This chapter is devoted to the tailor-made JCT contractor's designed portion supplement, introduced in Chapter 4 and to which JCT Practice Note CD/2 applies. The supplement is intended for a relatively large, fairly self-contained part of the works, such as a distinct structure or functioning element, as is described further under the first heading below. An alternative approach intended for smaller elements of work, usually less independent in character, is to use the clauses for performance specified work (at one time viewed as contractordesigned construction by standard methods of measurement) contained in the various editions of the JCT standard form of building contract. This approach is considered in Chapter 17, where the distinctions between the clauses and the present supplement are outlined. For suitable projects, both the supplement and the clauses might be used within the same contract.