Dayworks refer to works executed on a time basis (e.g., labor and plant) with payment made according to predetermined rates rather than a lump sum or unit rate contract price.

Option A is incorrect. Even if a Daywork Schedule is not initially included, the dayworks Sub-Clause (e.g., Sub-Clause 13.7 in Red and Yellow Books, 13.8 in Silver Book 1999) still applies to dayworks ordered during the contract execution. The schedule facilitates pricing, but the Sub-Clause governs the method and conditions for dayworks.

Option B is correct. The dayworks Sub-Clause is applicable not only to traditional construction works but can also be applied to other types of works, such as variations or additional works that cannot be precisely measured or foreseen and are charged on a time basis.

Option C is incorrect. The dayworks Sub-Clause is used in all FIDIC standard forms (Red, Yellow, and Silver Books), not only for remeasurement in the Red Book. In the Yellow Book (plant and design-build) and Silver Book (EPC/turnkey), dayworks are similarly applicable for certain variations or unforeseen works.

Option D is correct. The Engineer (in Red and Yellow Books) or the Employer (in the Silver Book, where the Engineer’s role is limited) may instruct that a variation be executed on a daywork basis. This instruction is typically used when the scope or quantity cannot be reasonably pre-determined.