What is typically used as a base sheet in BUR construction?

In built-up roofing (BUR) construction, saturated felt is typically used as a base sheet. Saturated felt provides a strong foundational layer that enhances stability and durability in the roofing system. This material is made of materials such as organic or fiberglass felt that has been saturated with asphalt or another waterproofing substance to create a barrier against moisture. By using saturated felt, the roof assembly gains additional strength and helps in maintaining integrity against various weather conditions.

The base sheet plays a crucial role in supporting the layers above it, which consist of additional felts and asphalt, serving to distribute the weight and stresses across the roof surface. This makes the use of saturated felt a common practice in BUR systems, as it allows for the effective layering necessary for optimal waterproofing and protection.

Choosing other materials like asphalt, fiberglass, or polyethylene as base sheets is less typical in BUR systems. While asphalt is indeed a key component of BUR construction, it is primarily used as a waterproofing agent in combination with felts, rather than serving as the base layer itself. Fiberglass is more commonly associated with reinforced products and is not a traditional base sheet. Polyethylene, while useful in other contexts, does not offer the same durability or performance for a base layer in BUR systems.