What QFD and the House of Quality are
QFD (Quality Function Deployment) is a method that translates the voice of the customer into measurable technical requirements, and the House of Quality is the matrix that makes the link: what the customer wants in the rows, how engineering will deliver it in the columns. The output is a ranked list of technical characteristics with numeric targets.
The method was developed in Japan by Yoji Akao starting in the 1960s and became known in the West through Hauser and Clausing's 1988 article "The House of Quality".
House of Quality visual map
The map shows the parts of the house, the worked example and the four QFD phases.
The parts of the house
- Customer requirements (the "whats"): the rows, written in the customer's words. They come from surveys, complaints and visits, and can be grouped with an affinity diagram.
- Importance: a 1 to 5 rating from the customer for each requirement.
- Technical characteristics (the "hows"): the columns, always measurable and with a unit.
- Relationship matrix: how strongly each characteristic serves each requirement, on a 9 (strong), 3 (medium), 1 (weak) or blank scale.
- Roof: correlations between characteristics, positive or negative.
- Competitive assessment: how your product and competitors perform, as in benchmarking.
- Priority and targets: the weighted sum per column and the target value for each characteristic.
Example: cordless drill driver
Fictional example from a power tool maker. Five customer requirements, five technical characteristics and the 9-3-1 relationship between them:
| Customer requirement | Imp. | Battery (Ah) | Weight (kg) | Torque (N·m) | Charge time (min) | Vibration (m/s²) |
|---|---|---|---|---|---|---|
| Lasts a full shift | 5 | 9 | — | 3 | 1 | — |
| Is light | 4 | 3 | 9 | 1 | — | — |
| Drives large screws | 4 | 3 | 1 | 9 | — | — |
| Charges quickly | 3 | 1 | — | — | 9 | — |
| Does not tire the hand | 3 | — | 3 | 1 | — | 9 |
| Score | 72 | 49 | 58 | 32 | 27 | |
| Relative weight | 30.3% | 20.6% | 24.4% | 13.4% | 11.3% |
Column score = Σ (importance × relationship)
For the battery: 5 × 9 + 4 × 3 + 4 × 3 + 3 × 1 = 45 + 12 + 12 + 3 = 72. The column totals add up to 72 + 49 + 58 + 32 + 27 = 238, and the relative weight is the score divided by 238. For example, 72 ÷ 238 = 30.3%.
The reading is straightforward: battery capacity (30.3%) and torque (24.4%) carry more than half of the weight (54.6%) and deserve engineering effort first.
Roof and targets
The roof shows conflicts between characteristics. In the example, four negative correlations call for a design decision:
- Battery × weight: more capacity adds weight.
- Torque × weight: a stronger motor weighs more.
- Torque × vibration: more torque tends to vibrate more.
- Battery × charge time: a bigger battery takes longer to charge.
With the priorities and the roof, the targets are set (fictional values for the example):
| Characteristic | Direction | Today | Target |
|---|---|---|---|
| Battery capacity | higher | 2.0 Ah | 4.0 Ah |
| Maximum torque | higher | 45 N·m | 60 N·m |
| Weight | lower | 1.9 kg | 1.6 kg |
| Charge time | lower | 90 min | 45 min |
| Handle vibration | lower | 4.0 m/s² | 2.5 m/s² |
A bigger battery at lower weight only works with a change of cell or motor technology. That is exactly the debate the matrix forces early, before production tooling.
The four QFD phases
The house described above is the first one. Full QFD carries the requirements down to the shop floor:
| House | Rows (what) | Columns (how) | Example |
|---|---|---|---|
| 1. Product planning | Customer requirements | Technical characteristics | Charge in 45 min or less |
| 2. Part deployment | Critical characteristics | Part characteristics | Cell and charger specification |
| 3. Process planning | Part characteristics | Process operations | Welding of battery connections |
| 4. Production planning | Critical operations | Production controls | Work instruction and control plan |
The critical characteristics also feed the FMEA and the deliverables of APQP.
When to use it
- New product development or a major redesign.
- Recurring customer complaints with no clear technical cause.
- Six Sigma projects in the define and measure phases, as in DMAIC, to choose what to measure.
Common mistakes
- Writing requirements as solutions ("use a lithium battery") instead of needs.
- Columns with no unit or target, impossible to verify.
- Building the matrix from internal opinion only, with no customer data.
- A giant house with 40 rows and 60 columns: limit it to the requirements that matter.
- Treating the score as mathematical precision: small gaps between columns are not decisive.
- Ignoring the roof and finding the conflicts only at the prototype.
Frequently asked questions
What is QFD?
Quality Function Deployment, a method that converts customer needs into technical requirements and then into parts, processes and controls.
What is the House of Quality?
The first QFD matrix. It crosses customer requirements (rows) with technical characteristics (columns), with a roof of correlations.
How do you calculate the priority of each characteristic?
Sum, down the column, the requirement's importance times the relationship (9, 3 or 1). For the battery in the example: 5×9 + 4×3 + 4×3 + 3×1 = 72.
Who created QFD?
Yoji Akao in Japan, starting in the 1960s. Hauser and Clausing popularized the House of Quality in the West in 1988.
What is the difference between QFD and FMEA?
QFD defines what the product must deliver to the customer. FMEA analyzes how the product or process can fail to deliver it.
How many requirements should the house have?
Usually 5 to 20 prioritized requirements. Beyond that the matrix gets hard to read and maintain.
Sources
- AKAO, Y. Quality Function Deployment: Integrating Customer Requirements into Product Design. Cambridge: Productivity Press, 1990.
- HAUSER, J. R.; CLAUSING, D. The House of Quality. Harvard Business Review, May-June 1988.
- REVELLE, J. B.; MORAN, J. W.; COX, C. A. The QFD Handbook. New York: Wiley, 1998.
- COHEN, L. Quality Function Deployment: How to Make QFD Work for You. Reading: Addison-Wesley, 1995.
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About the author
Lean Manufacturing & Behavioral Management Specialist
Over 20 years in the automotive and metalworking industries (GM and Dana), Lean Manufacturing practitioner since 2006. SENAI instructor and mentor in Brazil’s Brasil Mais Produtivo program, delivering consulting, training and audits for 50+ companies, combining quality, productivity and people development.
