Interior Designers are really the Interior Architects for the inside of your home or office space. And this is why Interior Designers and Decorators are uniquely separate professions.  Both possess many of the same professional responsibilities: principles of good design, theory of color(s), fabrics and furniture and accessory selections, purchasing and installing the products you select.
But there is a distinct difference and here is a brief explanation to help you understand and decide what is best for your needs. Interior Designers have a degree from an accredited college. A design degree is defined as: “The degree program includes such subjects as color theory and space planning, and more in-depth subjects as accessibility (handicap or ADA) and building codes, building structure and construction, plumbing mechanical electrical and structural issues that pertain to residential, commercial & retail design. “
If you are doing either a renovation or a remodel you would better suited working with a Designer/Interior Architect as they produce architectural working construction documents that can be stamped and sealed. These documents may include a space plan (demarcating egress and code compliance for doorways and clearances in kitchens and bathrooms for example), electrical & plumbing and reflected ceiling plans, millwork or special cabinetry detail plans, particular elevations. Designers assure your finish selections will arrive on time and be available for the contractor when he/she is ready to install.
Designers assist you in vetting any consultants along with reviewing and comparing project bids. During actual construction, we can perform Construction Administration, review pay requests and change orders or RFIs (request for more information) from General Contractors. Designers and Decorators are learned of the nuances and aesthetics of design principals; Decorators are better suited for strictly décor related projects. In essence, Designers are the interior architects even if we’re working with architects. As a homeowner making this distinction makes you a savvy client in assembling a comprehensive and knowledgeable team making for a successful design experience.