The latest kit homes and alternative methods of construction

Looking to self-build and pondering your construction system? Then read self-build expert Mark Brinkley’s take on four alternative methods that are worth adding to your research

The world of housebuilding tends to work along well-established lines. In England and Wales, masonry construction, otherwise known as brick and block, predominates. In Scotland and much of Ireland, timber framing is to the fore. Self-builders use both methods and, in addition, they have also adopted three others: structural insulated panels (SIPS), which is a specialised form of timber frame; modern-day oak frame, which is a hybrid system (the structural frame is wrapped in an encapsulation system); and insulating concrete formwork (ICF), which involves pouring ready-mixed concrete into polystyrene moulds. But there is no requirement to stick to triedand-tested techniques. Here we take a look at some of the alternatives.

Cross laminated timber

Cross laminated timber (CLT) is a relatively new development in the field of timber building. It grew out of our ability to glue thin strips of timber together to make strong beams, known as gluelaminated or glulam beams, and uses the same method to engineer whole-wall panels that are both strong and beautiful.

CLT is formed from timber strips laid on top of each other at 90° angles. Panels are built up into different thicknesses, depending on structural requirements, and can be up to 20 metres in length.these panels can be used to create an entire superstructure to very exacting tolerances. CLT is available in different grades at different price points.the top grade, known as ‘visual grade’, is designed to be used as a wall finish in its own right, which is one of the key selling points of CLT.

Building with CLT is still some way from mainstream in the UK.THE technique first appeared in Austria in the 1990s and, to date, all CLT panels have had to be imported from there or neighbouring Germany. As such its use is still rather limited. However, there is a small number of architects who specialise in CLT; Meredith Bowles, of Mole Architects, is a big fan. “As an over-simplification, people love exposed timber. Too much and people think it’s like a sauna, but leaving parts of the overall structure exposed as a solid wall, floor or roof adds warmth and interest. CLT is brilliant at this. How dull a plasterboard ceiling looks in comparison! It’s a modern version of exposed beams,” he says.

Steel frame

Long established as a construction material, steel forms the skeleton of every high-rise building in the world. In low-rise homebuilding, however, it has been used rather more sparingly, usually in specialised applications like supporting beams or buried within floor joists and as window lintels. There are very few homes that don’t use steel somewhere in their envelope, but only a tiny number that employ it as their main structural element.

There are many similarities with timber frame. Steel frame homes can either have post-and-beam structures, which mimic oak-framed homes, or can incorporate lightweight steel channels, made up into wall panels, similar in many way to timber studwork.while steel is inherently strong, it needs to be encapsulated with fireresistant materials, and requirements for lower U values in walls actually facilitates against steel: the sections are too thin to accommodate the insulation.

Where steel wins out is when you want to incorporate open-plan living space with wide glazed openings.the inherent strength of steel comes into its own here, and consequently it is often used as a hybrid material for extensions.

Currently, there are few businesses offering all-steel structures aimed at the self-builder. Glendale Engineering, a steel fabricator in Northumberland, is an example of a business that makes post-and-beam homes out of steel, but their main focus is more agricultural and industrial. There are currently no packagebuild companies offering bespoke steel framing for the self-build market and few architects design homes using steel.two decades ago British Steel had a successful housebuilding arm called Surebuild, based around lightweight framing. They produced several show homes aimed at homebuilders and their order book was so full that they were expanding. However, over the years interest gradually waned.

Perhaps this is because steel framing is too similar to timber frame, but is no cheaper and offers little in the way of the sustainable features that self-builders look for these days. However, there still some great examples out there.

The lessons learned by steel builders have lived on. Around the same time that Surebuild was at the height of its powers, a number of steel frame companies started

building homes using a new technique: onsite factory builds. The steel would turn up at the site in rolls and be fed into a mobile computer-controlled cutting machine, after which it would be immediately assembled at the specified location. This process would be controlled by computer-aided design (CAD). While no one is currently doing this with steel, we are now seeing timber frame builders using the same ideas.

Natural building methods

For a couple of decades now, there has been a small but growing interest in building homes out of natural materials such as straw, cob and hemp. Some of these techniques are very ancient, but straw bale building is relatively new; straw bales are a product of the baling machine, which was invented in the 1880s. The earliest straw bale buildings hail from Nebraska in the US where the lack of conventional local building materials led locals to innovate using the resources they had to hand. There are still several examples there of straw bale homes over 100 years old.

The original Nebraskan way was to build a house’s loadbearing external walls from bales, which would serve to support its roof. Since then many variants on this theme have emerged, perhaps the most common of which is a hybrid design that uses straw bales to infill timber. The acknowledged UK expert here is Barbara Jones, who has been leading straw bale projects for over 25 years. Her build methods are unusual, to say the least, and usually involve getting numerous people together to have a straw bale building party — a cheap and eco-friendly way to get a structure up. It’s a simple way to build that anyone can master. Some would say it is therefore the very essence of self-build.

Simple it may be, but it is not without its challenges. In order to get it right, great attention has to go into keeping the straw dry. There have to be foundations that are raised up off the ground, and there have to be significant roof overhangs to keep rain away from the façade. Hand in hand with these requirements, there is a palette of low-tech materials needed to construct straw bale homes. Their walls are invariably plastered with lime inside and out, which aids the evaporation of any trapped moisture. This tends to give a rounded edge to the external corners, leaving a visual clue to how the house was built.

Not all straw bale homes have this grainy hobbit-home feel. The technique has been adapted in a number of ways, including straw bale hybrid systems like Modcell’s ‘straw in a box’ walls for assembly on site. One of its best known examples is the Lilac co-housing scheme (shown on page 113).

Straw is not the only material used to construct natural homes. Hempcrete, a natural insulation made by mixing hemp with a lime-based binding, has a growing reputation. Cob building, once common in Devon, is still practiced by one or two specialists, notably Kevin Mccabe. It’s the nearest thing we have in the UK to earth building, which remains widespread in warmer climes throughout the world. In the UK, it fell out of widespread use in Victorian times, but the old skills are still put to good use maintaining existing homes and sometimes used to good effect to construct new homes.

New-wave timber factories

One such business is Facit Homes, which was formed 10 years ago by designer Bruce Bell. Bell noticed consistent inaccuracies in conventional processes and wanted to create a method for digital control of the whole building process. He created a build system based on digitally manufactured plywood boxes that formed a structure he called the Facit Chassis™. Facit Homes are designed using Building Information Modeling (BIM) and this information feeds into a computer numerical control (CNC) machine. Each individual plywood

Chassis component has its identification number routed into it, which makes it simple for on-site carpenters to erect the building in the correct order under the supervision of the site coordinator.

U Build is another architect-led business that works in a similar pattern, although their plywood boxes arrive on site as flat packs. Architectural practice Studio Bark undertake the design and cutting process from a remote office.

Both these new-wave timber frame companies are active on the Graven Hill site in Oxfordshire. Because the basic build unit is plywood, which can be prepared as a finish material, they offer the possibility of finishing a home without plasterwork walls and ceilings.

And getting a mortgage?

One of the problems with using non-standard build methods is that the resultant homes are often harder to sell, harder to mortgage and harder to insure. The financial services industries, which underpin the housing market, are very conservative and many are loathe to deal with anything but the most ordinary of homes. Even timber frame, which has been an established build method for 50 years and is the preferred homebuilding system in Scandinavia and North America, can cause some mortgage providers to run a mile. It’s therefore unsurprising that more unusual building methods have a hard time finding mortgage providers and insurers.

Thankfully, there are specialists out there who can help.your first port of call should be to look for a self-build warranty. A 10-year warranty acts both as a form of quality control and as a comfort for lenders. As an alternative, a new home can be signed off by an architect or a chartered building surveyor to say that it has been built in accordance with their plans.

If the conventional lenders don’t want to support your plans, there are specialists in the financial field as well. Notable here is the Ecology Building Society who support a couple of hundred innovative projects every year. If they can see an environmental benefit, and they are satisfied that you are building properly, they are more than likely to give you a mortgage.

And as far as insurance is concerned, there are green-tinted businesses that are happy to deal with unusual construction methods. Check out Insure Green and Naturesave Insurance.