Project Stages: post-tender client changes and the design freeze

You are appointed under a RIBA Standard PSC 2020 on a £5 million Cat B office fit-out of two floors of a Grade A office building in central Birmingham. The client is a professional services firm acting as both Employer and end-user. The project was procured under a JCT Standard Building Contract 2024 with Quantities, tendered to three pre-qualified contractors at the end of Stage 4, awarded to the lowest tenderer, and the building contract was executed three weeks ago. At Stage 4 you held a formal client design sign-off meeting. Drawings, finishes schedules, the M&E performance specification, and the FF&E schedule were all signed off and your stamped Stage 4 Information Release Schedule was issued to the contractor as part of the tender documents. The contractor's programme is 26 weeks to Practical Completion. Six weeks into construction (week 6 of 26), the client's facilities director emails you with three "small" changes which the firm's senior partners agreed at a board meeting the previous Friday. First, relocate the feature stair from the centre of the floorplate to a position adjacent to the south curtain wall, in order to "improve the wow factor for client visitors". Second, add a green roof to the existing tenant terrace area, including a new irrigation system. Third, convert the ground floor toilets from "standard" to "fully accessible" with universal use changing places. The client describes them as "minor" and says the project should "just absorb them". You ask the contractor for a budget impact. The contractor's quantity surveyor returns within two days with an estimate: £180,000 of additional cost and 4 weeks programme. The contractor confirms that the feature stair change alone will require structural revisions, new fire engineering input on the means of escape, and substantial mechanical service rerouting. The client telephones and says "they are tiny changes, just instruct them".