Understanding Built Up Roof Systems: A Comprehensive Guide

A built up roof (BUR) system is one of the oldest and most reliable types of roofing, particularly for commercial and industrial buildings. Composed of multiple layers of reinforcing fabrics and bitumen, this roofing method creates a durable, seamless membrane that offers exceptional protection against the elements. The term “built up” refers to the process of layering these materials, which are then topped with a protective surface. This article explores the components, benefits, installation process, maintenance, and comparisons of built up roof systems, providing a thorough understanding of why they remain a popular choice in construction.

The history of built up roofs dates back to the mid-19th century, and they have evolved significantly with advancements in materials and techniques. Traditionally, BUR systems used coal tar bitumen, but modern versions often employ asphalt bitumen due to its improved performance and environmental considerations. The core components include alternating layers of bitumen (asphalt or coal tar) and reinforcing fabrics, such as fiberglass or organic felts, which are built up to form a robust, multi-ply membrane. The number of plies can vary, typically ranging from three to five, depending on the desired durability and weather resistance. Finally, the surface is finished with a layer of aggregate, such as gravel or slag, or a reflective coating to enhance UV protection and energy efficiency.

One of the primary advantages of a built up roof is its exceptional durability and longevity. When properly installed and maintained, these roofs can last 20 to 30 years or more, making them a cost-effective investment. The multiple layers provide redundancy, meaning that if one layer is damaged, the others continue to offer protection, reducing the risk of leaks. Additionally, the surface layer of aggregate or coating offers excellent resistance to fire, UV rays, and physical damage from foot traffic or debris. This makes BUR systems ideal for flat or low-slope roofs common in commercial buildings, where water pooling and exposure are concerns.

The installation process for a built up roof is labor-intensive and requires skilled professionals. It begins with a thorough inspection of the roof deck, which must be clean, dry, and structurally sound. The first layer, known as the base sheet, is applied using hot bitumen or adhesives. Subsequent layers of reinforcing fabric are then embedded into heated bitumen, with each ply overlapping the previous one to ensure a watertight seal. This process is repeated until the desired number of plies is achieved. Finally, the surface is coated with bitumen and covered with aggregate or a reflective material. Proper installation is critical, as errors can lead to vulnerabilities like blisters or leaks.

Maintenance is key to maximizing the lifespan of a built up roof. Regular inspections, especially after severe weather, can identify issues early. Common problems include:

• Blisters: Caused by trapped moisture or air between layers, which can be repaired by cutting and sealing.
• Cracks: Often due to aging or thermal movement, requiring patching with additional bitumen and fabric.
• Ponding water: If not addressed, it can accelerate deterioration; solutions include improving drainage or adding tapered insulation.

Routine cleaning of drains and debris removal is essential. For minor repairs, materials like asphalt cement or patches can be used, but major damage may require professional re-roofing.

When compared to other roofing systems, such as single-ply membranes (e.g., EPDM or TPO) or modified bitumen, built up roofs offer distinct pros and cons. BUR systems are generally heavier and more expensive to install due to the material and labor costs. However, they provide superior impact resistance and longevity, outperforming many alternatives in harsh climates. Single-ply systems are lighter and easier to install but may be more prone to punctures. Environmentally, modern BUR systems can incorporate recycled materials and reflective coatings to improve energy efficiency, reducing the urban heat island effect. The choice depends on factors like building structure, budget, and climate conditions.

In conclusion, built up roof systems are a time-tested solution for commercial and industrial roofing needs. Their layered construction delivers unmatched durability, fire resistance, and protection, making them a reliable option despite higher initial costs. With proper installation and maintenance, a BUR can provide decades of service. As technology advances, innovations in materials and sustainability continue to enhance their performance, ensuring that built up roofs remain a relevant and valuable choice in the construction industry. For building owners seeking a robust, long-term roofing solution, understanding the intricacies of BUR systems is essential for making informed decisions.