Cross Laminated Timber: A Design Stage Timer – by Nic Crawley, RIBA Publishing, 2021

Blank Speculations on CLT – by Jennifer Bonner and Hanif Kara, Applied Research and Design Publishing/ORO Editions, 2022

Review by Anthony Thistleton

This trend is a consequence of the concrete age, where the formal potential of the material has allowed for endless possibilities, often at the expense of pragmatic considerations. This has resulted in plummeting productivity, escalating costs, and poor-quality development in many towns and cities. Despite widespread recognition that the world needs to shift away from extracting energy-intensive materials to those that can be naturally grown, the architectural profession’s addiction to concrete and formalism is difficult to break.

The advent of cross-laminated timber (CLT) represents a fundamental change in architecture and construction. It is not just a new material but also introduces an entirely new approach to building that re-establishes the crucial connection between design and construction. However, many architects view CLT as simply another aesthetic choice, offering a different surface to incorporate into their artistic creations. Some even use CLT as a cladding material to create the impression of timber architecture, masking the carbon-intensive structure with an apparent concern for the environment.

From left to right: Making the panels – the principle steps: i) Finger joint planks together with glue / ii) edge glue together to make single layer panels / iii) bond together the panel horizontally / iv) bond together vertically                   

So if the curiosity of the construction industry ends with what it looks like, then they must be led in the right direction. In the endeavour to transform construction and usher in a new timber age, two books published over the last two years offer an interesting portent and a good step forward.

The advent of cross-laminated timber (CLT) represents a fundamental change in architecture and construction. It is not just a new material but also introduces an entirely new approach to building that re-establishes the crucial connection between design and construction. However, many architects view CLT as simply another aesthetic choice, offering a different surface to incorporate into their artistic creations. Some even use CLT as a cladding material to create the impression of timber architecture, masking the carbon-intensive structure with an apparent concern for the environment.

So if the curiosity of the construction industry ends with what it looks like, then they must be led in the right direction. In the endeavour to transform construction and usher in a new timber age, two books published over the last two years offer an interesting portent and a good step forward.

Nic Crawley’s Cross Laminated Timber: A design Stage Primer is the first book on CLT that is written by an architect and published by the RIBA. As such it offers a degree of novelty in that it eschews the technical details associated with the majority of publications on CLT to date. 

With the key challenge to its implementation being the negotiation of the numerous functional and regulatory impediments, it is inevitable that most books on CLT up to this point have been written from an engineering and timber industry perspective. Previous guides are handbooks packed full of detailed design information about issues such as modelling shear deformation, transverse wall connections or calculating lateral resistance.

However, before we get to this level of calculation, the principal barrier to overcome is a lack of basic knowledge of what is involved and how to get an engineered timber building onto the drawing board. If one were new to the game of chess, a detailed guide on the minutiae of various strategies would not be of much use. A primer on how to set up the board, the way the pieces move and the rules would be a necessary first step, which is where this volume sits.

Blank Shots: Monolithic Desires and Laminar Inevitabilities

Crawley’s publication primarily serves as a guidebook for the application of CLT, yet it specifically targets architects and emphasises the provision of information to those unfamiliar with the material. Although several other texts cover similar content, this compilation presents a valuable resource for the sincere new apostle. As the title suggests, Crawley’s book – Crawley was head of sustainability and currently an associate at AHMM – centres on the design phase of CLT implementation.

The book provides a comprehensive guide on designing with Cross Laminated Timber (CLT), covering various aspects from its origins and manufacturing process to design, technical, and site considerations, as well as its usage and end-of-life issues. The text is enriched with numerous examples of successfully completed projects and further supplemented by six detailed case studies encompassing a diverse range of scales and types.

The architect who reads and digests this will be better placed to consider the delivery of a CLT building and have some insight into the challenges they, their client and their contractor will face. In this, it is essential reading for all of those who have a genuine desire to use the material to best advantage, avoiding pitfalls and optimising its performance. It is a book for any architect who wants to take their designs beyond the simple application of a timber texture to their visualisations.

This idea of surface and texture is amply picked up and amplified in Blank: Speculations on CLT, published a year ago. A collection of essays curated by Jennifer Bonner and Hanif Kara, it is the first attempt to develop an embryonic theory and cultural substance for the new timber revolution.

The blank of the title refers to the essential module of CLT, the 3m by 16m standard panel that is therefore the fundamental basis of all CLT architecture. As such it is a radical diversion from the existing forms – the additive process of brick, the linearity of steel and the plasticity of concrete.

The book is a rich collection of essays exploring the possibilities of a new architecture and pondering on the repercussions of one composed of planes. There are many beautiful assertions and observations with themes that run through the essays, brought together to provide a linear contention – sequenced to construct a proposition, each part interleaved, cross-laminated, with drawn examples of CLT projects from Kara and Bonner’s studio at the Harvard University Graduate School of Design. 

For someone who has practiced in the material for almost two decades, the book offers an exciting diversion from the practicalities of establishing a practical and compliant building system, exploring the novelty and potential in terms of architectural expression.

Photo: https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcSQyiaGiaaDm_l4cgV1KrbCtjXhNjYb5eNA2cXkBn80QfkAB1ghbA

CLT diagram by Hanif Kara (from Blank Speculations)

Some of these essays flag the need for a cultural and intellectual context for CLT, others include CLT in a broader diatribe about architectural future, general flow and current challenges.

The connection with craft and material, most notable in Erin Putalik’s ‘brief history of better wood’, which details the mechanics of tree growth and cell accumulation and the artificial nature of grain, taking is through the emergence of plywood as the pioneering material for the machine age: the first transformation of wood into an engineered material. Erin picks up on the theme, in common with several other contributors, of labour and the relationship with resource and environment.

There are others who expound on the theme of blank and the planar more specifically – Sam Jacob writes about the flatness – the cartoonish qualities of CLT cutouts. Specifically, that the act of extraction, of cutting, provides the definition and creates the object. Courtney Coffman’s philosophical piece on the nature of blankness and the subtractive vs. the additive. Chris Lee highlights the transformation from the frame paradigm of the modernists to the planar typology.

This theme of the plane, the blank, is familiar to most architects for whom the earliest three-dimensional expression came through the use of card to create models. The analogous process with building from CLT is drawn by several of the contributors, and much of the design proposals that intersperse the text are either explicit cut-out kits of parts or evoke the model-makers hand. Yasmin Vobisexpressly picks up on this connection and the naïveté employed, particularly by students in their making of CLT as fantasy – a generic surface, unencumbered by constraints.

Those who practice in the new material often draw parallels with the advent of reinforced concrete a century ago – an ancient material given new engineering possibilities through novel advances in technology. As practitioners developed techniques and capabilities we witnessed a revolution in architecture. Today we again look towards a new architecture, one that is rooted in the new materials and practices and the preoccupations of the society which forms it.

Several of the contributors to this collection pick up this parallel between the emergence of the two materials. The Maison Dom-ino and Corbusier’s five principles is repeated in essays and analogy is drawn with the current paradigm shift but for all the speculation, intellectual and conceptual analysis, nothing in this book really comes close to providing the new archetype, despite the advocacy of Chris Lee and Hanif Kara.

CLT panel detail – Photo Eurban

XLam Cross Laminated Timber Panels

Vers Une Architecture was published a quarter century after the first reinforced concrete building. CLT has been in use since the mid-90s, so we must ask what the gestation period for the thesis on CLT might be. Perhaps the transformation is not so radical – the glulam frame with CLT slabs is one of the most ubiquitous forms of mass timber construction meaning perhaps the evolution in thinking is not so large. Moreover the CLT honeycomb frame favoured in much of the early UK residential design is a reversion to much earlier cellular typologies – perhaps the revolution is the lesser still.

But what this does not recognise, but which does come through in several of the essays, is that this revolution is a reconnection to the means of production and a transformational change in the way we build, which in turn changes the way we design.

There was a heroism and grandiosity to the age of steel and concrete. The flatiron building, the image of builders lunching on a steel beam hundreds of feet up in the air. The embarking of the modern age, where everything was possible and progress was more, bigger and better. Perhaps we do not have these images because the paradigm shift is so much more fundamental. In the first century of the Anthropocene, we are not looking for daring, we require a more subdued and considered approach.

In their introductory essay, Kara and Bonner identify the need to consider CLT “beyond its sustainability”. We might consider that we are in the early stages of the world illustrated so compellingly in Chris Nolan’s Interstellar – a post-growth age where heroism and grandiosity are archaic and vilified. In which case is there anything other than sustainability?

This is where the thrust of the piece unsettles me. The paradigm shift that leads us to primarily consider whether we need to build at all and that if we do we utilise natural, carbon-storing materials, is so fundamental that placing this change within the context of a linear history which has centuries of the same approach embedded.

The images of tall timber buildings that evoke the lost age of optimism are unbuilt and to a large extent unbuildable. Neither should they be built as they are essentially oxymoronic. The architects, engineers and builders of the Anthropocene must still be visionaries, but the vision must be fundamentally altered.

As the use of CLT becomes more widespread there is much more to be researched, trialed, considered and written. As the anthology of material generated from the new material expands, these two books will have a place for some time.

Cross Laminate Timber Lever Architecture