Prioritizing Technical Requirements with a House of Quality [transcript]

As a design engineer, you’re tasked with translating vague customer statements into something technical and measurable. Like a customer says, “I have to pull too hard on this,” may translate to “The pull force of the device should be less than 45 N when loaded with 700 N of weight.” And you also need to identify what requirements are important. Filtering the “must meet” requirements against the “should have” requirements. And finally, you need to do this with your cross functional team. What if you miss something important? It’s difficult. There is a method that we can use. Let’s talk about the House of Quality and how you can use it no matter where you work, after this brief introduction.

Hello, and welcome to Quality during Design the place to use quality thinking to create products others love for less. My name is Dianna. I’m a senior level quality professional and engineer with over 20 years of experience in manufacturing and design. Listen in and then join the conversation at

QFD is Quality Function Deployment. It’s a planning method that shows the relationships between the customers and product development information. It’s based on a series of matrix diagrams. The goal of the matrix diagram is to ensure that our customer requirements are carried through the product development process through design, manufacturing, and quality control.

How did this method come to be? QFD originated in Japan in the 1970s with Mitsubishi and Toyota. Toyota, less than two years into using it, saw a 20% reduction in startup costs on the launch of a new vehicle. With time and iterations, they saw a 61% reduction in startup costs, development fell by one third, and quality improved. Xerox and Ford started using QFD in the mid 1980s, and now lots of industries and different companies use QFD, Quality Function Deployment.

QFD is a system that uses several matrices that follow a waterfall application where the top level matrix feeds into the next level matrix. It starts with a House of Quality: customer requirements against technical requirements. Then that feeds into technical requirements against component characteristics. That then feeds into another matrix of component characteristics against process operations. And finally, those process operations are mapped out in a matrix against a quality control plan. If you are working in a company that uses QFD, then you’re likely working with four to five matrices that are linked, that are built to ensure that customer needs are reflected in the requirements, components, manufacturing process, and the overall quality control. If your company isn’t using QFD in this way, then you’re probably not being supported to be able to do QFD for your project. It can be large and confusing. So you need to evaluate the benefits you’ll get from it against what your company is currently doing.

But that doesn’t mean that we can’t use elements of QFD, especially the first matrix, the House of Quality. The House of Quality maps that voice of the customer against the technical requirements that we’re trying to define. The House of Quality also lets us evaluate the technical requirements against each other because design decisions usually affect more than one technical requirement. We’ll have the main structure of the house and its roof, and that’s as far as we really need to take it, if we want. And if our company doesn’t use QFD, just out of this we’ll get a prioritized list of technical requirements. We’ll know the “must haves”, the “should haves”, and the ones that may not be a priority for our project. It’ll be based on what our customers are telling us. And we’ll have a map of what technical requirements may be linked to the same design decisions.

How do you build a House of Quality matrix?

First, like most quality tools, gather your team. You want people that know the customer, their space and people that can develop technical requirements.

Second, define the customer. If your customer base is broad, you might have voice of the customer data that contradicts itself. So consider a House of Quality for each customer base or prioritize one type of customer over another. Another option is to average out the importance of any one customer requirement over all of your different customer bases. Just figure out what the scope of your house is going to be to start and then move on to the next step. Don’t let analysis paralysis stop you from trying to build a house.

Third, list out the customer needs, or the voice of the customer in rows. List technical requirements in columns. If you get into 25 customer requirements and 25 technical requirements, this house may turn into a mansion and too big! Make sure requirements aren’t duplicated for customers. Check that we’re not listing trivial ones, things that a very small proportion of our customers happen to mention.

Our fourth step in building a basic House of Quality is to define a three level relationship legend: low, medium, and high relationships. It could be colors, shapes, or emojis! Choose whatever makes you happy. Just make sure you can differentiate between them at a glance. The typical symbols are a square, circle, and triangle.

The fifth step is where you want to show the interrelationships between the customer requirements and the technical requirements in the main structure of the house. Quality practitioners sometimes call this the relationship matrix. For each customer requirement and technical requirement relationship, you’re going to list one of your low, medium or high symbols in that square, or your square may be blank.

The sixth step is to make the roof. The triangle roof sits on top of the technical requirements, and there’s a box where any two requirements intersect. Quality practitioners sometimes call this the correlation matrix. Use your low, medium, and high relationship symbols to show how the technical requirements fit together.

Now let’s stop building and let’s just use what we have right now. Examine the main structure of our house, the relationship matrix: customer requirements in rows on the left – technical requirements and columns on the top – and low, medium high symbols or blanks in the matrix that’s between the requirements.

Do we have an empty row? Uh, oh, we have a customer requirement that doesn’t have a technical requirement. We should fix that.

Do we have an empty column? Now we have a technical requirement with no associated customer requirement. Did we miss something or do we need to remove a technical requirement?

Do we have a row or column that has no high relationship correlations? There should be at least one high correlation between a customer requirement and a technical requirement. Otherwise it’s going to be hard to make something our customer needs. We may need to rethink our technical requirements.

Are there rows that look identical? If so, that could indicate a problem with our customer requirements. Their level of detail may be different from one another. So we’re not evaluating customer requirements in a consistent manner. Or we may have a customer requirement listed that’s really a child requirement of another one that’s already in our matrix. We should reevaluate our customer requirements.

Is there a row or column with a lot of relationship? Then it might be an issue for reliability, for safety or for cost. We want to investigate this requirement more thoroughly to understand what’s happening here.

Overall in the matrix, which technical requirements have a strong relationship to a customer requirement? These are requirements that we should think of as a high priority because they’re strongly associated with our customer requirements. And we would also want to follow through and make sure that we follow through on those requirements through the rest of the product development process.

Now let’s look at the roof: the correlation matrix. Here, we’ll see tradeoffs between design options, because it shows the relationship between pairs of technical requirements. Which ones are similar? Which are opposite? Are there effects and consequences between requirements that we hadn’t thought about? Understanding the relationship between the technical requirements can help us ensure that customer requirements are met; that the quality is at least maintained, if not made better; and the cost is taken into account.

If you like this, then take it a step further. Add another room to the house. Compare our product to competitive products. For these we’re looking for areas of competitive advantage. Our competitive products don’t do well at meeting this customer requirement. So, if we build it into ours, we’ll have a competitive advantage. And that gets into key selling points and marketing strategies.

And there are many other ways you can correlate, compare, and rank relationships of design requirements to each other and to other product design decisions. We can get into building a basement and more rooms and levels to our house. We can make it a mansion, if we want. When we look up QFD or House of Quality, you’ll find many examples of how the house can be built out to include other aspects of product design.

Today’s insight to action is this. Sometimes it’s too much to start building a mansion. It’s okay to not build out the complicated House of Quality to start. We can start with the main house and the roof, and that will begin to give us insight into our concept development. Dr. Akao is the founder of QFD, and he’s quoted as saying, “The House of Quality alone does not make QFD.” And I cannot disagree! But we can try to build a house if it helps us better understand how we’re going to meet our customer requirements.

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