Tar and gravel roofs, commonly called built-up roofing (BUR), remain a durable choice for low-slope commercial and residential buildings; this article explains materials, installation, maintenance, costs, and common problems to help owners make informed decisions.
| Aspect | Quick Summary |
|---|---|
| Also Known As | Built-Up Roofing (BUR) |
| Typical Lifespan | 20–30 Years With Regular Maintenance |
| Best For | Low-Slope Roofs, Commercial Buildings |
| Key Benefits | Durability, Multiple Layers, UV Protection |
| Main Drawbacks | Weight, Labor-Intensive, Limited Aesthetics |
What Is A Tar And Gravel Roof
A tar and gravel roof, or built-up roofing (BUR), consists of alternating layers of bitumen (asphalt or coal tar) and reinforcing felts, topped with a surface layer of gravel or mineral aggregate.
This system Creates Multiple Waterproof Layers That Protect Low-Slope Roofs From Water Infiltration And UV Damage.
Components And Variations
Typical components include a base sheet, multiple ply felts, hot-applied or cold-applied bitumen, and a surfacing of loose or embedded gravel.
Variations Depend On Bitumen Type (Asphalt Or Coal Tar), Number Of Plies, And Gravel Or Mineral Cap Sheet Choices.
Base And Ply Materials
Base sheets provide adhesion and initial structural support; ply felts are usually organic or fiberglass-reinforced, offering strength and redundancy.
Bitumen Types
Asphalt is the most common modern binder and is compatible with many roof systems, while coal tar is more chemical-resistant but less commonly used due to environmental and odor concerns.
Surfacing Options
Gravel serves as ballast, protects the bitumen from UV degradation, and adds fire resistance; mineral-coated cap sheets are alternatives for enhanced aesthetics and performance.
Installation Process
Proper installation is critical; BUR is typically installed by professionals because it often requires heating bitumen and layering felts while ensuring proper flashing and drainage.
Installation Involves Deck Preparation, Vapor Retarder (If Needed), Application Of Multiple Bitumen And Felt Layers, And Final Gravel Or Cap Sheet Surfacing.
Step-By-Step Overview
- Inspect And Prepare The Roof Deck, Repairing Rot Or Structural Issues.
- Install Vapor Retarder Or Insulation Boards As Required By Code.
- Apply Base Sheet And Heat-Applied Or Cold-Applied Bitumen.
- Lay Subsequent Ply Felts With Proper Overlaps, Applying Bitumen Between Plies.
- Embed Final Surfacing—Loose Gravel Is Broadcast Or Set Into Hot Bitumen, Or Install Mineral Cap Sheet.
- Finish Flashing Around Penetrations, Curbs, And Parapets To Prevent Leaks.
Benefits And Drawbacks
Tar and gravel roofs offer significant advantages but also have limitations that owners should weigh carefully before selection.
Key Benefits Include High Durability, Excellent Waterproofing Due To Multiple Plies, And Good UV And Fire Resistance When Properly Surfaced.
Benefits
- Long Service Life When Maintained—20 To 30 Years Or More.
- Multiple Redundant Layers Reduce Sudden Failures.
- Gravel Protects Against UV And Mechanical Wear; Improves Fire Rating.
- Relatively Low Material Cost Compared To Some Single-Ply Systems.
Drawbacks
- Heavy System Requires Structural Assessment For Older Buildings.
- Installation Is Labor-Intensive And May Produce Odors During Hot Application.
- Aesthetics Are Limited; Not Ideal For Steep-Slope Or Visible Residential Roofs.
- Loose Gravel Can Clog Gutters And Require Periodic Cleanup.
Maintenance, Inspection, And Common Repairs
Regular maintenance extends life and prevents minor issues from becoming major leaks; inspections should occur at least twice a year and after major storms.
Key Maintenance Tasks Include Clearing Debris, Checking Gravel Distribution, Inspecting Flashings, And Promptly Repairing Blisters, Cracks, Or Punctures.
Inspection Checklist
- Look For Bare Spots Where Gravel Is Missing Or Bitumen Is Exposed.
- Examine Flashing Seams, Roof Penetrations, Drains, And Scuppers For Gaps Or Corrosion.
- Check For Ponding Water On Low-Slope Areas; Ensure Proper Drainage.
- Note Any Soft Areas Or Sagging That May Indicate Deck Rot.
Typical Repairs
Minor repairs can include patching with compatible bitumen and new felt plies, replacing flashing, and topping up gravel in eroded areas.
Cost, Lifespan, And Value Comparison
Costs vary widely by region, roof complexity, and materials; accurate budgeting requires onsite assessment and multiple quotes.
Average Installed Costs Typically Range From $3.50 To $7.50 Per Square Foot, With Lifespans Of 20 To 30 Years When Properly Maintained.
| Factor | Typical Range/Impact |
|---|---|
| Installed Cost Per Sq Ft | $3.50–$7.50 |
| Expected Lifespan | 20–30 Years |
| Maintenance Frequency | Biannual Inspections, Gravel Top-Up As Needed |
| Replacement Complexity | Moderate To High—Requires Professional Removal And Reinstallation |
Energy Performance And Environmental Considerations
Standard tar and gravel roofs absorb heat, which can increase cooling loads, but reflective cap sheets and light-colored gravel can improve thermal performance.
Applying Light-Colored Aggregate Or Reflective Coatings Can Reduce Roof Surface Temperatures And Lower Cooling Energy Use.
Sustainability Options
- Use Recycled Aggregate Or Mineral Surfacing To Lower Environmental Footprint.
- Consider Cool Roof Coatings To Improve Reflectivity And Energy Efficiency.
- Inspect For Proper Disposal Or Recycling When Replacing BUR To Reduce Waste.
Code, Structural, And Insurance Considerations
Local building codes may dictate insulation, wind uplift resistance, and fire ratings; some insurers consider BUR favorable for fire resistance but may require documentation of installation quality.
Before Installation, Have A Structural Engineer Or Qualified Roofer Verify That The Building Can Support The Added Weight Of A Tar And Gravel System.
Permits And Documentation
- Obtain Local Permits For Replacement Or New Installation As Required.
- Keep Manufacturer Technical Data Sheets And Warranty Documents Accessible.
- Document Regular Maintenance To Support Insurance Claims And Warranty Coverage.
Choosing A Contractor And Warranty Tips
Select a contractor experienced with BUR and check references, license status, and examples of completed projects to ensure quality workmanship.
Look For Contractors Offering Clear Warranties On Workmanship And Materials, And Verify They Carry Roofer’s Liability Insurance And Workers’ Compensation.
Questions To Ask Prospective Contractors
- How Many Years Of Experience With Tar And Gravel Roofs?
- Can You Provide References And Photos From Similar Jobs?
- What Warranties Are Offered For Labor And Materials?
- How Do You Manage Venting, Insulation, And Flashing Details?
Common Problems And When To Consider Replacement Or Alternative Systems
Recurring leaks, extensive ponding, widespread gravel loss, or a roof that has reached the end of its service life are signals to consider full replacement or an alternative roofing system.
If Extensive Repairs Are Needed Across Large Areas, Replacing The BUR With A New System Or A Modern Single-Ply Membrane May Be More Cost-Effective Long-Term.
Alternatives To Tar And Gravel
- EPDM Or TPO Single-Ply Membranes—Lighter And Often Easier To Repair.
- Modified Bitumen—Offers Some BUR-Like Benefits With Factory-Applied Surfaces.
- Built-Up With Cold-Applied Adhesives—Reduces Hot-Work Hazards.
Frequently Asked Questions
Is A Tar And Gravel Roof Suitable For Residential Homes? It Can Be Appropriate For Low-Slope Residential Sections Like Garages Or Additions, But Aesthetic And Weight Considerations Often Make Alternatives More Desirable For Visible Areas.
How Often Should Gravel Be Replaced Or Replenished? Gravel Should Be Checked During Biannual Inspections; Top-Up Frequency Depends On Weather Exposure And Foot Traffic—Often Every 5–10 Years.
Can A Tar And Gravel Roof Be Coated To Extend Life? Yes; application of compatible reflective coatings or a mineral cap sheet can extend life and improve UV resistance, but preparation and compatibility testing are essential.