As an American expert in home renovation, the subject that stands out as crucial is interior design. Interior design is the art and science of enhancing the interior of a space to achieve a healthier and more aesthetically pleasing environment for the people using the space. This subject is paramount because it directly impacts the functionality, comfort, and value of a home.

According to the American Society of Interior Designers (ASID), interior design can increase the value of a home by up to 10-15%. This is due to the strategic planning and execution that interior designers bring to a renovation project. They consider factors such as space utilization, color theory, furniture layout, and lighting design, all of which contribute to a cohesive and efficient living space.

Moreover, a well-designed home can significantly improve the quality of life for its inhabitants. The U.S. Census Bureau reports that home renovations can lead to increased satisfaction with one's living environment. For instance, a study by the National Association of Home Builders (NAHB) found that 75% of homeowners who invested in home renovations were satisfied with the results, with 65% reporting improved comfort and 58% noting increased functionality.

Interior design also plays a vital role in sustainability. As more Americans become environmentally conscious, the demand for eco-friendly home renovations has surged. Designers who specialize in sustainable interior design can help homeowners make choices that are not only aesthetically pleasing but also environmentally responsible. This includes selecting materials that are recycled, renewable, or locally sourced, and incorporating energy-efficient lighting and appliances.

In conclusion, interior design is the cornerstone of successful home renovation projects. It not only enhances the value and appeal of a home but also improves the quality of life for its occupants and contributes to environmental sustainability. The data from ASID, the U.S. Census Bureau, and the NAHB underscores the importance of interior design in home renovation, making it the subject that should be at the forefront of any renovation project.