Partially retired Eastern Cape architect Dave Muller’s self-built, low visual impact, passive solar house on the upper banks of the Gonubie River is the realisation of a lifelong dream.

As one of the founders of the Gqunube Green EcoVillage, north of East London in the Eastern Cape, Dave Muller’s home is a sustainable building highlighting the possibilities of low impact living. “I’d always wanted to build my own house, so when I turned 60 I took off three years to do it. Furthermore, my wife and I wanted a house that invigorated us so it had to have a dynamic quality in the design. I consider this an important sustainability attribute as we risk sliding into the lethargy of retirement. The house had to challenge us each day,” says Muller. His wife Sandy is an independent environmental consultant nearing retirement.

Dynamic space

Structurally, much of the dynamism the Mullers sought is imparted through the profile of the dominant design feature – a massive sweeping roof in place of what would otherwise have been a simple lean-to structure. “I’ve always wanted to experiment with interesting roof forms,” says Muller. He believes there is probably a strong element of his nautical yachting background in the whoosh-like design he came up with for the trusses, which, he emphasises, was “an intentional effort to put energy into the house”.

Other aspects of dynamism include an open plan living, entertainment and kitchen space, passive ventilation and ample fenestration, which allows a connection with the surrounding indigenous vegetation and the Gonubie estuary below. When accompanied by the changes in light during the different times of the day, this all contributes to a vast, diverse and undeniably spectacular panorama.

Yet, despite being located on such an elevated vantage point, the house is not visually intrusive from the opposite bank or the estuary below, and with only the top level visible, the curved shape of the roof enhances its ability to blend in with the surrounding coastal valley thicket.

The process

The house is built on an engineered concrete supporting structure comprising the foundations and an integrated water tank, where some challenges were experienced regarding soil conditions early on in the build. “We excavated a total depth of approximately two metres and encountered claysand material with a very high plasticity index,” says

Emmanuel Nemusombori, consulting structural engineer for the project. “We then conducted deep cone penetration tests and excavated an additional two metres down without encountering rock, and ended up founding the foundation of the building in the clay layer itself.” For this reason, the foundations are more substantial than initially planned, which allows for extra volume in the integrated water tank as well as the addition of a basement.

The concrete supporting structure provided enough of a base for Muller to effectively “bolt on” the rest of the house. “I was aware of my limitations so this gave me an accurate platform on which I could build. Basically, I could not mess up the setting out,” emphasises Muller.

Building the house as a team of two comprising Muller and a helper, Simphelo Fenqe, presented some logistical and mechanical challenges. This approach therefore also provided the duo with some much-needed covered work space early on in the building process for fabricating the various components of the house onsite, including the roof trusses, door frames, window frames and other components.

“The house had to be designed in a manner so that all other components [aside from the

reinforced concrete structure] were sized so that two people could fabricate and manhandle them into position.”

After modelling a miniature prototype, Muller fabricated his trusses by overlapping and bonding layers of 6mm plywood into the desired profile and then edged the plywood layers with wooden members, which he bent on-site. The result is a set of massive, curved I-beams with the desired strength-to-weight ratio, which fit the profile of the roof.

High performance passive design

“Passive solar design is overwhelmingly the most important feature of the house, which is very carefully orientated to maximise sun shading in summer and sun penetration for thermal mass warming in winter,” says Muller. “It is the least costly to apply and the one least understood by architects and designers who are now hooked into an unthinking reductionist approach using a pattern for design as regulated by the SANS 10400-XA energy efficiency standards.”

Although the plans for the Muller house were passed before the assimilation of the energy efficiency standards into the building code, today, compliance with the code would have necessitated double-glazing throughout, at exorbitant cost given the window surface area. Muller digitally modeled and tested his design extensively before committing to plan, and says the “passive solar design features are working well beyond expectations”. Since occupying the house, he has also continuously monitored the indoor temperature and the empirical evidence conforms with the initial modelling.

A vegetated roof on the northern side of the house contributes to its thermal performance while adding to the aesthetic. This part of the roof is constructed with a layer of 6mm plywood on rafters, another layer of 16mm shutterboard, a Derbigum root-resistant and waterproof coating, a black plastic sheet with dimples, a layer of geotextile and sand. Vegetation consists of succulents, indigenous plants and grasses which have been legally sourced as a result of search and rescue efforts from nearby construction sites.

Local materials

The house employs extensive use of local materials, and a key feature of the natural building component of its sustainability credentials is its low embodied energy rammed earth walls on the eastern and western elevations. These have good thermal regulation properties and may help to regulate humidity.

The 400mm thick walls were constructed from a mix of 35% clay, 60% sand and 5% cement. To keep them dry, the earth walls stand on the concrete base of the building with an overhanging lip. Large roof overhangs and multiple rows of embedded clay pavers at intervals assist with throwing water clear of the walls.

Water, energy, food

The integrated water tank, which serves as the base and foundation for the house, has 60 000 litres of storage, rendering the house self-contained with respect to water, both for household use and irrigation. Being largely indigenous except for food species, the garden is inherently water-wise.

As well as maximising roof surface area for rainwater catchment, Muller emphasises the need to size storage capacity to be able to catch all the runoff resulting from big rain events. “I have good data to show graphically the importance of collecting large volumes of water as rainfall patterns do seem to be following what is predicted by the climate forecasters, in that rain events are becoming fewer, but when they do occur, they are more intense.”

In addition to the energy-savings inherent in its passive design and use of energy efficient appliances and lighting, the house generates 50% of its electricity needs from solar photovoltaics. “We also tried a small wind turbine but it was an abysmal failure. Contrary to perception, the wind seldom blows in East London and when it does, the sun is usually shining – which is why it blows,” says Muller.

As far as solar thermal water heating technology is concerned, the house employs a structurally integrated solar collector as a pre-feed system to a conventional geyser.

In this instance, the solar collector consists of a glazed galvanised tray, painted black, which runs the length of the vegetated roof on the northern aspect.

Muller ran copper piping up and down the length of the tray, and the water is circulated by a small solar powered pump. The surface area of the solar collector far surpasses that of an off-the-shelf solar collector and is totally hidden.

Although living truly green has its challenges, the house itself is a thriving and inspirational start.

By: Stephen Forder

The full feature can be found in earthworks magazine issue 28, October-November 2015.