Sasha Bhavan and Ben Hair reflect on how issues relating to sustainability, reuse, and modern methods of construction, are reshaping the practice’s approach to materiality.
Established in 1995 by Simon Knox and Sasha Bhavan, Knox Bhavan Architects is a multi-award-winning practice whose work ranges from striking one-off houses to public buildings and conservation projects. Located in Peckham, south London, the architect’s self-designed studio (2016) encapsulates many of its key interests and preoccupations – not least a love of expressive materials that are meticulously detailed and expertly crafted. Other design hallmarks, including innovation and environmental responsibility are also much in evidence, and are central to the practice’s approach, as senior partner Sasha Bhavan and associate Ben Hair explain.
How is the materials library organised? And how does it function day-to-day?
Ben Hair Our Part I architects, Paris Feng and Vicky Pearce, are in charge of the library and have recently reorganised it so that everything is on show. The samples are stored and displayed in repurposed joinery units that came from our previous studio. Upstairs, in cupboards behind the central workstation, are materials and products relating to current ‘live’ projects.
Sasha Bhavan The theory is that the library is a reference resource, which is also there for the benefit of our clients. Material choice tends to overwhelm most clients, so we like to curate the selection and show only products that appeal to us and hopefully them.
TECU pre-patinated copper from KME, Cor Ten steel from Proteus Cladding, and zinc panel from Rheinzink. “We particularly like self-finished metals, and have used them on many of our projects, including Rigg Beck, Crowbrook, and Cassiobury Park. They acquire a patina, which makes further decoration or additional surfaces treatment superfluous, as well rendering them even more beautiful over time.”
Ben Hair Inevitably, there is a certain amount of doubling up when it comes to material samples, but most of these eventually find their way onto sample boards, which are then given to clients.
Sasha Bhavan It sounds very unexciting but we tend to keep lots of different types of extrusions, beads, profiles, and trims. These help enormously in the design process, allowing us to assess the durability, buildability and aesthetics of different details. They are also used to demonstrate – to more inexperienced staff members – what materials and components are involved in specific details, how these fit together, and what tolerances are needed to make them work properly.
Would you say contextuality and vernacular influences are the strongest drivers for material selection?
Ben Hair Contextuality is important, but it means different things at different scales. Materials need to fit their aesthetic context, but also respond to the climate context we’re practicing in. A retrospective carbon analysis on London Brownstones – a pair of stone-clad houses set within an Edwardian brick terrace (2015) – attests to this. Our gut reaction was to specify brick, but stone became the preferred choice to give the project its own unique identity. We now know that the stone is much lower in embodied carbon than its brick equivalent. The colour and dimensions of the stone cladding panels complement the surrounding red brick houses, so there’s a conversation going on between old and new.
Purbeck stone from WJ Haysom & Son. “We’ve specified Purbeck stone for the floors of several houses, including our own, because it is beautiful, has a varied appearance, and is incredibly hard wearing. It is often found in cathedrals and churches, which attests to its durability and quality.”
What is your approach to carbon reduction and how does this affect material choice?
Ben Hair The tension between really high performance and really low embodied carbon in terms of material choice is something that we are wrangling with at the moment.
Sasha Bhavan Yes, and cost, which along with everything else is a huge factor influencing material specification. Ben has been undertaking a number of environmental studies using our new house: Bushey Hill Road (currently under construction in Peckham). In this case, we were keen to use cork as an insulant and internal lining material. But by the time you’ve satisfied the Building Regulations and other statutory requirements there really wasn’t much cork left on show – and it’s expensive. This led us to specify wood fibre insulation made from waste timber, such as sawdust. It’s not as sexy as cork, but unlike cork it is not a virgin material, plus it’s cheap and readily available.
It’s easy to lose sight of what you are doing and become evangelical about certain materials and products. But you’ve really got to be prepared to use things where they are needed and in the way that you need them. I suppose the bigger message is about making choices; and when you make a choice you know exactly why you’ve made it. The practice, and Ben in particular, have been working very hard to develop a way of measuring carbon on small projects for small practices – like us – because there isn’t anything currently available, to our knowledge.
From left to right: Eucalyptus Burl, Douglas Fir Linear, Beech Crown, European Oak Crown, Walnut Quarter Cut, and Cherry Burl – from Capital Crispin Veneers. “The practice almost always selects veneers for timber panelling and other joinery items direct from the supplier’s warehouse. It’s a bit like fabric on a roll, where you can see exactly how much is still available from a specific tree. This is particularly important for book matching, slip matching or avoiding repetitious graining.”
Is this about comparing different materials so architects can make informed choices?
Ben Hair We started by asking the question, “what does sustainability mean to us as an office?”. We then audited all of our existing projects in terms of the embodied carbon of the different materials specified using our in-house KBe (KnoxBhavanenergy) tool. However, when we tried to compare different buildings, we discovered that the information was more useful in an elemental rather than a materials-based format. For example, how much carbon is in the walls, floors or roof ? It made us realise that what we are trying to develop is a tool for communicating carbon; and the metric has to fit the audience, whether they are architects or members of the public at an engagement event.
Sasha Bhavan Ben has been working through our historic projects and it’s helping us make informed decisions for new schemes. Instead of using complex spreadsheets, the environmental information is graphically represented in a form that can be understood by everyone.
Ben Hair Building a library of projects that are all analysed using the same methodology is really valuable. We are now inviting other practices to send us their buildings for analysis, so we can pin-point gaps in our knowledge and help others to improve the environmental performance of their designs. In doing so we’re returning to that question “what does sustainability mean?”. From project to project, practice to practice, the answer is always evolving.
Engineered light oak floorboard from Element 7, and engineered fumed oak floorboard from Waxed Floors. “These engineered oak samples demonstrate how the same natural material can vary enormously in terms of grain, colour and texture. We think it’s important to communicate this to our clients as we guide them through the design and specification process.”
How do you balance environmental concerns with contextuality?
Sasha Bhavan In many ways, we find contextuality lends itself to low-carbon construction. One of the problems we have today is that developers, such as housebuilders, try to do the same thing materially all over the country. Rigg Beck in the Lake District (private house, 2012) employed locally-sourced stone for the walls and reused roof slates from a nearby hospital that was being demolished. So it tends to happen naturally, and in this way vernacular buildings are often less carbon intensive because you grab whatever is close to hand.
Ben Hair We’ve really tried to test what localism means in a contextual sense. Working in London, for example, we are often encouraged by planners to specify London stock bricks. But it turns out that many ‘London stocks’ are actually produced in the Far East, because there is simply not enough London clay and aggregate left to produce bricks in the requisite quantity and colour. For Bushey Hill Road, we specified a yellow Ibstock brick that resembles a stock brick, but is actually manufactured in the UK rather than China.
Funton Old Chelsea yellow brick from Ibstock with ‘specials’ by Everything Now Design. “Specified for its resemblance to a London stock, this brick is being used on a new house in Peckham. Unlike many so-called London stocks it is manufactured in the UK, rather than overseas. The ‘specials’ photographs are actually the noses of cut and stuck bricks by Everything Now Design, which will be used to cover voids left by the scaffolding poles after construction.”
How important are issues relating to reuse and recyclability?
Ben Hair This is something that the practice is really interested in and currently exploring through live projects. We recently dismantled our old office and it is now being partly rebuilt to have a second life as carer accommodation for a project in Kent. The aim is to combine the recycled structure and roof with new MMC cassette walls that employ the same technology we developed on March House in Buckinghamshire (2020), and then evolved for Little Big House in Hertfordshire (2022). The process of taking the building apart is informing how we design now, and hopefully making the process easier in the future.
What roles do making, prototyping and testing play in the practice’s design approach?
Ben Hair As Sasha mentioned earlier, exploring and prototyping details using components and samples from the materials library, as well as the facilities in our workshop (located adjacent to the library) is an important part of our design approach. We also build 1:1 prototypes for clients and contractors as a means of demonstrating proof of concept, and the level of finish required on site. This can also help put contractors at their ease, and ensure that they don’t put a punitive price on something they might not otherwise have understood.
Sasha Bhavan We try to take the lessons learnt from material experiments through one project to the next. In designing and building the highly-adjustable, CNC-cut workstation table/desk for our office we built relationships with fabricators and developed the technical literacy that informed the construction of March House, which is made entirely from CNC timber cassettes. In turn, the lessons learnt on March House informed the design and construction of Little Big House, which was commissioned by a quadriplegic artist. Here, the cassettes were made smaller to ease construction on site and CNC making was used to improve precision and simplify the fixings – small tweaks that make a big difference.
Brass door pull by Knox Bhavan. “Designed for Pembury Pool House in Kent, this elegant door pull was made in-house by project architect and associate Ashwin Patel. Brass is another natural material that wears well over time and has a refined and pleasing aesthetic.”
Do you organise factory visits?
Ben Hair Yes. Recent visits include the Baufritz factory in Germany, where they produce prefabricated timber dwellings, and British Offsite in Essex, which employs robotics to produce steel-based floor and wall panels, among other building elements. The main thing we learnt from the two visits is that there is a marked cultural difference to building in timber in this country compared to Europe. The continental construction industry seems more open and forward thinking in this respect.
Sasha Bhavan There is still resistance to MMC from the small and medium-sized contractors, perhaps because their labour force relies heavily on traditional building techniques. Apparently, the average age of a bricklayer in the UK is 45, while the average retirement age of the same tradesperson is just 55, so there’s a juggernaut coming down the road in terms of skills provision in this area.
What materials are you currently interested in?
Ben Hair The practice has done a lot of embodied carbon research and recently become Passivhaus certified. We’re interested in the tension between these two things, as we want to employ natural, low-embodied carbon materials in a way that achieves Passivhaus levels of performance. This is not easy, as many go-to high-performance products, such as petrochemical-based insulants far out-perform renewable equivalents made from paper or wood fibre.
We’re currently talking to a company called Adaptavate who produces Breathaboard, a carbon-sequestering and biodegradable alternative to plasterboard made from natural and sustainable materials. Another product that we are interested in is Wienerberger’s Porotherm multi-cellular, extruded clay block. This uses less water and mortar, is lighter, has lower embodied carbon and better thermally efficiency than a traditional concrete block.
Sasha Bhavan As Ben alluded to, there is a clear conflict between making a building that is carbon-light and one that is Passivhaus compliant, and I don’t think many people realise this. It’s a bit like the conflict between fire and security; you can’t pretend that there isn’t one, but you have to try and achieve both. Passivhaus has a great reputation, but it’s very greedy in terms of resource consumption.
Brick E Nature 10 from Vande Moortel. “We like the aesthetic quality of these partially burnt or ‘kiln licked’ bricks, which are commonly discarded as seconds. They were chosen to complement the earthy, buried nature of the Pembury Pool House project.”
Are there certain materials that the practice returns to again and again?
Ben Hair Timber features heavily in our work, especially Douglas fir for joinery items. We particularly like its structural stability and the beauty of the wood grain.
Sasha Bhavan We frequently use OSB on our cassette-based projects as it’s made from waste wood and therefore can be more carbon efficient than plywood. It is also strong and comparatively lightweight.
Ben Hair Brick is another favourite, but we like to experiment when we use it. At Pembury Pool House, for instance, we purposely chose to use a ‘spoilt’ brick that had been partially burnt or ‘licked’ in the kiln. This complemented an architecture that forms part of the landscape and is partially buried beneath a heavily planted green roof.
Sasha Bhavan Burnt brick was used by [Alvar] Aalto on the MIT Baker House Dormitory in Cambridge, Massachusetts (1948), and by [Eero] Saarinen on the MIT chapel (1956). Quite often you see something and think, that’s interesting, we could do something like that. Taking the lead from buildings like these gives you confidence. Unfortunately, at Pembury we didn’t get as many burnt bricks as we wanted – the supplier thought they were doing us a favour by sifting them out! So instead, we made a panel for the ‘arcade’ element of the design, rather than try to cover the entire structure.
Steico Flex woodfibre insulation from Steico, and EcoCork insulation board from Tŷ-Mawr Lime. “These two low-impact insulants provide a sustainable alternative to petrochemical-based products and were considered for Bushey Hill Road house. We ended up choosing Steico Flex for reasons of availability, cost and waste content.”
Are there any new materials you are planning to use on future projects?
Ben Hair Porotherm blocks for sure. We are also interested in using clay plasters as an alternative to cementitious ones.
Sasha Bhavan Hempcrete would be interesting to work with, but you need clients who are prepared to accept its uncompromising aesthetic.
Ben Hair While we’ve used stone in the past, we would like to use it more often as an exterior facing material, particularly given its environmental credentials. Stone tends to be thought of only as a flooring product or cladding for civic buildings. I think the industry needs to work harder in communicating the sustainability of stone compared to other masonry products.
