NEW safety measures put in place across large complex construction sites could increase costs by up to 40%, the Construction Industry Federation (CIF) has warned.
Tom Parlon, director general of the CIF, said that infrastructure projects including the National Children's Hospital, could see costs spiral even further.
Mr Parlon, who was speaking at the special Covid-19 Oireachtas committee, also said that the new protocols could see additional costs of between 5-10% on new houses.
On Monday, thousands of construction workers returned to sites across the State as phase one of easing restrictions was brought into effect.
"It is the case there will be increased costs and different people have attempted to put a figure on that. I regularly talk to my colleagues across Europe and their view is that the extra costs will be between 5 to 10%," Mr Parlon said.
"I spoke to a very substantial house builder today and he thinks the cost per house he is turning out at the moment will be between €10k and €15k.
"He expects that apartments, which are more intense and more difficult to practice physical distancing, could be as much as €20k extra.
"He tells me that the programme for building a house is about 15 weeks and he estimates that it will go to 25 weeks.
"The industry are building data centres and highly sophisticated pharma plants so the industry has suggested it could be as much as 40% extra cost while the very strict regime is in place.
"One of the big sites that had 1,800 people on site but with physical distancing the maximum they can get in is 500. That will extend out the period of building and the cost of having cranes on site will increase costs."
Labour TD Duncan Smith said the increase in costs was "astronomical".
It is expected that around 100,000 construction workers can now gradually be taken off the Pandemic Unemployment Payment and the Wage Subsidy Scheme as they return to work.
"I want to assure people that companies are being sensible and practical in returning to work. There was no big bang return to work yesterday," Mr Parlon added.
"Larger contractors allowed a reduced workforce on site yesterday to assess sites, to test new measures and embed new protocols and safety culture.
"It would take months for the industry to reach previous output levels."
He said that larger companies are putting in place one-way walking systems and have reduced the number of people on site.
He added that companies that have been able to operate over the past month have said that implementing the measures has been "challenging" and companies are reporting a significant drop in productivity.
Meanwhile, Dr Sharon McGuinness, chief executive of the Health Safety Authority (HSA), said there are currently 67 inspection officers working across the State to monitor workplaces and checking compliance with the new protocols.
She told the committee: "We need additional resources to oversee compliance and we have been discussing that with Government and I am confident that the resources the authority needs will be there to oversee the compliance."
However, she would not disclose the number of type of resources the HSA needs to carry out its work.
Sinn Fein's David Cullinane said the number of inspectors was "woefully inadequate".
Patricia King, general secretary of the Irish Congress of Trade Unions (ICTU), also said that the number of inspectors is "not adequate".
"I think there is a resource issue and that the Government has to improve the resource in the HSA to do this job," Ms King added.
"We are talking about the first phase being construction and we are not even satisfied that the resource inspectorate is there to do that.
"As the other phases happens this will get much more acute."