Built Up Roof Materials: A Comprehensive Guide for U S Builders
Built up roof systems, commonly referred to as BUR, combine multiple layers of waterproofing and insulation to create durable, weather-ready roofs. This guide explains the primary materials used in BUR, how they contribute to performance, and practical considerations for selection, installation, and maintenance in typical American climates. It highlights key terms, longevity factors, and cost implications to help builders, facility managers, and homeowners choose the best built up roof materials for their projects.
What Is Built Up Roofing (BUR) And How It Works
Built up roofing is a multi-ply system that forms a robust, waterproof membrane by layering bitumen, reinforcing mats, and a surfacing material. Traditional BUR installations alternate a cold or hot application of bitumen with reinforcing plies, typically including felt or fiberglass felts. The top layer often features gravel, granules, or a reflective coating to protect against UV exposure and weathering. BUR systems are favored for their proven durability, wide service life, and ability to resist membrane punctures and membrane punctures in areas with foot traffic or mechanical equipment access.
Core Materials Used In Built Up Roofs
The performance of a BUR system hinges on the quality and compatibility of its components. The main materials are:
- Bitumen (asphalt, coal tar pitch, or cold-applied asphalt): Acts as the waterproofing glue between plies. Asphalt is common in new installations due to ease of workability, while coal tar pitch provides high temperature resistance and durability in some climates.
- Reinforcing Mats (asphalt-saturated felts, fiberglass, or polyester): Provide strength and dimensional stability. Glass-fiber or synthetic felts are preferred for better tear resistance and longer service life.
- Ply Membranes (additional plies of bitumen-saturated felt or fiberglass mat): Each ply adds redundancy and weather resistance, distributing loads and reducing the risk of membrane failure.
- Surfacing Layer (gravel ballast, mineral granules, or reflective coatings): The top layer protects the membrane from UV light, weathering, and foot traffic. Gravel ballast is common on flat roofs, while reflective coatings are used to improve energy efficiency.
- Asphalt BUR: Widely used due to ease of installation and cost-effectiveness. Pros include strong waterproofing and available local materials. Cons include heavier weight and higher long-term maintenance in extreme temperatures.
- Coal Tar BUR: Excellent chemical resistance and long track record. Cons include higher odor during installation and regulatory restrictions in some areas due to health concerns.
- APP And SBS Modified Bitumen BUR: Modified bitumen offers improved flexibility at low temperatures and enhanced hail resistance. Pros are resilience in cold climates; cons include higher upfront cost and specialized installation.
- Granulated Surfacing (gravel or stone ballast): Provides protection and ballast to resist wind uplift. Cons include additional weight and potential maintenance to keep ballast in place.
Insulation in BUR installations helps reduce heat transfer and improve energy efficiency. Common choices include polyiso or polystyrene boards placed beneath the bitumen plies. Vapor retarders may be added to control moisture movement, especially in humid climates or roof assemblies with interior occupancies. The exact configuration depends on climate, roof slope, and intended interior conditions. Proper detailing around penetrations, curbs, and HVAC equipment is critical to prevent leaks and thermal bridges.
BUR systems offer robust water protection when properly installed and maintained. Typical service life ranges from 15 to 35 years depending on climate, roof traffic, and maintenance. Key maintenance tasks include regular inspection after severe weather, resealing flashings, inspecting ballast, and replacing damaged plies or surfacing materials. Early repair of micro-cracks, punctures, or sea-salt exposure near coastal areas can substantially extend the roof’s life. A well-drained roof deck and clean drainage can prevent ponding and related issues.
Proper BUR installation requires skilled crews and careful sequencing. Important factors include:
- Surface Preparation: Clean and smooth the substrate; repair any deck deflections or damage before laying plies.
- Ventilation And Safety: Follow OSHA guidelines for hot asphalt work, including temperature control and fire safety measures. Use appropriate fall protection and PPE when working at height.
- Layering Sequence: Adhere to the manufacturer’s recommended ply count and order, ensuring even coverage and proper bonding between plies.
- Roof Drainage: Design to avoid standing water; ensure proper slope and confirm drain locations during installation.
- Edge Details And penetrations: Seal all flashings, penetrations, and terminations to prevent leakage paths; consider wind uplift resistance in exposed locations.
Selection of BUR materials can influence a building’s environmental footprint. Recycled materials and low-odor formulations are increasingly available for both bitumen and surfacing components. Reflective coatings and light-colored granules can reduce cooling loads in hot climates, contributing to energy efficiency credits and lower utility costs over time. Waste reduction during installation and using durable, long-life plies also lower lifecycle environmental impact. Building codes and green building programs may reward projects using BUR systems with appropriate energy and water performance ratings.
Initial BUR installation costs vary with ply count, material choice, and regional labor rates. Long-term costs factor in maintenance, potential repairs, and energy savings. A higher upfront investment in premium plies or reflective surfacing often yields lower maintenance costs and improved energy performance over time. Owners should request a detailed lifecycle cost analysis that includes expected service life, maintenance intervals, and potential downtime during repairs. Reliable warranties from manufacturers and qualified contractors add financial security and predictability.
Choosing the right built up roof material involves climate, building use, and maintenance capacity. In hot climates, reflective surfacing and lighter ballast can reduce cooling loads. In colder regions, dedicated ballast and robust waterproofing plies improve resilience against freeze-thaw cycles. Coastal or industrial settings may demand chemical resistance and UV protection. A qualified roofing contractor can help balance cost, longevity, expansion around penetrations, and compatibility with existing structures. Regular inspections and preventive maintenance extend roof life and protect interior spaces from weather damage.