Built Up Roof Materials: Types, Benefits, and Installation Tips
Built‑up roofs (BUR) remain a durable, long‑lasting option for commercial and some residential structures in the United States. This article explores the main materials used in BUR systems, how they work together, and practical guidance for selection, installation, and maintenance. It covers performance factors, lifecycle cost, and common challenges to help building owners and contractors make informed decisions about built up roof materials.
Overview Of Built Up Roof Materials
Built up roof systems combine multiple ply sheets with bitumen and a durable protective surfacing. The core components include a substrate, reinforcing plies, bitumen, and a ballast or reflective top layer. The choice of each element affects waterproofing, weather resistance, weight, energy efficiency, and overall longevity. Common BUR materials include coal tar or asphalt bitumen, reinforcing felts or fiberglass mats, asphalt or coal tar hot‑applied sections, and ballast such as gravel or a reflective coating.
Core Components In BUR Systems
Reinforcing Plys
Reinforcing plies provide tensile strength and dimensional stability. Historically, burlap and felt papers were used, but modern BURs favor fiberglass or polyester felts. Fiberglass offers greater strength and puncture resistance, while polyester provides improved tear resistance and slower aging. The number of plies typically ranges from three to five, depending on climate, roof slope, and loading conditions.
Bitumen And Adhesives
Bitumen is the waterproofing heart of BUR. Asphalt is the most common modern binder in the United States, while coal tar is still used in some older installations or specialty applications due to its high resistance to UV and chemicals. Bitumen is applied hot or cold, depending on material specifications, weather, and local codes. Proper application ensures seam integrity and long‑term waterproofing performance.
Surfacing And Ballast
The outer surface protects the BUR from UV exposure and mechanical wear. Surfacing options include aggregate ballast (gravel or stone), reflective coating systems, and protective cap sheets. Gravel ballast is heavy, durable, and good for UV protection, while reflective coatings can reduce cooling loads in hot climates and improve energy efficiency.
Material Options By Performance And Climate
- Fiberglass‑reinforced BUR offers high tear resistance and dimensional stability, suitable for moderate to severe climates.
- Polyester‑reinforced BUR provides excellent fatigue resistance and is well suited for roofs with movement or frequent foot traffic.
- Asphalt‑based BUR with asphalt or asphaltic modifiers is common for cost efficiency and versatility.
- Coal tar BUR delivers strong chemical and UV resistance but has higher odor and regulatory considerations in some areas.
- Ballasted BUR uses gravel or pavers for ballast, offering durable protection and simple inspection access.
- Reflective BUR coatings or cap sheets reduce heat absorption and may qualify for energy‑efficiency incentives.
Benefits And Limitations Of Built Up Roof Materials
- Durability: The multi‑ply construction provides robust waterproofing and resistance to punctures and hail, especially with fiberglass plies.
- Waterproofing: BUR systems offer excellent seam integrity when properly installed, with redundancies from multiple plies.
- Longevity: Typical service life ranges from 15 to 40 years depending on climate, maintenance, and materials used.
- Weight: BUR is heavy; structural assessment is essential to support loads, especially on retrofits or older buildings.
- Maintenance: Regular inspections are needed to address flashing, seams, and ballast settlement.
- Environmental/Regulatory: Some components, such as coal tar, have regulatory considerations due to emissions and VOCs in certain jurisdictions.
Installation Process And Best Practices
Proper BUR installation hinges on meticulous surface preparation, consistent material quality, and weather windows. The typical process steps are:
- Prepare the substrate by cleaning, repairing, and priming as required by the system specification.
- Install the first ply with the chosen reinforcement, ensuring alignment and secure adhesion.
- Sequentially add plies with proper heat application or cold adhesion per manufacturer guidelines.
- Seal flashings, penetrations, and edges with compatible materials and flashing membranes.
- Apply ballast or reflective top surfaces as specified for UV protection and energy performance.
Key installation tips include maintaining proper temperatures for bitumen application, protecting edges during curing, and validating seamless transitions at perimeters and penetrations. Regular contractor training and adherence to local building codes ensure proper bonding and performance.
Maintenance, Inspection, And Common Issues
Routine inspections help prevent leaks and extend BUR life. Check for:
- Ballast displacement or settling, which can expose underlying plies to UV damage.
- Cracking or separation at seams, especially after extreme temperature cycles.
- Flashing integrity around exhausts, curbs, and penetrations.
- Signs of ponding water, particularly on low‑sloped sections.
- UV degradation of surfacing coatings or cap sheets.
Address issues promptly with patching, resealing, or replacing degraded sections. For ballast‑based BUR, ensure ballast remains evenly distributed to prevent localized stress and moisture pockets.
Energy Efficiency And Environmental Considerations
Reflective BUR systems and reflective top coatings can reduce cooling loads in hot climates, contributing to building energy efficiency. Where possible, choose energy‑efficient surfacing materials and consider cool roof standards. Environmental considerations include the lifecycle impact of bitumen production and the potential for VOC emissions from certain bitumen formulations. Modern BUR designs emphasize recyclable or salvageable components and proper disposal of old materials.
Choosing The Right Built Up Roof Material For Your Project
Selection depends on climate, building use, structural capacity, budget, and maintenance capabilities. For high‑traffic roofs or mechanical penthouses, heavier plies and robust ballast systems provide resilience. In hot climates, reflective surfacing can improve energy performance and extend system life. For retrofit projects on aging structures, verify structural capacity to support ballast and weight requirements. A qualified roofing contractor can perform a feasibility assessment, conduct thermal and moisture analyses, and recommend an optimized BUR configuration that aligns with local regulations and warranty terms.
Cost Considerations And Life Cycle
Initial costs for BUR systems vary with materials, ply count, ballast, and labor. Long‑term costs should account for maintenance, potential energy savings from reflective surfaces, and the expected service life. While BUR can have higher upfront weight and complexity, its proven waterproofing track record often yields favorable life‑cycle cost outcomes in suitable applications. Comparative analyses with single‑ply membranes should consider climate, roof accessibility, and long‑term maintenance requirements.
Common Mistakes To Avoid
- Inadequate substrate preparation leading to poor adhesion.
- Improper primer selection or application, reducing bond strength.
- Insufficient seam reinforcement or improper ballast distribution.
- Failing to account for thermal movement and building settlement.
- Ignoring local code restrictions on coal tar usage or VOC limits.
By adhering to manufacturer specifications, ensuring proper surface preparation, and scheduling inspections after major weather events, BUR installations can achieve reliable performance and long service life.