Three-storey House with a Minor Dwelling – Fire Engineering Implication

2 Feb, 2022 |

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For a three-storey house with a minor dwelling, the Acceptable Solutions under Building Act is not the only method to comply with the Building Code, but it is the most commonly used method to demonstrate compliance with the performance requirement of the Building Code.

Without further justification or technical data, the Acceptable Solution is ‘deemed’ to comply.

For fire compliance, there are two documents available to adopt in Acceptable Solutions.

C/AS1 is commonly used for standalone housing, low-rise terraced housing development, boarding houses with limits, and outbuildings.

C/AS2 is commonly used for other types of building (except a few specialized buildings) not covered under C/AS1. It also includes more complex accommodation buildings such as apartments, and transient accommodation including hotels, motels, and educational accommodation.

It is also noted that other methods of compliance include the Verification method and Alternative solutions.

In the realm of low-level residential development, such as standalone housing or terraced house development, C/AS1 has been typically used to prove compliance.

The latest amendment of C/AS1 (amendment 5, at the time of writing) now includes additional scope clarification in relation to vertically stacked household units on top of the other, to be still included in C/AS1, but only when each household unit has a single-storey.

For example, C/AS1 does not include three-storey houses with a minor dwelling at the lowest level. This poses some challenges to designers and fire consultants to be able to present such buildings with suitable justification to demonstrate compliance.

One of the other options is to demonstrate compliance with C/AS2, but this raises other practical compliance problems. Compliance with C/AS2 usually brings in additional fire safety features, requirements that are not commonly found in such types of buildings – including commercial automatic fire alarm systems, emergency lighting, and so forth.

It is also noted that these systems would require scheduled maintenance to keep them effective under the building warrant of fitness regime. However, such a building does not require a building warrant of fitness, so it is most likely such systems will not be maintained, compromising the life safety provision as time goes on.

As far as we understand, at the time of writing, for such type of building, there has been no consensus compliance approach that has been universally accepted by the council. At some stage, someone may need to apply for a formal determination process to have clearer guidance to show compliance when submitting building consent applications.

For now, we have consulted with a few other consultants and councils to formulate our design strategy to tackle such issues to balance life safety risk with practicality. At this stage, we think an alternative solution approach may be required for such types of buildings that are backed up by robust justification. Some of our engineering approaches have been accepted by the council, but I am open to further discussions and other comments around this matter.

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