Flat roofs are a popular roofing choice for both residential and commercial buildings due to their aesthetic, cost-effectiveness, and practicality.
Unlike pitched roofs, which have a steep slope, flat roofs typically have a minimal incline, usually no more than 10 degrees, to allow for water drainage.
What is a flat roof?
A flat roof is a type of roofing system that has little to no pitch, meaning it appears level to the naked eye. However, most flat roofs are designed with a slight gradient to facilitate proper water drainage and prevent ponding.
These roofs are typically constructed using materials that create a continuous, waterproof membrane, such as bitumen, rubber, or synthetic materials like EPDM and TPO.
The history of flat roofs
Flat roofs have been around for thousands of years, with some of the earliest examples dating back to ancient Mesopotamia and Egypt.
In these dry climate areas, flat roofs were made of mud, clay and straw to insulate from the heat.
The design spread to Mediterranean and Middle Eastern cultures, where homes were built with flat roofs that served as additional living space.
In the 19th and early 20th centuries, the Industrial Revolution brought advancements in building materials and flat roofs became stronger and more widespread.
Asphalt-based roofing materials, tar and gravel systems improved waterproofing and flat roofs then became the choice for commercial and factory buildings.
By the mid-20th century, modern materials like rubber, PVC and thermoplastic membranes revolutionised flat roof construction, making them more long-lasting and weather-resistant.
Today, flat roofs continue to evolve with solutions like green roofing and solar panel integration.
Common uses of flat roofs
Flat roofs are used in various types of buildings due to their practicality:
- Residential – Flat roofs are found in modern homes, flats and extensions. They allow for outdoor spaces like rooftop gardens or terraces and increase internal space.
- Commercial – Most office buildings, shopping centres and warehouses have flat roofs as they can house HVAC systems, solar panels and other mechanical equipment.
- Industrial – Factories and manufacturing plants use flat roofs as they provide easy access for maintenance, ventilation systems and machinery.
- Public and Institutional – Schools, hospitals and government buildings use flat roofs for large infrastructure and upgrades like solar panels or reflective coatings.
Flat roof materials and construction options
Choosing the right material for a flat roof is important to guarantee strength, weather resistance, and cost. Different materials offer varying levels of protection, longevity, and maintenance requirements.
Modern flat roofing materials
Advancements in roofing technology have led to the development of more lightweight, and durable materials. These solutions offer better weather resistance, flexibility, and an easier installation process.
EPDM (Ethylene Propylene Diene Monomer) rubber roofing
EPDM rubber roofing is a synthetic rubber membrane known for its flexibility. It is commonly installed in large sheets to lessen seams, reducing the risk of leaks.
Advantages of EPDM roofing:
- Long lifespan (up to 50 years)
- Highly resistant to UV rays, ozone, and weather conditions
- Lightweight and easy to install
- Environmentally friendly and recyclable
Disadvantages of EPDM roofing:
- Can be punctured by sharp objects
- Requires professional installation for proper seam sealing
- Dark colour absorbs heat, which may increase cooling costs
TPO (Thermoplastic Olefin) roofing
TPO is a single-ply roofing membrane made from polypropylene and ethylene-propylene rubber. It is reinforced with polyester for added strength.
Advantages of TPO roofing:
- Highly reflective surface reduces heat absorption and improves efficiency
- Resistant to chemicals, grease, and UV exposure
- Lightweight and easy to install
- Seam welding ensures a watertight seal
Disadvantages of TPO roofing:
- Relatively new material, so long-term performance is still being studied
- Quality varies by manufacturer, requiring careful selection
- Can be prone to shrinkage over time
PVC (Polyvinyl Chloride) roofing
PVC roofing is a single-ply membrane made from plasticised polyvinyl chloride. It is reinforced with polyester or fibreglass for extra strength.
Advantages of PVC roofing:
- High resistance to chemicals, oils, and grease
- Strong and durable with a long lifespan (up to 30 years)
- Heat-welded seams create a watertight barrier
- Fire-resistant and recyclable
Disadvantages of PVC roofing:
- More expensive than EPDM and TPO
- Brittle over time in colder climates
- Can release toxic chemicals during production and disposal
GRP (Glass Reinforced Plastic) and fibreglass roofing
GRP, also known as fibreglass roofing, is a lightweight, and strong roofing option. It is applied in liquid form and reinforced with fibreglass matting.
Advantages of GRP roofing:
- Easy application reduces the risk of leaks
- Highly durable and resistant to weathering
- Can be moulded to fit complex roof designs
- Low maintenance requirements
Disadvantages of GRP roofing:
- Can be expensive compared to other options
- Installation requires skilled professionals for the best results
- Susceptible to cracking if not properly installed
Liquid-applied roofing (polyurethane, silicone, and acrylic coatings)
Liquid-applied roofing systems use coatings such as polyurethane, silicone, and acrylic to create a waterproof layer. These coatings can be applied directly to existing flat roofs for added protection.
Advantages of liquid-applied roofing:
- Fully adhered, preventing leaks
- Ideal for extending the life of an existing flat roof
- Provides high resistance to UV exposure and extreme temperatures
- Quick and easy application
Disadvantages of liquid-applied roofing:
- Requires regular reapplication for the most durability
- Can be expensive for large surfaces
- Susceptible to application errors if not done by professionals
Choosing the Right Flat Roof Material
Selecting the best material for a flat roof depends on several factors, including climate, durability, and cost.
Climate considerations
- Hot climates: Light-coloured roofing materials like TPO and PVC reflect heat, reducing cooling costs.
- Cold climates: EPDM and asphalt-based materials offer better insulation and flexibility to withstand freezing temperatures.
- Wet climates: BUR and GRP roofing provide excellent waterproofing and durability against heavy rainfall.
Durability and Lifespan
- EPDM: 30–50 years
- TPO: 20–30 years
- PVC: 25–30 years
- GRP/Fibreglass: 20–40 years
- BUR: 15–30 years
- Asphalt and Felt: 10–20 years
- Liquid-Applied Roofing: 10–25 years
Drainage solutions for flat roofs
Why drainage is important for flat roofs
Unlike pitched roofs, which naturally allow water to run off due to their steep angle, flat roofs have a minimal slope, making drainage a critical consideration. Without proper drainage, water can pool on the surface, leading to structural damage, leaks, and premature wear of roofing materials.
Below is a list of factors that can aid in draining the water from your flat roof:
Different drainage systems for flat Roofs
Internal drains
Internal drains are common in commercial and larger residential flat roofs. These drainage systems consist of small drains installed at low points on the roof, where water naturally accumulates.
Pipes run beneath the roof surface, directing water safely into the building’s drainage system. Internal drains are ideal for roofs with large surface areas, as they prevent excessive water buildup.
However, they require regular maintenance to avoid blockages from debris, which can cause backups and pooling.
Scuppers
Scuppers are openings in the parapet walls or edges of a flat roof that allow water to drain off the sides of the building. They are often paired with downspouts or extended chutes to direct water away from the building’s foundation.
Scuppers are a cost-effective solution that prevents water from accumulating on the roof, but they work best when the roof has a slight slope guiding water toward them.
Regular cleaning is necessary to prevent leaves and debris from clogging the openings.
Gutters and downspouts
Gutters and downspouts function similarly to those on pitched roofs, collecting rainwater from the roof edge and directing it down and away from the building. They are a simple yet effective drainage solution for smaller flat roofs or residential properties.
However, they must be installed with precision for proper water flow and require frequent maintenance to clear blockages from leaves, dirt, and debris.
If not properly maintained, clogged gutters can cause water to overflow and pool near the building’s foundation, potentially leading to structural issues.
Slope considerations for better water run-off
Although flat roofs appear level, they are typically designed with a slight pitch (usually between 1:40 and 1:80) to encourage water to drain toward designated drainage points. Without this slight gradient, water may stagnate, increasing the risk of leaks and damage. Roofing professionals often use tapered insulation systems or structural slopes to guide water flow.
Flat roof installation process
Installing a flat roof requires a qualified skillset to accurately plan, use the correct materials and construct adequately. Here is how professionals implement a flat roof on your property.
Pre-installation preparation
Before installing a flat roof, thorough preparation is important to ensure strength and performance. The first step is assessing the structure to confirm it can support the roofing material and identifying any necessary reinforcements.
Drainage planning is also crucial since flat roofs require a slight slope or an effective drainage system, such as internal drains or scuppers, to prevent water pooling.
Choosing the right insulation, either a warm roof (insulation above the deck) or a cold roof (insulation below the deck) can significantly impact energy and moisture control.
The roof deck must also be clean, dry, and structurally sound, with any uneven areas levelled to prevent weak spots. Lastly, selecting the appropriate roofing material, whether traditional built-up roofing (BUR), EPDM rubber, TPO, PVC, or fibreglass, should be based on climate, budget, and maintenance requirements.
Steps involved in installing different flat roofing systems
The installation process varies depending on the roofing material.
- Built-up roofing (BUR) involves layering bitumen, felt, and gravel to create a waterproof surface.
- EPDM rubber roofing requires rolling out the membrane, securing it with mechanical fasteners, and sealing the seams with specialised tape.
- TPO and PVC roofs involve heat-welding the seams after rolling out and fastening the membrane, for a weather-resistant finish.
- GRP (fibreglass) roofing is applied over a plywood or OSB base, using resin and fibreglass matting to create a hard surface.
- Liquid-applied roofing, such as polyurethane or silicone coatings, is rolled or sprayed onto the roof for a waterproof layer.
Each method has its advantages, but proper installation techniques, such as ensuring tight seams and adequate drainage, are important for performance.
Adding rooflights to a flat roof
Flat roofs can sometimes make interior spaces feel darker and more enclosed compared to pitched roofs. One of the best ways to counter this is by installing rooflights, which allow natural light to flood in while also offering additional benefits such as improved ventilation and energy levels.
Why install rooflights on a flat roof?
There are several reasons to incorporate rooflights into a flat roof design.
Natural light is one of the biggest advantages. A well-placed rooflight can transform a space by making it feel larger, brighter, and more inviting. This can reduce the need for artificial lighting during daylight hours, helping to cut energy costs. Discover more ways to make a room look bigger.
Ventilation is another key benefit. Certain rooflight designs allow for airflow, which is particularly useful in kitchens, bathrooms, and other areas prone to condensation and humidity. By improving air circulation, these rooflights help maintain a healthier indoor environment.
Finally, rooflights contribute to the overall aesthetics and value of a property. They create an open feel while also increasing resale appeal by boosting natural lighting.
Types of flat roof rooflights
There are various types of rooflights available, each serving different purposes:
- Flat Roof Skylight Windows: Our most popular product, flat roof skylight windows offer bespoke features and a stunning design at fantastic prices.
- Fixed Rooflights: Designed solely for letting in natural light, these do not open but provide excellent insulation.
- Opening Rooflights for Ventilation: Available in manual or electric options, these allow airflow to improve indoor air quality and reduce moisture buildup.
- Walk-on Rooflights: Made with reinforced glass, these are strong enough to support weight, making them ideal for roof terraces and balconies.
- Roof Lanterns: Featuring a multi-panel pitched design, these provide the most light and create an architectural statement.
Best rooflights for flat roofs
Choosing the right rooflight depends on factors such as strength, and aesthetics.
Quality glazing is quite important for thermal insulation, helping to retain heat in winter while preventing loads of heat gain in summer.
Aluminium frames offer a smooth finish, while uPVC options are more affordable and provide good insulation.
Some rooflights come in frameless designs, creating an uninterrupted glass appearance.
Our flat roof skylight windows tick every box, so get yours today.
Contact Toughened Glass Systems Today
At Toughened Glass Systems, we supply a range of skylights, rooflights, patio doors and glass products.
Our team of professionals are always here to help you find the perfect solution for your project.
See for yourself what customers have said about our range of products, and give yourself peace of mind as to what you’re getting.
Reach out to us today for professional advice, a free quote, or to discuss your unique needs.