Flat Roofs: Everything You Should Know

Written By Adam Paul - Waterproofing Expert

A flat roof is a horizontal or nearly level roof design that typically features a slight pitch. A flat roof has a 10-degree slope or 1/4 to 1/2 inch per foot for proper drainage over the surface. The most common flat roof types are  Built-Up Roofs (BUR), Modified Bitumen, EPDM Rubber, TPO, and PVC roofing systems. Green flat roofs and solar flat roofs are two types of eco-friendly flat roofs.

Using a flat roof instead of a pitched roofs offer several benefits. As well as there are some cons due to a lack of steep slope. It causes frequent maintenance and shortens the lifespan. Flat roofs are made from EPDM, TPO, PVC, Modified bitumen, and BUR. Flat roofs should be insulated by the thermal barrier to regulate temperature and increase the energy efficiency.

When using a flat roof, it should be waterproofed by using a liquid-applied membrane or sheet membrane waterproofing. Among them, sheet membrane waterproofing is the best solution for flat roofs. A flat roof drainage system has scuppers, interior drains and gutters and downspouts. These parts of the roof play a major role in the roof during the water removal process in rain or snow.

This roof type can be prone to leaking at the roof joints. In order to prevent them, you should follow the proper guide. Aqviz experts have included those in this guide. As well as flat roofs can be used as a roof deck and roof terrace. In a hot climate flat roof absorbs more heat than a pitched roof, and it tends to increase the indoor temperature. In a cold climate flat roof tends to accumulate rain, snow, and ice. Those increase the risk of water infiltration into the interior.

Different types of flat-roof buildings are available all over the world. So Aqviz experts always recommend you to choose a flat roof if you can maintain and repair it properly. Because homeowners have to pay more attention to flat roofs than pitched roofs.

What is the Definition of a Flat Roof?

A flat roof is a horizontal or nearly level roof design that typically features a slight pitch. Flat roof has a 10-degree slope or 1/4 to 1/2 inch per foot for proper drainage over the surface. Unlike pitched or sloped roofs, flat roofs are more accessible. Hence flat roof can be utilized as a functional outdoor space, especially in urban environments.

At Aqviz, we’ve worked with hundreds of flat roofs across residential and commercial buildings. Flat roofs demand precise roof sealing and moistureproof systems to prevent water stagnation, as they’re more prone to leaks without proper insulation and waterproofing. 

What are the Types of Flat Roofs?

Flat roofs come in several types based on the roofing. Each type has specific strengths and suitable use cases. The most common flat roof types are  Built-Up Roofs (BUR), Modified Bitumen, EPDM Rubber, TPO, and PVC roofing systems. Each type uses different materials and techniques to deliver long-lasting performance.

As waterproofing experts we recommend EPDM and TPO roofing, especially effective in hot climates due to their durability and energy efficiency. Meanwhile, Modified Bitumen offers excellent leakproof roof capabilities when properly coated. 

What are the 2 Eco-Friendly Flat Roofs?

Eco-friendly flat roofs are sustainable roofing solutions designed to reduce environmental impact while improving home efficiency. Eco-friendly flat roofs are mainly two types: Green flat Roofs and Solar flat roofs. These systems not only protect your home but also support energy conservation and biodiversity.

Green Flat Roof

A green flat roof, also known as a vegetative or living roof, is layered with vegetation and soil atop a waterproof membrane. This design helps absorb rainwater, reduce heat, and provide natural insulation.

We’ve installed many of these in urban homes where rooftop gardens double as relaxing retreats. They’re moistureproof, regulate indoor temperature, and reduce stormwater stress. Plus, they extend the roof’s life by shielding the surface from UV rays and temperature extremes.

Solar Flat Roof

A solar flat roof integrates solar panels directly onto the roof’s surface, converting sunlight into clean energy. It’s a smart way to make your roof productive while cutting down on utility costs.

What are the Benefits of Flat Roofs?

These are the benefits of a flat roof

1. Flat roofs are cost-effective and quicker to install
2. Flat roofs are easier to access for maintenance, inspections, and repairs
3. Ideal for roof decks, solar panels, and HVAC units
4. Flat roofs provide a modern, minimalist architectural appeal
5. Flat roofs are suitable for both residential and commercial structures
6. Flat roofs enhance insulation when sealed correctly
7. Flat roofs are compatible with eco-friendly solutions like green roofs and solar roofs
8. Flat roofs provide more usable space for leisure or gardening
9. Flat roofs are easy to integrate with drainage systems
10. Flat roofs are great for small-space urban construction

What are the Disadvantages of Flat Roofs?

Flat roofs have three main disadvantages due to their structure. 

1. Flat roofs lack the steep slope of pitched designs, water tends to pool, leading to leaks if not properly sealed. Over time, this can result in roof deck damage, mold growth, and compromised structural integrity.
2. Flat roofs require more frequent maintenance and inspections to ensure the roofing material remains intact. 
3. Flat roofs have a shorter lifespan compared to sloped roofs, especially if built using low-quality or permeable materials. 

Read More About: How to Inspect a Roof for Leaking?

What are the Common Flat Roof Materials?

Flat roofs can be constructed using a variety of materials, each with unique properties and water resistance levels. The most common materials include EPDM (rubber roofing), TPO (thermoplastic polyolefin), PVC roofing, Modified Bitumen, and Built-Up Roofing (BUR).

At Aqviz, we often recommend EPDM for its strong leakproof and UV-resistant qualities. TPO and PVC roofing offer excellent heat reflection and are impermeable to water when professionally installed and sealed. 

Modified Bitumen is known for its durability and added waterproofing when paired with torch-down methods. BUR systems, while older, provide solid moistureproof layers through multiple asphalt and felt coatings. Each material performs best when reinforced with expert roof coating and sealing techniques to create a fully water-tight roof surface.

What is Flat Roof Insulation?

Flat roof insulation is the process of thermal barrier installing between the roof surface and the building interior to regulate temperature and energy efficiency. Unlike pitched roofs, flat roof insulation is often laid above or below the roof deck depending on the construction style. The primary goal of this insulation is to reduce heat loss in winter and minimize heat gain during summer, keeping your indoor environment comfortable year-round. 

At Aqviz, we always integrate insulation into our waterproofing solutions to prevent condensation and maintain consistent indoor temperatures. High-quality roof insulation also extends the lifespan of your roofing materials by reducing thermal stress and helping prevent the formation of moisture pockets under the membrane.

What Waterproofing Method is Recommended for Flat Roofs?

The most reliable and long-lasting waterproofing method we recommend for flat roofs is the liquid-applied membrane system, particularly PU (Polyurethane) or Acrylic-based coatings. These systems form a seamless, elastic, and fully adhered waterproof layer that adapts to the roof surface and remains effective even under thermal movement.

At Aqviz, we’ve found that liquid-applied waterproofing provides superior resistance to UV exposure, water ponding, and minor structural shifts. It’s especially effective when combined with a primer and reinforced mesh in vulnerable areas like flashing joints and drainage points. This method is not only moistureproof but also helps achieve a completely impervious roof, which is crucial for flat roof structures that experience more standing water than sloped alternatives.

Read More About: How to Waterproof a Concrete Roof?

How Does a Flat Roof Drainage System Work?

A flat roof has a slight slope and flat roof drainage system includes scuppers, interior drains, and gutters. Slight slope direct the water one direction and roof drainage system channel the water efficiently away from the roof. 

Scuppers

Scuppers are rectangular openings cut into the edge or parapet wall of a flat roof. They allow water to exit directly from the roof’s edge, often connected to downspouts or allowed to drain freely away from the building. Scuppers are ideal for flat roofs with minimal slope and are best paired with metal flashing to resist corrosion. 

Interior Drains

Interior drains are positioned in the center or low points of the roof and connect to internal piping that directs water safely away through the building’s plumbing system. These are common in commercial and larger residential buildings where water needs to be hidden from exterior walls.

Interior drains are perfect for roofs with larger surface areas. When paired with proper roof insulation and drain flashing, they offer a leakproof solution even during heavy downpours. 

Gutters and Downspouts

Gutters and downspouts are external drainage components that collect rainwater from the roof’s edge and channel it down to ground level. They’re often used in combination with scuppers for added efficiency in removing water from flat roof surfaces.

How to Prevent Leaks on Flat Roof Joints?

If your flat roof joint tends to leak, you should follow the 7 steps below to fix it.

1. Use high-quality waterproofing membranes with excellent adhesion properties.
2. Apply sealant generously around joints, seams, and flashing overlaps.
3. Reinforce with mesh tape or fabric embedded in a liquid membrane for extra strength.
4. Ensure smooth surface leveling to avoid water pooling around joint areas.
5. Inspect roof joints regularly, especially after storms or seasonal changes.
6. Add flashing details properly where the roof meets vertical surfaces or protrusions.
7. Conduct water tests post-installation to identify hidden weak spots.

This 10 Ways To Stop Roof Leaking guide will help you to stop roof leaking permanently.

What are the Uses of Flat Roofs?

Flat roofs offer functional living spaces that enhance both lifestyle and property value. Flat roofs can be converted into roof decks and roof terraces. These spaces turn underutilized areas into extensions of your home, especially valuable in urban settings where outdoor space is limited. Before you use flat roofs, you should waterproof, insulate, and make a proper drainage system on the flat roof to protect it from water and sunlight. 

Roof Deck

A roof deck is a structural platform built over a flat roof. Roof decks are typically made from wood, composite, or concrete materials. It’s designed to support foot traffic, furniture, and recreational activities, serving as a place for relaxation, socializing, or dining outdoors.

Read More About: What You Should Know About Roof Deck Waterproofing

Roof Terrace

A roof terrace is a landscaped or semi-landscaped area on top of a flat roof, often featuring potted plants, seating zones, pergolas, or even outdoor kitchens. It offers a more permanent and decorative outdoor living experience.

Difference Between Roof Deck and Roof Terrace

A roof deck is usually a flat, open space intended for general use and recreation, while a roof terrace is more refined and landscaped, offering an aesthetic and luxurious outdoor environment.

What is the Impact of a Flat Roof in a Hot Climate?

In hot climates, flat roofs tend to absorb more heat due to their wide, horizontal surface exposed directly to the sun. This can lead to increased indoor temperatures, making the home harder to cool and driving up energy bills. The lack of slope also means less natural ventilation compared to pitched roofs. 

What is the Impact of a Flat Roof in a Cold Climate?

Flat roofs in cold climates present a different set of challenges. Snow and ice can accumulate and remain longer on the surface due to limited slope, increasing the risk of water infiltration, ice dams, and structural strain. If water penetrates any weak spot, it may freeze, expand, and worsen the damage.

What are the Famous Flat Roof Buildings?

Flat roofs are used all over the world. So here are some renowned buildings known for their flat roof designs.

1. Villa Savoye: France (Le Corbusier’s modernist icon)
2. Fallingwater: USA (Frank Lloyd Wright’s architectural marvel)
3. Bauhaus Dessau: Germany (symbol of minimalist modernism)
4. The Farnsworth House: USA (glass-walled residence with flat roof)
5. Barcelona Pavilion: Spain (Mies van der Rohe’s timeless structure)
6. The Getty Center: USA (a masterpiece of architecture and landscape)
7. UN Headquarters: New York, USA (international symbol of diplomacy)
8. Apple Park Main Building: USA (circular flat roof design)
9. Tel Aviv’s White City: Israel (Bauhaus-inspired flat roofs dominate the skyline)
10. The Broad Museum: USA (flat roof integrated with artistic design)

What are the Pitch Roofs?

A pitched roof is a roof structure with a noticeable slope or incline, typically ranging from 14° to over 45°. Pitch roofs are designed to efficiently shed rainwater and snow. This sloped design is one of the oldest and most common roofing types, particularly in residential construction.

Pitched roofs using materials like asphalt shingles, clay tiles, or metal roofing. These roofs offer excellent drainage and weather protection, reducing the risk of water pooling during rain and snow. The roof pitch also enhances durability in harsh climates and allows for attic or loft spaces beneath the roofline.

What is the Difference Between a Flat and Pitched Roof?

The key difference between a Flat and Pitched roof lies in slope and functionality.

Flat Roofs have a minimal slope (usually under 10°) and are known for their modern look and usable surface space. Pitched Roofs feature a steep slope, allowing for natural drainage of water and snow.

Flat roofs require precise roof sealing, drainage systems, and insulation to prevent water buildup while pitch roofs are typically lower maintenance in terms of waterproofing but offer less usable rooftop space, while flat roofs are ideal for urban areas and eco-friendly designs like green or solar roofs, pitched roofs are favored in regions with heavy rainfall or snow. 

What are the 9 Roof Types?

These are the 9 types of roofs types such as.

1. Gable roof
2. Hip roof
3. Mansard roof
4. Gambrel roof
5. Shed roof
6. Butterfly roof
7. Bonnet roof
8. Flat roof
9. Low-slope roof

What are the Water Damages on Flat Roofs?

A flat roof can be damaged by the water in various ways. These are the most common 5 types water damage on flat roofs.

1. Roof aligatoring
2. Roof blistering
3. Roof seepage
4. Ceiling cracks
5. Roof leaking 

Read More About: 13 Types of Roof Damages and How to Prevent Them?