the roof’s structural integrity. It also helps with restricting warm air from getting out, thus improving insulation.


Why Roof Ventilation Systems are Vital for Moisture Control

Without ventilation systems, excessive moisture can build up inside a roof, causing mould growth, rotting, and compromised structural integrity to name a few.   

There are four main types of roof ventilation systems that you should know about: ridge, soffit, gable, and turbine vents.


Drainage Solutions

Although it’s called a flat roof, it isn’t completely flat. It features a slight slope, often called a fall, which allows rainwater and other debris to flow towards drainage points. Without proper drainage, water can pool and accumulate, leading to a host of issues such as leaks, deterioration of roofing materials and compromised structural integrity.


Flashings and Sealing Techniques

Flashings are weather-resistant materials that are used to keep water away from getting into gaps and joints in a flat roof.  

There are various techniques when it comes to flashing.

Roof Edges: Drip edge flashing is a common technique which entails installing an L-shaped flashing along the edge of the roof. Step flashing is also common, which is used with shingles to create a watertight barrier in places where the roof meets walls and chimneys.

Openings: Pipe boot flashing is fitted to prevent water from entering any of the pipes that come out of a flat roof. Vent boot flashing is also a popular flashing technique, which is used around ventilation pipes, providing a watertight seal.


Condensation Control

Condensation occurs when warm air meets with a cold surface, causing the air to release moisture. If your flat roof has condensation inside it, this can create a whole host of errors such as structural damage, mould growth and reduced insulation and energy efficiency.  

However, you can control the condensation by ensuring adequate ventilation is in the flat roof, vapour barriers to prevent the warm air from reaching the cold surfaces and high-quality insulation that can resist heat from going through it.  


Regular Maintenance and Inspection

Routine inspections and maintenance are essential for preventing moisture-related issues on flat roofs. By regularly inspecting the roof for signs of damage, such as leaks, tears, or missing flashing, property managers can identify and repair any problems before they cause major damage.  

Here are some tips for property managers to identify potential problems on flat roofs early:  

1.    Walk the roof regularly and look for any signs of damage, such as leaks, tears, or missing flashing.

2.    Check the roof drains and gutters to make sure they are clear of debris and water is flowing freely.

3.    Look for any areas of the roof that are missing, or have damaged, insulation.

4.    Check the roof for signs of condensation, such as water droplets or mould growth. 5.    If you see any problems, have them repaired immediately by a qualified roofing contractor.


Sustainable and Green Roofing Solutions

Exploring eco-friendly roofing options to improve moisture management. There are a number of sustainable and green roofing solutions that can be used to improve moisture management on flat roofs. These solutions include:  

Green roofs: Green roofs are roofs that are covered with plants. They can help to improve moisture management by absorbing rainwater and reducing the amount of heat that is transferred into the building.  

Bio-based roofing membranes: Bio-based roofing membranes are made from renewable materials, such as plants or algae. They are more sustainable than traditional roofing membranes and can help to improve moisture management.  

Cool roofs: Cool roofs are roofs that reflect sunlight rather than absorbing it. This can help to reduce the amount of heat that is transferred into the building, which can help to reduce moisture problems.  


Green roofs offer a number of benefits.  

Improved moisture management: Green roofs can help to absorb rainwater and reduce the amount of heat that is transferred into the building. This can help to prevent moisture-related problems, such as leaks, mold growth, and structural damage.  

Reduced energy costs: Green roofs can help to reduce energy costs by cooling the building in summer and retaining heat in winter. This can save money on heating and cooling bills.  

Improved air quality: Green roofs can help to improve air quality by absorbing pollutants and releasing oxygen.   Increased biodiversity: Green roofs can provide a habitat for birds, insects, and other wildlife. This can help to increase biodiversity in urban areas.  


Best Practices and Industry Standards

Overview of industry guidelines and best practices for air and moisture management. There are a number of industry guidelines and best practices for air and moisture management on flat roofs. These guidelines and best practices are developed by organisations such as the Property Care Association (PCA) and the National Roofing Contractors Association (NRCA).  

Compliance with building codes and regulations. Flat roofs must also comply with building codes and regulations. These codes and regulations vary for different geographical areas, but they generally require flat roofs to be designed and constructed to prevent moisture-related problems.


Optimise Your Flat Roof Performance Today

By taking advantage of draining solutions and utilising proper ventilation, you can ensure that your flat roofs will be energy efficient as well as lasting for years to come.  

Contact us today to speak to our experts who can help you best optimise your flat roof performance.