We carry the design liability for a design we weren't allowed to make

Design and build is meant to trade risk for control: you carry the design liability because the design is yours to make. The version that goes wrong is the one where the employer's requirements dictate every product, dimension and detail - and the contract still hands you the liability for choices you were never allowed to make. If the prescribed detail fails, the argument about whose failure it is starts on their drafting, not yours.

This is a clause negotiation, and it has to happen before signature: liability aligned with actual design freedom, prescribed elements carved out or their risk priced, the design submission procedure made to mean something. Because design liability sits close to legal rights, the drafting itself is a solicitor's work; the commercial case for what the clauses should say - and what each version costs - is the part I build.