Sitting duck: Kevin Rudd.

The inquiry heard department staff worked on weekends and up to 10pm on weeknights to devise the Rudd government scheme to meet the deadline set by government. Photo: Andrew Meares

Public servants were already overworked when the massive task of devising an insulation scheme for millions of homes was dumped on them, an inquiry has heard.

They were working at 110 per cent capacity before the department of then prime minister Kevin Rudd allocated them the task in early February 2009, a senior bureaucrat has revealed.

Staffers then worked on weekends and up to 10pm on weeknights to devise the scheme so it was ready by the July 1, 2009 deadline set by the federal government.

A royal commission into the botched scheme that's been blamed for four deaths heard on Thursday how some bureaucrats were so stressed by their workloads they left the public service.

Senior environment department staffer Ross Carter said resources were stretched and recruiting new staff to work on the scheme proved difficult.

''We were given financial resources but in terms of getting the right staff and skill sets on board that was a more difficult task,'' he told the inquiry.

''In terms of recruiting new staff into the public sector - that can take some time to do.''

In his statement to the royal commission, Mr Carter said some employees were so stressed they ended up resigning.

''There are quite a number of staff that are still quite affected by the intensity of that time across most of the division,'' he wrote.

''Some have left the public sector and some may have ended up not working in management or executive roles because of the pressure and stress placed upon them during this time.''

That stress was exacerbated by the fact the scheme was associated with the tragic deaths of four people, Mr Carter added.

Queenslanders Matthew Fuller, Rueben Barnes and Mitchell Sweeney, and Marcus Wilson from NSW, died while working under the scheme that's also been blamed for one serious injury and hundreds of house fires.

The royal commission before Ian Hanger QC continues.

AAP