This is a common misconception. While BURs are traditionally constructed with four plies, modern BUR systems often utilize fewer plies due to advancements in material technology and installation techniques.

Here's a breakdown of a typical BUR system:

• Base Sheet: A layer of asphalt-saturated felt or fiberglass mat that acts as a foundation.
• Ply Sheets: Multiple layers of asphalt-saturated felt or fiberglass mat, typically two or three, are applied over the base sheet and mopped with hot asphalt.
• Flood Coat: A final layer of hot asphalt is applied over the top ply to seal the seams and create a continuous waterproof membrane.
• Ballast: A layer of gravel or stone is applied to the flood coat to protect the membrane from UV rays and wind uplift.

It's important to note that the number of plies in a BUR system can vary depending on factors such as local building codes, climate conditions, and the specific requirements of the project.

Advantages of BUR Systems:

• Durability: BURs are known for their exceptional durability and long lifespan.
• Waterproofing: The multiple layers of asphalt and felt create a highly effective barrier against water infiltration.
• Fire Resistance: BURs are fire-resistant, making them a suitable choice for buildings with high fire safety requirements.
Cost-Effective: BURs can be a cost-effective roofing solution, especially for large commercial buildings.

If you're considering a BUR system for your project, it's essential to consult with a qualified roofing contractor to determine the optimal number of plies and the most suitable materials for your specific needs.