Site Excavation – When Simple is Not Straightforward

Tuesday, December 23rd, 2014
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When excavating sites in residential construction, owner builders need to manage a number of risks.

This is especially true today, when smaller allotments and greater demand for storage, excavation and below natural ground development have become increasingly common in residential construction.

Unfortunately, however, excavation for vehicle access and storage often takes place close to neighboring boundaries, creating risks associated with damage not only to underground services such as sewerage but also neighboring properties.

So what should owner builders do to mitigate this?

In almost all cases, owner builders engage sub-contractors to undertake preliminary excavation work. These people should carry their own Public Liability insurance and owner builders are well advised to ensure this is the case with anyone they take on.

Whilst many owner builder insurance policies include sub-contractors, in many cases the wording of these policies means the owner builder is effectively vouching for the sub-contractor (whom they might not even know). More importantly, in the event of an incident, owner builders could be forced to undertake the often complex and difficult task of making a claim themselves.

In nearly all cases, excavation on a boundary or to depths beyond two metres from natural ground level will require the involvement of an engineer. In some instances, commissioning dilapidation or condition reports on surrounding property (or properties) or to existing structures may be needed. Engaging a suitably experienced, insured and qualified sub-contractor to undertake the actual excavation is also important. Provided he or she works to the engineer’s specifications, risks to owner builders are minimised.

Problems, however, can still occur as a result of gaps in insurance cover, which may expose owner builders to higher risks than initially expected.

These could happen, for example, as a result of the following sequence of events:

  1. Engineers issue work orders and excavation specifications
  2. The sub-contractor (excavation firm) is insured and carries out works as instructed
  3. Upon completion of these works, the owner builder awaits the arrival of second sub-contractor to construct the retaining walls
  4. Risks associated with the gap in time between steps two and three now reside with the owner builder. These include:
    • Landslide or soil movement (with no retaining structures in place) as a result of the setting in of rain.
    • Risks associated with soil movement or personal injury as a result of children playing in the ‘hole’.
    • Sites left ‘un-worked’ for days or weeks where the sub-contractor engaged to build the retaining walls is delayed.

Construction insurance policies contain a little-understood clause of duty of care with an overarching requirement that at all times the site must be safe with all reasonable care having been made to protect it. These clauses extend to an owner builder’s responsibility to be aware of weather alerts and take reasonable steps to protect the site from damage and prevent damage to other parties. For example, an open cut excavation left unattended and without reasonable retaining structures in place and with a forecast calling for heavy rain may trigger soil movements. How’s that residence next door feeling now?

In addition, construction site security is more often no more than a wire fence – easy evasion for young ‘Indiana Jones’ types. Children and construction sites are attracted to one another like magnets.

Owner builders are well reminded that they remain principle site controller and carry end to end responsibilities.

Six steps to mitigate high risks scenarios when excavating are as follows:

  1. Engage only properly qualified and insured sub-contractors. Diligently apply safe work practices. Request evidence of sub-contractors insurance before they start (golden rule: no insurance-no start, no matter how cheap they are)
  2. Pay particular attention to gaps in work schedules. Close these through:
    1. Extending the job requirements of each sub-contractor to reduce gaps. For example, a reputable excavation sub-contractor will assist with shoring up the excavated walls. This may mean installing a temporary retaining wall.
    2. Request that a sub-contractor construction the retaining wall or structures is available to temporary protect against soil movements
  3. Locate exact positions of underground services. Seek advice, mark it clearly and follow it
  4. Stay alert to weather conditions and take action accordingly
  5. Consider environmental matters such as damaging vibration activities or impacts to neighboring properties. Common sense is a great start; and
  6. Keep site safety at the forefront – don’t leave it to chance.

Owner builders reduce their exposure through planning, staying alert and not underestimating risks. They should seek advice with regard to doubts about any aspect of the project.

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