Matahiwi Cabin

Entrant: 
Studio Pacific Architecture

Category: 
05. Innovative Timber Manufacturing & Technology Award

Photographed by: 
Simon Devitt

Key team members: 
Studio Pacific Architecture - Evžen Novak, Juliet Barker, Samantha Zondag, Sarah Berry Dunning Structural Engineers - Hamish Strange, Thornton Engineers
Timber Fabrication and Overall Construction Contractor - Grant Douglas, Makers Fabrication Ltd

The Matahiwi Cabin is a small one bedroom 85m_² house built on a rural site on the outskirts of Masterton in the Wairarapa. It is designed to provide a sense of delight and use timber to create warm and inviting internal spaces within its small footprint. 

Timber technologies enable the cabin’s unusual curved form, deliver low-carbon construction, extend the capabilities of off-site manufacture, and respond to a site with access constraints.

The Cabin achieves a low 91kgCO2e/m_² (after accounting for biogenic carbon storage in timber) embodied carbon content.

The Cabin was designed to be built in easily transportable and liftable segments as the original building site had 4WD or helicopter access only. The design also avoids the use of wet trades. No concrete was used, and on-site work was minimised in response to the remote location.

To simplify construction, reduce embodied carbon, and minimise transport weight, the cabin was conceived as an almost entirely timber structure. This includes floor, wall, and roof framing (LVL), flooring (recycled matai on ply), internal and external linings (plywood), and timber windows and doors. The insulation was originally specified as low-density wood fibre, but Covid-era supply chain issues prevented its use.

Sheets of LVL are able to be CNC cut to any shape and plywood is able to be readily formed into curves – both characteristics are enablers of the Cabin design. The curved form reduces material usage through its inherent strength.

New high strength timber screws allowed the cabin to be constructed as a series of repeatable, pre-cut parts assembled into 1200mm-wide segments for transport to site.

The following innovations were used:

• Use of a BIM model to generate the nested CNC cutting regime for the required components;
• Use of CNC cutting machinery to create shaped components;
• Use of specifically made curved timber jigs for the assembly of 144 timber components into 13 segments;
• Use of specialised timber screws for construction.

The success of the project, including its low embodied carbon, relied on the use of timber.

The Cabin uses plywood sheets as both internal and external skins. Other materials such as plasterboard cannot be readily CNC cut and easily shaped into curves, have less structural integrity, have open air transport limitations and  would require further finishing work on site.

The LVL structure achieved a durable light weight shape within one prefabrication facility using new CNC technologies. Other materials, eg steel, would require more expensive fabrication, more complex jointing systems and markedly increase the transport weight.

Timber prefabrication enhanced the viability of the construction sequence. CNC cutting was organised to enhance workflows and minimise waste within the fabrication facility.

The 13 segments were transported to site on six trucks. The LVL-based construction meant no additional transport bracing or protection was required. The cabin was then assembled on site and fully enclosed in one day, ready for final finishing and connection of services.