The term Passive House refers to a rigorous, voluntary standard for healthy, comfortable and energy efficient buildings with a reduced ecological footprint. It results in ultra-low energy use and reduced utility bills for space heating and cooling. Buildings that meet this standard are also thermally comfortable with no cold drafts, and have extremely high air quality, free of toxins or mold. The standard is not confined to residential properties; office buildings, schools, and other commercial buildings have also been constructed to the standard. Passive House design is not an attachment or supplement to architectural design, but a design process that is integrated with architectural design. Although it is mostly applied to new buildings, it has also been used for remodels and retrofits.