Asphalt Built Up Roof: A Comprehensive Guide for Home and Commercial Roofs
The asphalt built up roof (BUR) system is a traditional, durable solution for flat and low-slope roofs. This guide explains what BUR is, how it’s constructed, and why it remains popular in the United States. It covers materials, installation, performance, maintenance, and common issues to help builders, property managers, and homeowners make informed decisions about asphalt built up roofing.
Overview Of Asphalt Built Up Roof
An asphalt built up roof consists of multiple plies of asphalt-saturated felts laminated with bitumen and topped with a gravel or cap sheet. The result is a resilient, waterproof roof surface designed to shed water and protect the underlying structure. BUR systems are versatile, accommodating roof penetrations, parapets, and detailing with relative ease.
Historically, BUR has been favored for its proven track record, long service life, and ability to becustomized for different climates. In many urban and commercial settings, BUR remains a practical choice due to available materials, established installation methods, and the option to repair segments without replacing the entire roof.
Materials And Layers
The core of a BUR system is a stack of alternating plies of felt and bitumen. The typical configuration includes:
- Base sheet or concrete deck prep to ensure a smooth, clean surface.
- Asphalt-saturated felt plies that are laminated with hot asphalt or cohesive cold adhesive. Common thicknesses range from three to five plies.
- Interply and cap sheets for added protection and waterproofing. The cap sheet often uses a mineral-surfaced surface or gravel.
- Final surfacing such as mineral granules, reflective coatings, or ballast (gravel) to protect the roof and provide UV resistance.
Bitumen used in BUR can be aluminum-modified or styrene-butadiene-styrene (SBS) modified for enhanced elasticity. The external ballast or gravel protects the roof from sun exposure, UV degradation, and mechanical damage, while also providing additional weight to resist wind uplift.
Installation Process
Installing a BUR system is a multi-stage procedure that requires skilled workmanship. The process typically follows these steps:
- Prepare and clean the deck, repair any surface defects, and install edge details and flashing.
- Seal and secure the base sheet to create a moisture barrier and a uniform substrate for subsequent plies.
- Apply successive plies of asphalt-saturated felt with hotAPP or cold adhesive, ensuring full embedment and uniform coverage.
- Install interply sheets and finally the cap sheet with proper adhesion and detailing around penetrations and parapets.
- Add the ballast or mineral surfacing to protect the membrane and improve durability, followed by any optional reflective coatings.
Quality control during installation focuses on proper adhesion, no air pockets, clean cut edges around penetrations, and proper sealing of flashings. A professional BUR installation helps minimize vulnerabilities to blisters, ridges, and open seams that can lead to leaks.
Durability And Performance
BUR roofs are well-regarded for their durability and long service life, often exceeding 20 to 30 years with proper maintenance. The layered construction provides excellent waterproofing capabilities and good resistance to punctures and impact when properly ballasted. The asphalt’s flexibility in temperature ranges helps prevent cracking in varying climates.
Energy performance can vary. Traditional BUR roofs with mineral cap sheets may absorb heat, while reflective or cool-roof ballast options can reduce heat absorption and improve energy efficiency in hot climates. Regular inspections help identify issues like membrane degradation, flashing failures, or ballast displacement that could compromise performance.
Maintenance And Repairs
Maintenance for BUR systems centers on keeping the surface protected and free of damage. Routine tasks include removing debris, inspecting flashings, and checking ballast retention. Periodic roof inspections are essential to catch early signs of trouble, such as blistering, ridging, or pooling water around drains.
Repairs are typically localized. Damaged plies or flashings can be repaired or resealed with compatible asphalt materials. If significant deterioration is present or structural decking is compromised, section replacement or reproofing of the entire roof may be necessary. A professional assessment helps determine the most cost-effective repair strategy.
Environmental Considerations And Life Expectancy
BUR systems have a long track record, but environmental considerations influence choice. The ballast layer adds weight and can hinder wind uplift but may complicate stormwater drainage. Some modern BUR installations incorporate reflective or cool-roof cap sheets to reduce urban heat island effects and improve energy efficiency. In terms of life expectancy, a well-installed BUR roof typically lasts 20 to 40 years depending on climate, maintenance, and workmanship.
Recycling options for BUR components exist, particularly for asphalt and felts, though recycling rates vary by region. When considering sustainability, builders may compare BUR with modern single-pply membranes or fluid-applied coatings to determine the best balance of durability, energy performance, and environmental impact.
Common Problems And Troubleshooting
Typical BUR issues include blistering from trapped moisture, pinhole leaks, cap sheet damage, and flashing failures at penetrations. Poor substrate preparation or improper adhesive application can compromise bond strength and waterproofing. Wind uplift on flat or low-slope roofs is another concern, especially if ballast is displaced or insufficient.
Effective troubleshooting involves a physical inspection, moisture testing, and reviewing historical maintenance records. Solutions range from localized resealing or re-balling to full deck repairs or partial reroofing. Using compatible components during repairs minimizes future compatibility problems and extends roof life.
Choosing An Installer And Cost Considerations
When selecting a contractor for an asphalt built up roof, prioritize licensed, insured, and experienced firms with BUR installation credentials. Request references and review project portfolios, focusing on systems similar in size and climate to the target project. Ask about warranty options, material specifications, and post-installation maintenance plans.
Cost factors for BUR projects include deck condition, ply count, asphalt type, cap sheet selection, ballast material, roof size, and labor. Initial costs are higher than some single-ply membranes, but BUR’s durability and repairability can yield a favorable lifecycle cost over time. A detailed inspection and written proposal help ensure accurate budgeting and anticipated performance.
Maintenance Plan And Long-Term Care
A proactive maintenance plan supports BUR longevity. Schedule annual or biannual inspections to assess ballast integrity, flashing tightness, and surface wear. Document any repairs, track weather-related impacts, and update maintenance logs. A proactive approach reduces the likelihood of major leaks and extends the roof’s service life.
In regions with severe weather, routine protective measures—such as reinstituting ballast after high winds or after winter thaw cycles—help maintain resistance to water intrusion. Property managers benefit from a clear maintenance cycle that aligns with roof warranty requirements and local codes.
Asphalt built up roofs continue to be a durable, proven option for flat and low-slope applications. With proper installation, regular maintenance, and timely repairs, BUR systems deliver reliable waterproofing and long-term performance for both commercial and residential structures.