Flat roofing essentials – key stages and material options for a successful project

Flat roofs are a popular choice for commercial buildings, apartments, and even some residential homes. However, they come with a unique set of challenges when it comes to waterproofing. A flat roof must be completely waterproof to prevent leaks and water damage to the building’s interior. In this blog, we will provide a holistic overview of the flat roof waterproofing process and its considerations.

Key stages in a flat roofing project

There are several key stages in a flat roof waterproofing project.  Each is vital to ensure a quality and long-lasting outcome.


The age, structure, current condition and the type of materials already in use on the roof will all impact decisions on the best waterproofing materials and process for that project.

Undertaking a thorough inspection will identify any issues with the current roof that need to be addressed before new waterproofing work or replacement can take place:

  • Ponding: This is when water pools on the roof and can lead to leaks and damage. To resolve this the roof may need to be re-sloped using timber firings or by installing a specially designed cut to falls insulation system. Drainage systems can also be installed.
  • Blisters: These are caused by trapped air or moisture in the waterproofing material that have been caused by poor installation and can lead to leaks. As part of the preparation the blisters must be cut open, and the waterproofing material repaired.
  • Cracking: This can be caused by thermal expansion and contraction or movement in the building or poor application. Again, the cracked area must be repaired with a suitable waterproofing material.


Roof preparation

An essential step in the waterproofing process. Ensuring the roof is in the best possible condition for applying materials before any work commences will improve the outcome. Contractors need to remove all or any problematic existing roofing materials, clean the surface, remove any vegetation and repair any damage or leaks identified by the inspection. The roof must also be dry before any waterproofing can take place.


The roof is primed to ensure the waterproofing material adheres properly.  This will reduce the chances of future problems with cracking, blistering or leaks.


The waterproofing process typically involves applying a waterproofing membrane or coating to the roof’s surface. Multiple layers of the membrane or coating may be required to ensure complete waterproofing There are several options for waterproofing a flat roof so getting the right solution for the roof in question is essential.  The advice of an expert supplier can be of great value with this.


Once the waterproofing material has cured or set, the roof should be inspected for any defects that need to be fixed.

Choosing the best waterproofing solution

There are several types of waterproofing products available for flat roofs and deciding on the best solution is often where the expertise of a trusted supplier can be of real value.

Using the right solution at an acceptable cost will ensure an effective and long-lasting flat roof is in place, avoiding any future issues.

  • Liquid waterproofing:

Liquid applied roofing systems provide a cost-effective, flexible, high quality waterproofing solution for a wide range of flat roofs and surfaces.  Simple and easy-to-use, they cure to form a seamless membrane that provides excellent waterproofing.

Great for small or large areas, and where there are vents and other roof furniture to work around. With their high durability they are recommended for areas with regular foot traffic/plant access.

Liquid systems are also ideal for repairing and refurbishing existing roof coatings, reducing the need for replacement. And depending on the quality of the system used, the roof can be protected for between 10 and 25 years.

  • Bituminous membranes

Bituminous waterproofing materials are made from asphalt which is then combined with a variety of other materials to create a strong, durable barrier that is resistant to water and other environmental factors, including UV radiation, providing long-lasting protection for the underlying roof substrate.

Bituminous systems are typically installed in multiple layers, with each layer adding additional strength and waterproofing properties to the roof.  They can be customised to meet the specific needs of the roofing project, including the type of substrate being used and the specific weather conditions in the area. This flexibility makes bituminous membrane systems a popular choice for both new and refurbishment flat roofing projects.

Different bituminous membrane systems can be warm applied, using gas torches or hot asphalt, or flame free applied, building up the layers using self-adhesive membranes or  adhesive and welding the lap with hot air welders.

  • EPDM Rubber

EPDM (Ethylene Propylene Diene Monomer) rubber roofing is made from a high-quality synthetic rubber compound that is durable, weather-resistant, and long-lasting. EPDM roofing systems consist of large, seamless sheets of rubber that are mechanically fastened or glued to the roof substrate.

Overall, EPDM offers an easy to fit, cost-effective and reliable option for flat roofs that require a durable and low-maintenance with a superb lifespan if well looked after.

EPDM is less flexible in terms of application compared to liquid roofing systems so is more suited to roofs without complex shapes or structures.

  • TPO and PVC Membranes

These are single-ply membranes that are heat-welded and provide a long-lasting waterproofing solution.

TPO and PVC membranes are made from thermoplastic materials, which means they can be softened and moulded when heated and then solidify when cooled.

They are known for their strength, durability, and resistance to ultraviolet radiation, moisture, chemicals and punctures.

Both are available in a range of light colours, including white, gray, and tan, which help reflect sunlight and reduce cooling costs.

TPO and PVC membranes come in large rolls and are installed using hot-air guns to heat the membrane and the underlying surface, then weld them together to form a watertight seal. This can make them typically easier to than bituminous membranes and liquid waterproofing systems.


Flat roof waterproofing is an essential process to protect buildings from water damage. By choosing the right products and following the proper steps, flat roofs can be effectively waterproofed to ensure long-lasting protection for up to 25 years and beyond.

With such a choice of materials, we would recommend seeking expert advice on the most effective and affordable solution for your project, especially on projects of scale or complexity.

And finally flat roofs benefit from regular inspection to identify any issues as they arise.  Combined with a programme of regular maintenance will ensure the integrity of the roof can be maintained for many years.

With over 30 years of experience in commercial flat roofing supplies, and a reputation for outstanding customer service, our team at Lancastria are here to help and advise on the right waterproofing solution for your project. Our product range covers everything needed from liquid systems to bituminous membranes, ancillaries, tools and hot air welding equipment.

Contact us on 0161 777 9009 or email and we will be happy to help.



Get in touch

Where to find us…

Lancastria Group
Unit J, Woodrow Way, Irlam,
Manchester, M44 6ZQ

Contact Us