The Health & Safety Executive has released figures following a month-long inspection initiative, which it says show 45% of sites visited in the region are failing to properly protect workers.
The HSE found "unacceptable conditions and dangerous practices" at nearly half of the 156 repair and refurbishment sites visited by inspectors in the North West throughout October, and it said one in four sites were so poor that formal enforcement action was required.
Inspectors issued 29 prohibition notices, which stops work immediately, and 27 improvement notices, requiring changes to working practices.
The initiative focused on the management of health and safety risks, such as working at height, temporary work, general housekeeping, failure to control exposure to harmful dusts including silica and asbestos, noise and vibration, and inadequate welfare.
Failure to provide basic safety measures for people working at height was the most common issue found by inspectors across the country.
Neil Jamieson, HSE principal inspector for construction in the North West, said: "These results show that whilst the majority of employers in the refurbishment sector are getting it right, a significant part of the industry is seriously failing its workers.
"The inability to properly plan working at height continues to be a major issue, despite well-known safety measures being straightforward to implement.
"We also find health is often overlooked as its implications are not immediately visible. However, the effects of uncontrolled exposure to deadly dusts such as asbestos and silica can be irreversible."