Flat Roof Types – A Comprehensive Guide

With such a diverse range of flat roof types to choose from, you may be wondering which is best. Understanding the nuances of different flat roof types is crucial for homeowners, architects, and construction professionals alike.

From the time-honoured elegance of Built-Up Roofs (BUR) using metal standing seams to the innovative resilience of Single-Ply Membrane Roofs, each type carries distinct advantages and considerations.

In this article, we explore all the different types of flat roof choices, addressing the intricacies of construction and the optimal materials and coverings that define different types of roofs.

By the end of this article, you’ll be clued up on the many different kinds of flat roof types, so you’ll be able to make the best decision for your property and project.

Understanding Flat Roof Constructions 

A Flat or low-pitched roof has a pitch between 0 and 10 Degrees. Flat roofs have a very slight pitch to allow for drainage, but they still appear predominantly level.

At Vertix Systems, we classify a low-pitched roof as anything between 5 and 15 degrees. This is because a standard Velux roof light can be fitted on roofs up to 15 degrees. Below this pitch, the roof light would need to be mounted on a kerb.

No roof surface should have ponding water. This is because, when it freezes, it can break down the surface of the roof covering. Typical terms used to describe a flat roof are 1:100 or 1:80 falls.  (These are 1-degree and 1.5-degree pitches, respectively). 1:12 fall would give a pitch of 4.8 degrees.

Flat or low-pitched roofs are used for building extensions. This allows the roof pitch to fit under windows.

The Importance of Flat Roof Construction 

Architectural Versatility

Flat roofs can provide architectural versatility and a modern aesthetic. They provide a clean, streamlined look that complements contemporary and minimalist designs.

Space Utilisation

Flat roofs can offer more functional space, such as rooftop gardens, patios, or recreational areas. This enhances a building’s usable space, making it more versatile and, depending on location, more valuable.

Cost-effective Construction

Flat roof construction is often more cost-effective than pitched roof construction. A simple design can have a big impact on the amount of materials required, resulting in lower construction costs.

Ease of Access for Maintenance

Flat roofs can often provide easy access for maintenance and repair activities.

HVAC Installations and Solar Panels

Flat roofs are well-suited for the installation of HVAC units, solar panels, and other equipment. The flat surface allows for convenient placement and maintenance of these systems.

Energy Efficiency

Flat roofs can accommodate green roofing systems. Such as cool roofs or rooftop gardens. This can contribute to energy efficiency and environmental sustainability. These features can help regulate indoor temperatures and reduce energy consumption.

Urban Development

Flat roofs allow for more floors in urban areas with limited space. Penthouses can also be built. without altering the external appearance. This is important to ensure the maximisation of land use in highly populated areas.

Commercial and Industrial Use

Because of their cheap costs, flat roofs are a popular option for commercial and industrial use.

Modern Design Aesthetic

Modern architectural designs often favour flat roofs for their sleek and contemporary appearance. The clean lines and unobtrusive profile contribute to a modern and visually appealing building design.

Drainage Solutions

Flat roofs have a minimal pitch. They’re designed to facilitate proper drainage. Effective drainage systems prevent water pooling. This reduces the risk of leaks and water damage.

Remember that proper design, construction, and maintenance are crucial for the success of flat roofs. Adequate waterproofing and drainage are essential to prevent issues such as water infiltration and structural damage.

Flat Roof Types: What Is a Felt Roof?

A felt roof is usually made up of:

1. A base sheet- which may be fibreglass, polyester or another similar material. It provides strength and stability to the roof. Old roofs can be constructed with asbestos.
2. Felt or fabric layers- which may be saturated with bitumen (asphalt or coal tar) to create a waterproof membrane.
3. Protective surface material- this could be gravel on top of the felt and bitumen layer. This top layer provides protection against weathering and UV radiation.

Advantages of felt roofs

• Durability. Felt roofs can withstand harsh weather conditions, including extreme temperatures, UV radiation, and heavy precipitation. However, due to the pitch, many materials are affected by frost and ponding water, which can shorten the life of the roof covering.
• Waterproof. The multiple layers of bitumen-saturated felt create a continuous and effective waterproofing membrane. This helps prevent water infiltration and protects the underlying structure.
• Fire resistance. The bitumen used in BURs, especially coal tar, is highly fire-resistant. 
• Stability in extreme temperatures performs well in both hot and cold climates. They have thermal stability and can expand and contract without compromising their integrity.
• Versatile. Felt roofs can be adapted to various roof configurations. This includes flat roofs and low-slope roofs. They are suitable for both residential and commercial buildings.
• Ease of repair. When damage does occur, repairs to built-up roofs are usually straightforward. Additional layers of bitumen and roofing felt can be added to address localised issues. This makes repairs a much more simple process.
• Sound insulation. The multiple layers of bitumen and roofing felt provide sound insulation, reducing the transmission of external noise into the building.

Key Considerations for Felt Roofs

Layer Count

The number of layers in a felt roof will impact its durability and strength. Typically, a built up felt roof consists of multiple layers of roofing felt and bitumen. Higher-ply systems often provide better protection against weather elements.

Bitumen Type

The choice of bitumen, whether asphalt or coal tar, can impact the performance of the felt roof. Asphalt is more commonly used due to its availability and cost-effectiveness. Coal tar is known for its resistance to water and chemicals but is less commonly used today due to environmental concerns.

Surfacing Material

The top layer of a felt roof is often covered with a surfacing material to protect it from UV rays and physical damage. Common materials include gravel, mineral granules, or a reflective coating. The surfacing also provides additional fire resistance.

Insulation

Consideration needs to be given to the insulation beneath the felt roof. Adequate insulation helps regulate the building’s temperature. This helps improve energy efficiency and prevents condensation issues.

Installation Method

Felt roofs are installed using various methods,. These can include hot mopping (applying hot bitumen). Torch application (melting modified bitumen). Or cold application (using adhesives). The chosen method may depend on factors such as:

• budget
• building regulations
• specific requirements of the roofing project.

Maintenance and Repairs

Regular maintenance is essential to extend the lifespan of a felt roof. Inspections should be conducted to identify and address issues. Common things to look for include punctures, blisters, or areas with worn-out surfacing. Timely repairs can prevent water infiltration and structural damage.

Felt roofs can also be heavy, especially when multiple layers are used. The building structure should be designed to support the roofing system’s weight, and structural engineers may need to assess the building’s load-bearing capacity.

Environmental Impact

Some bitumen products may have environmental concerns, which can lead to the consideration of alternative roofing materials with lower environmental impacts.

Climate Conditions

Climate plays a significant role in the performance of felt roofs. In areas with extreme temperatures, UV exposure, or heavy precipitation, the roofing system must be selected and installed to withstand these conditions. Proper drainage is crucial to prevent water ponding.

Planning and Building Regulations

Checks will need to be made to ensure felt roofing systems comply with relevant planning and Building Regulations.

Warranty and Lifespan

Check the manufacturer’s warranty and consider the expected lifespan of the felt roof. It’s important to understand the terms and conditions of your warranty in the event of a potential future claim.

Flat Roof Types: What Is a Metal Standing Seam Roof?

This is typically made up of:

1. Structural Metal Deck or OSB wooden board.
2. Breather membrane
3. Metal standing seam – this has concealed fixings.

Advantages of Metal Standing Seam Roof

• Highly durable and can withstand elements like wind, rain, sunlight and snow.
• it’s a fix-and-forget system that requires minimal ongoing maintenance. 
• High-end appearance and finish- a sleek appearance that looks less industrial than traditional metal profile systems.
• A metal roof can last in excess of 50 years. 
• Metal roofs are recyclable at the end of their life.
• Generally classed as the standard form of construction, so you get standard house insurance and a mortgage on the property.
• Concealed fixings / Secret fixings help to improve aesthetics and remove potential leakage at fixing points.
• Metal standing seam roofs naturally reflect heat back into the environment instead of allowing heat to build up inside the building. This means a building can remain cooler in summer and warmer in winter, helping to reduce heating/cooling energy costs depending on the time of year.
• Perform well in both hot and cold climates, making them a stable choice, no matter what the weather
• Can be adapted to various roof configurations, including flat roofs and low-slope roofs. They are suitable for both residential and commercial buildings.
• Damaged roof sheets can easily be replaced.

Key Considerations for Metal Standing Seam Roofs

1. Material selection. Common materials include pre-finished (painted) steel, aluminium, and zinc. Each material has its own set of characteristics. Such as durability, corrosion resistance, and cost. 
2. Panel design and profile. Standing seam roofs come in a variety of panel designs and profiles, which can impact their appearance, strength, and performance. Common profiles include double lock, snap lock, and mechanical lock.
3. Coatings and finishes. Some metal standing seams are painted to enhance durability, aesthetics and weather resistance. When choosing a coating and finish, local climate needs to be considered.
4. Colour. The colour of the metal standing seam roof can influence the building’s aesthetics and energy efficiency. Light colours reflect more sunlight, reducing heat absorption and contributing to energy efficiency. Dark colours may absorb more heat but can enhance the appearance of a building and add a more contemporary feel.
5. Installation method. Metal standing seam roofs are installed using a series of raised seams that interlock with adjacent panels. The installation method may involve mechanical seaming, snap locking, or other techniques. Proper installation is crucial for weather-tightness and long-term performance.
6. The base layer on which the metal standing seam is laid may be board or metal decking. It must be in good condition and provide a suitable base for the metal standing seam. Appropriate breather membranes may also be required.
7. Ventilation. Adequate ventilation is required for metal standing seam roofs to prevent condensation. This will also promote airflow beneath the roof system. Ventilation strategies may include ridge vents, soffit vents, or other systems that allow for proper air circulation.
8. Expansion and contraction- metal standing seam roofs expand and contract with temperature fluctuations. Roofing installers must account for thermal movement by incorporating expansion joints and detailing to accommodate these changes without causing damage to the roof.
9. Wind uplift resistance. Metal standing seam roofs are known for their excellent wind uplift resistance. Checks need to be made with the manufacturer to ensure that their roof system can meet required wind resistance levels. Especially in areas prone to severe weather conditions.
10. Maintenance and inspections. Regular inspections and maintenance are essential for the longevity of metal standing seam roofs. Check for loose fasteners, damaged panels, or any signs of corrosion. Address any issues promptly to prevent water infiltration and ensure the roof’s integrity.
11. Cost considerations. Metal standing seam roofs are durable and have a long lifespan. However, they can be a significant investment. Different metals have different price points. Pre-finished steel can often work out to be the most cost-effective option. Consider the upfront costs, but also factor in the long-term durability and minimal maintenance requirements, which can make them cost-effective over time.

For a more detailed explanation of what a standing seam roof is, we have covered that in a separate article.

Flat Roof Types: Single-Ply Membrane Roof 

Single-ply membrane roofs consist of a single layer of synthetic or elastomeric material as the primary waterproofing element. This type of roofing is commonly used on flat or low-slope roofs in both residential and commercial buildings. There are different types of single-ply membranes. The most common are:

• Ethylene Propylene Diene Monomer (EPDM)
• Thermoplastic Olefin (TPO)
• Polyvinyl Chloride (PVC).

Advantages of Single-Ply Membrane Roofs

• Single layer: contributes to efficient installation and maintenance.
• Lightweight: It reduces the load on the underlying roof structure, which can be advantageous, especially for buildings with load-bearing considerations.
• Ease of installation: It can be quicker and less labour-intensive than some other roofing systems. The large sheets of material allow for efficient coverage of large areas.
• Flexibility: makes them well-suited for roofs with complex or irregular shapes. This flexibility also allows the membrane to expand and contract with temperature variations.
• Energy efficiency: Some single-ply membranes, particularly TPO, are known for their reflective properties. This can contribute to energy efficiency by reducing heat absorption and lowering cooling costs.
• UV resistance: Many single-ply membrane materials are designed to resist UV radiation. This prevents degradation and extends the lifespan of the roofing system.
• Resistance to chemicals and environmental elements: Single-ply membranes are often resistant to chemicals, pollutants, and environmental elements. This is why they last as long as they do.
• Ease of repairs: In the event of damage, single-ply membrane roofs are generally straightforward to repair. Repairs often involve patching or heat-welding new material onto the damaged area.

Key Considerations for Single Ply Membrane Roofs

1. Material types. Single-ply membranes are typically made of different materials. This includes TPO (Thermo plastic olefin) which is known for its heat-welded seams and energy efficiency. PVC (Polyvinyl Chloride), which offers good chemical resistance and durability. EPDM (Ethylene Propylene Diene Monomer) is synthetic rubber offering good weather resistance. 

2. Installation method. Single-ply membranes can be installed using various methods. These include mechanical, fully adhered, or ballasted systems. The choice of installation method depends on factors such as building design and wind uplift requirements.

3. Seam integrity- this is crucial for the performance of single-ply membrane roofs. Hot air welding or chemical bonding is commonly used for TPO and PVC membranes, while EPDM membranes often use adhesives or tape. Ensure proper seam sealing during installation to prevent water infiltration.

4. Roof insulation. Consideration needs to be given to the type and thickness of the insulation beneath the single-ply membrane. Adequate insulation helps with energy efficiency and temperature regulation. This prevents condensation within the roofing system.

5. Condition of the base layer. Care needs to be taken to ensure that the base layer is clean, smooth, and in good condition. Failing to avoid these can affect membrane performance.

6. Compatibility with other materials. Checks need to be made to ensure that the single-ply membrane is compatible with other roofing materials and components. This can include flashings, sealants, and adhesives. Compatibility is crucial to prevent issues like chemical reactions or material degradation over time.

7. Compliance with Planning and Building Regulation – checks need to be made to ensure the chosen single-ply membrane roofing system complies with Planning and Building Regulations. This includes ensuring that the system meets the required fire ratings, wind uplift resistance, and any other performance requirements.

8. Roof pitch and drainage whilst single-ply membranes are versatile, they perform best on low-pitch roofs. A proper roof slope and effective drainage need to be designed in to prevent water ponding, which can lead to membrane degradation and leaks.

9. Maintenance and repairs. Single-ply membrane roofs require regular inspections for signs of damage or wear. Issues identified, such as punctures, tears, or seam failures, need to be promptly addressed. Doing so can help prevent water infiltration and extend the lifespan of the roof.

10. UV protection and reflectivity. Some single-ply membranes come with reflective surfaces or coatings. This enhances UV resistance and reduces heat absorption. Consider these features for energy efficiency.

11. Warranty and manufacturer support. Review the warranty offered by the manufacturer. Make sure it aligns with the project’s requirements. Choose a reputable manufacturer that provides support for proper installation and maintenance.

12. Environmental considerations- some single-ply membrane materials are more environmentally friendly than others. Consideration needs to be given to the environmental impact, recyclability, and sustainability of the chosen material.

Flat Roof Types: Green Roofs

Green roofs incorporate vegetation, soil, and drainage layers to create a green space on the roof surface. They provide a range of environmental, energy, and aesthetic benefits and can be installed on various types of buildings, including residential, commercial, and industrial structures. 

There are two main types of green roofs: 

1. extensive green roofs
2. intensive green roofs.

Extensive Green Roofs

Extensive green roofs have a shallow growing medium. They are characterised by low-maintenance vegetation. Typically, drought-tolerant plants such as sedum and grasses. The depth of the growing medium is usually less than 15 centimetres. 

Green roofs are a low-maintenance and lightweight option. This makes them suitable for a wide range of buildings. They provide energy efficiency benefits and stormwater management.

Intensive Green Roofs

Intensive green roofs have a deeper growing medium, allowing for a more diverse selection of vegetation, including larger plants, shrubs, and even small trees. They resemble traditional gardens and require more maintenance. 

Intensive green roofs deliver greater biodiversity and aesthetic appeal. They have the potential to create recreational or usable spaces. However, they are heavier and require more intensive maintenance than their extensive counterparts. 

All green roofs require the following:

1. Waterproof layer to prevent water from infiltrating the building structure. It is typically made of a material like rubber, asphalt, or synthetic membrane.
2. A root barrier is placed on top of the waterproof layer to prevent plant roots from penetrating the roofing system and causing damage.
3. The drainage layer ensures proper water management and prevents excess water from accumulating on the roof. It often consists of gravel, drainage mats, or other materials that facilitate water flow.
4. Filter fabric. This is placed on top of the drainage layer to prevent fine particles from clogging the drainage system. It allows water to pass through.
5. Growing medium/substrate. This is a specially engineered soil-like layer that provides nutrients for plant growth. It is designed to be lightweight and conducive to plant health.
6. Vegetation. This consists of a variety of plants, such as sedum, grasses, herbs, or even small shrubs and trees. The plant selection depends on factors like climate, local conditions, and the desired aesthetic.

Key Advantages of Green Roofs

• Energy efficiency. Green roofs provide insulation. This reduces the heat transfer between the building and the external environment. This can lead to energy savings in both heating and cooling.
• Stormwater management. Green roofs absorb and slow down rainwater runoff. This reduces the risk of flooding.

• Air quality improvement. Plants on green roofs capture pollutants and particulate matter from the air. This helps improve air quality.
• Urban heat island mitigation. The vegetation on green roofs helps mitigate the urban heat island effect by providing shade and cooling the surrounding air.
• Biodiversity enhancement. Green roofs can support a variety of plant species, attracting insects, birds, and other wildlife. This contributes to urban biodiversity.
• Aesthetic appeal. Green roofs enhance the visual appeal of buildings and provide a natural and calming environment. Especially in urban settings.
• Noise reduction. A combination of vegetation and growing medium on green roofs can absorb and dampen sound. This provides acoustic benefits, especially in urban areas.

Key Considerations for Green Roofs

1. Structural capacity: An assessment will need to be made of the structural capacity of the building. This is to understand if it can support the additional load of a green roof. Consult with a structural engineer to ensure that the roof can safely accommodate the extra weight
2. Waterproofing and drainage: Proper waterproofing is crucial to prevent water infiltration into the building. Install a high-quality waterproofing membrane. Incorporate an efficient drainage system to avoid water ponding on the roof.
3. Growing medium: choose a lightweight and well-draining growing medium for the green roof. The medium should provide adequate support for plant growth while allowing water to permeate easily.
4. Plant selection: Choose plants that are well-suited to the local climate. Plants that require minimal maintenance are also a good choice. Drought-resistant and native plant species are often the best option.
5. Irrigation system: Consideration needs to be given as to whether an irrigation system is required, especially if the area has limited rainfall. Irrigation ensures that the plants receive sufficient water for healthy growth. 
6. Access and safety: A plan for safe and controlled access to the green roof for maintenance purposes will need to be developed. Safety measures such as guardrails or warning signs should be implemented to prevent accidents.
7. Microclimate effects: It’s helpful to understand the potential microclimate effects of the roof on the building and surroundings. Green roofs can provide insulation, reduce heat island effects, and improve air quality. Consider these benefits in the overall building design.
8. Biodiversity enhancement-green roofs provide habitats for birds, insects, and other wildlife. Consideration should be given to incorporating features such as bird boxes or insect-friendly plants to enhance biodiversity.
9. Maintenance requirements: Regular maintenance is essential for a successful green roof. This includes tasks such as weeding, pruning, and monitoring the irrigation system. Establish a maintenance plan to ensure the long-term health of the vegetation.
10. Cost considerations: Green roofs may have higher upfront costs than traditional roofing systems. However, consider the long-term benefits, such as energy savings and improved environmental impact.
11. Compliance with Planning and Building Regulations: Checks need to be made to ensure the green roofing system complies with Planning and Building Regulations. Ensure the system meets the required:
    • fire ratings
    • wind uplift resistance
    • other performance requirements.
12. Rainwater management: Green roofs can help manage rainwater by reducing runoff and absorbing rainwater.
13. Aesthetics and design: green roofs can enhance the visual appeal of a structure, especially in urban environments.

What Is The Best Material for a Flat Roof?

Choosing the right material for a flat roof is crucial. It directly impacts the roofing system’s performance, durability, and overall success.

These are the main factors to consider when deciding on the best material for a flat roofing project. They also serve as a useful checklist for comparing different roofing materials.

Waterproofing & Weather resistance

Flat roofs are more prone to water pooling, making proper waterproofing essential. The right roofing material should provide a reliable barrier against water infiltration, protect the building’s interior from leaks and water damage, and withstand exposure to various weather conditions, including rain, snow, and UV radiation.

Durability & Longevity

The longevity of a flat roof depends on the durability of the chosen material. Materials that are resistant to environmental factors can contribute to the durability of the roof. Consider materials resistant to things such as UV rays and temperature fluctuations. Choosing durable materials can extend the lifespan of the roof and reduce the frequency of repairs or replacements.

Structural Integrity & Load-Bearing Capacity

Different roofing materials have varying weights and structural requirements. It’s crucial to choose a material that aligns with the building’s structural capacity. Overloading a structure with a roofing material that exceeds its load-bearing capacity can lead to structural damage and compromise the safety of the entire building.

Energy Efficiency

Some roofing materials contribute to a building’s energy efficiency. Reflective or cool roofing materials can help reduce heat absorption, lowering cooling costs and creating a more comfortable interior environment. Choosing the right material with suitable reflective properties can positively impact energy consumption.

Installation & Maintenance Costs

The upfront costs of materials, as well as installation and maintenance expenses, should be considered. Whilst some materials may have a higher initial cost, they could result in lower maintenance costs over time. Conversely, choosing cheaper materials may lead to increased maintenance and repair expenses in the long run.

Compatibility With Roof Design & Use

The chosen roofing material should align with the design requirements and intended use of the building. Some materials may be better suited for commercial or industrial applications. Others are more appropriate for residential structures. The material should also be compatible with other roofing components. Such as insulation and drainage systems.

Climate Considerations

Climate significantly influences the performance of flat roofs. Materials should be selected based on their ability to withstand the specific climate conditions relevant to the building location. This includes any extremes in temperature, humidity and precipitation. A material that performs well in one climate may not be suitable for another.

Fire Resistance

Fire resistance can often be a critical factor. Choosing a fire-resistant roofing material helps enhance safety.

Compliance with Planning and Building Regulations

It’s essential to choose a roofing material that complies with Planning and Building Regulations. Failure to meet these can result in legal issues, delays, or the need for costly modifications.

Aesthetic Considerations

The appearance of the roofing material contributes to the aesthetics of the building.

The right material should align with the property owner’s architectural style and visual preferences and local planning considerations. A well-chosen material can enhance curb appeal and potentially increase a property’s value.

Summary of the Pros and Cons of Different Materials for Flat Roofs

Flat roof material	Description	Advantages	Limitations
Felt	Layers of roofing felt or fabric with bitumen (asphalt or coal tar) are applied to create a durable and weather-resistant roof.	Affordability, Ease of installation, Versatility in application, Effective waterproofing,	Susceptibility to damage from UV rays and weathering over time, Limited lifespan compared to other roofing materials, Maintenance and repair requirements.
Metal standing seam	Layers of roofing felt or fabric with bitumen (asphalt or coal tar) are applied to create a durable and weather-resistant roof.	Durability, Longevity, Energy efficiency, Modern aesthetics, Resistance to weather elements	Higher initial costs, the potential for noise during precipitation, and susceptibility to denting in severe weather.
Single ply membranes	A single layer of flexible, synthetic material which acts as the waterproofing membrane.	Lightweight design, Ease of installation, Flexibility, Energy efficiency options, Suitable for a variety of climates.	Vulnerability to punctures, varying performance based on material type, and higher susceptibility to damage from UV exposure.
Green roofs	Incorporates living vegetation, soil, and a waterproofing membrane on the roof of a building.	offer benefits such as energy efficiency, stormwater management, improved air quality, biodiversity enhancement, aesthetic appeal, extended roof lifespan, and noise reduction.	Higher upfront costs, Potential structural load concerns, Maintenance requirements, and need for specialised expertise in installation and care.

Conclusion 

Selecting the right material for a flat roof depends on many factors, including waterproofing, durability, structural capacity, energy efficiency, climate, and cost.

The choice between materials like felt roofing, membranes, or metal standing seam should align with the project’s specific needs and priorities.

A well-informed decision should take into account both immediate and long-term considerations.

Additionally, adherence to planning and building regulations is crucial to guarantee compliance and the overall success of the roofing system.

If you have any questions about flat roof types or have a specific building project that you’d like to talk through with one of our technical experts, please get in touch with us here