If you own a flat or low-slope commercial building, you’ve probably heard about built-up roofing—but what is a built-up roof exactly? A built-up roof (BUR) is a traditional roofing system made by layering asphalt or coal tar with reinforcing fabrics, topped with protective surfacing like gravel. Known for its durability and waterproofing capabilities, this time-tested solution has been protecting buildings for over 150 years.
In this complete guide, we’ll break down everything you need to know about built-up roofs in simple terms. You’ll learn about the different types, where they work best, and why many building owners still choose this reliable roofing method today.
How Built-Up Roofing Works
Built-up roofs get their name from their layered construction. Roofers build them up by alternating waterproofing materials to create a seamless, durable membrane. Here’s what makes them special:
✔ Multiple layers (usually 3-5 plies) for extra protection
✔ Hot or cold application methods available
✔ Reinforcing fabrics between each layer
✔ Final surfacing with gravel, coating, or mineral granules
✔ Seamless finish that prevents leaks
3 Main Types of Built-Up Roofing Systems
1. Hot-Applied BUR
Uses heated asphalt applied between layers
✔ Best for: Large commercial roofs
✔ Pros: Superior bonding, long lifespan
✔ Cons: Requires special equipment, safety precautions
2. Cold-Applied BUR
Uses liquid adhesives instead of hot asphalt
✔ Best for: Schools, hospitals (no fumes)
✔ Pros: Safer installation, lower odor
✔ Cons: Longer curing time
3. Modified Bitumen BUR
Combines traditional BUR with modern polymer-modified sheets
✔ Best for: Buildings needing extra flexibility
✔ Pros: Handles temperature swings better
✔ Cons: Higher material cost
Built-Up Roof Layers Explained
| Layer | Purpose | Common Materials |
|---|---|---|
| Vapor Barrier | Prevents moisture buildup | Asphalt-saturated felt |
| Insulation | Energy efficiency | Polyiso, EPS, or XPS boards |
| Base Ply | First waterproof layer | Fiberglass or polyester mat |
| Interior Plies | Reinforcement | Fabric sheets (2-4 layers) |
| Top Ply | Weather protection | Mineral-surfaced cap sheet |
| Surfacing | UV/impact protection | Gravel, coatings, or granules |
Top Benefits of Built-Up Roofing
1. Unmatched Durability
Lasts 20-30 years with proper maintenance
Handles foot traffic better than single-ply roofs
Resists punctures from hail or debris
2. Superior Waterproofing
Multiple layers create redundant protection
No seams means fewer leak points
Self-healing properties with asphalt
3. Energy Efficiency
Light-colored surfacing reflects sunlight
Thick insulation options available
Reduces HVAC costs by 20-30%
4. Fire Resistance
Gravel surfacing provides Class A fire rating
Asphalt layers resist flame spread
Meets strict building codes
5. Cost Effectiveness
Lower lifetime cost than many alternatives
Easy to repair instead of replace
Local materials keep prices stable
Where Built-Up Roofs Work Best
Ideal Buildings:
• Warehouses and factories
• Shopping centers
• School buildings
• Apartment complexes
• Government facilities
Best Climates:
✔ Areas with temperature extremes
✔ Regions with heavy rainfall
✔ Locations with high UV exposure
✔ Cities with strict fire codes
Built-Up Roof Maintenance Tips
Annual:
• Clear debris from drains
• Inspect flashings and edges
• Check for blisters or cracks
Every 3-5 Years:
• Recoat worn areas
• Replace loose gravel
• Seal penetrations
When Problems Appear:
• Repair small cracks immediately
• Address ponding water issues
• Replace damaged sections
Built-Up Roof vs. Other Flat Roof Systems
| Feature | BUR | EPDM | TPO | PVC |
|---|---|---|---|---|
| Lifespan | 20-30 yrs | 15-25 yrs | 15-20 yrs | 20-30 yrs |
| Cost/Sq Ft | 4−4−8 | 5−5−10 | 4−4−8 | 6−6−12 |
| Installation | Skilled | Moderate | Easy | Moderate |
| Repairability | Excellent | Good | Fair | Good |
| Eco-Friendly | Medium | High | High | Medium |
FAQs About Built-Up Roofing
1. How long does built-up roofing last?
Typically 20-30 years—some last 40+ years with excellent maintenance.
2. Can you walk on a built-up roof?
Yes, the gravel surface and multiple layers make BUR very walkable.
3. Is built-up roofing heavy?
Yes—a full gravel-surfaced BUR weighs 6-8 lbs/sq ft (more than most alternatives).
4. Can built-up roofs be recycled?
Yes—asphalt from BUR is America’s most-recycled construction material.
5. How do you repair a built-up roof?
Small repairs involve cleaning the area and applying new asphalt and fabric.
When to Choose Built-Up Roofing
Consider BUR if you need:
✓ Maximum durability for the price
✓ Proven long-term performance
✓ Superior waterproofing
✓ Fire-resistant construction
✓ Local contractor expertise
Final Thoughts
Now that you understand what a built-up roof is, you can see why it remains popular despite newer options. While not right for every building, BUR systems offer unmatched reliability for flat and low-slope commercial structures. The multiple layers create a fortress-like barrier against weather, while the gravel surface protects against sun damage and foot traffic. If you value time-tested performance over flashy new technology, a built-up roof might be your perfect solution. Just be sure to work with experienced contractors—proper installation makes all the difference with these systems. With good care, your built-up roof could protect your building for decades to come.
