The Unique Design Challenges of House Llandudno by Bomax Architects

The Unique Design Challenges of House Llandudno

House Llandudno has been shortlisted for the Residential Architectural Property category in The Design Et Al International Design and Architecture Awards 2023. The results will be announced in mid-September.

The architecture of the unique Llandudno home is a composition of bold concrete cast forms, an engineering challenge achieved by a selected team of architects, engineers, and concrete construction specialists. The designing architect and structural engineer share insights into the unique features, construction challenges, and innovative design techniques adopted to bring this design to reality.

Design factors

The Cape Atlantic Coast at the southern tip of Africa has both picturesque idyllic days and inclement weather that takes a toll on the coastal architecture. Corrosive sea air and challenging site terrain pose additional challenges in designing for this location. Given the location’s extreme latitude, orientation is critical as well. These factors shape the unique architecture of this building.

Design process

The goal for House Llandudno was to create a unique building that would suit the client’s minimalist ideals and respond well to the extreme site conditions. The clients, who live between Paris and Hong Kong have an intimate understanding of contemporary architecture and worked closely with Bomax Architects to realise this project.

To achieve the ideal form of the building, it was necessary to create deep, unsupported eaves that could endure the harsh Cape storms without obstructing the stunning ocean views. In response, Bomax designed a cantilevered concrete form, meeting both structural requirements and optimising the building’s exposure to sunlight. Specifically, the form is oriented to the late morning sun over Judas Peak while being closed off to the garish, reflective sun from the West.

The concrete cave structure tapers to a 50mm leading edge to reduce visual weight and creates a lighter structural load. The forms are designed to resist and moderate the weather and elements. The off-shutter cast concrete allows for casting long spans and deep cantilevers, while remaining maintenance-free. The illusion of weightlessness is created by the chamfered edge.

This lightness of structure has an elegance about it. The way it opens to the energy of the beach below, it’s stunning. It sits in the water, the building appears to float. At the same time, it’s connected with nature”. – Dion Walters, Bomax Architects

The concrete form of the main house was repeated below to accommodate the planning of an annex wing for visiting family. This reduced the scale of the building, created rhythm, and enabled the project to comply with site limitations. A funicular lift shaft was built underground to connect the main house and annex building, a task that was nothing short of a granite mining expedition.

As part of the design process, the Bomax utilised 3D modelling in virtual reality (VR) to assist with design development. Through VR immersion, the clients and engineers were able to gain a realistic perception of the space, which enhanced their ability to understand the architecture and collaborate more effectively. As a result, this cutting-edge approach helped to ensure that the final design was optimised for both functionality and aesthetics.

Engineering Challenges

The stand-out design feature is the cantilevered edge, which minimises and disguises the significant structural support required behind it. It is an amalgamation of unique architectural design, an essential structural system, and the practicality of the contractor. The ambitious construction is a testament to collaboration and the innovative approach of these disciplines. – Ian Marais, Arup Structural Engineers

Designing the cantilevers was a complex process that demanded careful consideration of multiple factors. While the four-meter unsupported length was one such factor, the team also had to account for the effects of shrinkage and temperature changes on a varying section with solar gains exposure in the concrete. Additionally, the analysis was complicated by the long-term effects of creep in a heavy concrete cross-section and alternating live loads, primarily from wind in the location. The team also had to ensure that the concrete surfaces could withstand the harsh marine environment’s long-term weathering effects. Although concrete strength wasn’t a significant issue, achieving low shrinkage and well-compacted concrete was challenging. Even so, the team was able to resolve the issues through workshops and mock-ups, ultimately implementing the cantilever design successfully.

Razor-Edge Detail

Arup Engineering formed the sloping edge using pre-built rafters with standard formwork available in South Africa. To achieve smooth off-shutter concrete, they considered crucial aspects including weight per square meter (about 3 tons), and depth of the starting point (700mm sloping to 50mm). The design also featured sloping slab soffits made of Peri Birch vinyl face boards, machined off-site. The degree of connecting angles was also critical. For that reason, the team used a hanging top shutter secured by rodding through the decking.

The biggest challenge with pouring concrete was releasing air entrapment. With ongoing load shedding in South Africa, you are not guaranteed to receive your concrete mix from the same batching plant. Therefore, Arup Engineering opted to use a standard concrete mix instead of a unique mix with a specific colour.

Passive design for sustainability

Sustainability and architecture is a collective thought process. It starts at design inception. It involves the whole team. It runs through the build and passes on to the owner and how they live and use the building, how they manage the systems. The systems implemented here involve passive solutions like heat-sinking concrete, photovoltaics and origin sourcing materials. These systems are implemented to help us look after the planet. – Dion Walters, Bomax Architects

The site has a magnificent north-facing view of the bowl of Llandudno. In the deep South latitudes of Cape Town, the sun’s East-to-West path tracks to the North side, allowing large format North-facing glazing that draws in the warmth without compromising the building’s thermal performance. The deep eaves create a suitable shadow depth to prevent excessive heat gain in summer. When the sun dips lower in winter, any heat that penetrates the building gets absorbed by the heat-sinking concrete for when you need it most. The energy is then released slowly at night as the building cools. With the addition of a good cross-ventilation design, the building becomes a passive temperature moderator, facilitating comfortable living without the need for energy-consuming usages like air-conditioning and underfloor heating.

The main house concrete roof was designed to accommodate a Tesla PV Solar System for generating electricity, while the annex roof was designed as a cooling roof garden. The insulation of every surface of the building envelope was carefully considered to assist thermal performance. These passive design systems all work together to mitigate energy demand.

In harmony with nature

Bomax Architects aimed to integrate the building into nature, which involved incorporating the coastal thicket, found in the nearby ravines that run down to the beach, into the design of the house. Bomax constructed a pathway leading up to the front door made of granite boulders that were excavated from the site and planted endemic milkwood trees and other local species that can withstand the salty air in the area. This journey to front door evokes the feeling of traveling down to the beach.

The material selection of the home is a tactile response to the surrounding environment. The material palette is kept to a minimum. This allows the artwork to draw the attention.

The interior itself is more about the architecture, the spaces that it’s created than the things inside. This allows for a space that’s in harmony with nature. It’s serene and peaceful. – Dion Walters, Bomax Architects

In conclusion, the unique design and construction challenges of House Llandudno in Cape Town, South Africa, showcase the collaboration and ingenuity required to bring complex architectural projects to life. The result is an aesthetic and functional home that incorporates passive solutions for sustainability. The architecture reflects the location’s extreme weather and challenging terrain, as well as client’s minimalist ideals. The cantilevered concrete form creates an illusion of weightlessness that blend seamlessly into the natural surrounds.