Sustainable Design Is Not a System You Add at the End - It Is a Process You Follow From the Start
The most persistent misconception about sustainable building design is that sustainability is achieved by specifying better mechanical equipment, more insulation, or high-efficiency lighting at the end of the design process. This approach - applying efficiency measures to a building that was designed without considering sustainability - always costs more and performs worse than designing the building for sustainability from the first day. The integrated design process (IDP) reframes sustainability as a fundamental design driver from schematic design onward, with cross-disciplinary input from the architect, engineers, sustainability consultants, and key owner stakeholders at every major decision point. The LEED Integrative Process credit, the ARE PPD exam's sustainable design content area, and the practical experience of high-performance building designers all converge on the same point: the earlier sustainable decisions are made, the more impact they have on building performance and the less they cost to implement.
The MacLeamy Curve
Patrick MacLeamy's influential diagram (the "MacLeamy Curve," published by the AIA) illustrates the relationship between the time in the design process, the ability to influence design outcomes, and the cost of making changes. The curve shows: in early schematic design, the ability to influence the building's design (and therefore its performance) is at its highest, while the cost of making changes is at its lowest. As the project progresses through design development, construction documents, construction, and post-occupancy, the ability to influence outcomes decreases dramatically while the cost of changes increases dramatically. The integrated design process moves design decision-making earlier - investing more time and energy in the pre-design and schematic design phases to make better decisions when the impact of those decisions is greatest.
What Changes in an Integrated Design Process
In an IDP project: the entire design team (architect, structural, MEP, sustainability consultant) is engaged from the beginning of schematic design, not phased in after design decisions are already made; energy modeling is used in schematic design to evaluate the impact of building orientation, form, window-to-wall ratio, and shading strategies before those parameters are fixed; daylighting analysis informs the placement and sizing of windows before interior layouts are finalized; structural and MEP systems are selected based on integrated analysis of how they interact with each other and with the building envelope; and owner goals for performance, operations, and total cost of ownership are explicitly considered alongside first cost.
Key Exam Points
- IDP: all disciplines engaged from early schematic design; sustainability decisions made before design is fixed.
- MacLeamy Curve: ability to influence outcomes is highest early; cost of changes is lowest early - invest in early decisions.
- Energy modeling in SD: evaluates orientation, form, and window-to-wall ratio before these are committed.
- LEED Integrative Process (IP) credit: rewards early energy and water analysis in the design process - 1 point.
- IDP is a process change, not a technology add-on - it requires owner and team commitment from project kickoff.
Study PPD on AREprep
AREprep’s PPD flashcards cover every concept on this exam with spaced repetition, and the practice exams mirror the real question formats so the actual test feels familiar.