The Benefits of Prefab Homes

Offsite-manufacture is a buzz phrase in the housing industry – but is prefabrication suitable for self builders looking to create one-off bespoke homes?
by Chris Bates
11th August 2018

Prefabricated homes are hugely popular in Germany, Australia and the United States, but so far they’ve only managed to corner a relatively small part of the UK housing market – despite presenting the big developers with an opportunity to benefit from speedy construction and economies of scale.

The government has clocked this and has been pushing for greater uptake in a bid to help solve the housing crisis, but the fact is that until recently the main group investing in offsite-manufactured homes has been (you guessed it) self builders. And some of us don’t even realise we’ve technically gone prefab.

What is a prefab home?

If the idea of a prefab house fills you with dread, fear not. The industry has moved on completely from the practice of throwing up cheap and cheerful boxes that pervaded the mid-20th century.

Speed of delivery is still important, of course, but modern offsite-manufactured homes are all about design flexibility, accuracy and quality control.

One thing that’s worth clarifying early on is that prefab is a broad church covering a range of options – and it doesn’t necessarily mean craning in entire pre-finished rooms. In fact, by far the most common route for self build projects is to engage a company that specialises in highly pre-manufactured closed panel timber frame.

Read more: What is closed panel timber frame?

Site operatives install a Hanse Haus internal wall panel, which has been manufactured with service channels and some plumbing infrastructure in place
Last year, Legal & General moved into the modular housing market. It has recently revealed its first prototype – a turnkey one-bed apartment designed by architect Wimshurst Pelleriti

Source it: Find more Hanse Haus projects in the Build It Directory

This is the type of product that’s come to our shores via the German package home suppliers, such as Baufritz, Hanse Haus and Meisterstueck. It’s something of a hybrid route, where much of the internal fit-out work is still carried out onsite.

With this kind of structural system the wall and roof panels are produced in the factory, with the door and window openings pre-cut and insulation added under controlled conditions. All fairly basic stuff so far – but what sets the prefab versions apart is that a lot more of the work is done offsite.

“Our external wall panels will be fitted with doors, windows and ideally the cladding – or at least as much of it as you can possibly put on in the factory,” says Robert Lumme from Baufritz. Ducting may be included for plumbing and electrics, too.

Some suppliers can take things a stage further, with plasterboard pre-applied internally and sections of the services already run through the channels. This will save even more time on the ground; but Robert warns that going too far can be restrictive.

“Apart from maybe pre-drilling a few holes for sockets that we’re certain will be in a particular position, we prefer to put the electrics, plumbing and heating in onsite for the simple reason that sometimes people like to amend things once they actually see the house shell in reality,” he says.

The next step up is a fully prefab build – often referred to as modular or volumetric construction. With this route you’re dealing with large, 3D building elements that could represent whole rooms or sections of building; sometimes with the services, internal fit-out and finishes already installed and commissioned. In some cases, entire homes can be delivered in a matter of weeks.

The modular method is pretty rare for one-off houses as the level of factory manufacture makes for a high upfront cost; but it could make sense for some custom build or community self build schemes.

Interestingly, in terms of domestic projects modular construction is currently more frequent for extensions, perhaps because the ability to crane in an entire single-storey room or habitable loft pod can be useful in certain circumstances – such as where there’s tight access to terraces. There are a number of firms specialising in this area, including Ecoqube and Moduloft.

Is prefab right for me?

If you’re looking for a hands-off route to achieving a high-quality bespoke scheme, then it could well be the best option. But every project and every self builder is different, so to help you decide, here are five key areas to consider when figuring out how to approach your project:

1. Design

It’s a common myth that extensive levels of factory manufacture lead to more standardised architecture; in fact your home can be totally tailored to your needs, both in terms of aesthetics and how it suits your lifestyle. Many firms put a real focus on high-quality design and construction; and a number of architects, including the likes of Ecospace, have moved into the arena.

The key difference to the traditional route is that you need to think through all the details at an early stage – prior to manufacture. But you still get all the design control you would expect with a bespoke project. “There is a lot of pre-planning, because the panels have to be drawn up in detail so they can be made to exact millimetre-precise dimensions,” says Robert. “But we’re able to quite flexibly create very different shapes, sizes and styles of building.”

Large-scale wall panels are produced with speed and accuracy in the Baufritz factory
Fitted complete with fenestration in the factory, they're then craned in place onsite

If you’re going all-out for a modular scheme, changing things on site is likely to be difficult and potentially cost prohibitive. There’s slightly more flexibility with the closed-panel route; but it won’t come cheap and you’ll need to involve a structural engineer if you want to do things like make a window bigger or move a wall slightly.

2. Quality control

It’s a simple fact: the more work gets done in the factory, the more accurate the finished house will be. This can help underpin key areas for self builders, such as attaining the proposed level of energy performance and being certain about the standard of materials that go into the home.

“At Baufritz, we believe the buildings we live, work and sleep in should be as healthy as possible and only use the cleanest materials,” says Robert. “The prefab process means we can guarantee a home with healthy air and high-quality living because we have full control over the supply chain – right down to defining the kinds of paints that should be used throughout the build.”

There are some considerations to bear in mind, though – perhaps most notably the fact that groundworks and foundations have to be absolutely spot on to cater for such a highly-engineered product.

3. Speed

With less work to do on site, the main construction phase on a prefab project can be significantly quicker than with traditional building methods – which means you’ll be in your house that much faster. Offsite-manufactured homes are more independent from the vagaries of the British weather, too; so there’s no waiting for frost or heavy rain to pass.

The shell of a typical Baufritz house can be up in as little as three to four days, and made weather- and airtight in another week to 10 days. “After that you’re into the fit-out, which averages about four to five months including things like waiting for the screed to dry out,” says Robert.

4. Simplicity

With the amount of planning that goes into a prefab, and the fact so much of the work is done in the factory, running the build should be straightforward. You’ll have a fixed programme for the manufacture, delivery, erection and – if you choose a turnkey or modular route – even the fit-out of your new home.

You’ll also have a single point of contact for the vast majority of the design and construction work. All told, that puts you in a strong position to complete your home stress-free and on schedule.

5. Cost

While some prefab firms focus on delivering affordable starter homes, they tend to work to a restricted design palette so they can deliver greater economy of scale. Most self builders are keen to create something more bespoke, which makes it difficult to repeat construction elements.

Add to that the fact you’re putting more of the work and financial risk into a single supplier’s hands, and it’s no surprise that offsite manufacture tends to cost more than using a traditional route (such as an architect and main contractor). What you do get, however, is certainty: both in the price you’ll pay for the finished house, and in the quality of what will be delivered at the end of the day.

Top image: Meisterstueck-Haus completed the structural design and pre-manufactured shell for this 200m2 contemporary self build. The main house was erected in two weeks, while the internal fit-out took 14 weeks.

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