The involvement of the client is essential in construction contracts. Without it, a complex construction project often cannot be successfully realized. This work addresses the legal consequences of the client's failure to participate, such as missing plans, inadequate pre-performance, or delayed approvals. Starting from the general contractual classification of the client's participation actions as mere duties to cooperate, the study examines whether this system should be maintained in construction contract law according to the German Civil Code (BGB) and the German Construction Contract Procedures (VOB). While the majority of literature and case law largely elevates the client's necessary participation actions for the construction of the building to genuine obligations, the author concludes that the duty to cooperate model of the BGB should largely be upheld. This is justified by a dogmatic analysis of the legal system, taking into account the special interests of the parties involved in the construction.