Tar and Gravel Roof Pros and Cons: A Comprehensive Guide

Tar and gravel roofs, also known as built-up roofs (BUR), offer a long-standing option for flat or low-slope roofing in many American homes and commercial buildings. This guide examines the advantages and drawbacks, typical lifespans, maintenance needs, installation considerations, and cost factors. By understanding the pros and cons, homeowners and builders can decide if a tar and gravel roof aligns with climate, budget, and long-term performance goals.

Overview Of Tar And Gravel Roofs

Tar and gravel roofs are constructed from multiple asphalt or coal tar layers bonded together with hot or cold asphalt and topped with a layer of protective gravel or ballast. The ballast protects the roof from UV exposure, aids drainage, and provides ballast to resist wind uplift. These roofs are most common on low-slope commercial buildings and some residential flat-roof applications in the United States. The system is known for strong waterproofing when properly installed, but requires periodic maintenance to manage wear and membrane protection.

Tar And Gravel Roof Pros

• Proven Waterproofing: Built-up roofs create a durable, continuous barrier that resists water intrusion when installed correctly.
• Low-Slope Suitability: Ideal for flat or gently sloped rooftops where other roofing types struggle with drainage.
• Long Track Record: BUR systems have decades of performance data in varied climates, making them a trusted option for many projects.
• Thermal and Sound Accommodations: The layered design provides good thermal resistance and can help dampen outdoor noise in some applications.
• Economical For Large Areas: Per-square-foot cost can be favorable for large commercial roofs, especially when lifecycle costs are considered.

Tar And Gravel Roof Cons

• Maintenance Intensity: Periodic re-ballasting, membrane inspections, and crack repairs are common to maintain performance.
• Weight Considerations: Gravel ballast adds substantial weight; structural assessment is necessary for existing buildings.
• Solar Reflectivity: The gravel surface absorbs heat; some systems use lighter colored ballast but may reduce durability or increase costs.
• Walking and Access Limits: Service access and foot traffic can damage the surface if not properly protected.
• Labor-Intensive Installation: Installation requires skilled labor and multiple layers, potentially increasing lead times.

Durability And Lifespan

Tar and gravel roofs typically show a lifespan ranging from 15 to 30 years, depending on climate, maintenance, and installation quality. In harsher environments with temperature extremes or heavy hail, repair frequency may increase. Regular inspections, prompt leak repairs, and ballast reapplication help maximize longevity. UV exposure and aging of the underlying asphalt can influence performance, making periodic rejuvenation or resealing beneficial in some markets.

Maintenance Considerations

Maintenance for BUR systems includes inspecting for blisters, cracks, punctures, and seam separation. Gravel ballast should be checked for displacement, with any exposed membrane repaired to prevent erosion. Drainage conditions must be monitored to prevent water pooling. In coastal or freeze-thaw regions, extra attention to edge details and flashing reduces moisture ingress. A professional roof inspection every 2–4 years, plus targeted repairs as needed, keeps the system reliable.

Cost And Value

Initial installation costs for tar and gravel roofs vary by region, roof size, and complexity but are often competitive for large, flat commercial roofs. Ongoing costs include periodic maintenance, ballast reapplication, and potential membrane replacement. When evaluating lifecycle cost, BUR systems can be economical due to proven waterproofing, relatively simple field repairs, and a long service life when well maintained. Financing terms and local labor rates affect the total cost over time.

Installation Considerations

Professional installation is essential for BUR performance. The process involves layering asphalt or coal tar, reinforcing fabrics, and applying a gravel ballast. Key considerations include:

• Structural capacity to carry ballast weight
• Proper ventilation and insulation to prevent heat buildup
• Quality of asphalt or coal tar, with attention to compatibility with climate
• Seam integrity and flashing at parapets, skylights, and vents
• Quality of ballast material and ballast confinement systems

Environmental And Energy Implications

Tar and gravel roofs can offer durable waterproofing with long service life, reducing replacement frequency. The ballast material and asphalt components have environmental considerations, including potential volatile organic compound (VOC) emissions during installation. Some markets encourage reflective or cool-roof ballast in hot climates to reduce cooling loads. Selecting low-VOC products and proper aging practices can mitigate environmental impact.

When Tar And Gravel Makes Sense

Tar and gravel roofs are a practical option for large, flat or low-slope buildings where a proven waterproofing system is prioritized, and where regular maintenance is feasible. Regions with extreme temperature swings, heavy rainfall, or high wind uplift may benefit from additional ballast or a more modern membrane technology. If future roof access and maintenance are concerns, a contractor should assess accessibility and long-term maintenance plans before choosing BUR over alternatives.

Alternatives To Tar And Gravel

• Single-Pply Membranes such as TPO or EPDM offer excellent reflectivity and lighter weight, with simpler installation and often lower maintenance.
• Modified Bitumen combines asphalt with reinforcement for enhanced durability and flexibility, suitable for medium-slope roofs.
• Metal Roofing provides long life, high resistance to weather, and is increasingly used on retrofit projects with low slopes.
• Hybrid Systems combine BUR with newer membranes for improved performance and reduced weight.

Key Takeaways: Tar and gravel roofs deliver reliable, well-understood waterproofing for flat to low-slope structures, with strong longevity when properly maintained. They require careful installation, ballast management, and ongoing inspections to maximize life and performance. For projects prioritizing proven protection and cost efficiency on large roofs, BUR remains a viable choice, though modern alternatives may offer better energy efficiency and lighter weight in some cases.