This architect-designed self build was prefabricated almost entirely in Germany by Baufritz — the shell was erected and made watertight in just five days
A few weeks before Christmas 2015, I was cycling through a leafy suburb in my home town of Cambridge, when I spied a huge 40-tonne truck trying to make a right turn across my path. As I got closer, I noticed the lorry had German plates. Why would a vehicle this size, coming from another country, be turning into a quiet suburban side street?
I knew the answer the moment I clocked the German plates. It could only be a prefabricated house from a nation where self build is far more common than speculative building. Germany is home to over 100 fertighaus (or prefabricated house) builders and several of them are active in the UK market. This one was being supplied by Hanse Haus, who have been trailblazers in our home market and have been supplying UK-customised homes for many years.
I followed the truck down the side street and found another already parked up on the roadside, waiting to start unloading the house. The assembly gang had also come over from Germany and were being put up in local B&Bs. They knew their job and aimed to have the structure of the house up in three days. The customers were replacing an older house and had been told that they would have the keys to their new home in just eight weeks.
Four months later, the finished house sits easily in the street, the construction phase long finished — only the garden and the landscaping await to be completed. This, in essence, is what people are talking about when they use the phrase ‘modern methods of construction’ (or MMC).
- Prefabricated homes are big news in Germany and becoming increasingly popular for UK self builders. Building a home under controlled conditions off-site can result in a build delivered on time and on budget
- ‘Modern methods of construction’ (MMC) is a term often used to describe this approach to building
- In the UK, a hybrid model has evolved, whereby the superstructure is typically prefabricated off-site and erected (usually with the aid of a crane) on site, with the self builder taking over to manage the finishing trades
What are ‘Modern Methods of Construction’?
Modern methods of construction are all about taking as much of the grunt work away from cold, wet building sites as possible. Instead of struggling to construct brick and block layers and working from a set of plans in all kinds of weather, much of the process is moved under cover, into an environment where the structure of a house can be built with greater speed and to engineering standards.
Which begs the question: why aren’t all houses built this way? Why are the majority of new homes in this country still built on site?
The answer is not straightforward, but usually boils down to one or two factors. Factory housebuilding sells itself on being quick, but not everyone is in a hurry to complete. In fact, our big housebuilders have a vested interest in not being too speedy because they want to release their output at a measured pace to match a predicted market demand, thereby keeping their prices high. The second factor is cost: there is often little to choose between on-site and off-site builds, and shipping houses across continents is never cheap.
The main drivers for the uptake of modern methods of construction are quality combined with predictability. I very much doubt my Cambridge self builders (who incidentally I never met) were drawn to this route because it was a cheaper option. I suspect that they valued the certainty of the outcome (more than simply the speed), combined with the reputation that German manufacturing enjoys across all sectors. Buy a German fertighaus and you know precisely when you can move in. You could book a holiday for the following week, safe in the knowledge that you wouldn’t have to cancel at the last minute because of unforeseen snags; there won’t be any.
That’s a very appealing prospect for many people, compared with a typical on-site self build where the finished date is always “a few months away” and the hope of being “in for Christmas” so often turns into a cruel joke.
Pros and Cons of Prefabrication
- Less time spent on site
- The project is less likely to be affected by bad weather
- More control over the engineering standard
- More predictable and fewer set backs (which always have cost knock-ons)
- Prefabricated homes tend to be more expensive (although there are fewer costly surprises)
- Early design lock-down reduces the chances for adaptation
An Emerging Prefabrication Hybrid Model in the UK
The total number of entirely prefabricated houses being built each year in the UK is still very small. Even within the self build community, it accounts for less than a hundred homes each year. It’s an expensive business to ship a home across the Channel, and the overall size of the business doesn’t yet warrant the investment in local plants, although this may change as one company in Scotland plans to do just this (watch this space).
What has instead evolved in the UK is a hybrid version of fertighaus, where only the superstructure of the house is factory built and erected on site and the self builder then takes over and manages the finishing trades. Technically, if we take timber framing as an example, the difference between the German approach and the British approach is referred to as closed panel vs open panel.
Closed-panel framing sees entire walls finished in the factory. The external cladding is fixed, as are the doors and windows and the ducting for cables and plumbing. A closed panel itself tends to be larger and heavier and a crane is therefore essential to the assembly.
In contrast, open-panel construction leaves the external cladding and the joinery to be fitted on site. The process can often be carried out without a crane. This makes it suitable for sites where access is restricted, a factor common in the UK.
Open-panel timber frame developed in Scotland, riding the back of the oil boom around Aberdeen in the 1960s. Americans were arriving in droves and needed lots of housing quickly. They were more than happy with timber buildings, as that is how they were built back home, but the Scottish weather meant that American-style stick building was always going to be a challenge on site. So the process was brought into a factory and the UK-style timber frame was born. In England, Potton picked up the baton and led the way in introducing factory construction in the 1970s.
While the major housebuilders have been happy to stick with traditional methods, the self-build market has been a different story and has embraced different build systems and techniques.
Modern Methods of Construction: The Systems
But there is more to modern methods of construction than just a choice between closed and open-panel timber frame systems, and timber is not the only construction system that lends itself to this approach.
Concrete Insulated Panels
Danilith, a Belgian company that also operates in the UK, provides prefabricated panels of highly robust insulated concrete with a brick outer leaf (render, timber cladding and even flint can be specified too), complete with external windows and doors. These are transported to site and craned into position as described before.
SIPs (Structural Insulated Panels)
In the past 20 years, alternative construction systems have also emerged that are rather different from either closed or open-panel timber frame, and they all vie to be included as ‘modern methods of construction’. Timber frame has spawned variants, most notably SIPs (structural insulated panels) which are characterised as being like timber frame without the timber. Here you are essentially building walls and roofs out of solid slabs of insulation, producing excellent thermal performance, in tune with today’s concerns over energy efficiency and sustainability.
SIPs are an American idea and were first used in the 1950s. They appeared in the UK in 2000 and have established a successful niche in both the self build and developer markets. There are other framed systems using steel, too, though these have yet to make a significant impact on the self build scene.
ICF (Insulated Concrete Formwork)
Even on-site blockwork construction is going through something of a rethink, using methods which simplify and speed up masonry construction — and in the case of insulated concrete formwork (ICF), completely rethink it.
ICF construction is based around the use of expanded polystyrene moulds which are used to build walls with readymix concrete, then poured into the cavity to form the structure. No way can this be characterised as ‘off-site construction’ but, used well, it can be very speedy and the result is often a better insulated house that ticks many of the sustainability boxes that modern methods of construction tend to benefit from.
It can be difficult to shake the perception of oak frame as a centuries’ old way of building, but prefabrication is key to modern oak framing; after all, the majority of oak framers construct their frames off-site, ready to be erected on site — the quick erection of the frame being one key benefit. What’s more, no longer are infill panels of brick or wattle and daub acceptable; today’s oak frame builds are typically encased in a highly insulated, airtight envelope in order to meet Building Regulations.
Structural insulated panels (SIPs) are often used, but Oakwrights has developed its own series of encapsulation systems (the WrightWall Natural system, shown here, being just one) — wall and roof panels are built off-site to exacting standards (below), reducing build time on site.
Prefabrication in Volume Housebuilding
To completely understand all aspects of modern methods of construction, it is necessary to delve into the world of commercial building (where many aspects of car manufacturers have been incorporated into building design). Here we see developments such as prefabricated craned-in bathrooms and living spaces fitted with wiring looms.
This sort of building needs economies of scale – typically 50 or more very similar units – so it is usually only seen in blocks of flats, hotels or student accommodation. Its interest to self builders is little more than academic at this stage.
The Benefits of Prefabrication to the Self Builder
Which brings us to ponder what this all has to offer the prospective self builder. There is no straightforward answer to this, partly because there is no clear-cut definition of what modern methods of construction represents.
Many non-conventional build methods like to call themselves modern methods of construction because this distinguishes them from the mainstream or traditional methods. However, this doesn’t mean that the so-called modern methods always share common features.
SIPs and ICF are poles apart in their approach to housebuilding. SIPs are all about factory-produced panels used for their energy efficiency and airtightness characteristics; ICF is very much an on-site method, appealing to the hands-on self-builder who wants to be in control of the whole process of the house assembly. Paradoxically, what they have in common is their heavy use of plastic-based insulation and also their designed outcomes, providing very energy-efficient homes.
Interestingly, neither SIPs nor ICF are widely used in Germany which many see as the spiritual home of modern methods of construction. The choice in Germany is somewhat simpler: on-site (or traditional) construction versus the off-site fertighaus methods, which we are slowly seeing becoming established over here. In the UK, we seem to be more open to other construction systems, many of them emanating from North America, but the wider choice doesn’t necessarily make it better or a better place to build; the plethora of choices sometimes just adds to the confusion.
The choices for the self builder are not simply restricted to wall systems either — component parts such as prefabricated floors and roof cassettes, for instance, can make for a more efficient build and speed up the construction of the shell of a new home.
Should you Choose a Prefabricated Home?
If you are hoping to build a home in the coming years, it probably pays to keep an open mind about potential build methods, whether modern or traditional. Off-site construction has many attractive benefits for the self builder. It delivers a certainty of outcome at a predictable cost that most on-site methods cannot match. But off-site modern methods of construction do not suit every design or every site, and only rarely does it work out as being significantly cheaper.
One thing modern methods of construction don’t do is remove the human element in building. Whichever method you choose to build your home, make sure that you are dealing with people who know what they are doing and are able to show you how their system will meet your needs and your budget.