The two-day planning inquiry into the controversial building on the slopes of Carn Ingli started on Wednesday at Newport Memorial Hall.
Like many of the buildings at Brithdir Mawr, near Fishguard, it was built without planning permission in the Pembrokeshire Coast National Park.
The two-day planning inquiry into the controversial building on the slopes of Carn Ingli started on Wednesday at Newport Memorial Hall.
Pembrokeshire National Park has instructed Tony Wrench to demolish the round turf-roofed building erected in open countryside.
But Mr Wrench - who built the house - said the bio-degradable home blended with the environment and was central to the community's philosophy of organic conservation agriculture.
He feels the house - which has no mains and no cement base - was the sort of low-impact dwelling that should be encouraged.
Expert witnesses
The national park has given retrospective planning permission to many of the homes at Brithdir Mawr.
But the park authorities have said the roundhouse does not conform to the strict planning regulations which exist to protect it from unnecessary development.
Several experts in the field of bio-diversity and permaculture are expected to be called as witnesses including Malcolm Parry, presenter of the TV series "On The House".
After the inquiry, Ian Osborne - the National Assembly for Wales inspector - will take several weeks to reach a decision.