Learn English – In-house vs out-of-house

What word or expression would you use to describe an employee who is contracted by a company on a project-by-project basis but who cannot be considered a freelancer as he or she works exclusively for this company? In other words, what'd you call a specialist who is not on the payroll, works from home, gets paid per project but is commited to one company? Is it possible to use the expression "an out-of-house specialist" to denote a staff member who is not an in-house employee but cannot be really considered a freelancer? Thanks.