Flat Roof Waterproofing for Built-Up Roofing Systems

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Flat roofs are a common feature in commercial and industrial buildings. They provide numerous advantages, including easy access for Maintenance and installation of HVAC equipment. However, one of the primary concerns with flat roofs is their susceptibility to water leakage. This article aims to explore various flat roof waterproofing solutions specifically designed for built-up roofing systems, providing essential information to property owners, Contractors, and facility managers.

Understanding Built-Up Roofing Systems

Before diving into the waterproofing solutions, let us first understand what built-up roofing systems are. Built-up roofing (BUR) consists of multiple layers or plies of roofing felts alternated with bitumen layers. These felts are made from materials such as fiberglass, organic felt, or polyester and are saturated with bitumen to create a strong and durable membrane. The final layer is typically coated with small aggregate or gravel.

BUR systems have been used for decades and are known for their longevity, flexibility, and ability to withstand extreme weather conditions. However, over time, the bitumen layers can deteriorate, leading to water infiltration and potential damage to the building.

Flat Roof Waterproofing Solutions for BUR Systems

To ensure the longevity and effectiveness of built-up roofing systems, it is crucial to implement appropriate waterproofing solutions. Here are some popular options:

1. Liquid-Applied Waterproofing Membranes

Liquid-applied waterproofing membranes offer a versatile and seamless solution for flat roofs. These membranes are typically made of a combination of polymers and additives designed to provide exceptional durability and resistance to water intrusion. They are applied directly to the BUR system substrate, forming a continuous and watertight seal.

Benefits of liquid-applied waterproofing membranes include:

  • Ease of application: The liquid nature of the membranes allows for easy and efficient application, ensuring a quick installation process.
  • Seamless protection: The absence of seams reduces the risk of water infiltration and potential leaks.
  • Flexibility: These membranes accommodate the natural movements of the BUR system without compromising the waterproofing barrier.

2. Modified Bitumen Membranes

Modified bitumen membranes are another popular choice for waterproofing flat roofs with built-up systems. These membranes are manufactured from asphalt that is modified with synthetic rubber or plasticizers. The modification process enhances the membrane’s elasticity, elongation capabilities, and resistance to temperature fluctuations.

Advantages of modified bitumen membranes include:

  • Enhanced durability: The modified composition of the membranes enhances their resistance to aging, weathering, and UV radiation.
  • Easy Repairs: In the event of damage or punctures, modified bitumen membranes can be easily repaired, extending the roof’s lifespan.
  • Excellent waterproofing properties: The combination of bitumen and modifiers ensures a reliable and long-lasting waterproofing solution for flat roofs.

3. EPDM Membranes

Ethylene Propylene Diene Monomer (EPDM) membranes offer exceptional resistance to water penetration and are commonly used in flat roof waterproofing. EPDM is a synthetic rubber material known for its durability, flexibility, and longevity. These membranes are usually adhered or mechanically fastened to the underlying BUR system.

Key benefits of EPDM membranes include:

  • Long lifespan: EPDM membranes can last up to 40 years with proper installation and maintenance.
  • Excellent weather resistance: EPDM membranes perform well under extreme temperatures, UV radiation, and harsh weather conditions.
  • Low maintenance: EPDM membranes require minimal maintenance, resulting in cost savings over the roof’s lifetime.

Frequently Asked Questions (FAQs)

Q: How long do liquid-applied waterproofing membranes last?

A: Liquid-applied waterproofing membranes can last anywhere from 10 to 25 years, depending on the product quality, substrate conditions, and maintenance.

Q: Can modified bitumen membranes be installed on existing built-up roofing systems?

A: Yes, modified bitumen membranes can be installed directly over existing BUR systems, providing an efficient and cost-effective solution for roof refurbishment.

Q: Are EPDM membranes environmentally friendly?

A: Yes, EPDM membranes are considered environmentally friendly due to their low environmental impact during manufacturing, recyclability, and long lifespan.


Proper waterproofing is essential for preserving the integrity of built-up roofing systems. Liquid-applied waterproofing membranes, modified bitumen membranes, and EPDM membranes are all effective solutions for protecting flat roofs from water infiltration. When choosing a waterproofing solution, it is crucial to consider the specific needs of the building, budget constraints, and the advice of roofing professionals. By investing in the right waterproofing solution, property owners can ensure the longevity and performance of their flat roofs for years to come.

Cape Town Waterproofing

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