Why a project has phases
A project is not designed from less to more detail out of habit or bureaucracy. It works that way because every decision makes the decisions after it more expensive. Choosing the structural system in month one costs a meeting. Changing it in month fourteen costs redoing the MEP, the façade, the foundations and the budget.
Phases exist to put doors in the way: moments where the project freezes enough that the next layer of work can rest on it without fear. Without those doors, everybody builds on sand and everybody does it twice.
A phase is not a period of time. It is an agreement about what is no longer up for discussion.
Which leads to the practical consequence: the effort you put into a task has to match the phase the project is in. Measuring to three decimal places off a drawing that is still going to change is not rigor. It is work that will be thrown away, and it manufactures a confidence the number has not earned.
The equivalence table
This is the translation that prevents half the misunderstandings between teams in different countries. The first column is the only real thing. The rest is what it happens to be called in the contract in front of you.
| Project maturity | Buildings · AIA (United States) |
United Kingdom RIBA 2020 |
Civil works (percentages) |
Industrial (process) |
Latin America and Spain |
|---|---|---|---|---|---|
| Idea and brief | Pre-design · Programming | Stages 0–1 | Concept · 15% | FEL 1 · Conceptual | Prefactibilidad |
| General scheme | SD · Schematic Design | Stage 2 · Concept Design | 30% | FEL 2 | Anteproyecto |
| Definition and coordination | DD · Design Development | Stage 3 · Spatial Coordination | 60% | FEL 3 · FEED | Proyecto básico |
| Documents to build from | CD · Construction Documents | Stage 4 · Technical Design | 90% → 100% | Detailed engineering | Proyecto ejecutivo |
| Tender | Bidding & Negotiation | End of Stage 4 | Bid documents | EPC award | Licitación |
| Construction | CA · Construction Administration | Stage 5 | Execution | Construction and commissioning | Obra · Interventoría |
| Handover and use | Close-out | Stages 6–7 | Acceptance | Start-up | Entrega · Operación |
Three details worth the whole table
- In 2020 the UK renamed its Stage 3 from «Developed Design» to «Spatial Coordination». They named the phase after the work that actually happens in it, which is the best possible hint about what matters at that point.
- In civil works the percentages mislead. 60% does not mean 60% of the work is done — it names a defined package of deliverables. A well-executed 60% may already have consumed 75% of the effort.
- If you work with Latin American teams, know that Colombian public roadway projects run on Fase I, II and III studies, which correspond to prefeasibility, feasibility and final design. It is a vocabulary that catches out anyone arriving from buildings.
What each discipline delivers in each phase
The phases are the same for everyone, but «being in DD» means very different things depending on whether you are the architect, the structural engineer, the MEP engineer or civil. And since the budget and the schedule feed off all of them, this table is what lets you work out which discipline the gap is coming from when something does not add up.
| Discipline | SD | DD | CD | CA |
|---|---|---|---|---|
| Architecture | Scheme, areas, envelope, general plans | Dimensioned plans, sections, elevations, wall types, defined fenestration | Construction details, door, window and finish schedules, specifications | RFI responses, submittal review, record drawings |
| Structure | Structural system chosen, spans, preliminary sizing | Member sizes fixed, loads coordinated, foundation scheme | Reinforcement drawings, schedules, notes and specifications | Shop drawing approval, testing, rebar acceptance |
| MEP | Estimated loads, space reserved for equipment, conceptual services | Main routing, equipment selected, plant rooms sized | Installation drawings, final sizes, supports, single-line diagrams | Fabrication drawing approval, testing, commissioning |
| Civil and site | Siting, general levels, access, preliminary earthworks | Profiles, external utilities, drainage, paving | Final sitework quantities, utility details | Grade control, compaction testing, utility acceptance |
| Estimating | Parametric or cost-per-area estimate. Class 4 or 5 | Measurable quantities by system. Class 3 | Quantities by line item with unit price analysis. Class 2 or 1 | Control against actuals, change orders, final account |
| Scheduling | General milestones and overall duration | Sequence by work front, preliminary rates | Detailed schedule with supported durations | Updates, actual progress, delay analysis |
A project is almost never in a single phase. It is in DD for architecture, SD for MEP and CD for structure, all on the same day.
Which produces the rule almost nobody applies: a project's phase is the minimum, not the average. If you are taking off MEP quantities and MEP is in SD, it does not matter that architecture is in CD. Your number is an SD number, and it should be delivered as one.
How firm can a budget be at each phase
There is an international scale for stating how firm a cost number is. It comes from the process industries, where being wrong at the wrong stage costs hundreds of millions, and it is used worldwide under the name estimate classes.
| Class | Project definition | What it is for | Typical range |
|---|---|---|---|
| Class 5 | Essentially nothing defined | Screening whether it is worth thinking about | ±20 to 50% |
| Class 4 | General concept | Feasibility study | ±15 to 30% |
| Class 3 | Design defined at system level | Budget authorization | ±10 to 20% |
| Class 2 | Advanced design, measurable quantities | Control and bidding | ±5 to 15% |
| Class 1 | Complete documents | Firm bid, check estimate | ±3 to 10% |
The ranges vary by sector: buildings and process industries publish different tables. What does not vary is the idea that a number travels with its uncertainty.
A number without its class is not an estimate. It is an opinion with two decimal places.
How this is used in practice
- Label it. The estimate goes out with its class written on the cover, next to the project phase and the date. Three facts, one line.
- Support it. Contingency is not an inherited percentage: you explain why this class needs that much cushion.
- Protect yourself. When the client compares the SD estimate against the final bid and asks why it went up, the answer was written down from the start.
The most common mistakes
- Measuring architecture and estimating MEP, then handing both numbers over with the same confident face. It is the most expensive error in estimating, and it is not a measurement error.
- Issuing a number without its class. The client files it as final, because to them it is.
- Pricing off a drawing issued for coordination. Its own author does not consider that drawing settled yet. The issue state is printed on the sheet; almost nobody reads it.
- Mistranslating the phase in an international contract and delivering a DD set where a CD set was expected, or the other way around.
Frequently asked questions
What do SD, DD and CD mean?
They are the three design phases in the American system. SD (Schematic Design) is the general scheme, DD (Design Development) is definition and coordination between disciplines, and CD (Construction Documents) is the set you build from. They correspond to anteproyecto, proyecto básico and proyecto ejecutivo respectively.
What is the difference between Schematic Design and Design Development?
SD settles what the building is: massing, areas, layout, the structural system. DD settles how it works: dimensions fixed, systems routed, equipment selected, disciplines coordinated against each other. The clearest test is that in SD you can still change the scheme; in DD you can only change details of it.
How do 30%, 60% and 90% design map to SD, DD and CD?
Roughly, 30% corresponds to SD, 60% to DD, and 90–100% to CD. But the percentages do not measure effort spent: they name packages of deliverables defined by contract.
What is FEED?
Front End Engineering Design, the definition phase in the process and industrial world. It corresponds roughly to DD, and it is usually the stage on which the final investment decision is taken.
Can you give a budget at SD?
Yes, as long as you state its class. At SD a reasonable estimate is Class 4 or 5, with a range that can reach ±30% or more. What you cannot do is issue that number without declaring its uncertainty: whoever receives it will treat it as final.
Can a project be in two phases at once?
It almost always is. Architecture in CD, structure in DD and MEP in SD within the same project is normal. For the purposes of what can be promised, the project's phase is that of the least advanced discipline, not the average.