Which material would be the least suitable for building drains?

Polyolefin is considered the least suitable material for building drains primarily due to its properties and characteristics. Building drains are exposed to various environmental factors, including high humidity, sewage, and drainage conditions. Polyolefin materials are generally known for their resistance to chemical and moisture damage but may not perform well under the conditions typically encountered in building drainage systems.

In contrast, other materials listed, such as CPVC, ductile iron, and Type L copper, have specific attributes that make them more appropriate for use in drainage applications. CPVC is recognized for its ability to handle high-temperature water and has strong chemical resistance. Ductile iron is durable and can withstand heavy loads, making it suitable for all kinds of drainage systems, especially in areas subject to ground movements. Type L copper, being thicker and more robust, is well-suited for water distribution and can also resist corrosion, which is crucial in drainage applications.

The specific characteristics of polyolefin, such as its potential for lower thermal and pressure resistance, make it less favorable when considering long-term service in demanding environments typical of building drainage systems.