The clever use of wood is changing our homes

Thanks to my trendy glasses, the bulky Augmented Reality headset didn’t quite fit, but holding it in place gave me a steady view. Through it I found myself gazing at what I could already see in front of me — a half completed wall, made from rectangular plywood boxes.

Through the headset, however, each box was outlined in slightly fluorescent orange. Above the boxes, a fluorescent green outline, bearing a number code, showed exactly where to position the next box in the construction process. No further instruction necessary.

This “emergent technology”, says Wilf Meynell of architects Studio Bark, is designed “to empower selfbuilders. We are almost trying to do our architect business out of a job. It’s so simple you might only need an architect or architectural technologist to do basic plans.”

Studio Bark are the inventors of U-Build (u-build.org), an ingenious form of DIY housebuilding you may have seen featured in Grand Designs’ The Street on Channel 4 earlier this year.

It’s a flat pack system, based on boxes cut from standard 1220mm x 2440mm sheet materials. Once delivered to site they are simply slotted together, secured by screws then bolted onto the surrounding boxes.

They can form wall, floor or roof sections. “We are really trying to break it down into the smallest possible module to avoid heavy lifting gear,” says Meynell.

The boxes forming the external walls are left lidless, allowing them to be filled with sheep’s wool insulation and sealed with a weatherproof breathing membrane. External covers can range from timber cladding to a brick leaf.

Internally, the walls can be left in their natural state. OSB, the economical option, may be a little extreme for most; the elegant grain of birch is likely to have more appeal.

The flatpacks come with instructions but help is available on site, though I wouldn’t count on the Augmented Reality option moving far beyond press or public demonstrations.

U-Build is very much in the hands-on self build tradition championed by pioneers like Walter Segal, who in the 1970s devised a simple form of timber-frame house construction also based on standard sizes of sheet materials. This minimised cutting, waste and the need for professional skills like bricklaying and plastering.

But what U-Build also highlights is the extraordinary advances made in recent years by the most humble and basic of building materials — wood.

‘Bricks and mortar’ may be how most Britons describe housing, but in reality over a quarter of all UK new builds – three quarters in Scotland – are now timber frames behind a shell of brick or stone. Often the only way of telling is by tapping the interior walls, which prove to be hollow-sounding plasterboard.

Why has this happened? The simple answers are cost-saving, new regulations and the declining numbers of skilled tradesmen. Most timber frames are factory made, delivered to site in wall-sized sections. They can be open frames, braced with plywood or OSB, to which insulation, vapour barriers, services and plasterboard are added on site. Or, increasingly, all of these items — even including doors and windows — can be pre-fitted in the factory. Either way, labour costs and time on site are significantly reduced.

Timber frame can also meet ever-rising energy efficiency regulations more easily. Insulation can be inserted inside it, saving space; the vapour barrier necessary to protect the wood from moisture makes it easy to meet airtightness requirements; and wood itself is both more thermally efficient than masonry and a renewable resource, soaking up carbon dioxide.

Timber and wood has what is known as the biophilia effect. According to studies, wood interiors improve our mood, lowering heart rates and reducing stress levels.

All these factors have fostered a range of new technologies and techniques — from the increased efficiency and quality of prefabrication to improvements in conventional timber elements to stronger and more durable forms of wood itself. Here are just a few of them.

1. Structural insulated panels (SIPs)

An ingenious, US-developed technology for combining insulation and structure. Each panel consists of two wall-height sheets of OSB sandwiching a polystyrene or polyurethane core.

Walls – and roofs – are formed simply by gluing and nailing the panels together, producing a structure that is around six times as strong as a conventional timber frame. Because the polystyrene cores abut each other, highly efficient airtight insulation is also created.

This makes SIPs one of the most effective ways of building a highly insulated house with the slimmest possible walls – a point emphasised by Kingspan with its TEK building system.

2. Cross-laminated timber (CLT)

A form of super plywood, instead of just three or more thin layers of wood glued together, each at right angles to each other, boards are glued together in a similar way, creating solid volumes of wood up to 300mm thick. Using computer controlled cutting machines, wall, floor and roof panels can be produced and are simply slotted together on site. The interior surfaces can be left unfinished, though the exterior will need insulation and a protective shell.

3. I-joists

Timber floor and roof joists are strongest at their upper and lower edges. An i-joist exploits this by reducing a joist to an upper and lower batten, joined by a web either of engineered wood or open steel members. This makes it much lighter and easier to handle than a solid timber joist. Wiring and pipework can be run easily through the web without diminishing its overall strength. And, because engineered wood is used, shrinking or movement is dramatically reduced. No more creaking new floors.

4. Modified wood

Timber cladding, windows and doors are often rejected because of the need for regular maintenance or because low-maintenance hardwoods are too expensive. But in recent years techniques have been developed to modify softwoods — typically by heating in a vacuum or acetylation (a form of pickling) — to produce wood that is exceptionally stable, durable, and rot-resistant. Trade names include Accoya, ThermoWood and Brimstone.

September 2019