The turf-roofed roundhouse built for Simon Dale, Jasmine Saville and their family is the first building at the eco-village to be completed.
An eco-village has won £350,000 for a centre for research, education and promotion of low-impact development.
It will form the centrepiece of a community with nine smallholdings in Pembrokeshire's Preseli Hills.
It was one of 10 winning projects to share a £10m fund as part of the Low Carbon Communities Challenge.
The charity behind the centre, Lammas, said it would help it "reach out and inspire people to create their own sustainable land-based lifestyles."
The controversial eco-village near Glandwr was granted planning permission in August after an appeal to the Welsh Assembly Government following refusal by Pembrokeshire Council.
The small holdings are being built from straw, turf and timber and residents will source all their water, heating fuel and electricity from the land and develop land-based enterprises supplying food and crafts.
Work will start on the community hub in February and take a year to complete
The Department of Energy and Climate Change launched the competition in July to promote low carbon living.
Lammas will receive a grant to pay for a "community hub" building which will become a centre for launching the low impact housing initiative, as well as pioneering alternative farming and land-use technologies, carbon-positive food, fuel and craft production.
Energy and Climate Change Minister Joan Ruddock said more than 300 communities registered an interest in the competition.
She added: "There's a real appetite out there to save energy to help tackle global warming and save money on fuel bills.
"The ten winning projects will now spend the money on things like community wind turbines, solar panels, heat pumps, insulation or green transport projects to cut emissions."
Lammas co-ordinator Paul Wimbush said: "The community hub building will be a launchpad that will celebrate and promote the new opportunities that are available to create eco-smallholdings in the open countryside.
"Opportunities that provide self-build homes, create carbon-positive livelihoods and revitalise our rural economy, all in a way that benefits our natural environment."
The first building of the Lammas project is nearing completion.
It is a turf-roofed roundhouse which will provide temporary accommodation for Simon Dale, Jasmine Saville and their two children whilst the family builds the rest of their smallholding.
It took took two months to build, cost under £4,000 and attracted help from over 50 volunteers.
It incorporates straw-bale walls and a rammed earth floor.
Construction on the community hub will begin in February and take 12 months to complete.
It will be made largely from locally sourced tree-trunks stacked up in a Canadian log-cabin style and will include a cafe and a shop selling produce from both Lammas residents and other local land users.