With such a diverse range of flat roof types to pick 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 seam. To the innovative resilience of Single-Ply Membrane Roofs. Each type carries distinct advantages and considerations.

In this article, we’re exploring the multifaceted landscape of flat roof choices. We’re going to be addressing the intricacies of construction in this article. As well as 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.

Types of Flat Roof Construction  

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

At Vertix Systems we would classify a low-pitched roof as anything between 5 and 15 degrees.  This because a standard Velux rooflight can be fitted on roofs up to 15 degrees. Below this pitch the rooflight 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 roof are used for building extensions. This allows the roof pitch to fit under windows.

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 the usable space of a building. This can make it more versatile and dependent on location, more valuable.

Cost effective construction.

Flat roof construction is often more cost-effective compared with pitched roofs. 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. It’s essential to have adequate waterproofing and drainage in place. This is to prevent issues such as water infiltration and structural damage.

Felt roofs

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. This includes extreme temperatures, UV radiation, and heavy precipitation. Due to the pitch, many materials are affected by frost and ponding water. This 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 BUR’s, especially coal tar, provides a high level of fire resistance. 
  • Stability in extreme temperatures perform 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 including 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. This reduces the transmission of external noise into the building.
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 improves 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.

Weight considerations-felt roofs can be heavy, especially when multiple layers are used. The building structure should be designed to support the weight of the roofing system. Structural engineers may need to assess the load-bearing capacity of the building.

Environmental impact

Some bitumen products may have environmental concerns. This can cause alternative roofing materials with lower environmental impact to be considered.

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

Checks should be made to the warranty provided by the manufacturer. Consideration should be given to 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.

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.
Supported standing seam roof

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- 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 standard form of construction so you get standard house insurance and a mortgage on the property.
  • Concealed fixings / Secret fixings which help to improve aesthetics and remove a potential point of leakage at fixing points.
  • Metal standing seam roofs naturally reflect heat back into the environment. This is instead of allowing heat to build up inside the building. This means a building can remain cooler in summer and warmer in winter. This can help 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 roofs sheets can easily be replaced.
Considerations for metal standing seam roofs
  1. Material selection. Common materials include pre-finished (painted) steel, aluminum, 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. These can impact the appearance, strength, and performance of the roof. 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. Base layer on which the metal standing seam is laid. This 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.

If you’re wondering what a standing seam roof is, we have covered that in a separate article.

Single-Ply Membrane Roof 

Single-ply membrane roofs consists 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- reducing the load on the underlying roof structure. This can be advantageous, especially for buildings with load-bearing considerations.
  • Ease of installation- can be quicker and less labour-intensive compared to some other roofing systems. The large sheets of material allow for large areas to be covered efficiently.
  • 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 extending 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.
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), which 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 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 reduce 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.

Green Roofs

Green roofs incorporate vegetation, soil, and drainage layers to create a green space on the roof surface. These roofs provide a range of environmental, energy, and aesthetic benefits. Green roofs can be installed on various types of buildings. These include 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 storm water management.

Intensive Green Roofs

Intensive green roofs have a deeper growing medium. This allowing for a more diverse selection of vegetation. For example, 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 for creating recreational or usable spaces. However, they are heavier and require more intensive maintenance than their extensive counter-part. 

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. Root barrier on top of the waterproof layer to prevent plant roots from penetrating into the roofing system and causing damage.
  3. Drainage layer ensures proper water management. This prevents excess water from accumulating on the roof. It often consists of a layer 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.

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. This is done 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. Combination of vegetation and growing medium on green roofs can absorb and dampen sound. This provides acoustic benefits, especially in urban areas.
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 in an area with limited rainfall. Irrigation ensures that the plants receive sufficient water for healthy growth. 
  6. Access and safety. There will need to be a plan for safe and controlled access to the green roof for maintenance purposes. 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 an essential requirement 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 compared with traditional roofing systems. Consider the long-term benefits, such as energy savings and improved environmental impact.
  11. Compliance with Planning and Building Regulation. 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 performance, durability and overall success of the roofing system.

These are the main factors to consider when deciding the best material for a flat roofing project. It also doubles as a useful checklist to compare different roofing materials.

1.Waterproofing and 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. It should protect the building’s interior from leaks and water damage. It should also withstand exposure to various weather conditions, including rain, snow and UV radiation.

2.Durability and longevity

The longevity of a flat roof depends on the durability of the chosen material. Materials with resistance 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. It can also reduce the frequency of repairs or replacements.

3.Structural integrity and 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.

4.Energy efficiency

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

5.Installation and 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.

6.Compatibility with roof design and 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.

7.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.

8.Fire resistance

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

9. 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.

10.Aesthetic considerations

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

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

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

Flat roof materialDescriptionAdvantagesLimitations
FeltLayers of roofing felt or fabric with bitumen (asphalt or coal tar) 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 seamVertical standing seam raised above the flat surface of the metal panel with hidden fixings. The standing seam design contributes to the roof’s durability, weather resistance, and energy efficiency.Durability, Longevity, Energy efficiency, Modern aesthetics, Resistance to weather elementsHigher initial costs, Potential for noise during precipitation, Susceptibility to denting in severe weather.
Single ply membranesSingle 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 roofsIncorporates 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, Need for specialised expertise in installation and care.

Conclusion 

Selecting the right material for a flat roof depends on many factors. These include: 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 specific needs and priorities of the project.

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 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 

If you have any questions 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