FAST (Function Analysis System Technique)
A diagram that asks what something must do before asking what it should cost.
Quick Answer
FAST (Function Analysis System Technique) is a value-engineering method that diagrams the functions a project or component must perform. Each function is written as a verb and noun, then arranged left to right using how and why questions. The map shows which functions are essential, so the team can search for cheaper ways to deliver them.
The Full Picture
Value engineering usually begins with the design as drawn and asks how to reduce cost. FAST starts one step earlier and asks what the design is for. The team lists the functions the project or system must perform, each phrased as an active verb and a measurable noun, such as support load, enclose space or control temperature. The method is generally credited to Charles Bytheway and dates to the mid-1960s.
The diagram is built by logic rather than by drawing. Reading left to right, you ask how a function is accomplished and the answer is the function to its right. Reading right to left, you ask why the function is performed and the answer is the function to its left. The far left is the highest-order function, which is the objective of the study, and a critical path of functions runs between it and the basic function. Supporting functions that do not sit on that path are placed above or below it.
That structure lets a team see where cost is going. Each function can be assigned a rough cost, and a function that is expensive but sits far from the objective is a candidate for a cheaper approach. The team then brainstorms alternatives for the function rather than for the specific product, which opens more options than swapping one finish for another.
FAST is one tool inside the value engineering job plan. Public owners use value engineering formally on large projects; for example, federal highway rules define a VE analysis as a systematic process of review by a multidisciplinary team not directly involved in its development. The wider process, including the cost-saving proposals that result, is covered on the value engineering page.
For a GC preconstruction team, the practical value is in workshops. A FAST diagram keeps the conversation on required function so that value engineering does not degrade performance by accident, and it gives the owner a clear reason to accept or reject each idea.
Real Examples
Common Misconceptions
People assume: A FAST diagram is a flowchart of construction steps.
Actually: It does not show sequence or time. It maps functions using how and why logic, so it describes purpose rather than process.
People assume: Value engineering with FAST is just a way to cut cost.
Actually: Federal descriptions of value engineering stress improving value and quality as well as lowering cost. FAST protects required functions so savings do not come from removing them.
Frequently Asked Questions
What does FAST stand for?
FAST stands for Function Analysis System Technique. It is a function-mapping method used in value engineering and value analysis.
How do you read a FAST diagram?
Read left to right by asking how each function is done, and right to left by asking why it is done. The highest-order function sits at the left and the basic function is on the critical path leading from it.
Why are functions written as a verb and a noun?
A verb-noun pair, such as support load or enclose space, forces a specific statement of purpose that is independent of any product. That makes it possible to compare very different solutions to the same function.
When in a project is FAST used?
It is most useful during a value engineering study in schematic or design development, when the design can still change at low cost. It can also be used on a single system, such as the building envelope.
Who takes part in a FAST workshop?
Usually a multidisciplinary group: owner representatives, designers, the contractor or estimator, and sometimes operations staff. A trained facilitator leads the logic so the diagram stays about functions.