Final answer:
The extra layer of material installed over the subfloor is called underlayment, which helps create a smooth surface and may offer insulation, sound reduction, or moisture protection.
Step-by-step explanation:
In construction, an extra layer of material installed over the subfloor is often referred to as an underlayment. This underlayment provides a smooth, flat surface for the floor covering and can also offer additional features such as insulation, sound reduction, and moisture protection. Popular choices for underlayment materials include plywood, cement board, and foam padding, each serving a specific purpose depending on the type of floor covering that will be installed on top of it.
The extra layer of material installed over the subfloor is called the underlayment. It provides additional support, insulation, and a smooth surface for the final flooring. For example, in laminate flooring installations, an underlayment may be used to reduce noise and make the floor more comfortable.