BICC excavation policy framework

Architect and chairman of the Building Industry Consultative Council within the Ministry for Resources and Infrastructure Robert Musumeci explains a new concept regulating excavation works

As property prices go up, planning regulations to curb urban sprawl become more restricted and policy regulations compel more developers to provide on-site car park provision, our local construction industry has been witnessing a marked increase in excavation works.

Under these circumstances, the BICC has prepared a guiding framework aimed to review current legislation consistent with emerging building needs and general public safety.

For the first time, this document proposes a framework that binds the person undertaking the works to submit a method statement, which can be viewed by neighbours, supported by an insurance policy, before the excavation works begin.

The methodology adopted by the BICC is therefore not intended to restructure current civil code provisions, which lay down a minimum 0.76 metres distance, which should be retained from the face of party walls during excavation works, but is rather aimed at reinforcing third party civil rights and existing legislative mechanisms on current legislation.

This rationale is further tied to activate Mepa's Structure Plan Policy, BEN 1, which places a strong presumption against any development of any characteristic or nature, which would constitute bad neighbourliness.

The strategic intent behind the proposed framework underlines that excavation works should not prejudice any of the neighbours' rights to undertake similar future development on their respective property, while it must be ensured that the issue of safety is safeguarded at all times.

For this reason, it is being suggested that a method statement should be mandatory for all excavation works falling within 45° of the face of existing building's party walls. The statement should highlight the design philosophy underlying the proposed works.

In parallel, it is being recommended that neighbours have the possibility to inspect the method statement before works begin, in the same way that they have a right to inspect plans tied to a Mepa development application at the initial stages of the application.

If there is technical proof that the proposed works constitute an unsafe solution, it should be more straightforward for the health and safety authorities or the courts of law to prevent further works.

Method statement guidelines

¤ As a preliminary step, the architect in charge of the excavation works is expected to give an indication of the existing ground founding material, thereby making reference to local geological survey maps and any other relevant documentation, which might indicate particular features, such as deep backfilling to the site. This survey should extend to all sides of the proposed development for a distance at least equal to the proposed excavation depth.

¤ A detailed survey of the adjoining existing properties supported by photo documentation should follow with a view to establish the state of repair of the adjoining property, further outlining the specification of the existing finishes together with the identification of the high risk items, such as swimming pools, retained material, which is a primary source of concern with many wall failures, and other material risks.

Given the fact that most people do not take note of minor cracks in buildings unless some specific event actually brings them to their attention, it is paramount to take note of them due to other causes, such as poor design, inadequate foundations, shrinkage and ambient thermal and moisture variations at this stage in order to be able to relate potential damage to excavation works.

¤ Although it is not simple to pre-assess potential damage, which might be caused by vibration, noise intensity produced at a point may be an indication of damage which potentially might be caused.

It is elsewhere proven that stressed or poorly installed windowpanes may fracture at 150 db, while cracking to plaster occurs above 170 db. If safety of ear damage from impulsive noise is to be considered, then any single impulsive noise should not exceed 140 db.

Against this background, the magnitude of the maximum'peak component particle velocity' (PPV) is considered to be the best criterion in relation to the possibility of structural damage occurring.

For many years a safe PPV limit had been established from American practice at 50 mm/s, which however does not prevent residents' complaints. As this is generally related to timber buildings, lower limits are being suggested for sturdy masonry building outlining the probability risk (See table).

The table offers guidance on the value of PPV at which there may be a probability that the vibration would be likely to cause structural damage to a sturdy masonry building. The probability of damage tends towards zero at 12.5 mm/s PPV.

British standards note that very minor crack extensions result from velocities of 20 mm/s and many non-damage observations were made at levels exceeding 50 mm/s. From the table, 20 mm/s is considered to be a good minimum criterion.

On the other hand, if buildings with existing defects, have visible cracks in masonry, then PPV is to be limited to 5 mm/s, as taken from DIN 4150, which appears not to be damage-based, but intended to minimise the perceptions and complaints of nearby housing residents. If ruins and buildings of great historical importance or pools and water retaining structures are in the vicinity, then PPV is to be limited to 2 mm/s.

The selected excavation machinery must therefore ensure that the excavation work is undertaken in line with the these requirements, depending on the nature of works.

The framework also takes other health and safety considerations into account. The contractor has an obligation to safeguard the health and safety of both his crew and the public in terms of active occupational health and safety legislation.

This should be targeted by reducing both the time of exposure and level of vibration. If noise is a nuisance to the public, then a silenced compressor with a silenced engine is to be used.

Additionally, the crew is to be provided with a soundproof cabin and ear protection. If dust is a nuisance to the public, then a dry dust collector is to be used. Also for the crew a pressurised and air-conditioned cabin is to be provided.

¤ The method statement must include a detailed time schedule, which must take into consideration the season that excavation works are to be undertaken since it may possibly be unwise to undertake large excavations during the wet seasons, due to possible fault slippages.

¤ The BICC is further suggesting that the method statement should be supported by an insurance policy issued on behalf of the building owner and the contractor (and sub-contractors), which shall cover third party risk and liability for damage, which results in the total or partial collapse of abutting properties resulting from the execution of contract.

¤ The responsibility of the contents of the method statement should ideally be vested with the applicant's architect, while the adherence to the contents of the statement during the course of works need to be vested with the developer and the contractor.

Nothing in the proposed framework is intended to relieve the building owner from any liability to which he would otherwise be subject for physical or material damage, as well as injury to any adjoining owners or any adjoining occupiers because of work executed by him.

The BICC framework previously suggested that neighbours have the possibility to inspect the methodology of excavation works before the actual works begin - in the same way as neighbours may inspect plans at the Mepa during the initial stages of a development application.

This would give neighbours the possibility to inspect the methodology of works and seek immediate legal remedy before the works begin (if it results from the method statement that the works constitute an unsafe solution).

Although the BICC document does not offer a definitive solution applicable for each and every situation, which might be encountered in practice, it provides a clear direction intended to improve the current scenario, which in turn aims to single out responsibilities and reinforce third party civil rights.

rmperiti@onvol.net