Wolverhampton magistrates heard that Astbury Design and Build Ltd had been employed to build an extension at a property in Blackburn Avenue.

The firm’s owner Paul Astbury dug a foundation trench to the left of the house but it was far too close to, and the same depth as, the foundations of the neighbouring semi-detached home.

On the night of 23 February 2012, the night after the trench was dug, part of the house, an upstairs bedroom and integral garage collapsed.

Around a third to a half of the property had to be demolished, but the house has since been re-built. Fortunately, the tenants were not at home, and there were no injuries.

An HSE investigation found Astbury Design and Build had failed to notify the owner of the next door property of the intention to dig the trench, or how he would be doing it, as required under Party Wall Notification laws.

The neighbour had already appointed a party wall consultant regarding the ongoing works as there were negotiations about shared guttering and the fact the party wall blocked an existing window in the garage.

The consultant had warned Astbury not to undermine the foundations.

Astbury Design and Build of Wolverhampton, pleaded guilty to breaching safety law and was fined £7,500 and ordered to pay costs of £4,500.

Speaking after the hearing HSE inspector Gareth Langston said: “This was a serious incident that could have easily been prevented had Astbury Design and Build Ltd followed the recognised procedure relating to party walls and detailed the work to the neighbour’s consultant.

“The consultant would have realised the implications and stopped him. Even so, Mr Astbury is an experienced builder and should have known better in the first place.

“The trench should have been dug in metre-long sections, pouring in concrete and waiting until it had set before digging the next section.

“This would have underpinned and supported the wall of the neighbouring house.

“It was extremely fortunate that the occupants were out of the house at the time of the collapse. This could so easily have had much more serious consequences.”