Beginner’s Guide to Timber Systems

Anna-Marie DeSouza shares the key considerations when choosing the right timber system for your build project
by Anna-Marie DeSouza
29th April 2018

There’s a whole wealth of reasons why timber is such a popular structural option for self-builders. Although it’s one of the oldest construction materials around, the use of wood in modern construction is continuously evolving.

This is a flexible, sustainable, attractive and affordable material. So, what makes timber so special, and how can you use it to help you build an eco-friendly, cost efficient and attractive home?

Timber frame construction comes in many guises, lending itself equally well to modern and vernacular designs. From conventional timber panels through to characterful oak frames, you’re sure to find a system to suit your requirements – whether your focus is on style, sustainability, cost or other practical considerations. What’s more, all the systems have short onsite turnaround; so you can have a weathertight shell in a matter of days.

Almost all timber frame options include factory-made elements, and modern production techniques have reduced defects and improved quality overall. It’s this use of prefabrication that significantly lessens the amount of construction time required onsite, giving you certainty in terms of both scheduling and costs.

Timber frame

The most common timber construction method is an open or closed planel system. In basic terms, this comprises storey-height walling panels, which are factory built and made up of softwood studs attached to plywood or OSB sheathing to provide all-round strength. Insulation is then fitted between the studs, with window and door apertures pre-cut (in some cases, elements such as the fenestration may even be fitted on the production line).

The attraction

As so much is done offsite, build times are super speedy – a typical house shell can be erected in under five days. What’s more, there’s plenty of design flexibility. Whether you work with an architect or a specialist timber frame company, you’ll be able to achieve pretty much any style you can imagine – think cantilevers, full-storey glazing and open-plan interiors (although if you wish, you can just as easily create a cosy cottage).

The sector is also constantly evolving; for instance, Kingspan Timber Solution’s Ultima, a 2017 Build It Awards winner, uses ultra high-spec insulation to deliver exceptional efficiency with slimline walls.

This low-energy timber frame home was built using Hanse Haus’s pre-manufactured thermo-efficiency wall system. The structural shell reached watertight stage in three days

The system

With open setups, once the panels arrive to your site, they will be fixed together according to the manufacturer’s specifications to create the structural shell. The panels are left unboarded on the internal side until the building is weathertight. You then get to choose what insulation is fitted onsite, before the walls are closed and – usually – battened out on the inner face to create a service void and provide a fixing for the plasterboard.

Closed-panel systems are very similar, but they involve a greater degree of offsite prefabrication. The walling elements are typically supplied with insulation, a vapour control layer, and window and door linings – but this could stretch to service voids, all the fenestration and even external finishes.

This is the method used by many of the popular German and Scandinavian housebuilders, such as Meisterstueck-Haus and Stommel Haus – mainly because it enables better accuracy and efficiency. Many UK timber framers now lean towards closed panels, too. With more of the house finished, assembly is very quick, and the building can be made airtight and weathertight in double-quick time.

Need to know

Most of timber frame’s flexibility comes at the planning and specification stages. Because of the prefabricated nature of this system, the structural elements are bespoke engineered to your specific project – so once you give the green light to start the manufacturing process, it’s tough to make changes to the design.

That said, if there is a design feature that you decide you simply can’t live with – or without – there are ways to remedy this; you just have you decide you simply can’t live with – or without – there are ways to remedy this; you just have to be willing to spend the extra time and money.

Good thermal protection and impressive airtightness are fairly straightforward to achieve within relatively slim wall thicknesses – especially if high-quality insulation is used. For instance, Turner Timber’s Super Advanced system can achieve U-values (a measure of thermal effectiveness, where lower values are better) of 0.09 W/m2K – compared to the Building Regulations threshold of 0.30 W/m2K.

Oak frame

When asked to picture their ideal house, many people will instantly envisage something packed with charm. Robust, natural and beautiful, oak framing can deliver that in spades. It has been used in home building projects for centuries and remains hugely popular for bespoke schemes.

The attraction

It’s safe to assume that much of the appeal of this construction method is down to the innate character the beams add. They create instant focal points throughout a house, injecting extra interest and warmth in even the smallest corner. Today’s specialist oak framers mix heritage techniques with modern materials and production methods to create some of the most stunning self-builds around.

The system

In many ways, oak framing methods have stayed the same for centuries. Traditional post-and-beam techniques use large, widely-spaced wooden members for structural support.

The owners of this home worked with Welsh Oak Frame to create a bright and spacious property that linked to the garden and suited the country setting
The structural skeleton was delivered to site and erected by Welsh Oak Frame’s expert team, before being wrapped in a highly-efficient encapsulation system

Structural insulated panels

Widely known by its acronym (SIPs), this system has a lot in common with timber frame. The key difference is the panels’ insulation and sheathing are glued together under pressure, so there’s no need for internal studwork. This creates strong, lightweight elements that offer distinct pros and cons in comparison to conventional panel systems.

The attraction

SIPs is ultra-quick to build with; some standard house designs can go up in just a couple of days, with fewer tradespeople needed onsite than with many other construction methods.

The vertical posts and horizontal beams carry the building’s loads, while diagonal braces are required for lateral restraint. As the beams also support the roof, there’s no need for large numbers of load bearing interior walls, which makes creating open-plan spaces easy.

Frames can be made entirely by hand or machine cut (and possibly hand-finished) in a workshop. Onsite, they’re put together in sequence according to the frame drawings. The oak is usually craned into place rather than erected by hand (as would have been done in years gone by).

The timbers are connected using pegged mortise and tenon joints, which tighten over time as the wood matures. Some contemporary designs use stainless steel rods and bolts.

Need to know

Oak moves (and cracks) as it dries, so it’s hard to achieve modern levels of efficiency and airtightness by simply infilling the frame in the traditional way. This is why the shell is usually wrapped in insulating panels.

Many oak companies have their own encapsulation systems, designed specifically to work with their frames, but it’s also common to use SIPs for the same purpose. Either way, the result is an airtight and highly-insulated home; Oakwrights has recently even completed a Passivhaus-standard show house.

Architect Liddicoat & Goldhill has transformed a cluster of 18th-century buildings, which were once a threshing barn, dairy and stables, into a stunning family home
The property makes use of the dilapidated green oak frame structures – which had to be dismantled and repaired offsite before being wrapped in SIPs and clad in timber

It also offers a straightforward route to achieving high standards of thermal efficiency and airtightness, reducing the chance of poor site practice compromising performance and delivering obvious benefits for heating bills. Less waste is produced with SIPs, too, which can help reduce your project’s overall carbon footprint.

The system

SIPs are pre-insulated panels that can form part or all of a self-build. The panels are usually made of two sheets of oriented strand board (OSB) that sandwich a layer of high-quality rigid insulation, such as polyurethane. The resulting structural kit includes the walls and roof (which can be pre-fitted with windows, doors etc much as with timber frame) plus the floor and other core elements of the shell.

One of the big advantages of SIPs is that their innate strength makes it easy to create a barrier-free and ready-insulated habitable loft. Design-wise, you can achieve pretty much anything and all the usual cladding suspects are available – including brick, stone, timber and render.

With no studwork in the panels, cold bridging can be kept to a minimum, too – another boon in the efficiency stakes. This quality, combined with the method’s airtightness benefits, is one of the key reasons SIPs is often used as an encapsulation system for techniques such as oak framing.

Need to know

Building a home with SIPs requires precise measurements and small tolerances; there is little room for error in foundations, for example. Price-wise, the shell tends to be around 5%-10% more expensive than conventional timber frame – but some of this can be recouped in a speedier build and easier airtightness detailing.

The high level of prefabrication and accuracy means, provided you use a reputable supplier, you can be confident the finished house will deliver the performance level you’ve specified.

Top image: Located in a Cambridge City conservation area, Treehouse is an efficient closed-panel build by Baufritz.

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