Tar and Gravel Roof Pros and Cons

Tar and gravel roofing, also known as built-up roofing (BUR) with a gravel ballast, is a long-standing option for low-slope commercial and some residential structures. This article outlines the key advantages and drawbacks, how it performs in different climates, maintenance needs, and typical cost considerations. Understanding the pros and cons helps homeowners and builders decide if tar and gravel roofing is the right choice for their project.

What Is Tar And Gravel Roofing

Tar and gravel roofing combines multiple asphalt or coal tar layers (plies) sealed with a protective surface, topped with a layer of loose stone or gravel. This ballast protects the asphalt from UV exposure, adds weight to resist wind uplift, and provides a long-lasting, watertight barrier on flat or low-slope roofs. The system can include vapor barriers and reflective coatings to improve energy performance. Correct installation and maintenance are critical to maximize durability.

Tar And Gravel Roof Pros

• Durability: BUR systems offer robust protection against wind-driven rain, hail, and temperature fluctuations, often lasting 20–30 years with proper care.
• Water Resistance: The layered construction is designed to shed water effectively, reducing penetration risks when installed correctly on low-slope surfaces.
• Excellent Waterproofing: The multiple plies provide redundancy; if one layer degrades, others continue to protect the structure.
• Fire Resistance: Traditional coal tar and asphalt plies contribute to a fire-resistant roof assembly in many climate zones.
• Sound and Insulation: The dense layers add insulation and can dampen impact noise, contributing to indoor comfort in some designs.
• Low Maintenance Needs: Compared with some membrane systems, BUR can require fewer frequent surface replacements once installed, though inspections are essential.
• Repairability: Localized repairs to plies or blisters are often straightforward, allowing targeted fixes without complete replacement.

Tar And Gravel Roof Cons

• Weight: The ballast and multiple plies create substantial weight, necessitating structural assessment and possible upgrades in some buildings.
• Installation Cost: Initial installation can be more expensive than single-ply membranes due to materials, labor, and the need for skilled workmanship.
• Labor-Intensive Construction: BUR installation is complex and requires experienced crews, which can impact timelines and costs.
• Maintenance and Repairs: While durable, BUR can suffer from blisters, cracks, and paving loss in hot climates; regular inspections are essential.
• Needing Proper Drainage: Poor drainage or ponding water can accelerate deterioration and cause leaks over time.
• Environmental Considerations: Petroleum-based materials raise concerns about environmental impact; recycling options exist but may be limited by local programs.
• Gravel Shedding: Gravel ballast can loosen or migrate, potentially impacting wind resistance and creating debris on surrounding areas.
• Limited Aesthetics: Some property owners prefer the cleaner look of modern single-pply membranes or reflective coatings.

Maintenance And Longevity

Proactive maintenance extends life and preserves performance. Schedule annual inspections to identify blisters, cracks, or separating plies, and check for ponding water on flat roofs. Keep the gravel ballast intact to protect the underlying membrane from UV exposure; replace gravel as needed to maintain even coverage. Periodic resealing and occasional re-surfacing—typically every 12–20 years depending on climate, traffic, and material quality—can restore water resistance and energy performance. Cleaning debris and ensuring proper drainage reduce wear and hidden damage.

Cost Considerations

Tar and gravel roofs involve higher upfront costs than some modern single-pply systems but often deliver favorable life-cycle pricing due to their durability. Key cost factors include square footage, roof complexity, local labor rates, and required structural enhancements for weight. Insurance premiums may reflect the roof type and its fire resistance and durability. A professional estimate should itemize plies, ballast, waterproofing layers, and any required insulation upgrades. Over the roof’s lifespan, maintenance and occasional re-coatings influence total cost of ownership.

Installation And Repairs

Professional installation by licensed contractors with BUR expertise is essential. The process includes surface preparation, ply installation, hot or cold application of asphalt or coal tar, and ballast topping. Regular inspections help catch issues early, enabling targeted repairs that are cost-effective and less disruptive than full replacement. For repairs, sections may be removed and re-layed, or localized patches applied, depending on access and the severity of damage. Ensure compatibility with any existing insulation and attic ventilation to maintain energy efficiency.

Environmental And Energy Considerations

Tar and gravel systems contribute to energy performance through reflective coatings and proper insulation, potentially reducing cooling loads in hot climates. However, the petroleum-based materials involve embodied energy and end-of-life disposal considerations. Some components are recyclable, and repurposing project waste minimizes environmental impact. When selecting products, consider reflective caps or cool roof finishes to enhance energy efficiency and mitigate heat absorption.

Choosing The Right Roofing System

Deciding whether a tar and gravel roof is appropriate depends on building type, climate, budget, and maintenance willingness. For flat or low-slope roofs in regions with strong wind or hail, BUR with gravel ballast offers durability and proven performance. If a lighter system or a highly energy-efficient solution is needed, alternatives like single-pply membranes or modified bitumen may be considered. A qualified roofing professional can assess structural load, drainage, and compatibility with existing components to tailor a long-term maintenance plan.