The fate of a building is largely decided in the first weeks. What we think through at the design desk goes smoothly on site; what is left open there costs money and time during construction. This relationship is shown by the MacLeamy curve – and it is why we work the way we do.
What does the curve show?
The diagram was published in 2004 by the American Construction Users Roundtable (CURT) in a paper on collaboration between design and construction; it was popularised by the architect Patrick MacLeamy, which is why it bears his name. It puts four curves side by side:
- the ability to influence: at the start of a project almost anything can still be changed, with a big effect on cost and usability – this ability decreases quickly over time;
- the cost of change: what is a crossed-out line at the start later means reorganisation, demolition and remanufacturing – the cost of a change rises steeply over time;
- the traditional workflow: most of the design work comes late, during detailed design, when changes are already expensive;
- the proposed workflow: the focus of the work moves forward, to where decisions are still cheap and have a big effect.
Once two-thirds construction, now two-thirds design
In our experience, on a traditional construction project about one-third of the total time used to be design and two-thirds construction. With prefabricated CLT and modular construction this is reversed: roughly two-thirds is design, and only one-third is construction.
The literature supports this. According to a design manual for multi-storey timber buildings, because of prefabrication important decisions in timber construction must be made earlier than in traditional construction; producing modular elements requires final decisions at an early stage, and subsequent corrections on site are almost impossible. At the same time, the longer design phase is usually offset by a shorter construction time: part of the time saved on construction has to be invested in careful design.
What do you gain?
- Precision. The elements are made on computer-controlled machines from the 3D model – including openings and penetrations. What is in the design is what arrives on site.
- Fewer problems on site. Clashes, missing service openings and questionable connections are discovered in the model, not under the crane.
- Shorter, calmer construction. Assembly is short, dry and fast; according to an international analysis, modular construction can shorten construction time by 30–50%.
- Predictable cost and schedule. What is decided in time does not cause later changes – and late changes are the most expensive.
The total time is therefore not longer – it is just spent elsewhere: at the design desk, where a mistake can still be fixed with a click.
What does this mean for you?
- Involve us early. We can help most at concept stage, when the structural system, spans and panel layout can still be freely shaped.
- Allow enough design time. The design phase will be longer than you are used to from traditional construction – it is worth fixing this in the schedule in advance.
- Decide in time. Prefabrication does not tolerate changes along the way; what you decide before production starts goes smoothly.
- Let the team work together. The literature also recommends bringing timber construction expertise into the team at the early design stage – not only after the contractor has been selected.
How we help
That is why we move the larger part of the work to the start of the design: we first build the building in a shared 3D model and settle every question where it is still cheapest to get it right. Read more on our How we work page.