An idea is formed. A new product or service is required. A need for a building emerges. What is the next step – a napkin concept sketch of a building form?
The first steps should be to define the owner’s requirements. What people, equipment, processes, and performance must the building accommodate? All of these questions should be answered before the first line is drawn. The design must respond to and embrace the project requirements rather than forcing the project to fit the design.
Preliminary Project Descriptions (PPDs) provide a structured means for owners and design teams to communicate the overall project needs before design is started. PPDs are more than architectural programming that sets occupancy, equipment, finish, and environmental requirements for individual spaces. Overall project performance and design requirements for each building functional element can be documented to inform the resulting designed solution. With a fact-based description, the design can be measured and tested to ensure the project requirements and the owner’s expectations are met.
Because PPDs are hierarchical, requirements can be written at the highest (overall) level at the start of a project. Later, as development decisions are made, data can be added as lower level detail to refine the high level requirements. When the owner’ project requirements are defined, owner’s project budgets will be meaningful and a useful way to measure the design team’s response.
One of the most important aspects of the process is developing a realistic budget to meet the owner’s expectations. Reliance on square foot building costs from the last project or a similar project may not suffice. Many considerations affect construction costs. Many of these are identifiable before design begins.
Bay spacing may be determined by the desire for flexibility to reconfigure interior spaces as the owner’s needs change over time. Bay spacing may be set by the size of typical project spaces – hotel guest rooms, for instance. Nevertheless, bay spacing influences costs. The greater the bay spacing the deeper the floor structure to make the span. The deeper the floor structure the greater the floor-to-floor heights to accommodate the structure.
Floor-to-floor height can have a significant impact. When spaces requiring the greatest heights are stacked, the volume of the entire building grows. All the resulting volume may not be useable. Take a courthouse for example. Courtrooms require a greater clear height than the administrative offices that support the courtrooms. Stacking courtrooms on multiple floors will increase the overall building height. Grouping courtrooms on a single floor will make the most efficient use of the building volume.
Building shape impacts the ratio of exterior wall area to the floor area. The more exterior building enclosure that is required, the greater the building cost. A circle encloses the greatest area with the least perimeter. However, circular buildings are not typically conducive to efficient interior layouts. The next most efficient plan shape is a square.
These illustrations show the dimensions and perimeter length for the same unit area enclosed by basic geometric shapes. Squares require 13% greater perimeter than circles, and rectangles require even more. This is not to suggest that every building should be a circle or square. Simply, shape impacts cost.
Building shape is not the only cost factor. Articulation and glazing percentage will both have significant impacts. Articulation, the ins and outs and zigs and zags, of the building facade add complexity and enclosure area. Glazing systems are more expensive than opaque wall assemblies and are less energy efficient. It’s a balancing act to achieve an optimum design meeting the owner’s expectations. Trade envelope area and complexity for improved performance. Trade glazing percentage for natural lighting and occupant views.
So what is the point ?
Well, all of these factors and more are identifiable and controllable. PPDs provide the means to document project constraints. The result is a quantifiable, measurable description of the owner’s expectations.
Project budgets developed without defining the factors affecting costs can lead to disappointment. Without direction, the owner’s cost consultant will make assumptions – assumptions based on past experience, but not necessarily the correct assumption for the project.
Without the benefit of documented requirements, the design team will proceed based on their own assumptions and experience. When this happens, as it routinely does, there should be no surprise when the designed solution is determined to cost more than the budget.
Make good use of available tools
PPDs are a valuable asset to help define the owner’s project requirements. PPDs provide the means to verify the resulting design meets the defined requirements. Then if a design exceeds the budget, avoid cost cutting. The entire team can evaluate the cost with factual value engineering weighing requirements against results. Adjust the requirements, if needed, and re-evaluate. And ultimately, deliver a design meeting the owner’s expectations.