The DfMA Housing Manual

An introduction to the principles of Design for Manufacture & Assembly (DfMA) for Homes by Open Systems Lab

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Contents

0. Home construction as it is today

1. What is Design for Manufacturing & Assembly?

2. Examples

3. Design principles

4. Regulation, certification & warranties

5. Digital design + supply chains

6. Procurement

7. Pilot projects

8. Where should I start?

All information in this document is for guidance only. You are responsible for your project. Read the full WikiHouse terms here↗.

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0. Home construction as it is today

It is no secret that the way we build homes has changed very little in the last century. Not just in terms of the physical building methods themselves (brick, concrete, carpentry etc.) but also in terms of the design and supply chains behind them, and in turn the business models behind those supply chains.

It is also widely recognised that in the face of the systemic challenges of the 21st century – such as climate change, resource depletion, changing labour markets, growing populations, ageing societies, rising health costs and land market failure – these building methods are no longer fit for purpose.

They are slow Typically it takes around 6–9 months to build a house, which is preceded by a design / preparation period of at least 1 year.

They have poor energy performance Buildings account for 40% of energy consumption and 36% of CO2 emissions in the EU. Homes represent the majority of this consumption (around 30%).

They have high embodied carbon Due to the extraction processes involved in their production, this especially applies to bricks and concrete. Often over 600kgCO2/m2

They are linear That is, they use materials extracted from the earth, then ‘demolished’ and sent to landfill at the end of their life. Buildings are the single biggest consumer of raw materials (around 60%), and the biggest contributor to landfill waste (around 32%).

They are wasteful On-site material wastage rates are high, typically between 10–20%.  

They are imprecise Imprecise building can cause mistakes, defects or have knock-on effects later in the project. For example, it is not untypical to delay ordering windows until after the window openings have been constructed.

They are skill and labour intensive Their complexity requires experience and skill, which comes at a high cost. For example, the cost of bricklaying in the UK is increasing around 6% every year, a trend likely to be accelerated by tighter immigration controls post-Brexit.

They are complicated In that they require knowledge of multiple materials, methods and trades, and the experience to weigh these factors against each other.

They are often defective Because it is so easy to make mistakes, the rate of defects is high. 98% of UK new home occupants report a defect of some kind, and they are often hard to repair. Mistakes during design and construction are estimated to contribute up to 7% of build costs.

They are unsafe Construction still has one of the highest fatality rates, responsible for 32% of all fatal workplace accidents.

They are unhealthy In terms of air quality, insulation, daylight, ventilation and visual contact with greenspace. It is estimated that poor quality housing in the UK costs the NHS over £760m per year, and £1.9bn to society overall.

They are risky In that it is hard to predict costs in advance, so unlike other products there is no way of knowing how much a building will cost before you commit to buying it. Because multiple trades and critical pathways are involved in producing a building, even small problems tend to cascade into big ones. As a result, the majority of construction projects run over-budget. Typically projects experience delays while waiting for parts or services (such as scaffolding). This risk prohibits many small-builders and self-builders entirely, and also necessitates ‘bad’ procurement models.

They are ‘dumb’ In that they do not record any in-use performance data with regards to durability, use, health and energy performance.

One-size-fits-all Outside the bespoke, high-end housing market there is often little or no room for customisation to different sites and people. This excludes many groups, and contributes to poor quality places.

They are manual Each project has to be designed and made from scratch every time, with very little automation or replicability and a lot of negotiation / arguing. This makes the ‘marginal cost’ of each product very high. These high design overheads have been estimated to add between 20–30% to the cost of every building.

They are undemocratic All this means that the act of building homes is largely controlled by the wealthy, and executed by a small number of large companies. In particular, we have tended to leave it to speculative developers who build homes directly for the secondhand market, and therefore have little incentive to build good quality, sustainable homes. Today, building is a top-down activity driven by supply-side profit, not the wishes or needs of end users. We have become used to the idea that housing is something done to people, not done by people. This is a problem. Because ultimately, the only people with a direct incentive to build the best, most healthy, most sustainable homes they can, are those that will live in them, raise their children in them, and pay the heating bills.

1. What is Design for Manufacture & Assembly?

Although acronyms like ‘DfMA’ sound complicated, the basic idea is very simple: what if we were to make buildings using the same kind of factory manufacturing methods we use to make most other products? To take an obvious example, let’s look at the way we make cars:

Breaking the product into modular components like this allows the work to be done in stages, with more complex, standardised, precise work done by machines and assembly teams in advance in factory conditions, where the product can be checked for quality. The parts can then be rapidly assembled.

Another, simpler example would be IKEA flat-pack furniture. This really demonstrates the power of DfMA, in that unlike traditional furniture making which requires extraordinary skill, the final assembly is so simple that it can be done by almost anyone, even without particular skill or knowledge.

If we apply this approach to a house (in this case using the WikiHouse Blackbird structural system as an example), it might look something like this:

Of course, unlike cars or a set of drawers, buildings are not ‘one-size-fits-all’ products. Different homes need to respond to different sites and different people. However, by developing standardised, LEGO-like systems it becomes possible to ‘productise’ and generalise all the components of a building, while still allowing each individual building to be a unique assemblage of those components. It is like developing a language. Once you create the language, you can say almost anything.

Generally speaking, the more independent these components and systems can be from one another, the easier it gets. This is true not just when making the home, but also years later, when it comes to maintaining the building over its life. Buildings tend to have a longer lifetime than most products, and the different systems within them tend to change or need replacing at different speeds. Frank Duffy and Stewart Brand broke buildings down into different systems or layers. We have versioned their diagram slightly:

A key aspect of DfMA is treating these layers as separate, interoperable systems within a home that are as independent as possible from each other.

However, the most important aspect of DfMA is the ‘Design-for’ part. Traditionally, architects tend to design their buildings with use in mind, but leave it up to others to work out how to build their designs. The idea of DfMA is to apply innovation and design thinking to optimise for all stages of the product’s life, especially the production process.

Design for Manufacture

Design to minimise cost, time, material consumption during manufacture. This also includes optimising factory set-up cost vs efficiency and precision, and simplifying factory floor processes or shipping.

Design for Assembly

Design to lower thresholds of time, cost, skill and complexity during assembly. This includes making components ‘plug and play’ wherever possible, but also other factors such as just-in-time delivery, the cost of site equipment, allowing different teams to work independently of each other. It also includes trying to design-out health and safety hazards as far as possible.

The same mindset can also be extended to:

Design for Maintenance

Design to reduce the cost and difficulty of maintaining, repairing and replacing components during the building’s life, for example by ensuring easy access to services.

Design for Disassembly

Design to make the building as simple and safe to disassemble as possible, so as many components as possible can be reused.

Of course, behind the ambition of ‘optimisation’ is the question of ‘optimising for what?’. Designs can be optimised for an endless range of possible factors, such as material cost, labour cost, speed, energy performance, weight, embedded carbon, skill thresholds, compliance barriers, health, wellbeing, local jobs, cultural adoption etc. There is no perfect or ‘correct’ solution, you always have to trade-off one outcome for another. Different situations and differing priorities require different solutions.

The DfMA Spectrum

There are a number of common DfMA methods in use today, and many more in development or yet to be invented. They can be broadly mapped onto a spectrum:

Distributed Manufacturing

We are also increasingly seeing the emergence of what could be called ‘Design for Distributed Manufacture & Assembly’ (DfDMA), driven by the web and the falling cost of fabrication machines such as small scale CNC machines and 3D printers. In this model, instead of large, centralised factories with set-up costs running to £50m+ and huge daily running costs, it becomes possible to license manufacturing across distributed networks of small scale, local ‘microfactories’, ‘flying factories’ and on-site robots. These are often flexible factories (in that they can manufacture more than one type of product).

Although such small, flexible factories may be strictly less efficient than larger ones, they may be more effective in that they are more resilient, more commercially accessible for small businesses, they can save money on transportation, as well as even allowing customers to reduce costs by setting up their own microfactory to fabricate in-house. They can also have a ‘local economic multiplier’ effect in that they create manufacturing jobs near to the homes themselves, so every pound / euro / dollar is recycled within the local economy.

2. Examples

3. Design principles

All DfMA methods are underpinned by a set of common design principles & tactics. Following as many of these as possible is the secret to making DfMA work.

4. Regulation, certification & warranties

All DfMA homes will always, of course, have to meet or exceed existing local building codes, which cover, for example, structural fitness for purpose, fire safety, energy performance, accessibility etc. In some places it may be possible to use an ‘approval by type’ mechanism accompanied by quality control standards and procedures, instead of requiring every building to be inspected and signed off.

If homes are going to be sold onto the open market, buyers will probably need to be financed by mortgage finance.

In some countries (such as the UK), this will require DfMA systems to be product certified and a warranty issued for different projects (In the UK a ‘warranty’ is usually 10 year defects liability insurance on a new home). Warranty insurers are notoriously conservative and have been slow to respond to innovations in building methods, however a number of new insurance products are coming onto the market to address this issue. It is something for customers, designers and innovators to be aware of: that new DfMA systems will probably need to have a warranty insurer in place before many projects can proceed. In some cases, customers may invest in the up-front cost of this. But beware; in the words of Craig White, inventor of the Modcell building system, “the road to insolvency is paved by expensive product certifications.”

5. Digital Design + Supply Chains

DfMA makes it dramatically easier and faster to physically build high-performance homes. However, this is only part of the story.

Many of the overhead costs, delays and uncertainty come from the wider design process, and the work of managing the project. This means each project is reliant on a string of consultants who have to design and deliver every project from scratch, making drawings, estimating costs and checking compliance with regulations. In fact it’s worse than this, because every time the customer needs to make a change to the design, the consultants have to re-draw, re-check, re-cost the project. So every project is designed from scratch on a case-by-case basis. In fact, every project gets designed several times over, in emails, meetings and phone calls.

Data based on UK public sector procurement suggests that for every £ spent on a building, only 51.3p ends up in the product itself. Most is spent on process overheads, and the cost of risk (more on this in the next section).

Original graph by Bryden Woods, based on public sector procurement data

This is where digital design comes in.

Instead of producing one off designs, teams develop one or more standard types or systems (think LEGO), and then document those solutions as pre-designed products, or rules and data. The same principles apply to computational design tools, for example Dynamo or Grasshopper.

This is powerful, because it effectively flips the order in which knowledge is applied to a project. Instead of producing a design without any knowledge of its engineering or costs, each project begins with R&D knowledge already baked into a customisable product. This allows a design to be produced within those parameters, and all the variables being calculated simultaneously, with the designer instantly able to see the impact of their decisions on cost and performance. The aim is to dramatically improve transparency and productivity, and lower the marginal cost of producing homes.

This can be done using existing technology (such as CAD, BIM or offline parametric tools such as grasshopper), albeit in a constrained way. Increasingly however, new tools will allow those rules and data will be accessible via an online customiser, where customers and their architects can modify a pre-designed house type, or produce a design using the LEGO-like system, and the parametric model will instantly calculate the cost and performance of their design.

The rules and data behind the customiser can be updated at any time, without invalidating the rest of the design. Once the customer is happy, they can, in effect, ‘order’ the home they want, production can be timetabled, providers given the information they need and work can go ahead.

The building information model or customiser ‘engine’ will automatically generate useful outputs, such as ready-to-manufacture files, a bill of materials and a bill of tasks.

Whole-life digital design
Parametric customisers will be a key platform for digital design, but they are only one part of the picture. In future, design must link seamlessly into a stack of digital technologies and services that will support the building over its entire development and life cycle, including:

– Digital twins Detailed 3D digital models and datasets of each building. These are used as reference points for future operation, maintenance and modification. These will need to be owned by the owner of the building.

– Sensors That capture in-use data, and invite the owner (or occupant, in cases where such data may compromise their privacy) to share back performance data to the designers and product companies.

– ‘Smart home’ operating systems That allow the occupant of the home to monitor and control the home.

– Smart contracts New forms of finance, land tenure, and performance-based (or ‘preventative’) investment.

However, to begin to unlock the benefits of this, a fundamental mindset shift is required both for the customer and the consultants working for that customer, in terms of how homes are procured. We will explore this in the next section.

6. Procurement 

DfMA also allows – and in fact requires – a different approach to procurement. It is this stark: if you try to deliver innovative DfMA methods using conventional ‘lump sum’ procurement models it is likely that you will see little or no benefit in terms of cost savings or performance improvements. In fact it is likely to cost even more.

How we procure today

The levels of difficulty, opacity and duplicated effort involved in paper supply chains doesn’t just create cost, it also creates risk, in particular the risk of budget overruns.

No one really knows precisely how much a house will cost until it is built. Everything is based on guesswork. Budget overruns are normal, and once they happen, costs can rapidly spiral, because all the participants then become much more cautious, argumentative and litigious, which in turn can escalate consultant costs even further.

There are many different models for building procurement, but all of them revolve around one question: who carries the risk? Traditionally, it was the customer who owned the risk. But over the years, customers have increasingly moved towards contracting methods that protect them from risk, and pay others (usually the contractor) to carry the risk instead, as is the case with ‘Design and Build’ contracts, for example. Once a design has been prepared, the customer invites lump-sum bids from Main Contractors to deliver the whole project for an agreed price. The main contractor then engages a number of subcontractors to deliver the project.

Once this happens:

1. The contractor owns most of the risk In other words, if it costs more to deliver than the quoted price (for example because the cost of materials or labour goes up, or because it takes longer than expected), the contractor will make a loss. (There will be exceptions to this, such as the customer changing the design, or an unforeseen external factor that was missed in the original design information.)

2. The price is fixed, and risk is bundled-in When preparing this lump-sum price the contractor has to balance their desire to win the job with the need to add-in a risk buffer cost (or ‘contingency budget’). Often they may hide this buffer among the costings, so it is very unclear what the true costs are. For anything they see as ‘a bit unusual’ or unknown they will add in even more risk buffer. In this sense, Risk has a very real cost. It has been estimated that these ‘buffer’ contingencies add between 10–20% to the cost of every building.

Crucially, should it be possible – through innovation – to deliver the project for less than the original quoted price, this saving will not be passed back to the customer, but retained by the contractor as profit.

3. Costs and information are ‘black boxed’ Unless a specific ‘open book’ contracting agreement is made, all the customer can see is the end price. They cannot see detailed cost data, so have no way of knowing where future cost savings could be made. Even if open books are used, it can be difficult to track true costs, due to the risk-buffer issue. If the customer wants to do ‘repeat’ projects in future, the contractor is unlikely to pass on information as to where the possible cost-savings might be to their customer or the competitors who will be bidding against them. Instead, they will keep a note of where the savings might be, so they can keep the difference.

4. The contractor has an incentive to minimise quality Once the lump sum has been agreed, the contractor is obliged to deliver the design as specified in the design documents, but where there is any wiggle room, they will always seek to reduce the quality of the materials used for the final result, in order to build the homes as cheaply as possible, and thus increase their margin. Increasingly – seeking to further insulate themselves from risk – customers have left more and more aspects of a project’s design and specification to the contractor (known as ‘contractor’s design portion’) as well as the construction work. This is known as ‘Design and Build’ contracting. It is good for managing the customer’s level of risk, but bad for innovation and product quality / performance.

How to procure homes using DfMA

Instead of just ‘black boxing’ and financialising the risk, digital design and manufacturing is all about using design innovation to reduce or eliminate the uncertainty and guesswork that caused the risk in the first place. However, in order to control risk, you first need to own that risk.

There is clearly huge scope for innovation in the area of procurement. It seems reasonable to say that the main procurement models of the 21st century probably haven’t been invented yet.

However, we do know the core principle of DfMA procurement, and it is actually very simple. It is this: instead of producing a design first, then later employing consultants to engineer, cost and build it, we do it the other way around. First we engineer and cost elements of a system, then we design within those constraints.

To put it simply, the first model is like an architect sketching a building on a napkin and then handing it to an engineer and saying “work out how to make this” and to a builder, asking ”how much will this cost to make?”. The second model is like developing a set of lego blocks, putting a price tag on each, then giving those blocks to your architect and saying “design what you like, but only using these components.”

If you want to make a solution predictable, scalable and replicable, clearly the first approach is absurd. Imagine if every time you wanted to buy a car you had to draw a sketch of the car you wanted, approach a car manufacturer and they had to guess how much it would cost to make it.

Instead, companies develop a standardised product (sometimes with a few customisation options) and a supply chain capable of producing that product, then they work to constantly collect feedback so they can incrementally improve the product and supply chain.

Clearly, this means being ready to invest more money up front into product R&D, and supply chain infrastructure (eg a factory) in order to then save on per product costs later on.

The critical question is, who invests-in and owns this supply chain?

With DfMA for housing, it doesn’t have to be a huge manufacturer who owns a supply chain. It can also be small companies and even customers: councils, housing associations or developers who want to produce many homes, creating their own supply chains.

Here are four general approaches to DfMA procurement for homes, that will suit different organisations and approaches:

1 Buildings as products: the closed one-stop-shop

In this model, a single company develops a manufactured product offering and a supply chain. To do this, they will have to invest money and effort into developing that product, getting it certified etc.

Customers then approach that company and can simply order a house for a predictable price, just as they might if they were ordering a kitchen or a car. Examples of this include Huf Haus and Facit homes. In Japan, it is possible to buy a customised house from the Muji catalogue.

Of course, there are still project-specific elements that are hard to standardise, such as navigating the planning process, and site preparation costs (for example, dealing with land contamination and the installation of foundations and utilities), and even finance. The manufacturer can either expect the customer to address these in advance, or offer an in-house service to help the customer navigate these hurdles.

The strength of this model is that it is simple and streamlined; everyone is on the same team. The weakness of this model is in that companies have to put in a lot of capital investment into developing their products and factories, and are then reliant on external demand to stay afloat and recoup their investment. Scale is also limited to the bandwidth of their factory or in-house teams.

These companies are therefore fewer in number, and their products often come at a premium cost and/or a lower level of design flexibility in the product.

2 Buildings as products: open, collaborative chains

This model is much like the first, in that the supply chain is owned by the providers rather than the customer, and any customer can approach it and order a house. But in this case it is not just one company doing everything in-house, it is a number of companies collaborating together to collectively form a standardised, streamlined supply chain, and sharing their knowledge through that supply chain in order to offer customers a more complete product offer. This obviously requires a degree of trust and collaboration between the companies.

This model also requires R&D, but may be less reliant on initial capital cost, because they use existing factories and resources.

There are fewer examples of this but we expect this to become more common in future.

3 Modular contracting: open supply chain framework

In this model, because the customer is planning to build many homes, they develop and own their own supply chain, and commission their own standardised house type(s). They break down the project into modules, and assembles a ‘stack’ of the different types of products or companies required to fulfil the key roles.

They are not engaging the stack of companies on a one-off basis but effectively recruiting them onto an open procurement framework, then later awarding them jobs on a task-by-task basis.

The most crucial part of this framework approach is the terms of agreement between these providers and the customer, which must be pre-conditions of participation on the framework.

The providers must:

– Provide design rules regarding their product or service. For example spans, sizes, specifications, ideally through a customiser, but this can also be done on paper or through existing design tools.

– Provide transparent cost rules for the customer sufficient to cost their product or service. For example, a company providing foundation installation services could give material costs, number of days indicators, a daily rate (eg €200 per person day). A profit margin might be agreed (eg 20%) and where necessary, an emergency contingency budget defined (eg 10% – use of which does not affect the profit margin, but only covers costs). Once they are ready to move ahead with the project, the customer and provider will use these rules of thumb to generate a contract sum, which the provider can choose to accept or not in each case, but they cannot deviate from the originally advertised price.

– Commit to ‘open book’ accounting, where a project’s costs (money and time) are recorded in a shared data environment (eg a project engine) before, during and after the project, allowing the customer, as supply chain owner, to see where savings can be made.

– Understand that getting onto the framework is not a guarantee of work, and that their competitors will also be invited onto the framework, offering their products or services under the same terms; if not immediately, then in future.

However, only customers with a sufficiently large building programme planned are likely to have the critical mass to command such a framework, and frankly, only customers with a large building programme planned are likely to be willing to invest the time and cost involved.

Some companies may offer to do type R&D work for free in exchange for a guaranteed number of orders. Customers should consider whether this kind of lock-in represents a good deal, or whether it would be better to pay money towards initial fees and leave themselves the flexibility to switch providers later on, encouraging competition.

4 Modular contracting: provider chain

For smaller customer organisations building fewer homes, an entry-level version of this might be something closer to the ‘construction management’ approach. This is much like the previous approach, in that the customer owns the risk and may recruit a construction manager to oversee the project. The customer engages a stack of providers to deliver the project.

Ideally, a similar approach would be taken, getting all the providers around the same table (and crucially, the same spreadsheet) early on, sharing costs and rules of thumb to develop a type, and using an open book approach. This means you do not need a quantity surveyor, because the actual costs are being shared, although the project is more exposed to costs changing.

If there are parts of the process that this is absolutely not possible for, or it is impossible to find a contractor willing to join in, it should be managed by separating those modules out into simple, separate tasks, so they can be lump-sum contracted on a clear, task-by-task, ‘trade-by-trade’ basis.

For example, a small contractor might be contracted in a traditional way to prepare the site and install the foundations and services. However this work should ideally be completed before anything else proceeds. Or the customer may decide to contract an electrician to fit out the building once the main shell is assembled. These modular tasks need to be managed to avoid knock-on delays.

7. Pilot projects

Start small, start somewhere

As with most things, you only learn what will work for you by trying it. As the design agency IDEO put it, “a prototype is worth a thousand meetings”.

When exploring pilots, there is a temptation to commit to a large scale project in order to justify the up-front cost of R&D. Care should be taken here, since also, by going large, you are amplifying the level of risk. It is better to test (and fail) small for the first one or two, then roll it out at scale later if it works.

This, in turn means you need to beware the danger of setting up pilots to fail. Pilot projects are always expensive. Do not expect savings straight away. Costs, hours and materials should be carefully accounted for, and feedback carefully collected, such that at the end of the project it is clear to see not just the cost of the pilot, but also (based on the data you now have) what the cost of building the next 1 home could be and after that, what the cost of building the next 100+ homes would be (and what investments in infrastructure would be required to make that possible). If done well, this should allow you to have the best of all worlds, taking small risks, trying out radical innovation, and getting a clear, pragmatic, data-driven perspective on whether the experiment merits further exploration, whether a different approach should be tried – or whether you are even asking the right question in the first place. In the famous words of Thomas Edison:

“I haven’t failed. I’ve just found 10,000 ways that won’t work.”

Another approach is to partner with R&D departments at Universities. These departments generally push the envelope in design, technology and research and also use the existing local environments as a laboratory for validations of concept development. This kind of partnership between local universities and investors can accelerate development and pilot projects.

8. Where do I start?

1. Design your supply chain

Map out your procurement strategy for your project. Who owns the land? Who will be developing it? What are the constraints and priorities it will need to be designed around? What are the appropriate technologies? What companies will you need? What are your targets? Who will replicate it, and what are the barriers to them doing so?

2. Design your house type

Once you understand what building technology you’re going to use, begin to design an outline ‘house type’. What are the range of ways users / customers might want to customise it? How much choice or design flexibility is practically useful? This could take the form of a set type with a customisable layout and materials, a series of reconfigurable design elements (or ‘blocks’) or a modular Meccano or Lego-like system with clear rules. Structure the menu such that it is more or less impossible for users to get it ‘wrong’, and in such a way that the cost implications of their decisions can be instantly recalculated. Communicate the menu as simply as possible (for example using diagrams, plans or 3D models).

Links & resources

Platforms: Bridging the Gap between Manufacturing and Construction Bryden Woods

DfMA on Designing Buildings Wiki

An introduction to cost-effective DfMA by David Stienstra

Factory Made Housing by New London Architecture

A framework definition for zero carbon buildings by the UKGBC

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