Brettenham House moved from March to August — price the risk of designing around what strip-out reveals

What happened

McLaren Construction has completed a £90m cut-and-carve refurbishment of Brettenham House, the 1932 art deco building beside Waterloo Bridge, for developer Helical.

The project moved the building’s main plant from the roof into constrained basement vaults, inserted four new cores through the existing steel frame, added new pavilions and terraces at level 9, and restored the Portland stone façade.

Completion was initially announced for March 2026 but took place in August 2026. Helical said finalising the basement plant-area design was the main reason for the later finish, and acknowledged that the earlier programme was provisional while design development continued with the subcontractor.

Strip-out also exposed differences between the existing building and the design assumptions. The team used 3D surveys to map actual wall and ceiling positions, removed screeds where additional space was needed, and changed several construction solutions—including fire protection and core-wall build-ups—to make the design work within the retained structure.

The commercial lesson is not simply that the project finished five months later than first announced. It is that a provisional programme, incomplete package design and uncertain existing conditions must be identified, allocated and priced before they become someone’s unrecorded cost.

Does this affect you?

Directly, this is one completed London project. The same risk pattern appears on many two-stage design-and-build refurbishments: headline dates are set while services coordination is still live, and the true condition of the building is not known until strip-out.

It matters if you provide building services, drylining, blockwork, fire protection, ceilings, structural alterations, façades or finishes on refurbishment projects. Whether the risk becomes your cost depends on your subcontract, the information you priced, the agreed programme and who carries responsibility for existing conditions and design development.

If you work only on straightforward new-build projects with settled designs and clear access, the direct lesson is more limited.

Subby Mate: if you are on the tools

The one thing: Ask your authorised site or contract contact: “Which parts of my package are approved for construction, which parts are still being designed, and which programme am I expected to work to?” Get the response in writing through the project’s agreed communication route.

• If your start date, sequence or access changes, do not rely on a private note to yourself. Tell the contractor promptly, record what changed and issue any notice your subcontract requires. Track the effect on labour, supervision, plant, procurement and preliminaries. Whether you are paid will depend on the cause and the contract, but without a proper record you may struggle to demonstrate the effect.

• If the stripped building does not match the information you priced, stop before concealing or altering the condition. Photograph and measure the exact location—with a tape, laser or survey reference where appropriate—and send the evidence to the authorised contact. Follow the project’s photography and security rules. Ask for a written instruction before carrying out additional work.

• If a wall, ceiling or fire-protection build-up changes, treat it as more than a simple material swap. It may change quantities, labour, sequencing, interfaces, design responsibility and testing. Ask for the revised drawing or instruction and assess both additions and omissions before proceeding, subject to any immediate safety obligations.

If you are a subcontractor QS

• Establish what the tender programme actually is: a contractual programme, a target, or an indicative date based on unfinished design. State in your tender the mobilisation date, access sequence, working duration and number of visits included in your price. If those assumptions change, follow the subcontract notice procedure and record the resulting cost and time effects.

• Check who carries the risk that the retained building differs from drawings, surveys or models. On Brettenham House, post-strip-out surveys were used to compare the real structure with the design assumptions. If your work follows a similar survey, obtain the output, compare it with the tender information and raise discrepancies while the evidence is current.

• Define your design-assist allowance. Coordination workshops, surveys, builders-work information, samples, mock-ups and value-engineering proposals consume real resource, but they may already be included in your scope. State what your price includes, identify the deliverables and seek an instruction before providing additional services.

• Track reductions as carefully as additions. Brettenham House used revised solutions that saved space or cost, including a thinner ceiling build-up and refurbishment of existing handrails instead of wholesale replacement. Maintain a change register showing instructed additions, omissions, design-development work and any agreed savings so the final account reflects the complete movement in scope.

• Do not assume a later public completion date automatically creates entitlement. Test the cause against the subcontract, the accepted programme, access obligations, relevant events and notice requirements. Build the claim from contemporary records rather than the headline delay.

If you are a main contractor QS

• Where the client has placed early packages before the main contract, establish how each one enters your delivery structure: novation, assignment, retained client appointment or another arrangement. Record who owns design completion, payment, delay, defects, warranties and interfaces. Do not leave those responsibilities implied.

• If work starts under a letter of intent while design remains live, maintain a weekly record of the authorised scope, financial cap, expiry date, committed cost and outstanding contract terms. Obtain written authority before commitments exceed the letter rather than treating the eventual main contract as retrospective cover.

• Put existing-condition risk into the control process. Define what surveys will be undertaken, when design assumptions become verified and how discoveries after strip-out are instructed, assessed and incorporated into the programme. A model or tender survey should not quietly become a warranty of an inaccessible existing structure.

• Changes to fire-rated walls, ceilings or protection systems need formal technical review. Confirm the tested evidence, penetrations, interfaces, mock-up requirements and the party authorised to approve the solution before instruction. The time and cost of validation should sit with the party allocated that responsibility—not automatically with the installing subcontractor.

• Two-stage involvement can create value as well as exposure. Early specialist input on Brettenham House helped develop buildable solutions and identify savings. Capture that benefit transparently, but agree how design contributions and savings are valued so useful engineering is not treated as free tender support.

Risks and what to do about them

• A provisional date is priced as if it were fixed: State the programme and access assumptions used in your price, then clarify which dates become contractual when the subcontract is executed.

• Existing conditions differ after strip-out: Agree the survey baseline and risk allocation before starting. Photograph, measure and notify discrepancies before carrying out corrective work.

• Live design changes package boundaries: Require revised information or a written instruction, then assess quantities, omissions, interfaces, testing, design responsibility and sequence—not just the material-rate difference.

• Fire solutions require additional verification: Identify who provides tested evidence, who approves departures and who pays for modelling, mock-ups, testing and repeat attendance.

• Out-of-sequence working creates repeat visits: Price the assumed work sequence and number of mobilisations. Record withheld areas and later returns against the approved programme.

• Early packages or letters of intent leave responsibility unclear: Maintain a responsibility matrix and do not commit beyond the written authority, value cap or expiry date.

Do this week

Ten minutes: Ask the main contractor which parts of your package are approved for construction, which remain live and which programme your price is expected to follow. Save the written response with your contract records.

A day, if you can spare it: Audit every live refurbishment package against six headings: programme basis, design status, existing-condition risk, survey requirements, early-package or letter-of-intent interfaces, and notice rules. Add the missing assumptions and responsibilities to your tender qualifications, change register or project risk register before the next strip-out discovery turns into an argument.

Source: Adapted from publicly available construction industry news, analysed by QS-AI.