Angus Kell poses the question: is minimum compliance adequate for external walls in attached dwelling construction?

The recent trend for attached dwellings to meet the current housing boom in the affordable segment of the market and the altered development model being implemented by the developers of the housing estates, places into question the adequacy of the National Construction Code (NCC) to ensure the delivery of housing stock which provides basic amenity for its occupants.

Historically, attached dwellings (which were usually in the form of townhouses) were built by a single developer who bought and subdivided the land, constructed the dwellings and arranged the title deeds for the property. If the dwellings were pre-sold they were limited to a small deposit (usually 5% of the package price) and received the majority balance on settlement with the owner.

These developments are suited to well-known standard lightweight party wall (the NCC advises that a party wall is another name for a separating wall) systems including: double stud timber framing with fire-rated plasterboard on the internal linings; or double stud timber and steel framing with an inner fire-rated shaftliner with non-fire rated internal linings. Such systems are acknowledged to meet the objectives of the Performance Provisions for Class 1 and 10a buildings as required by Volume 2 of the NCC. Including Objective 2.3 of Part 2.3 Fire Safety, and Objective 2.3 of Part 2.4 Health and Amenity, and the requirement to:

Safeguard the occupants from illness or injury by alerting them of a fire in the building so that they may safely evacuate,
Avoid the spread of fire from one building to another, and

Safeguard occupants from illness or loss of amenity as a result of undue sound being transmitted between adjoining dwellings.

The more recent and growing trend is that the developer of the housing estate sells the land to multiple builders, often in single or limited allotment numbers, then the builder on-sells a land and house package to prospective owners.

The developer becomes the obvious beneficiary as they get a faster return on their investment by receiving full payment from the builder on the land component which is often up to two-thirds of the total land and house value. With this new development model is an additional requirement placed on the builders by their finance companies to ensure the dwellings are separated and not dependant on the construction of the neighbouring building, thereby reducing the risk to the finance company of a neighbours default or inability to complete.

Unfortunately this new development model poses questions of the NCC as to what constitutes compliance for the walls between dwellings in Class 1 buildings. As if the independently constructed wall adjacent the boundary is determined to be an external wall (defined as “an outer wall of a building which is not a separating wall”) and not a separating wall (defined to mean “a wall that is common to adjoining Class 1 buildings”) then compliance may be limited to construction as required by Volume 2 of the NCC, Clause 3.7.1.3 and Clause 3.7.1.5 of Part 3.7.1 Fire separation which when summarised requires that:

External walls which are less than 900mm from an allotment boundary other than the boundary adjoining a road or other public space, or 1.8m from another building on the same allotment are required to have an FRL of not less than 60/60/60 when tested from the outside.While there is no specific reference in the NCC to safeguard occupants in respect to undue sound being transmitted between adjoining dwellings in the construction of External Walls, it is likely that failure to address this could jeopardise compliance with Objective 2.3 of Part 2.4 Health and Amenity, and surely would fail the court of public expectation.

With the expected boom in the attached dwellings segment, developers and builders should resist the temptation for minimum compliance and ensure they meet the full objectives of the NCC to provide the amenity the occupants both expect and deserve.

Note: Lightweight wall options are proprietary solutions and require compliance with the installation requirements of the manufacturer. Where necessary, consultation with the manufacturer is recommended at the design stage.