You will need to check how the storage provision was incorporated in to the contract. If it was a tender amendment that is referenced in the Form of Agreement and which refers to the Specification then it should be considered as part of the Works Information.
Changing the requirement would then be a change in the Works Information and a compensation event the assessment of which should reflect the cost saving (actual Defined Cost saving).
Changing the requirement would then be a change in the Works Information and a compensation event the assessment of which should reflect the cost saving (actual Defined Cost saving).