An investigation was launched following the outbreak of the fire at the site on Bowness Road, Holytown in Bellshil.
Police and Fire services are both looking into the incident which saw flames rip through the nearly completed two and three-bedroom houses.
Firefighters, who received a report of the fire at 10.15pm on Sunday, faced flames and thick smoke.
Four appliances were called to the scene from Bellshill, Coatbridge and Motherwell fire stations and officers used two main water jets, multiple hand-held hoses and foam jets, in case of electrical fire, to fight the flames.
Police closed Bowness Road between Eurocentral and Main Street, Holytown, as firefighters battled the blaze for an hour.
By 11.15pm, the main flames were extinguished and firefighters began a dampening down operation.
This was suspended at around 2.30am yesterdaydue to unsafe underfoot conditions, and a re-inspection took place at 7am.
No-one was injured.
Doug Law, managing director of Persimmon Homes West Scotland, said: "We are disappointed this act of vandalism has taken place. The matter is in the hands of the police.
"Three of the four properties had been sold and we are now in the process of removing the fire damage and will commence re-building the properties."
A spokesman from Strathclyde Fire and Rescue, said: "An entire block was destroyed.
"It took some time for the fire to be extinguished.
"At around 2.30am that work was suspended due to poor under-foot conditions
"The police and fire services remained in attendance throughout the night."
A spokeswoman for Strathclyde Police said: "A joint investigation into the cause is under way between Strathclyde Police and Strathclyde fire and Rescue.
"However, at this time the fire is being treated as wilful."
Anyone with information is asked to contact CID in Wishaw on 01398 202 600 or alternatively Crimestoppers on 0800 555 111, where information can be given anonymously.