Thermally treated ash makes a modern home

The interiors and the stair wall cladding remains true to the thermally treated ash’s original base colour. (Pictures courtesy: Haus Architecture)

American architecture studio, Haus, has completed a countryside home in Indiana that comprises interlocking boxes clad in ash, concrete and cement board. Its name, Copperwood House, is inspired by the colour of the surrounding woods and landscape.

It is an untouched natural site adjacent to farmland and bustling with wildlife, but itself not ideal for agriculture. Of the 20 acres, about 3 acres were available for construction, with much of the remaining acreage wetlands.

The design solution was a balance of the unique site opportunities, paired with the owner’s simple lifestyle needs and love of travel. Haus chose to specify thermally modified American ash for the exterior walls of the house.

“We researched the product and liked the appearance of the thermally treated ash samples more than some of the others. Grain and colour were the biggest factors,” said Christopher Short, Principal of Haus Architecture.

Durable material

The owner of the house chose not to protect the thermally modified treatment (TMT) through oils or lacquer and instead let the material naturally weather into a darker grey. In the Indiana climate, the architects expect the material to last about 25 years.

Haus was set on detailing the wall as a rain screen system, and Woodhaven, who supplied the timber, offered a clip/furring system supporting that approach, allowing water to drain out of the wall cavity.

The exterior materials are continued through the interior to the bedroom wings and the stair wall cladding and, although the interior has lightened somewhat, it remains true to the thermally treated ash’s original base colour.

According to the American Hardwood Export Council (AHEC), the external use of thermally modified American hardwoods is growing significantly year on year not just in Europe but around the world, including in the US, as this project demonstrates.

TMT turns non-durable hardwoods such as ash and tulipwood into durable materials that don’t decay or deteriorate in outdoor use.

Architects now have a sustainable timber option that ages well, without finishing, and provides increased stability in use. Together with the rich darkening of the wood it means that TMT hardwoods are also being used internally as well.

Internal applications

Haus wanted to design the spaces for passive solar with an east-west primary orientation, but this was counter to the angled pipeline. Ultimately the pipeline became a major driver of the design concept, resulting in an offset series of bars forming the bedroom wing, living wing, and garage wing – each perpendicular to the other forming a Z-shaped layout.

Each component steps with the angle while maintaining the desired solar orientation and orthogonal relationships, which also happened to work perfectly for desired views and site access.

It was no problem achieving abundant natural light to the primary living spaces and bedrooms, but the architects also wanted a nice quality of light in the lower level, which includes a partial walk-out to the south.

The desire for more light led to a north-facing light well garden on the entry side of home, which then led to the idea for the covered bridge feature. The architect also served as the construction manager for the project.

AHEC is the leading international trade association for the US hardwood industry, representing the committed exporters among US hardwood companies and all the major US hardwood production trade associations. For more information visit:



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