Tar and Gravel Roof: Complete Guide for Commercial Buildings

If you manage a commercial building with a flat roof covered in small stones, you likely have a tar and gravel roof. This roofing system has been protecting buildings for over a century and remains a practical choice for many property owners today.

A tar and gravel roof uses multiple layers of asphalt and reinforcing fabric topped with gravel to create a durable waterproof barrier that typically lasts 20-30 years. The system works through redundancy-if one layer develops an issue, the other layers continue protecting the building. The gravel surface shields the waterproofing layers from sun damage and provides excellent fire resistance.

Understanding how these roofs work, what maintenance they need, and when repairs make sense helps property managers make smart decisions about their buildings. This guide covers everything from installation and common problems to repair options and how tar and gravel roofing compares to modern alternatives like TPO and EPDM systems.

What Is a Tar and Gravel Roof?

A tar and gravel roof is a multi-layered flat roofing system that has protected commercial and residential buildings for over 100 years. This type of roof is also called built-up roofing or BUR.

The roofing system gets its name from its two most visible components: tar (actually asphalt bitumen) and gravel. But there's more to it than just these two materials.

How the Layers Work Together

A built-up roof consists of several key layers:

• Base layer: Attached directly to the roof deck

• Alternating layers: Multiple plies of reinforcing fabric with hot asphalt between each layer

• Top coat: A thick layer of asphalt called a flood coat

• Gravel layer: Pea gravel or crushed stone spread across the surface

Most systems have between 3 and 5 plies. More plies mean better protection and longer life.

Why the Gravel Matters

The gravel layer does more than just look industrial. It protects the asphalt beneath from damaging UV rays that would otherwise break down the waterproofing. The stones also provide fire resistance and add weight to hold the roofing system in place during high winds.

Where You'll Find These Roofs

Built-up roofing works best on flat or low-slope roofs. Commercial buildings, warehouses, apartment complexes, and industrial facilities commonly use this system. Many older buildings in urban areas still have their original tar and gravel roofs because these systems can last 20-30 years or more with proper care.

What Makes Tar and Gravel Roofing Effective

Tar and gravel roofing works through a simple but powerful design. The system uses multiple layers of waterproofing material that work together to protect buildings. Each layer acts as a backup to the others, creating a thick barrier against water.

The Multi-Layer Defense System

BUR systems build protection through repetition. A typical roof includes 3 to 5 layers of reinforcing fabric with hot asphalt between each one. Water must break through several barriers before reaching the building interior. This design makes leaks much less likely than with single-layer roofs.

Gravel Protection Benefits

The gravel layer on top does more than just look industrial. It blocks harmful UV rays that would otherwise break down the asphalt over time. Without this protection, the waterproofing materials would wear out much faster. The stones also provide Class A fire resistance, the highest rating available for roofing systems.

Practical Performance Advantages

Built-up roofing handles foot traffic well, which matters for buildings with rooftop equipment. The thick construction adds thermal mass that helps reduce temperature swings inside the building. This can contribute to better energy efficiency compared to thinner roof systems.

Cost and Durability Balance

At $3 to $7 per square foot, tar and gravel roofing offers cost-effective protection. The system typically lasts 20 to 30 years with proper care. The weight of the completed roof (10 to 25 pounds per square foot) helps it resist wind damage without relying only on adhesives. The gravel surface also provides good impact resistance against hail and falling debris.

Key Limitations to Consider

Tar and gravel roofs have serious weight requirements that property managers must address before installation. These systems add 10-25 pounds per square foot to a building structure. Older buildings may need structural reinforcement to safely support this load.

Installation challenges include working with extremely hot asphalt that reaches 400-500°F. This creates safety risks and produces strong odors that can affect building occupants for several days. Professional installation is the only option, as specialized equipment and safety training are required.

Maintenance becomes more complex with gravel surfaces. Wind and foot traffic move gravel around over time, requiring periodic redistribution. The stones can also clog drains and gutters if not properly managed.

Weather and drainage issues pose ongoing concerns:

• Poor drainage allows water to pool on the surface

• Standing water accelerates deterioration and shortens roof life

• Cold weather, rain, or high winds delay installation schedules

• Repairs require removing gravel and cutting into multiple layers

The system works only on flat or low-slope roofs. Buildings with pitched roofs need different materials entirely.

Tar and gravel roofs have a traditional appearance with visible gravel that some property owners find less appealing than modern membrane systems. While repairs are possible, they involve more steps than patching single-ply membranes.

Building owners should verify their structure can handle the weight and confirm adequate drainage exists before choosing this roofing type. These factors directly affect long-term performance and total ownership costs.

How Tar and Gravel Roofing Is Installed

Installing a tar and gravel roof requires specialized equipment and professional expertise. The process begins with thorough surface preparation. Contractors inspect the roof deck for damage and ensure proper drainage slopes exist to prevent water pooling.

The installation follows a systematic layering approach:

1. Base sheet attachment - A base layer is mechanically fastened to the roof deck with screws or fasteners

2. Heating the bitumen - Asphalt is heated in specialized kettles to 400-500°F

3. Applying hot asphalt - Workers spread the hot bitumen using mops or spray equipment

4. Laying reinforcing fabrics - Felts or fiberglass mats are rolled onto the hot asphalt while it remains liquid

5. Building additional plies - More asphalt and fabric layers are added, with most systems using 3-5 plies total

6. Final flood coat - A thick layer of asphalt covers the top felt layer

7. Gravel application - Pea gravel is spread across the surface while the asphalt is still hot

Each layer of reinforcing fabric gets embedded in hot bitumen. This creates multiple waterproofing barriers that work together. More plies mean better protection and longer lifespan.

Safety is critical during installation. The asphalt reaches temperatures that cause severe burns. It also produces toxic fumes that require proper ventilation. Only trained professionals with the right equipment should perform this work.

The entire process typically takes 2-5 days depending on roof size. Weather conditions must be dry and mild for proper installation.

Typical Issues Found on Aging Tar and Gravel Roofs

As tar and gravel roofs age, certain problems become more common. Recognizing these issues early helps property managers plan repairs and avoid larger problems.

Blistering appears when air or moisture gets trapped between the roof layers. These bubbles can burst and create openings where water enters. Blisters often form when the roof was installed in humid conditions or when moisture works its way up from below.

Cracking and splitting develop as the bitumen loses flexibility over time. UV exposure and temperature changes cause the material to become brittle. Cracks allow water to penetrate the membrane and reach the roof deck.

Ponding water is a serious concern for flat or low-slope roofs. Water that remains on the roof for more than 48 hours after rain accelerates deterioration. Ponding breaks down the bitumen and can lead to leaks and structural damage if left unaddressed.

Gravel displacement happens when wind, rain, or foot traffic moves the ballast. Areas with thin or missing gravel lose protection from UV rays. The exposed membrane ages faster and becomes more vulnerable to damage.

Flashing failures occur around roof edges, vents, and other penetrations. Metal flashing can rust, and sealants dry out and crack. Most leaks start at these weak points rather than in the main roof surface.

Edge lifting develops when the membrane pulls away from the roof perimeter. Wind can get under loose edges and cause more damage. Regular inspections help catch edge problems before they spread.

Repair Strategies That Actually Work

Tar and gravel roofs require specific repair methods to maintain their protective seal. The most effective approach starts with properly cleaning the damaged area and removing loose gravel to expose the tar layer beneath.

Surface Preparation Steps:

• Sweep away all loose gravel from the repair zone

• Clean the area with a broom or blower to remove debris

• Let the surface dry completely before applying materials

For small cracks and minor damage, silicone-based sealants work well as a quick fix. Property managers should apply the sealant directly into cracks and smooth it evenly across the surface. This method handles minor issues without requiring a full tar application.

Larger damaged areas need more attention. The repair process involves cutting out the damaged section of roofing material and replacing it with fresh tar and fabric layers. Workers apply hot tar or cold-process alternatives in thin, even coats to build up the protective barrier.

Key Materials for Repairs:

• Roofing cement or hot tar

• Fiberglass mesh or roofing fabric

• Matching gravel for surface protection

• Trowels and spreading tools

After applying new tar, the area needs a fresh layer of gravel. This protects the tar from UV damage and maintains the roof's weatherproof qualities. The gravel should match the existing surface and be pressed firmly into the tar while still tacky.

Timing matters for these repairs. Warm, dry weather allows materials to bond properly. Cold or wet conditions make tar difficult to work with and reduce repair effectiveness.

When It's Time to Replace

Most tar and gravel roofs reach the end of their useful life between 20 and 25 years, though proper maintenance can extend this timeline. Property managers need to evaluate several factors beyond age alone, including recurring leaks, exposed intermat, and the cost of ongoing repairs versus replacement.

Replacement Options Suitable for Commercial Buildings

When a tar and gravel roof reaches its limit, commercial property owners have several proven replacement options. Modified bitumen roofing offers similar waterproofing benefits with enhanced durability and easier repairs. This system uses polymer-modified asphalt sheets that resist thermal shock better than traditional tar and gravel.

TPO (thermoplastic polyolefin) and EPDM (rubber membrane) roofing provide lightweight alternatives that work well on flat commercial structures. These single-ply membranes reflect heat effectively, which can lower cooling costs.

Some facilities choose spray polyurethane foam roofing, which creates a seamless barrier and adds insulation value. This option works particularly well for buildings with complex roof layouts or multiple penetrations.

Built-up roofing systems remain available for those who prefer the proven track record of layered construction. Modern versions incorporate improved materials like fiberglass reinforcement and elastomeric coatings that address the traditional weaknesses of older tar and gravel installations.

The right choice depends on budget, building use, local climate conditions, and long-term facility plans.

Maintenance That Extends Roof Lifespan

Taking care of a tar and gravel roof properly can add many years to its service life. Regular attention helps these roofs reach their full potential of 20 to 25 years or more.

Inspection Schedule

Property managers should arrange roof inspections at least twice per year. Spring and fall are the best times to check for problems. These regular checkups catch small issues before they turn into expensive repairs.

During inspections, trained professionals look for these common problems:

• Missing or displaced gravel

• Cracks or blisters in the tar surface

• Clogged drains or standing water

• Damaged flashing around vents and edges

Limiting Foot Traffic

Walking on tar and gravel roofs causes damage over time. Each step can move the gravel layer and expose the tar underneath to harmful sun rays. Limiting unnecessary roof access can extend the roof's life by up to 50%.

When workers need to access the roof, they should use walk pads or boards. These items spread out body weight and protect the surface.

Quick Repairs

Fixing problems right away prevents bigger damage later. Small cracks can be sealed with roofing membrane. Larger damaged areas may need section replacement.

Professional Service

Some maintenance tasks need expert help. Professional roofers have the right tools and training to spot hidden damage. They can perform thorough repairs that keep the roof performing well for decades. Regular professional maintenance often doubles a roof's expected lifespan compared to neglected systems.

How Tar and Gravel Roofs Compare to Other Systems

When evaluating flat roofing options for commercial properties, tar and gravel systems stand alongside several modern alternatives. Each low-slope roofing material offers distinct advantages depending on building requirements and budget considerations.

TPO (Thermoplastic Polyolefane) membranes cost $5-8 per square foot and provide energy efficiency through their white reflective surface. However, they lack the proven track record of tar and gravel roofs and may not handle heavy foot traffic as well.

EPDM (rubber membrane) systems run $4-6 per square foot with easier installation than built-up roofing. The single-layer design means no redundant protection if punctures occur, unlike the multiple layers in tar and gravel construction.

Modified bitumen shares similarities with built-up roofing but uses fewer layers. Installation costs range from $3-6 per square foot. This system offers some redundancy but less than traditional tar and gravel applications.

PVC roofing provides excellent chemical resistance at $6-10 per square foot. The higher cost and heat-welded seams require specialized installation skills that exceed the expertise needed for other low-slope roofs.

Tar and gravel systems excel in specific situations where other roofing materials fall short. The gravel surface withstands foot traffic better than exposed membranes. The multi-layer construction provides superior leak protection through redundancy. Fire resistance meets Class A ratings without additional treatments.

Weight requirements distinguish tar and gravel from lighter alternatives. Buildings must support 10-25 pounds per square foot compared to 1-3 pounds for single-ply membranes. Property managers should verify structural capacity before selecting this system.

Installation complexity varies significantly among flat roofing options. Single-ply membranes install faster with less odor than hot-applied tar and gravel systems. The proven durability and repairability of built-up roofing often justify the more involved installation process.

What Owners Want to Know Most

Property owners typically want straight answers about three key areas: cost, lifespan, and maintenance requirements.

How much does a tar and gravel roof cost? Installation ranges from $3 to $7 per square foot, depending on the number of plies. A 3-ply system costs $3-4 per square foot and lasts 15-20 years. A 4-ply system runs $4-5 per square foot with a 20-25 year lifespan. The most durable 5-ply system costs $6-7 per square foot and can last 25-30 years or more.

Can the building support the weight? This concerns many owners considering tar and gravel roofing. These systems weigh 10-25 pounds per square foot. Buildings constructed before the 1970s or with lightweight framing may need structural evaluation. A structural engineer can determine if reinforcement is necessary.

What maintenance is required? Owners should inspect the roof twice yearly and after severe storms. Gravel needs redistribution every few years as wind and foot traffic move it around. Drains and scuppers need clearing of debris and gravel. Small problems should be addressed quickly to prevent larger issues.

How long will it last? A properly installed and maintained tar and gravel roof lasts 20-30 years. Some well-maintained systems reach 40 years. The number of plies, quality of installation, drainage design, and regular maintenance all affect lifespan.

Is it repairable? Yes, tar and gravel roofs can be patched and recoated. Damaged sections get cut out and replaced. The entire surface can receive a new flood coat and gravel layer to extend its life without complete replacement.

Why Property Owners Choose Crown Industrial Roofing

Crown Industrial Roofing brings decades of specialized experience in tar and gravel roof installation and maintenance across Toronto's commercial properties. The company has completed projects for small businesses, large corporations, property managers, and construction contractors throughout the region.

Comprehensive Flat Roofing Services

Crown Industrial Roofing offers a full range of commercial flat roofing services designed to protect buildings. Their team handles everything from new tar and gravel roof installations to repairs and emergency leak response.

Proven Track Record

Property managers and building owners trust Crown Industrial Roofing because of their extensive work with industrial buildings, warehouses, and multi-family residential properties. The company understands the unique demands of commercial roofing projects and the importance of minimizing disruption to business operations.

Professional Installation Standards

Crown Industrial Roofing follows strict safety protocols during hot asphalt application. Their crews use proper equipment and techniques to ensure each layer is installed correctly. This attention to detail helps tar and gravel roofs achieve their full lifespan potential of 20-30 years.

Long-Term Value Focus

The company provides detailed cost comparisons to help decision makers understand how tar and gravel roofing stacks up against other flat roof options. Their approach emphasizes long-term value rather than just upfront costs.

Crown Industrial Roofing works with clients to develop maintenance plans that extend roof life and prevent costly emergency repairs. Their knowledge of built-up roofing systems helps property owners make informed decisions about whether tar and gravel roofing fits their building's needs.

Schedule a Roof Assessment

Property owners with tar and gravel roofs should arrange regular professional inspections to protect their investment. A roof assessment identifies current problems and potential issues before they become expensive repairs or replacements.

Professional roofing contractors evaluate several key areas during an assessment:

• Overall condition of the gravel surface and coverage uniformity

• Drainage systems and signs of water ponding

• Flashing around penetrations, vents, and roof edges

• Bitumen layer integrity and visible cracks or blistering

• Structural deck condition and load capacity

• Age-related wear patterns and deterioration

Most roofing companies offer free initial assessments for commercial properties. During the visit, experienced technicians inspect all roofing components and document their findings with photos and detailed notes.

The assessment typically includes a written report that outlines immediate deficiencies, potential concerns, and recommended maintenance schedules. This documentation helps property managers budget for future repairs and make informed decisions about roof maintenance versus replacement.

Building owners should schedule assessments:

• Every 2-3 years for roofs under 15 years old

• Annually for roofs over 15 years old

• After severe weather events or suspected damage

• Before purchasing or selling commercial property

Crown Industrial Roofing provides thorough roof assessments that give property managers the information they need to plan maintenance budgets and avoid unexpected failures. Professional evaluation costs far less than emergency repairs from undetected problems.

Regular assessments extend roof lifespan by catching small issues early. A qualified contractor can spot warning signs that untrained eyes miss.

Frequently Asked Questions

Property owners often have specific questions about maintenance needs, expected lifespan, installation methods, benefits, climate considerations, and warning signs of damage for tar and gravel roofing systems.

What are the typical maintenance requirements for a tar and gravel roof?

Tar and gravel roofs need regular inspections twice per year, typically in spring and fall. These inspections check for gravel displacement, ponding water, and membrane damage.

Gravel requires redistribution every few years because wind and foot traffic move it around. Areas with thin gravel coverage expose the waterproofing layers to UV damage.

Drains and gutters need cleaning several times per year. Gravel can wash into drainage systems and cause blockages that lead to water pooling on the roof surface.

Small cracks or blisters should be repaired promptly to prevent water infiltration. Professional contractors can patch damaged areas by removing gravel, cutting out bad sections, and applying new layers with hot bitumen.

How does the lifespan of a tar and gravel roof compare to other roofing materials?

A properly maintained tar and gravel roof lasts 20 to 30 years. Some well-maintained systems reach 40 years or more with periodic recoating.

Three-ply systems typically last 15 to 20 years. Four-ply systems last 20 to 25 years, while five-ply systems can reach 25 to 30 years or longer.

TPO and EPDM single-ply membranes last 15 to 25 years on average. Modified bitumen roofs last 20 to 25 years. Metal roofing systems can last 40 to 70 years but cost significantly more upfront.

The multi-layer construction of tar and gravel roofs provides redundant waterproofing that extends lifespan. When one layer develops problems, the other layers continue protecting the building.

Can a tar and gravel roof be installed over an existing roofing system?

Installing a new tar and gravel roof over existing roofing depends on several factors. The existing roof must be structurally sound without significant damage or deterioration.

Building codes typically allow one or two layers of roofing on a structure. If the existing roof already has multiple layers, complete removal is required before installing new roofing.

The roof deck must support the additional weight. Tar and gravel roofs weigh 10 to 25 pounds per square foot, which adds substantial load to the structure.

Installing over existing roofing saves on tear-off and disposal costs. However, trapped moisture between layers can cause problems if the existing roof has leaks or water damage.

Most roofing professionals recommend complete removal when replacing a tar and gravel roof. This allows inspection of the deck and ensures the new system starts with a clean, dry surface.

What are the primary benefits of choosing a tar and gravel roof for a flat or low-slope structure?

The multi-layer construction provides excellent waterproofing through redundant barriers. Water must penetrate multiple layers before reaching the interior, which rarely happens.

Gravel surfacing delivers Class A fire resistance, the highest rating available. This makes tar and gravel roofing ideal for buildings where fire safety is important.

The gravel layer protects the waterproofing from UV radiation. This extends the roof's lifespan compared to exposed membrane systems that degrade from sun exposure.

Tar and gravel roofs handle foot traffic well. The gravel creates a stable walking surface for maintenance personnel accessing rooftop equipment.

Installation costs range from $3 to $7 per square foot, making tar and gravel roofing cost-competitive with other flat roofing options. The long lifespan of 20 to 30 years provides good value over time.

How does weather and climate affect the performance of tar and gravel roofing?

Tar and gravel roofs perform well in most climates when properly installed and maintained. The multi-layer design handles temperature extremes from hot summers to cold winters.

Ponding water is the biggest weather-related concern. Poor drainage allows water to pool on the surface, which accelerates deterioration and can lead to leaks. Proper slope of at least one-quarter inch per foot prevents this problem.

Hot climates benefit from gravel's reflective properties. Light-colored gravel reflects sunlight and reduces heat absorption compared to dark membrane roofs.

Cold climates require attention to thermal movement. The roof expands and contracts with temperature changes, which can cause cracking if the system lacks flexibility.

Heavy snow loads add weight to an already heavy roofing system. Buildings in snowy regions need strong structural support to handle the combined weight of the roof and snow accumulation.

Wind rarely damages well-installed tar and gravel roofs. The weight of the system resists wind uplift better than lighter roofing materials.

What are the common signs that a tar and gravel roof needs repair or replacement?

Interior water leaks are the most obvious sign of roofing problems. Water stains on ceilings or walls indicate the waterproofing layers have failed.

Blisters or bubbles in the roof surface show trapped moisture or air between layers. Small blisters can be repaired, but extensive blistering may require replacement.

Large areas of exposed black waterproofing indicate gravel loss. The bitumen becomes visible when gravel wears away, leaving it vulnerable to UV damage.

Ponding water that remains for more than 48 hours after rain signals drainage problems. Standing water accelerates roof deterioration and often indicates structural sagging.

Cracks or splits in the surface allow water penetration. These typically appear in areas with heavy foot traffic or where the roof meets walls and equipment.

A roof approaching 20 to 25 years old should be evaluated even without obvious problems. Age-related deterioration may not be visible from ground level but can be detected during professional inspection.