3.1.18 PPPs are procurement of services. Thus, output- or outcome-based specifications should be used as much as possible to allow the private sector as much flexibility as possible to provide innovative solutions that meet the need of the GPE at the lowest possible whole lifecycle cost.
3.1.19 Nonetheless, it is hard to achieve 100% use of output- or outcome-based specifications for PPP contracts. Some input-based specifications will usually be necessary, such as specifying the key defined materials to construct a building or an outline but not detailed design for the PPP provider's reference.