Building Efficiently Act of 2018 This bill amends the Internal Revenue Code to expand the new energy efficient home tax credit to allow, in lieu of the existing credit, a credit for 3.3% of the cost of constructing a new energy efficient home that is a qualified energy efficient residential rental property. An energy efficient residential rental property must be certified as being constructed, reconstructed, or retrofitted under a plan designed to reduce energy and power consumption of the building by at least 40% compared to: (1) the baseline annual energy and power consumption of the building in the case of a retrofit made to an existing building, or (2) a reference building which meets the minimum requirements of the International Energy Conservation Code 2004 in any other case. The bill also eliminates the basis reduction requirements for low-income housing properties receiving: (1) the new energy efficient home credit, (2) the energy efficient commercial buildings deduction, or (3) the credit for investments in energy property.