CLT facade arises from developer’s sustainability ethos

by Ofentse Sefolo
CLT facade arises from developer’s sustainability ethos

By Gareth Griffiths

Driving down Dock Road in Cape Town, in the direction of the Watershed at the V&A Waterfront, one cannot help to notice the impressive and completely unique engineered timber-pleated facade warmly cladding the Waterfront’s newest building, which is currently nearing completion. Slow down and ponder, as there is a lot more to this feature than a pretty face or an architectural fancy. It is all about the facade.

Incorporating cross-laminated timber (CLT), the Ridge’s new facade speaks to the sustainability ethos of the developers, who are hopeful that the development may well become one of South Africa’s most sustainable buildings.

A significant contribution towards this vision is in the form of an exterior timber “wall”. In a nutshell, the new timber facade plays a very important part in a range of measures facilitating natural indoor temperature control and fresh air inside the building, instead of conventional air-conditioning, for most days of the year. This yields not only savings in operating costs for heating and cooling, but also greatly benefits the health, productivity and well-being of building users.

The Ridge showcases a new way of restoring the imbalance between humans and nature. In fact, it is conceptualised as a living, breathing organism, explicitly configured to support health, productivity and worker well-being. To be occupied by Deloitte, the developer is targeting a high Green Star design rating, and is hopeful of six stars under the Green Building Council of South Africa’s (GBCSA’s) system.

“Increasingly, the negative effects of building in the ‘business as usual’ way for people working in a conventional office building are being identified worldwide. With our existing successful rollouts of people-centric designs in the Silo District and Merchant House (formerly BP Headquarters), we wanted to raise the bar further by providing a working model that could be adapted and applied elsewhere. At the same time, we are meeting the sustainability aspirations of our client, Deloitte,” explains the development director at the V&A Waterfront, Mark Noble.

Sean Mahoney, project architect.

The lead architect on the Ridge, Sean Mahoney of Studio MAS Architecture and Urban Design, comments that structurally graded engineered timber is the most natural choice for walling on a sustainability building, where the aim is to incorporate biophilic design principles. The developer and client wanted something that would raise the bar into the realm of natural ventilation and people-centric design.

“It seems obvious, but one of the key questions was: ‘On a good day, can the occupant open a window?’ Designing around a suitable response to this question to set the building apart from the sealed glassed-in prevailing corporate standard, would take our team on a three-year path defining the Waterfront’s new normal standard. It also presents something fresh and unique,” Mahoney explains.

Indeed, the development of the Ridge has been a team success. Mahoney says the multi-firm, multi-disciplinary team spent many productive days together, workshopping a sustainable design that was acceptable to both the developer and their client/tenant, Deloitte.

Design response at the Ridge – the role of the facade

Tessa Brunette, lead engineering and facade consultant for Arup on the project, says that the use of CLT is a large contributor to the green credentials of this building.

The Ridge’s extraordinary facade is designed to compensate for the slightly off north-south orientation of the building. While an ideal orientation for a building in the Southern Hemisphere is north-facing, the Ridge actually orientates northwest/southeast in relation to the main entrance and the Dock Road side of the building, owing to the constraints of the ground available for development.

It is the job of the saw-tooth angle facade to correct this to a north-south, east-west orientation for the exterior. Effectively, this means that you can control the effect of direct sunlight in line with a traditional northern orientation.

The Ridge’s extraordinary facade is designed to compensate for the slightly off north-south orientation of the building, with the saw-tooth angle facade correcting it to a north-south, east-west orientation for the exterior – in effect controlling the direct sunlight in line with a traditional northern orientation.

Benefits of the timber facade

1. The timber facade forms part of a range of measures facilitating natural indoor temperature control and fresh air inside the building, instead of conventional air-conditioning, during most of the year.

2. The use of a natural material instead of brick, concrete or additional aluminium and glass in the facade has greatly reduced the Ridge’s as-built carbon and energy footprint by lowering its embodied carbon and energy.

3. The final benefit is that the structurally graded, FSC-certified engineered timber used in the production of the CLT is sourced from sustainable plantations largely located within the Western Cape. So, this material is both a net sequestrator of carbon dioxide from the atmosphere and, as sourced within the province, also minimises the transport carbon and energy considerations.

Arup’s engineers have calculated that 354Mt of CO₂ has been saved by using timber on this project in lieu of conventional materials (e.g. brickwork), in addition to the usage of a natural material which itself enters the lifecycle of the project with a negative embodied carbon content.

Doubling the carbon saving
“The Ridge features double carbon savings by adopting CLT timber facade construction, making this mode well worth promoting in an age of climate change. Firstly, by choosing CLT, GHG (COe) emissions from concrete, steel and aluminium are avoided, all of which have high carbon footprints. And secondly, the CLT stores the carbon dioxide that was absorbed when the tree was growing and locks it away for as long as that building stands,” explains Brunette.

“Effectively, we have proposed a new normal – our normal – with the new V&A Waterfront building, the Ridge,” says Noble.

Mahoney says that ultimately, the value proposition put to the client, who required maximum bulk on site, would be based on:
● Natural ventilation including opening windows, providing climate control most of the year instead of switching on air-conditioning, hence engaging occupants with the outside environment.
● Reduced running costs, due to the natural ventilation/hybrid design model that is in use.
● Keeping the material use as locally sourced as possible.
● Maximising the use of pre-manufactured elements.

Origami-inspired facade

Mahoney admits that the inspiration for the pleated facade came in part from doing origami at his desk in the office. “Triangles as per origami shapes take on a special meaning in this building, as borne out by the facade design and several other design elements. But ultimately the pleated facade is driven by logic: It creates a north-south, east-west orientation for the facade, meaning that you can control the effect of direct sunlight. <PIC: Sean Mahoney> include pics of the origami inspire façade.

“Working hand in hand with Arup, we took this concept to its conclusion – a surface made from a natural material which is predominately local, sustainable and at room temperature. It is as green as you can get under the design parameters.”

Timelessness in architecture is something that many designers strive for. This timber facade will evolve and keep functioning over the years, changing colour as its weathers, developing a patina and making the building stand out as unique.”

Key material considerations

Brunette adds: “It is also vital to make sure that the timber is as durable as conventional cladding materials. This has been done by adding a rain screen of timber cladding outside the CLT structural panels, which are not in themselves weatherproof and are protected by a breathable membrane.

“The rain screen consists of Accoya, a type of board that is made from acetylated South African pine cuts, which have a long service life and are guaranteed by the supplier. They can also be replaced separately, leaving the building still enclosed by the CLT panels so that occupation is not disrupted.

“The glazed and timber saw-tooth facade is prefabricated to enable a swift installation time and ensure a high-quality assembly. Using timber as a key component of the facade allows for the strong but light properties of this material to be taken advantage of in an innovative way, further strengthening the landmark nature of this building as prestigious corporate headquarters. Timber is ideal for prefabrication because it can be machined to very high tolerances.”

Considerable engineering modelling

“Using the initial parametric modelling, we were able to identify a more refined set of options to assess which combinations worked best. It was found that the zigzag facade that we adopted for level 2 and 3 performs as well as a straight deeply shaded facade.

“In essence, orientating the glazing towards the north and south allows for a more glazed facade, without external shading devices that can obstruct views to the outside and reduce the amount of internal natural light. This design significantly reduces the amount of sunlight entering the building, which in turn means that the internal spaces can largely rely on natural ventilation and not air-conditioning to remain comfortable.

“Together with the building’s intrinsic thermal mass, the facade itself is the most important ‘machine’ in the building,” Brunette concludes.

What is CLT?
Cross-laminated timber (CLT) is classified as an engineered timber, made into panels and used in the construction of houses and commercial buildings. It is manufactured to specifications issued by the relevant authorities.

First developed and used in Germany, CLT is regarded as a fast-rising star in the use of natural materials in construction. The usage of CLT in Europe grew from the early 1990s and the first national specifications were issued by the Austrian authorities in 2002. Usages included housing and for multi-storey buildings. As recently as 2015, the United States of America’s (USA’s) National Building Code incorporated CLT, followed by the International Building Code.

CLT is made by gluing together layers of solid-sawn lumber. Each layer of boards is usually oriented perpendicular to adjacent layers and glued on the wide faces of each board, usually in a symmetric way so that the outer layers have the same orientation.

An odd number of layers (3, 5, 7 etc.) is most common (the Ridge uses 5), although even number configurations do exist. Regular timber is an anisotropic material, meaning that the physical properties change depending on the direction at which the force is applied.

By gluing layers of timber at right angles, the panel can achieve better structural rigidity in both directions. It is similar to ply-timber, but with distinctively thicker laminations (Ref: https://en.wikipedia.org/wiki/Cross-laminated_timber).

Termed mass timber construction, numerous buildings internationally have been made from this timber, although it is still regarded as a rarity in South Africa.

Interview with the facade fabricator and erector

Ter de Villiers is the project manager for Geustyn & Horak (G&H) in Bloemfontein on the Ridge project. De Villiers says: “A G&H team is based on site in Cape Town under the supervision of Eugene Markram, who has the very challenging task of bringing everything together by delivering an end-product that reflects a high standard of quality, on time. With all the variables at play in the industry, it is not an easy task.

“The Ridge facade project is different because the facade is a combination of aluminium and timber. The interface between the two materials posed quite a few challenges, but I think the end-product is something unique.”

In total, 960m² of CLT timber panels were used in cladding the building, which is the equivalent to 36 tons of timber. The CTL timber panels were fabricated at XLAM, a dedicated factory in Cape Town. This is at present the only CLT factory in South Africa, according to the company’s Jamey Smily.

Assembling the opening window/CLT façade sections on the N-E elevation of the building.

CLT timber fast facts
1. CLT stands for cross-laminated timber. Whilst it is similar to Glulam, or “shutter-board”, the timber grain runs in perpendicular directions in each layer, imparting great cross-direction strength to the product.
2. CLT has become increasingly popular in Europe, the USA and Canada. Building codes and specifications have been issued governing its use. It offers unique benefits to the environmental performance of a building by way of lowering the building’s contribution to greenhouse gas emissions.
3. CLT has a very long lifespan.
4. At the Ridge, the CLT panels installed feature a sacrificial layer of timber skin on the outside, which will weather and produce beautiful colours over its lifecycle. It can theoretically be replaced, although it is unlikely that this will be necessary. <photo>
5. CLT is a warm and people-friendly material. Inhabitants of the building will benefit by working in an office that features a low emission and low human toxicity material.
6. The Ridge is one of the first commercial buildings in South Africa to feature a timber exterior and interior cladding.

Facade design, manufacture and installation team
Developer: V&A Waterfront
Architect: Studio MAS
Engineering/consultants: ARUP
CLT fabricator: XLAM
Facade – aluminium and glass fabricator and erector: Geustyn & Horak

Acknowledgement and thanks are given to Gareth Griffiths, a materials scientist and professional sustainable construction writer, for the information contained in this article. For more information, contact him on 082 784 5616.

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