Both owner and architects, ADDARC, were keen not to tread the usual pathway of dual lot developments, common to the Asia Pacific region, which result in houses that are carbon copies of one another. “We wanted to give this development a unique identity” says ADDARC’s Rohan Appel who led the project. “Whilst two homes, we wanted it to read as a singular composition”.
A key to achieving this was clever selection and arrangement of materials with elements running across the two properties and extending from external to internal spaces giving a sense of cohesion and flow.
“We chose a monochromatic palette which included Danish Petersen Bricks in a light grey hue which are elevated and then looked to contrast that against a deeper, darker tone to anchor the lower ground floor and set a backdrop for the richness of landscaping” says Appel.
Seeking the appropriate solution ADDARC wanted a natural material that would be robust enough for a growing family, yet timeless in aesthetic and so they turned to timber. Having explored several options, thermally modified American ash was chosen with the guidance of expert importers, Britton Timbers. “Having initially considered charred timber we were introduced to the benefits of thermally modified ash and were completely sold because of the beautiful grain. It was different from other finishes including charred and stained options which tend to lose character in their processing”.
Thermally modified timber (TMT) is not a new concept. The ancient Vikings knew that when building defensive fencing for fortifications, poles made from timber with a burnt surface lasted longer than those that hadn’t. More modern studies on possible benefits of TMT began in the 1930s and ’40s in Europe and the USA but the technology was not developed commercially. It wasn’t until the late 1990s that Scandinavia first introduced the commercial method of thermal modification that we recognise today, as a way of improving the durability and stability of native softwoods. More recent experimental and development work has shown that the thermal modification process works extremely well with some North American hardwood species and commercial TMT kilns were first introduced into North America in the mid 2000s.
The TMT process is essentially a high intensity kiln schedule that lasts between 3 to 4 days. The temperature reaches between 180 and 215 degrees Celsius depending on the level of durability required. The process requires an inert atmosphere devoid of oxygen to prevent combustion, this is usually either steam or a vacuum. During the process, the chemical and physical properties of the timber undergo permanent change.
The two most beneficial effects of the TMT process are to dramatically improve the stability and the durability of timber species. After the process, the moisture content is lowered to around 4–6% and the equilibrium moisture content is permanently reduced which means that thermally modified timber is less affected by atmospheric changes in humidity, reducing the ability of the timber to absorb moisture, and so greatly improving its stability. The durability is improved by removing the hemicelluloses and carbohydrates from the wood which are the main food sources for wood-destroying fungi.
Other benefits include a reduction in thermal conductivity by around 20–25% compared to its untreated state, a significant benefit when used in outdoor applications. It also appears to improve the surface hardness of some species although more research is needed to fully quantify which species and by how much. The other characteristic of TMT is a change in appearance leading to rich and dark colour tones. Whilst in this project a further stain was applied for an even darker finish, frequently TMT in external applications is left in its natural state.
“Enduring design and sustainability were key drivers, but as with every development project there are certain choices that need to be balanced” says Appel. “For this project the decision was obvious as
the timber selection was an environmentally responsible choice but one that delivered the desired aesthetic outcome”.
“The arrival experience into the house was important to us” he continues. “We wrapped the thermally modified ash around the garage and then adapted with a subtly different finish that highlighted the grain and texture for the internal entry corridor”. The result is an extension of materiality from outside to in. The continuous vertical cladding renders the garage almost invisible from the outside and permits a seamless, consistent visual when viewed from the road which reads as a singular residence and settles into the environment as if it has always been there.
