Freedom of Information requests sent to 27 police forces around the UK have revealed the shocking level of site thefts.
Secure storage unit supplier Mobile Mini made the requests which revealed more than 6,000 separate raids between September 2012 and September 2013.
The requests also revealed how thieves are gaining access to supposedly secure sites.
Raiders used force – such as breaking windows, cutting padlocks or compromising perimeter fences – in around 35% of incidents.
A further 5% were due to “legitimate access” in cases where the thieves either had a key, or turned up to a busy site and took equipment unnoticed.
And in 21% of incidents sites were simply left unsecured, or were protected only by a fence that was easily scaled by intruders.
Commonly-stolen items included materials, such as lead and copper piping, and power tools like saws, drills and jackhammers.
Plant equipment, such as cement mixers, diggers and excavators, were also frequent targets of theft while personal items, such as laptops and mobile phones left by staff, were also stolen by opportunistic thieves.
The figures obtained only represents the value of the goods stolen, and the cost of lost working time while expensive equipment is being replaced can easily exceed this.
Ron Halchishak, Managing Director at Mobile Mini, said: “We were surprised to see that as many as one-fifth of thefts were due to a lack of on-site security and this should act as a wake-up call to many in the industry.
“The FOI data revealed that criminals are all too prepared to force their way into a secured site too.
“Construction site managers should give careful consideration to their security arrangements and make life as difficult as possible for Britain’s construction site thieves.”
For a full breakdown of the regional theft data click here