Flat roofs have been around for a long time. Across the world especially in areas with high temperatures, flat roofs have been the roof of choice. In these areas the traditional method of building flat roofs was with concrete, this was not only cheap and easy to construct but was also very effective at protecting from the heat of the sun and the elements of weather. Flat roofs are very predominant in the American Southwest due to the high temperature of the region.

Flat roofs came into widespread use in the late 19th century when advances in technology brought about better waterproofing materials and the use of structural steels and concrete in building construction. These made flat roofs the main choice of roofing for high rise buildings, government offices, commercial property and some residential buildings. In fact, it was given legal backings as it was made the only roof of choice for high rise buildings in the building codes of major American cities.

Flat roofs are any roof structure with a roof pitch of less than 1.5 degrees. From a view, they are horizontal or near horizontal and they can be constructed using different materials and structure with different types of coating systems. It is important that you understand the differences between flat roof construction materials and the flat roof coating systems.

In some text and sources, the coating systems have sometimes been used to classify flat roofs and sometimes roughly interchanged with classifying flat roofs along the lines of material type. In this article I will clearly differentiate between material types for flat roofs and coating systems across the various types of flat roofs.

In the time past, flat roofs have only referred to roofs made of concrete but today many different materials have been used to construct flat roofs. We have flat roofs made from Concrete, Timber, Steel and fiber glass. In this article, I will educate you on the various materials and systems used in the construction of today’s flat roofs. I will also examine the challenges of this type of roofing and the possible solutions. It is important to note that we would be referring to both systems used in coating casted concrete roofs and other materials that are in use today for the construction of flat roofs (roofs with pitch of less than 1.5 degrees).


The major structure and materials of flat roofs include timber, concrete, steel and glass fiber.

Timber: This is the use of wood as roofing material and structure. Usually, there are wooden roofs made from tiles but with flat roofs made from wood, the roof material are usually ply woods. These are large sheets of wood that can the laid flat on the roof structure.  They very inexpensive and durable if properly maintained. These roofing material type is mostly found in country homes and garden sheds. The best form of coating for Timber flat roof type are the Single Ply and Liquid Membrane.

Concrete: This is the traditional flat roof material. Since the early days of flat roofs, this has been the material of choice for most builders and developers. In most cities in America, building codes stipulate that concrete is the only material of choice for flat roofs just as flat roofs are the only approved roof types for high rise buildings in most American cities.

Concrete roof structures are very durable and efficient. They can serve a multi purpose function of being a roof, a relaxation area, a packing lot or a landing base for helicopters. Like I have said before, only recently are cities like Los Angeles cleaning off their building codes that stipulate flat roofs (Concrete flat roofs) as the only roof type for high rise buildings. Concrete flat roofs can be insulated using any of the flat roof systems.

Steel: This is one of the flat roof materials that has gained traction and has become a popular choice for developers. It is visually appealing, requiring very little maintenance and it is very durable. Steel roofing for flat roofs started with the introduction of steel into building construction. They come in various materials such as Aluminum, Steel, Copper or Tin. Though, Copper and Tin seems to have been phased out leaving just Steel and Aluminum.

Steel roofing material can be coated and insulated using the liquid membrane, single ply or the green roof system. They can also stand alone as steel is water resistant but coating is advised to prolong and protect the useful lifespan of the roof.

Fiber Glass: This roof material type has just started to gain popularity. They are made from glass fiber as the name imply, they are durable and are highly efficient. Fiber glass are water resistant and as such would only require coating to protect the surface.


There are 4 systems of flat roofs I will be discussing today. Below is the list of the various systems applied to flat roofs.

  • Bitumen or Mineral felt
  • Liquid Membrane
  • Single Ply roofing
  • Green Roofs

Bitumen or Mineral Felt

This is usually applied to either timber or concrete slabs roofs. It is the oldest method of insulating and water proofing concrete slabs or Timber flat roofs. After the roof have been constructed, bitumen is then applied by screeding to the surface of the roof, this is to ensure that the roof is properly insulated and waterproofed in compliance with regulations.

This system is the most cost effective but not the most efficient as there have been cases of failure only after a short period of time. In fact, in the early days of flat roofs, this was the main system of insulation and waterproofing but due to its level of failure over time, it almost caused the flat roof a negative reputation. Further advancements in technology has brought a new lease of life to flat roofs and they are being reintroduced in the building and construction industry across America. It is today the roof of choice for most contemporary Designers and Architects.

Liquid Membrane

This is also known and marketed as EPDM Liquid roofing systems. They are liquid coating systems similar to the single ply but in this case, it is a liquid compound with adhesive components rather than plastic sheets. It is applied as single or double coats to most types of flat roofs. The Liquid Membrane system is quite efficient and effective but also comes with its own challenge.

Because one of the major components of the Liquid Membrane is adhesive, overtime, the adhesive seals wears off and they require regular maintenance making the Liquid Membrane system one of the most maintenance-intensive flat roof option.

Single Ply Coating

This is one of the very popular systems for flat roofs. It can serve as a covering for any of the traditional (Concrete, Timber or Steel) flat roof structures. This consists of very durable sheets of PVC plastics that comes in rolls. It is very effective at waterproofing and it serves as a good insulator. The PVC sheets are rolled and taped on the roof structure and they can last for up to 10 years without maintenance.

The PVC sheets comes in size range of 1.1 mm to 2 mm, some are homogeneous in their composition while others can be reinforced with glass fiber or polymer for added strength and durability. Asides the benefits of resisting ponding and effective waterproofing, the PVC system is also very cost effective. It is one of the cheapest and easiest to install and maintain flat roof option.

Green Roofs

This is the option of the 21st century. In our quest to go green and fight green house gases, government, city officials and property developers have come together to find ways to making buildings more energy efficient and also make our cities less polluted. The benefits of the green roofs are to create a cleaner environment and in large cities where they have been installed, they are meant to also serve as recreational and relaxation area for residents and occupants.

The green roof system combines any of the other roof systems with the cultivation of plants to give that insulation and visual appeal.

The green flat roof system consists of the drainage, the filter and the vegetation areas. Regular maintenance is required to ensure that the roof continues to be in great shape. It is also important that the roof structures are properly reinforced to withstand human traffic.


The image of flat roofs has been battered over time due to the failings of coating systems like the mineral felt (Bitumen Coating) which required regular and expensive maintenance but with advancement in the roofing technologies, flats are coming back and renewing its reputation. For one, flat roofs are the major choice for most contemporary designs and Architects are recently appreciating the visual allure of flat roofs.

The major challenge to all flat roof types and coatings is the failure of the coating material overtime. This can be mitigated by embarking on planned preventive maintenance on your roof structures.  Ensure also to always engage professionals in the maintenance of your roofs.