Timber comes first in Hackney

Since the early 2000s, Waugh Thistleton Architects has developed a reputation as a pioneer in the use of cross-laminated timber (CLT) in the urban context – often creating buildings for sites only miles away from its London office in Shoreditch. Setting up on their own, straight out of university, enabled Andrew Waugh and Anthony Thistleton to question established practice and has given them the freedom to pursue their own interests. The first practice in the UK to start building in CLT in 2003 it has since focussed on exploring the potential of engineered timber.  

Its latest project, Dalston Lane, is soon to be completed in Hackney, East London. How it differs, though, is that at 10 storeys with 121 apartment units, it can lay claim to being the world’s largest CLT building. This modest tower is one of a number of recent developments that revolutionised the application of timber in the UK: from one largely confined to one-off homes and bespoke buildings to larger scale housing and commercial blocks.

Partner Andrew Waugh believes timber belongs in the city, and that it’s time for architects to ditch concrete for trees.

Is your interest in timber construction driven by a commitment to sustainable architecture?

We live on a small island with a burgeoning population. We need to produce sustainable, environmentally low-impact buildings, for high-density, mid -to high-rise housing.

With the introduction of Ecohomes and similar policies around 2003, we felt that environmental awareness was treated merely as an appendage to the building; it began to be about checklist architecture.

So we started to look at the impact of our buildings on the environment. The carbon footprint of a building is around 50% due to the materials involved. That wasn’t a conversation anybody else was having and we saw it as something that needed to be confronted.  At the same time we liked the idea that you could build from a renewable material.

What are the environmental benefits of building in timber over concrete, for example?

Concrete is a terribly inaccurate material, it is a material that you have to burn for five days, that creates 12% of all greenhouse gas emissions. When you build in timber you’re building with a material that is completely renewable,  that stores carbon and that is proven to be healthier to live in.

In Dalston Lane we used 2000 tons of timber. Had we built in concrete, it would have been 12,000 tons of the material – more than 750 concrete deliveries into the city. 2000 tons of timber is less than 100 trucks.

Do you do carbon calculations?

We do, for every building. When we submit a planning application we tell the local authority about the carbon captured in the timber, about the carbon saved by not building in concrete, and we demonstrate how many negative years in use that gives the building. For instance in Dalston Lane, the amount of carbon stored in the timber is the same as 18 years of the building’s use if benchmarked against a notional Code level 4 building – that is 5000 tons.

Does timber compare favourably to concrete in terms of indoor temperature and insulation?

This is really interesting. We are discussing a research project on thermal resistance with Graz University at the moment. The way we measure thermal performance according to European directives is by measuring the resistance of materials to heat loss. This is a way of measuring heat loss in masonry buildings, but thermally timber works differently to masonry. We know that timber does not have the cold bridging effect that is suggested by thermal resistance calculations. A timber house with the same U-value as a concrete house uses far less energy to heat than the concrete house. So we try to demonstrate that timber insulates much better than concrete.

How do you convince clients to build in timber?

To begin with, we are a timber first practice. We talk to our clients about the fact that timber buildings are cheaper, that they are faster and simpler to build and that they make better buildings. Most UK housing is concrete frame – concrete floor slabs and light gauge steel stud walls. Light gauge steel is seen as a modern method of construction, but actually it has a very poor long term thermal performance  – and depends solely on the quality of workmanship. We explain that to our clients. We explain that there is no site waste, there’s no noise, no hammer drills, no grinders and that it’s completely silent to build. You have a tenth of the deliveries turning up for a timber building, so you have no road closures. You can build 12 months a year; you can build in rain, snow and wind. You don’t need a tower crane; you can build with a mobile crane up to 20 storeys. We have a seven storey timber building going up at the moment. At the same height, we could have done only six storeys in concrete. We don’t talk about sustainability with our clients, at least not at the beginning.

Are there any measurable health and safety benefits to CLT construction?

An electrician told me that when you apprentice as an electrician in the UK, you first use a hammer drill to drill into concrete. Your shoulder joint disintegrates after about 18 months, and then you learn about electrics. When we began to build Murray Grove the electricians were contracted to be on site for six weeks. After a week they had finished two-thirds of the work using only cordless screw drivers.  So they took the additional money they’d made and the whole crew went to Ibiza for two weeks; then they came back and finished it.

Are there any drawbacks working with CLT?

I haven’t found any yet.  Admittedly it’s no wonder material. You need to waterproof it properly and, you need to understand how to prevent the spread of fire. You also need to be careful about the acoustics because it’s light weight; you need to build responsibly as with all buildings. But because you’re prefabricating the structural elements to the specifications of an engineer, you end up with a very robust building.

Do you have to work with specialist contractors?

CLT is a technology in its infancy, so it’s important that you work with a licensed contractor that understands the material.  There are three major manufacturers in the UK: B&K, Stora Enso, and KLH. Those three share 95% of the UK market, and we work with all three of them all the time.

Do you also involve them in the design process?

We used to. It was exciting and imperative to work with the manufacturer from the beginning of the project to understand the capabilities of the material and to meet building regulations: fire, thermal, and acoustic. It was important that the manufacturer was invested in the process. 

What role does procurement play?

It is key. The process has to be easy, and we are learning how to do that. For Dalston Lane, we have two engineers: a retained engineer of record for the foundations and the concrete at ground- floor level, and a timber engineer. The timber engineer takes the timber to tender and is involved in the selection of the timber manufacturer, as contractor, and then it novates to that contractor. The engineer of record stays on board with the client and signs off the timber engineer’s loadings.

Dalston Lane is exciting for us because it is the first fully tendered CLT building in the UK. We asked each of the manufacturers for a compliant bid and a variant bid. They came back within 5% of each other, and within about one month of each other on programme.

Do you import the timber or do you source locally?

We currently import timber from Austria. We need to promote a better understanding of timber construction [in the UK]. Everybody says UK timber is not good enough, it’s too weak. It’s not. It’s good enough for CLT. CLT comes from the outside of the trunk, it’s the material that is made into MDF or paper. Laying it in perpendicular layers is what makes it so incredibly strong. The good news is there are two CLT plants being built in the UK right now.

How much further can you push the use of CLT  and is there a race to build the tallest CLT building?

About 25 -30 storeys is the maximum height you can go all in timber. In my view, that is as tall as you want to build housing anyway. Beyond 30 storeys you get into trouble with servicing, it’s not efficient in terms of lifts and cores.

The ‘tallest’ debate is interesting. My view on it is that it’s great PR, at the moment. Great PR turns into bad PR if you’re not careful.

A lot of these buildings are purporting to be timber buildings, but one in Chicago, for instance, has a concrete core and steel frame. One in Austria was completely built in concrete and only clad in timber, yet it was called the tallest timber building. I recognise the strength of PR in those projects. It engenders debate and promotes an interest in the material. But I think the time has come to do it properly.

My big concern is that CLT is fashionable at the moment, and unless we can establish it as a mainstream solution with in this small window of opportunity, it will soon be last year’s material.

Are you concerned clients will turn away from it?

Clients are not the problem, at the moment it’s the architectural profession. We have a multinational developer client who wants to build in CLT, but its architects are not interested. But slowly the interest in the UK is growing.

---

Gesine Kippenberg is practice policy and projects officer at the RIBA. This interview is  part of an RIBA series on construction innovation driven by British architects