Building Design and Documentation Are Iterative

Building design starts with a concept, a sketch at a macro scale. At the first stroke of the designer's hand, there is no concern for concrete strength, nor concrete as a building material. The initial sketch may be a simple massing study to determine what a site will allow.

Each iteration (and there will be many in the process) will refine the design's response to available information that shapes the design. Iterate to respond to zoning restrictions: height, setbacks, volume. Iterate again for building code restrictions. And iterate several more times to optimize energy performance, aesthetics, and the owner's program.

Eventually, designers will be concerned about specific materials and details - not during schematic design, and rarely during design development. It's not until the construction documents phase that the details are explored, refined, and finally documented in the drawings and specifications. The construction specifications will record all the material and installation quality requirements for every product, assembly, and system incorporated into the project.

Specifications Are Not Iterative
The specificity, the detailed nature, of specifications does not accommodate an iterative process well. When writing specifications, even outline specifications, the first consideration is the particular material to be specified.

It is not enough to know that brick is required. What material: clay or concrete? What type of brick: solid or hollow? And the list of questions goes on, and on, and on. Without knowing the answers the specifier cannot correctly specify the brick.

So why do design teams use on specifications, especially during early design phases, to define project requirements and design intent?

How Do Architects Describe Buildings?
Ask an architect to describe the brick on the building. You will hear the architect begin describing the exterior wall - not the brick material, but the exterior wall as a building element. This common response is borne out by thousands of design team interviews to begin the specifications writing process.

Architects describe the building by element, the same way they design the building. So let's try to accommodate the obvious and provide a better way capture the design, especially during schematic design and design development phases.

Iterative PPDs Respond to Architects
Preliminary Project Descriptions (PPDs) have two distinct advantages over specifications. The documents are hierarchical and they are arranged by functional element. The PPD concept is explained in PPDFormat published by the Construction Specifications Institute and our PPDFormat Prezi.

PPDs rely on UniFormat for its organization. UniFormat describes buildings by functional element from the bottom-up and from outside-in. There are five hierarchical levels of specificity for functional elements. For example:

  Element   Title   Level
  B   Shell   Level 1
  B20   Vertical Exterior Enclosures   Level 2
  B2020   Exterior Walls   Level 3
  B2020.10   Exterior Wall Veneer   Level 4
  B2020.10.MV   Masonry Veneer   Level 5

Information can be documented at any or all levels, depending on how well the design is developed. If the brick cannot be defined, it is perfectly acceptable not to specify at Level 5. If the Level 4 veneer material is unknown, specify at Level 3.

Because of the hierarchy, information can be inserted into the PPD at each design iteration and at any level as the information becomes available. Start at high levels and fill in the lower level detail later. The higher levels will contain performance and design requirements. The lower levels will contain component and attribute requirements that make up the element construction.

I advocate developing PPDs to Level 3, where possible, but no deeper. This is the same level at which estimators usually report constructions costs. Use the lower levels as a checklist to be sure all required information is accounted for in the PPD. Matching the PPD level to the cost estimate level will allow direct cost comparisons of alternative design solutions for the individual elements.

Within each functional element, PPDFormat allows the element to be specified by a variety of methods. This flexibility permits the design team to document what is known without the temptation to guess about what is unknown. For B2020 Exterior Walls, the Level 3 PPD might be:

  • Descriptively - veneer clad insulated masonry cavity wall
  • By performance requirements - maximum 0.10 overall U-value
  • By design requirements -15 inches total thickness, maximum
  • By components - brick veneer, CMU backup, and board cavity insulation
  • By attributes - 3 inch thick mineral fiber insulation

More Than Words
PPDs are not limited to words. Graphics included in PPDs can be a powerful supplement to explain the intent for an element. Graphics can depict an element snapshot showing the basic construction, an element image borrowed from a photo library of existing buildings, or location and extent with a simple graphic overlay on a plan or elevation.

PPDFormat provides a structure for presenting information. It allows flexibility within the format to permit accurate, understandable project descriptions that reflect the current design progress.

Learn More
Schedule a live WebEx session about PPDs to earn 1.0 LU/HSW AIA CES credit. Write to me at

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