Building giant the Delta Group was demolishing Belconnen's Cameron offices on January 17, 2008, when a blunder sent 15 tonnes of steel and metal crashing on to a busy street.

No one was hurt in the lunchtime incident but a late model Ford Falcon was crushed by the falling debris.

In the aftermath of the collapse, it emerged that ACT WorkCover inspectors, acting on a complaint from the construction union the CFMEU, had declared the site safe just minutes before the section of wall collapsed.

Delta has been charged with two counts of failing to comply with its safety duty and in the ACT Magistrates Court yesterday lawyers for the builder said it was pleading guilty to the charges.

A statement of facts agreed between the company and prosecutors identified a number of failings that led to the collapse.

According to the statement, a senior staff member noticed that a section of the wall of the Cameron offices bordering Chandler Street had become unstable and decided to carry out a ''controlled emergency demolition'' on the section of the building. ''The controlled emergency demolition was performed without due regard to Delta's safety duties.''

The statement says Delta failed to follow its own job safety analysis before moving to take down the section of structure and it did not adequately plan to lower or control the insecure material.

It was also agreed that Delta should have obtained a structural engineer's report before starting to demolish the section of the building.

Delta will return to court in February for sentencing.