Four of the six homes at the Ashline development on the outskirts of Ennis were targeted in previous attacks and were later boarded up by the local authority.
The remaining two houses, which were unoccupied at the time, were set alight late on Friday night, with one building being completely gutted.
The alarm was raised shortly before midnight when the fire service received a report of a house on fire. However, crews discovered that two buildings were ablaze.
Firefighters had to run water hoses and carry equipment 100m to reach the burning homes as the local authority had placed concrete bollards at the entrance to prevent unauthorised access.
Three units of the fire brigade from Ennis battled the two blazes for almost three hours, while Shannon fire service had to be called in to deal with another incident in the town at the same time.
The Ashline scheme was built at a cost of €1.7m and was first occupied in 1998.
There have been several arson attacks at the site, culminating in the closure of the development last November.
Following the latest attack the scene was sealed off pending completion of a technical examination. Gardaí are investigating the incident.
Last December, €80,000 worth of damage was caused to three units in a double arson attack at the nearby Beech Park development.
That site was completed in 2004 at a cost of €2.2m and originally comprised of six units. One was demolished following an arson attack in 2010, while the council spent €51,000 refurbishing other units.
The authority confirmed that it had been experiencing difficulty letting the units because of “intimidation and threats within the Traveller community”.
The two sites at Ashline and Beech Park accounted for 11% of all Traveller specific accommodation in Co Clare, before their closure.
A spokesman for Pavee Point said: “Pavee Point does not condone antisocial behaviour of any kind and we believe that people who engage in this should be brought to account.”