what clauses would you use for the scernaio below?

Can anyone help me advise the contractor whether the comment (below) is correct using the appropriate clauses from the JCT SBC/Q 2016? The scenario is below:

The project concerns a privately funded new build multi-rise leisure complex.

The design had originally allowed for a traditional timber roof comprising joists, rafters and purlins. To reduce costs the Architect/Contract Administrator (CA) subsequently issued an instruction that changed the roof construction to trussed rafters. As a consequence of the change from traditional roof to trussed rafters the contractor has incurred difficulty in installing the ventilation ductwork in the roof space. The contractor’s labour costs have increased by 50% because of the restrictions imposed by the trussed rafters and material costs have increased by 30% because of the rerouting and extra wastage. The quantity surveyor is adamant that the contractor is not entitled to any extra payment for the ventilation work affected by the change in roof design as it has not been the subject of a variation.