Changes made to the interior of a commercial or industrial property by its owner to accommodate the needs of a tenant such as floor, wall coverings, ceilings, partitions, air conditioning, fire protection, and security. Who bears what portion of TI costs is negotiated between the lessor and the lessee, and is usually documented in the lease agreement. Tenant Improvements/Leasehold Improvements The real estate definition of Leasehold improvements, also known as tenant improvements (TI), are the customized alterations a building owner makes to rental space as part of a lease agreement, in order to configure the space for the needs of that particular tenant. These include changes to walls, floors, ceilings, and lighting, among others. In actual practice, these customized tenant improvements usually have a useful economic life of 5 to 10 years