ADUs are one of the most environmentally-friendly forms of housing due their small size, efficient use of land and existing infrastructure, and the energy efficiency built into each unit. As small houses, ADUs use fewer materials and therefore lessen the impact on natural resources and the costs associated with manufacturing and transporting building products. In addition, an ADU’s small size also means that the units use less water and electricity.

Given that most of the environmental impact from a house is due to its energy use, a new ADU is extremely energy efficient. In addition to their small size, most ADUs have been recently constructed using updated building codes and utilize electric heat pumps, the most energy efficient heating and cooling systems. Modular ADUs, which are factory-built under tight tolerances designed to meet stringent building codes, also offer energy efficiency benefits over site built ADUs.