Build lean: Why good projects must get built

Viability has dominated the construction industry’s agenda for years and the numbers are stark. Just 5,547 private homes were started in London in 2025, according to Molior, down 84% on a decade earlier, while JLL found the first quarter of 2026 delivered only 7% of the capital’s 88,000-a-year target.

London is also the fifth most expensive city in the world to build in, according to Turner & Townsend, and BCIS expects tender prices to rise a further 15.5% over the next five years.

Land values, finance and demand sit largely beyond the reach of design but construction cost does not. That is the focus of Build Lean, a Hawkins\Brown research initiative that examined six projects in detail and tested the findings with clients, contractors and consultants.

The projects - from across workplace, life sciences, residential, civic and mixed-use sectors - were deliberately chosen to cover a range of outcomes from completed and progressing schemes to stalled and redesigned ones. Each cost plan was broken down by building element to trace the main cost drivers back to the brief, design decision, standard or policy behind them, and to discover if each driver delivered value proportionate to its cost and carbon impact.

Three themes emerged, and each tends to cut carbon as well as cost, because the decisions that drive one so often drive the other.

Challenge the brief

The first is to challenge the brief. Some elements of a brief add cost and carbon without adding equivalent value, and project teams should be more willing to question them, with flexibility being the clearest example. Buildings are routinely briefed to accommodate a wide range of future uses from day one, including some that are highly unlikely.

Buildings are routinely briefed to accommodate a wide range of future uses from day one, including some that are highly unlikely

That built-in optionality has a price, leading to heavier structures, tighter vibration criteria, more extensive services and poorer net-to-gross ratios. Adaptability is different because it creates a building that can be sensibly altered when a new need actually arises, rather than one that pays up front for every need imaginable.

The industry is good at adapting buildings over time, so we should ask ourselves how we find that sweet spot between flexibility and a future that might never materialise.

The same scrutiny should apply where standards, certifications and policies overlap. BREEAM has given the industry a common language for environmental performance but an Outstanding building within these criteria is not automatically the most sustainable one; particularly because the system can reward process as much as outcome. Adopting adaptive thermal comfort ranges, for example, can reduce MEP plant requirements by up to 20%, with no credits required.

Be prepared to change course

The second theme is to be prepared to change course, radically if necessary. Conventional value engineering accepts the fundamentals of a scheme and looks for savings within them, element by element.

However, sometimes the largest cost lies in an assumption that the whole project has been designed around, made for good reasons but under different conditions.

Our research identified potential savings of tens of millions of pounds by revisiting those early decisions

On certain schemes, our research identified potential savings of tens of millions of pounds by revisiting those early decisions. These conversations are difficult because they reopen work that designers, clients and planners have invested heavily in but treating an early decision as permanent is not the same as protecting its value.

Rethink collaboration

The third theme is to rethink collaboration. Our industry follows a linear process, the RIBA Plan of Work, in which programme is king, and we found examples where that approach actively hampered viability. Stage 2, squeezed between feasibility and planning, is under particular pressure. Reaching planning quickly is sometimes the right call when it unlocks funding but teams should then be explicit about what becomes locked in and how it will affect viability. Where programme allows, a few extra weeks in Stage 2 can pay back many times over.

Viability transparency should be the norm rather than the exception

The most important finding, though, concerns who owns viability. On too many projects it is treated as a separate workstream, understood by some and shared with few, so the people making design decisions cannot see the numbers those decisions affect. Where the whole team had visibility of what was driving viability, the research found consistently better decisions and better outcomes. Viability transparency should be the norm rather than the exception, with these conversations happening together, and early.

Build Lean is not a call for less ambition but for more deliberate ambition, one which is clear about what decisions cost and what they delivers in return. Design teams cannot change land values or interest rates, yet they can create room for better conversations, bring the right people into decisions earlier and be candid about where cost and value part company.

Teams also need the courage to revisit decisions that no longer serve the project, however much has been invested in them. With so many good schemes stalling before they reach site, this is how we make sure the best ideas actually get built.

Oliver Milton is managing partner at Hawkins\Brown