The house is being built by Mike Hodges and Cathy Mann and overlooks the Clutha River from a rocky outcrop.
Ms Mowatt said it was being being built ''completely out of straw and hemp'' with floors made from clay, lime and earth, and other features from schist and kanuka.
"It is a grand design in every sense of the word.''
The house was "almost completed'' and was expected to feature about halfway through the series, Ms Mowatt said.
When asked for comment, Mr Hodges referred the ODT to the programme producers, saying he would be happy to talk after the programme went to air.
The programme is being hosted by Wellington architect Chris Moller.
A concrete house being built in the Catlins will also feature in the series.
• Grand Designs New Zealand will start on TV3 on October 4.