Offsite Structural Options: The Case for Timber

This is the last in a trilogy of articles focusing on the three main offsite structural options, concluding with timber.

I feel like this introduction needs to start with a conclusion to my findings. The essence of all three articles has shown me three things:

1. Design no longer needs to be stifled.
2. Thanks to digitisation, offsite buildings can lose their “repetitive” shackles.
3. Each construction type could be replaced by either of the others.

In a previous article called Modular Trends, I concluded by saying timber structures were my preference and this still stands. However, depending on the project, client and design aesthetic aimed for, any of the three could be used – although there is always the exception.

Later in this article I have chosen three projects which exemplify the fact that off site no longer impedes or stifles design if the team so wish. This gives architects more tools to add to our tool box. Waugh Thistleton Architects are a great example of a practice which has fully embraced offsite.

Additionally, even on large scale projects where there is always a degree of repetitiveness with traditional materials, designs using offsite construction can now show by example that they have cast off the repetitive boring shackles.

So, with all its advantages slowly being recognised, the future is finally looking good for offsite construction. Jump on the bus before you miss out!

Options using timber

There are five basic systems when it comes to timber, not including various hybrid systems.

• Timber Frame
• Glued Laminated Timber (Glulam)
• Cross Laminated Timber (CLT)
• Structural Insulated Panels (SIPS)
• Laminated Veneer Lumber (LVL)

Timber frame has been around for centuries and is by far the biggest player in the residential market. Glulam tends to be more of a framing system. CLT has become a very versatile panel system. SIPS is also a panelised system, typically for external walls that then use combinations of the other systems for floors and roofs. Lastly, LVL is a similar product to plywood, but the veneer sheets are not rotated.

All of the above are being used, but I am finding that CLT has the capability to produce more exciting designs.

Impact on Design

I have chosen a few examples of CLT projects which dispel the myth that off site is anything but repetitive. It’s a huge positive for residential developers to know that they can offer top quality, beautifully designed housing projects which will be highly sought after in the market place.

As digitisation becomes stronger and has more impact, further benefits will be available to the developer. In particular, several off site manufactures are teaming up with business improvement companies to further streamline workflow and ensure that all applicable standards are being met – and as the process evolves, it will get even more streamlined so buildings can be erected, designed, managed and procured quicker.

I firmly believe good design sells and good design does not necessarily have to cost extra.

The following residential developments will demonstrate that offsite can look unique and far from repetitive. Additionally, the use of timber as an external cladding makes them feel more holistic.

The warmth timber can give to an internal space, producing immediately calming and rich spaces, should not be underestimated. As interiors are critical to catching the eye of prospective owners, they can make the difference between a good apartment building and a great apartment building.

The two images above are of Mazarin House, Redbridge London

The two images above are of Wenlock Close, Hackney, London

The image above is of Sussex House

While roughly a third of all housing in the UK is timber frame, sadly much of it is the same-old same-old mass-produced housing seen in Wales, Scotland and England, with no local distinction. This is a great concern from a design perspective.

The projects depicted above are some of the best examples around and show what can be done. They probably also took a lot of blood, sweat and tears by some very committed designers, consultants, clients and contractors as the pressure to make them succeed is critical to this sector. It’s not a field for the faint-hearted as a lot hangs on these developments driving the offsite phenomenon and paving the way for the next.

Buildability / Benefits

The examples above definitely help to break the mould and push the envelope further as they do not look like your typical “traditional” brick-faced residential buildings. However, there are plenty of good examples of more “traditional” type developments. Hence I have chosen two projects by Waugh Thistleton Architects and one by dRMM which, while still using CLT, have used more traditional materials externally.

Image above is of Woodberry Down, Hackney

Image above is of Trafalgar Place, Southwark

Image above is of Stadthaus / Murraygrove, Hackney

Woodberry Down is a good example. The development consists of 20 apartments on a compact urban site. The design has a modern look and apartments have large windows and balconies, key selling features in apartments. The building frame took six and a half weeks to erect, which is very quick and in fact ahead of programme.

Trafalgar Place is a bigger development but cleverly steps the scales of the blocks to create a dynamic series of buildings at an urban scale. Again, traditional brickwork external skin, large balconies and windows are all good selling points. The design has the feel of the many wharf buildings but with a modern crisp aesthetic. This development, like several at the time, was testing the viability of CLT as a long-term approach. As with Woodberry Down, the structural frame was erected quickly.

The overall size of the Trafalgar Place development meant that the architects and landscape designers were able to create important urban spaces around and through the buildings for the benefit of the community. Such a critical intervention is important and goes hand in hand with good safe urban spaces around the buildings, as needed and valued by future owners.

Although smaller developments tend to have less impact on the urban design the spaces around a building and how they are approached and used every day are also critical to their success.

The last building example – Stadthaus – was a trail-blazer over ten years ago as it was then the tallest residential timber building in the world and a mixture of affordable and private housing. Even the façade panels used are formed from recycled timber pulp.

As with the other examples, typically CLT is used above the ground or first floor, with lift shafts and stairwells formed with CLT. The main walls forming apartments are structural CLT as are some internal partitions. These form a sort of honeycomb structure giving the building its structural stability.

One relatively minor drawback with timber, particularly CLT, is future flexibility. Changes to the system later are far more tricky. Although I haven’t heard of many instances in residential developments where layouts are revised, they tend to happen more during the marketing phase of a project while the design is being finalised. Estate agents give feedback on what’s selling in the market and as Clients are keen to maximise their profit, they may request changes to the sizes and mix of apartments. It’s generally a phase of the project where changes aren’t the team’s best friends.

CLT offers so much:

• Its ability structurally to replace the traditional concrete or steel core.
• The fire integrity of CLT has been established, as charring during fire affects the outer layer of timber. This can easily be cut out if damaged and replaced with new timber strips.
• There are obvious thermal as well as acoustic benefits. Vibration has been raised as a concern, but additional stiffening of the structural frame would address this.
• Digitisation has allowed all shapes and sizes to be possible so modern quality design can easily be achieved.
• The level of detailing is better and hence buildings perform better and use less energy.
• Buildings are better finished and have a better health and safety record.

Cost and programme

As mentioned in the previous two articles, the time saving on site is no different for timber.

Two quick statistics:

• Off site projects are said to be on time 96% of the time, whereas traditional projects are only on time 63%.
• From a budget perspective, off site tends to stick to budget 94% of the time whereas traditional is only on budget 49% of the time.

If these figures are indeed correct, it would show that the very nature of this method of procurement also gives benefits. This is probably because so much work is done up front, with time spent on detailing, programming and cost, that it helps to smooth the process on site.

The Stadhaus, for example, if designed today could use 30% less timber according to “100 Projects UK CLT” – a fabulous document showing the versatility of CLT across a range of building typologies.

What’s wonderful is that there can be hybrids of all these approaches. These three articles have tended to concentrate on the purest forms of each, and I haven’t even touched on what the immediate future holds or the alternative and pioneering work out there.

Feedback

One aspect of off site which is less clear is feedback on design, occupant satisfaction, robustness of finishes and detailing, particularly the external fabric, and on thermal and heating performance. There seem to be one or two instances where monitoring is taking place, though most projects didn’t pursue this – definitely a wasted opportunity in my opinion.

As the Green Building organisations heavily promote the “as-built” analysis, it would be good if off site pushed more for a similar retrospective review. By all accounts, owners and users seem very happy with their CLT buildings, but I feel this is something that needs to be embraced, particularly as systems are being developed further and further. It really should not be difficult to monitor the finished product, although all too often monitoring can be one of the first budget cuts during the value engineer exercises.

I feel the industry is missing the cherry on the cake here as this would show and prove that off site is the way to go.

In Summary

Here in South Africa, off site is taking hold as an affordable alternative to traditional building which dominates the residential market, although there is a lot of work to do as steel and timber are seen as inferior to bricks and mortar and concrete.

A good friend who is a designer is assisting his friend to design and build a timber-framed house made up of 1m wide x 2.7m high timber cassettes. What’s great about this small house build is that the Client is going to build a small test mock up on the site to see how the system performs. It’s wonderful to see these alternative solutions, and especially good that a so-called “lay person” is so switched on that he wants to test what he’s buying. All going well, the test mock up will form part of the final built work.

Concrete, steel and timber are equally appropriate to use depending on what you’re looking for. Timber has the edge for me personally as it’s renewable, relatively lightweight and has a great design aesthetic.

Solid wood products such as CLT and Glulam are more natural, renewable, and far less energy intensive to produce than concrete or steel, with timber being the lightest of the three.

So yes, offsite construction is more than proving itself. The digitisation of this sector has meant there is already an inbuilt streamlining process which is just part and parcel of the offering. Therefore, change is not an issue but something that’s expected and embraced.

Image credit: iStock.com/LiuNian

About James Finnie

James has been based in Cape Town for the last 14 years, trained in Scotland, and has worked with some prodigious practices over the years. He recently started his own architectural practice where the philosophy of Kind Design puts kindness at the centre of the creative process.