The inter-unit wall system benefiting builders and residents alike

The number of medium-density housing (MDH) developments has sharply increased in the last few years. In the year ended June 2022, for the first time ever, the number of multi-unit home consents in a single year nationwide was higher than the number of consents for stand-alone houses. The multi-unit consents for that year were up 36% compared to the year ended June 2021 – and in Auckland, a whopping 70% of all new homes consented for that period were multi-unit homes.

A boom in construction of these types of buildings naturally leads to a heightened demand of the specific materials and products needed to build them. Some are ubiquitous and overlap with any other type of building construction, but others serve very particular functions, essential for medium-density living.

The Enviro AAC Intertenancy Wall System from Masons is a prime example. The nature of MDH means that every home is adjacent to at least one other – vertically, horizontally or both – so for the sake of the occupants, minimal sound transmission, insulation and fireproofing are critical.

Arthur Whitfield, Technical Manager for Masons, says the Intertenancy Wall System aims to kill as many birds with one stone as possible when it comes to MDH. 

“We describe it as a simple acoustic and fire-rated wall system, that facilitates faster construction because of its tried-and-true materials,” says Whitfield.

Time is a notoriously limited resource in the construction industry, and with the amount of MDH building sites around the country, any element of the design that can reduce overall time spent on construction is highly valued. The Intertenancy Wall System achieves this by making it as easy as possible to construct: as few as two builders can install the system, and installation can flow around other work on site. 

But what exactly makes it so easy to install?

“The key component of the Enviro IT Wall System is the autoclaved aerated concrete (AAC) panels,” says Whitfield, “which are stack-bonded mortared together and fixed to the framing using screws and L brackets. Fire-rated mineral wall insulation and a Soudal fire-rated sealant complete the assembly.”

The panels are light, too: each is 50mm thick and weighs only 33kg per sheet – and at 2200mm x 600mm, they each cover 1.3 sqm for rapid assembly. Walls are constructed in manageable blocks with no need for a crane, and installation time for two builders can be as little as two hours.

They’re also made with consideration for our unpredictable weather. No weather protection is needed for the panels when work stops, Whitfield says, making on-site storage straightforward as the panels can be left in the elements.

But the advantages extend past those beneficial to the builders – the Intertenancy Wall System also ensures good acoustics and helps prevent unwanted sounds and noise from ‘leaking’ from one unit to another. Acoustic engineers Marshall Day reported a lab performance of 64 dB – higher than the minimum STC requirement of 55 dB for intertenancy walls. 

“The system utilises the acoustic principles of mass and separation,” says Whitfield. “The Enviro AAC panels are very good at absorbing sound frequencies. There are several factors that make this happen: the air gap on either side of the central wall; the supporting framing; and the added layer of 10mm plasterboard linings.

“All of these features combine to reduce sound transfer rate considerably compared to standard interior walls.”  

Then there are the fire safety benefits – crucial for any modern MDH build. The Intertenancy Wall System exceeds the NZ Building Code’s minimum requirements for fire resistance, scoring a rating of -/120/120 for walls up to 10m high. 

“The system is fully FRR & STC compliant,” says Whitfield. “The panels play their part in helping to ensure people are separated as much as possible from flames if a fire breaks out, and to allow time for a safe escape.”

Learn more about Masons and its Intertenancy Wall System.

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