The Four Ply Built Up Roof (BUR) system stands as a proven, durable solution widely used in commercial and residential roofing. This layered roofing method offers exceptional waterproofing, strength, and longevity by combining multiple asphalt and fabric layers. Understanding the components, installation, advantages, and maintenance of a four ply BUR is essential for property owners and building managers seeking reliable roofing options that withstand harsh weather conditions.
| Feature | Description |
|---|---|
| Roof Type | Built Up Roof (Buried layers of asphalt and fabric) |
| Number of Plies | Four (four layers of roofing felt) |
| Materials | Asphalt, Roofing Felt, Gravel or Smooth Surfacing |
| Applications | Commercial Buildings, Low Slope Roofs |
| Benefits | Durability, Waterproofing, Fire Resistance, UV Protection |
| Maintenance | Periodic Inspections and Prompt Repairs |
What Is a Four Ply Built Up Roof?
A Four Ply Built Up Roof (BUR) consists of four layers or “plies” of roofing felt bonded together with hot asphalt or coal tar pitch. Each ply reinforces the structure by adding waterproof protection and mechanical strength. The system’s outermost layer often includes a gravel or mineral surface to shield the asphalt from ultraviolet (UV) rays and physical damage.
This method has been the standard roofing solution for decades, favored for its reliability on low slope roofs where water drainage is limited. Four ply BURs balance structural integrity with waterproofing capabilities, making them ideal for large commercial facilities, warehouses, and multi-unit residential buildings.
Components of a Four Ply Built Up Roof System
Roofing Felts (Plies)
The roofing felts are typically made of organic or fiberglass mats saturated with asphalt. Each ply is compacted and bonded over the previous layer, creating a composite membrane that is extremely resistant to water penetration and wear.
Asphalt or Coal Tar Pitch
Hot applied asphalt or coal tar pitch serves as the adhesive, unifying the plies into a continuous membrane. Asphalt is the most common because of its fire resistance and flexibility, while coal tar offers superior chemical resistance but is less common due to environmental concerns.
Surfacing Layer
The final layer is a protective surfacing material, usually crushed stone (gravel) or mineral granules embedded in a smooth coating. This layer protects the underlying plies from UV damage and physical abrasion.
Installation Process of a Four Ply Built Up Roof
The installation of a four ply BUR involves precise steps to ensure longevity and performance:
- Deck Preparation: The roof deck must be clean, dry, and structurally sound before installation.
- Base Sheet Installation: A base sheet is mechanically fastened or adhered to the deck, providing a foundation for the BUR layers.
- Hot Asphalt Application: Hot asphalt is heated to a specified temperature and applied evenly over the base sheet.
- Layering Felts: Each roofing felt layer is embedded into the hot asphalt, rolled to remove air pockets and ensure adhesion.
- Repeating for Four Plies: Steps of asphalt application and felt embedding are repeated for all four plies.
- Surfacing Installation: The final layer typically includes a gravel or mineral cap to protect the assembly.
Professional installation is critical, as temperature control of asphalt and precise ply placement affect the roof’s performance and lifespan.
Advantages of Four Ply Built Up Roof Systems
The four ply BUR offers significant benefits that make it a preferred choice in various applications:
- Superior Waterproofing: Multiple layers create a reliable barrier against water infiltration, reducing leak risk.
- Longevity: With proper maintenance, BUR roofs can last 20-30 years or longer.
- Fire Resistance: Asphalt and gravel provide good fire protection for commercial buildings.
- UV Protection: Surfacing layers shield the membrane from sun damage, preserving material integrity.
- Sound Insulation: The multiple layers dampen outside noise, improving interior comfort.
- Cost-Effective: Though labor-intensive, BUR systems use relatively affordable materials compared to some single-ply membranes.
Common Applications and Suitability
The four ply BUR is especially suitable for low slope and flat roofs. It performs well in:
- Commercial buildings such as shopping centers, offices, and warehouses
- Institutional buildings including schools and hospitals
- Apartment complexes and condominiums
- Industrial facilities requiring durable waterproofing
Its ability to withstand foot traffic and environmental stress makes it ideal for roofs where durability is crucial and minor repairs are easier without major disruptions.
Maintenance and Repair of Four Ply Built Up Roofs
Regular inspections are essential to extend the life of a BUR roof. Key maintenance points include:
- Checking for cracks, blisters, or splits in the membrane
- Ensuring the surfacing gravel remains intact and evenly distributed
- Clearing debris that can retain moisture or damage the surface
- Repairing localized damage promptly to prevent leaks
Periodic maintenance, including reapplying gravel or coating repairs, can prevent premature roof failure and costly replacements.
Environmental and Energy Efficiency Considerations
Modern four ply BUR systems can be paired with reflective surfacing coatings to improve energy efficiency, reducing heat absorption and lowering cooling costs in hot climates. Additionally, BUR materials can be sourced with regard to sustainability standards, and the roof’s longevity means fewer replacements and less waste.
Cost Factors and Lifespan Expectations
The cost of installing a four ply BUR depends on material prices, labor, roof size, and local market conditions. While installation costs are moderate, laboratories estimate an average lifespan of 20 to 30 years for these roofs, provided proper upkeep.
This lifespan is generally longer than many single-layer roofing systems, positioning the four ply BUR as a smart investment for building owners prioritizing durability and long-term value.