What Is a Built Up Roof?: A Durable & Time-Tested Roofing Choice!
Building owners prioritize durability, cost-effectiveness, and longevity when selecting roofing systems. A Built-Up Roof (BUR), often called a tar and gravel roof, has been a trusted solution in the industry for over a century. Known for its multi-layered construction, BUR combines bitumen, reinforcing fabrics, and protective surfacing materials to create a seamless, weather-resistant barrier. This tried-and-true roofing system has stood the test of time, proving its reliability in commercial and residential applications.
Whether you’re looking for a robust solution for a flat or low-slope roof or need a system that offers superior waterproofing and energy efficiency, BUR is a strong contender. However, like any roofing system, it has its advantages and challenges. In this guide, we’ll explore everything you need to know about Built-Up Roofing—from its components and benefits to maintenance tips and comparisons with other roofing systems—so you can make an informed decision for your property.
Why Choose a Built Up Roof System?
Opting for a Built-Up Roof (BUR) system means choosing superior protection and long-term reliability. Its multiple layers create a redundant, waterproof surface, ensuring the others provide protection even if one layer is compromised. With proper maintenance, a BUR can last anywhere from 15 to 40 years and sometimes even up to a century.
Additionally, BUR systems are highly energy-efficient. Modern features like white-coated cap sheets and rigid insulation enhance reflectivity, reducing heat absorption and keeping interiors cooler. This makes BUR an excellent choice for buildings in harsh climates. From my experience, most roofing projects I have overseen demonstrate that BUR systems provide an extended lifespan and have warranties that enhance their value and appeal. Whether upgrading an existing roof or installing a new one, BUR systems offer a dependable, cost-effective solution.
How Long Does a Built Up Roof Last?
A built-up roof is constructed with multiple plies of asphalt-impregnated materials, such as reinforcing fabric layers and fibreglass mats, which are adhered together using hot asphalt or cold-applied adhesive. This assembly forms a watertight barrier that protects against water intrusion, UV damage, and environmental stressors like temperature fluctuations and severe weather. The durability of this system is further enhanced by the inclusion of reinforcing felt and a mineral-surfaced cap sheet, which adds an extra layer of protection against UV radiation and moisture.
The flexibility of a built-up roof allows it to withstand environmental stress while maintaining structural integrity. Critical components such as flashing around walls, vents, and chimneys and waterproofing at joints and transitions ensure long-lasting functionality. The incorporation of slag or mineral granules not only improves performance but also adds weight for stability. When paired with insulation materials like polyiso or a cover board, BUR systems become a robust barrier against environmental factors, ensuring longevity with proper care.
Components of a Built-Up Roof System
A built-up roof consists of several key components that work together to create a durable and functional roofing system:
- Base Sheet: Typically made of asphalt-impregnated materials, the base sheet adheres to the structure using hot asphalt or cold-applied adhesive.
- Reinforcing Layers: Various reinforcing fabrics, such as fibreglass mats or polyester, are layered with bitumen to form a strong, watertight barrier capable of withstanding temperature fluctuations and environmental stress.
- Top Layer: A mineral-surfaced cap sheet, slag, or gravel provides additional protection against UV damage and moisture.
- Flashing & Waterproofing: Seals around walls, chimneys, and vents prevent leaks and ensure adaptability to vertical surfaces and other structures.
- Insulation: Materials like polyiso or a cover board enhance energy efficiency, provide additional stability, and improve overall system performance.
- Surface Coating: Mineral granules or reflective coatings increase UV resistance and help maintain the adhesive bonds within the system.
These components create a highly durable roofing system that protects against environmental elements.
How Do Built-Up Roofing Systems Work?
Built-up roofing systems are designed to provide durability and resistance against harsh elements like wind, fire, and extreme temperatures. These systems are constructed by layering roofing felts or ply sheets—typically made of fibreglass or tar fabric—bonded together using bitumen or cold-applied adhesive. The process begins with a base sheet installed over the roof deck, followed by multiple reinforcing fabrics and asphalt layers to create a sturdy, seamless barrier. This installation method ensures the system remains resilient against environmental stress while maintaining aesthetic versatility.
One key benefit of built-up roofing systems is their ability to reduce energy costs. By incorporating surfacing aggregate or a reflective roof coating, these roofs improve energy efficiency by reducing cooling requirements, particularly on flat or low-slope structures. From my experience, combining BUR roofing membranes with coal tar or bitumen creates a fire-resistant, durable surface that is both functional and long-lasting. Whether prioritizing durability or energy efficiency, built-up roofing systems consistently deliver exceptional performance.
Advantages of Built-Up Roofing
- Cost-Effective: BUR systems are budget-friendly and have low repair costs.
- Durability: Built with protective bitumen and fibreglass layers, BUR withstands weathering, UV rays, and sun damage, lasting up to 100 years.
- Low Maintenance: BUR requires minimal upkeep when properly installed and inspected regularly.
- Energy Efficiency: Reflective mineral granules and insulation minimize heat absorption, reducing energy consumption and improving cooling.
- Flood Protection: The reinforced roof membrane prevents water penetration, adding flood resistance.
- Flame Resistance: Provides an extra layer of fire protection for the structure.
- Redundancy: Multiple layers ensure continued protection even if one layer is compromised.
- Warranties: Typically includes warranties of up to 20 years, ensuring peace of mind.
- Versatility: Well-suited for commercial buildings, high-rises, and low-slope structures, offering durable protection in various environments.
Disadvantages of Built-Up Roofing
- Water Pooling: Poor slope design can lead to ponding water, causing surface deterioration over time.
- Surface Damage: The top layer is susceptible to blistering, cracks, and separation, especially in extreme weather conditions.
- Foot Traffic Sensitivity: Frequent foot traffic and heavy equipment may cause tearing or warping, requiring repairs.
- Complex Installation: Requires skilled professionals for proper torch-down application and underlayment placement.
- Maintenance Needs: Without routine inspections, surface waves and undulations can worsen.
- Preventive Measures: Regular patchwork and moisture control are crucial to avoid expensive repairs or replacements.
- Fire and Moisture Risks: Poor maintenance can increase the risk of fire hazards or steam-related warping.
Challenges of a BUR Membrane System
A Built-Up Roof (BUR) system, commonly used on low-slope roofs, faces several challenges that can lead to early failure:
- Ponding Water: Poor drainage can cause water accumulation in depressions. For example, a 10’ x 10’ area with 1” of standing water adds over 520 lbs of weight, potentially leading to sagging. This excess weight, along with debris, accelerates roof breakdown.
- Moisture Infiltration: Rain, snow, or condensation can seep into asphalt layers, leading to cracks and leaks.
- HVAC and Ventilation Issues: Stagnant water evaporates at ¼” per day, while condensation from HVAC units or kitchen and bathroom vents can increase moisture buildup.
- Point Loads and Roof Penetrations: Rooftop equipment like air conditioning units and vents create pressure points, causing roof depressions and leaks.
- Insulation Degradation: Exposure to moisture can degrade insulation, impacting building energy efficiency.
Protecting Your BUR Membrane System
To extend the lifespan of your BUR system, follow these maintenance practices:
- Regular Inspections: Clean and inspect ponding areas frequently; water left for over 48 hours can cause damage.
- Drainage Maintenance: Keep roof drains clear to prevent water accumulation.
- Seal Vulnerable Areas: Address penetration points like vents, HVAC units, and rooftop structures to prevent leaks.
- Temperature Adaptation: Expansion and contraction due to temperature fluctuations can cause cracks. For resealing, use materials like rubberized asphalt cement or KarnaFlex SEBS Mastic.
- Protective Coatings: Applying silicone or other protective coating can prevent deterioration and extend roof life.
- HVAC Considerations: Ensure rooftop equipment is appropriately supported and resealed regularly to prevent structural stress.
Comparing BUR to Other Roofing Systems
When selecting a roofing system, consider how BUR compares to alternative options:
- Metal Roofing vs. BUR: Metal roofs last up to 70 years, whereas BUR typically lasts 20-30 years. Metal roofing is more flexible and waterproof but has a higher initial cost. BUR is more affordable and easier to install.
- EPDM vs. BUR: EPDM, a single-ply system, is cost-effective and has a similar lifespan, but BUR is more resistant to punctures and UV damage.
- Modified Bitumen vs. BUR: BUR is highly tear-resistant, whereas modified bitumen is easier to install with self-adhered cap sheets. Modified bitumen offers good UV protection but may not perform as well in extreme weather.
- TPO vs. BUR: TPO offers better energy efficiency and is ideal for hot climates. However, BUR is more tear-resistant and has a lower upfront cost, making it suitable for high-traffic areas.
By understanding the advantages, challenges, and maintenance needs of BUR systems, building owners can make informed decisions to maximize roofing durability and performance.
Conclusion
Built-up roofing has long been a staple in the construction industry. It offers durability, weather resistance, and cost-effectiveness for commercial and residential buildings. Its multi-layered design ensures redundancy, making it one of the most reliable flat roofing options. However, proper maintenance, drainage solutions, and regular inspections are essential to maximizing its lifespan.
Choosing the right roofing system depends on various factors, including climate, budget, and maintenance capabilities. While BUR provides excellent waterproofing, fire resistance, and longevity, building owners must weigh its installation complexity and potential for surface wear against alternative roofing options. By understanding the strengths and challenges of BUR systems, you can make a well-informed decision ensuring long-term property protection.
What Is a Built Up Roof? (FAQs.)
Q: What is a Built-Up Roof (BUR)?
Ans: A Built-Up Roof (BUR) is a multi-layered roofing system consisting of alternating bitumen (asphalt or coal tar) and reinforcing fabrics with a protective surfacing material like gravel or a reflective coating. Due to its durability and waterproofing properties, it is commonly used for flat and low-slope roofs.
Q: How long does a Built-Up Roof last?
Ans: A BUR system can last 15 to 40 years with proper installation and maintenance, sometimes even up to 100 years. Climate, drainage, and routine inspections are crucial in extending its lifespan.
Q: What are the main advantages of BUR?
Ans: BUR systems are known for their durability, waterproofing, fire resistance, and energy efficiency. Their multi-layer construction provides extra protection, ensuring longevity and reducing the risk of leaks. Additionally, they require minimal maintenance compared to other roofing options.
Q: What are BUR’s everyday challenges?
Ans: Some potential challenges include ponding water, susceptibility to surface damage from extreme weather, and a complex installation process that requires skilled professionals. Additionally, minor issues can develop into costly repairs over time without proper maintenance.
Q: Is BUR a good choice for all buildings?
Ans: BUR is ideal for flat and low-slope commercial buildings, high-rise structures, and even some residential properties. However, alternative roofing options like TPO or metal roofing may be worth considering for buildings with excessive foot traffic or extreme weather fluctuations.
