As more apartment buildings rise to grace the skylines of New Zealand’s three main centres it is important to consider their long term maintenance requirements, sound resistance and fire performance, as well as initial construction costs.

Despite the growth in multi-unit construction there seems to be no consensus as to an ideal construction material - with steel, concrete and (on occasions) timber being preferred in isolation or combination. Cost (short and long term), along with performance must always be considered in combination.

“This article seeks to inform the debate around which construction material offers the optimum return for multi-unit buildings in terms of initial expenditure, on going maintenance costs and overall performance,” says Ralf Kessel, Cement & Concrete Association of New Zealand (CCANZ).

A comparison of initial building costs, using concrete, steel and timber as the structural material, was undertaken using a multi-unit apartment building case study model. The design was based on the CCANZ entry in the 2012 Breathe international competition that challenged entrants to develop a concept for medium density mixed-use living for a site on Latimer Square in Christchurch.

The multi-unit apartment building case study, as modeled here, was deemed to perform best, in terms of whole-of-life costs and living experience, if its primary structural and cladding material was concrete.

While lightweight materials offer advantages in terms of internal partition repositioning, the study found heavyweight inter-tenancy walls provide extended fire safety, superior airborne sound attenuation, as well as impact resistance and protection against moisture ingress.

When considering floors the study identifies concrete systems, such as TI (timber infill) or ComFlor slabs as ideal in terms of mitigating sound and fire related issues. Lightweight floors can achieve a similar performance, but come at a higher cost, and remain susceptible to impact damage while demanding increased maintenance.

Throughout the study the importance of the building’s performance in terms of sound attenuation and fire resistance are considered paramount. However, the building’s energy efficiency was not assessed as this can be dramatically influenced by factors other than building material. The issue of seismic performance was also not considered. All three materials considered can be used to design buildings that offer protection during an earthquake.

Cost (short and long term), along with performance must always be considered in combination. Such an approach, as demonstrated by this study, sees a concrete solution offer a superior alternative over steel or timber solutions.

To download a copy of the full report, including the case study, click here.