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Design

Parau container home – compact and low waste

Brenda Kelly has designed her own container home in Parau, at the entrance to the Manukau Harbour – an example of compact and low waste housing design.

Containing her enthusiasm

Compact and strong, shipping containers have found an alternative life as building modules for homes. Auckland-based Brenda Kelly is the first to have a New Zealand Homestar rating for a container home, achieving eight points out of a possible ten.

Brenda purchased new, two standard shipping containers, one six metres (20 feet) and the other 12 metres (40 feet) long. The containers are linked in an L-shape, together providing two bedrooms, a lounge, kitchen and bathroom in a 45m² footprint. A 33m² covered deck comes in handy when entertaining more than one or two visitors.

Her choice of containers came down to finding affordable alternatives to standard building design. Containers are strong, recognised as earthquake, fire and cyclone resistant and need little maintenance. They can be placed on wooden pile footings at each corner, a cost-effective foundation solution that also minimises site disturbance and suits sloping sites.

The containers were fitted out offsite and then trucked in to the site in Parau, a suburb west of Auckland.

While designed to connect to the grid, the house also features rainwater catchment and storage tanks, and a grid-tied PV (photovoltaic) solar array to generate power for use during the day.

An on-site wastewater treatment plant uses worms to compost human waste. The treated wastewater is then passed through a field of native grasses to “polish” it before it is dispersed to the ground. This worked out to be about the same cost as a standard septic tank system, and is more efficient at processing the waste. 

Brenda says “incorporating these features into small homes is a lot more practical and affordable than their big brother equivalents”.

More compact buildings use fewer resources in construction and, when well-built, also have lower running costs. Since building her home, Brenda has found there is a demand for quality, compact prefabricated housing.

“Consumers are waking up to the realisation that running costs need to be factored into the affordability of housing. With schemes like Homestar gaining traction, the building industry would be wise to consider investing a little more up front for superior insulation, energy and water efficient appliances, fixtures and fittings and the likes of solar power and rainwater harvesting,” she says.

A holistic approach

The home has extra thick R3.2 soy-based polyurethane insulation sprayed onto the inside of the walls, and R4.5 insulation on the ceilings. The floor has a layer of R2 polyester insulation on the underside.

The double-glazed windows have highly insulating uPVC frames, achieving R0.41 (standard, non-thermally broken aluminium double glazing achieves R0.26). Investing a little more up-front for superior insulation provides the long term benefits of a warmer, healthier home and reduced power bills.

Hot water is supplied by a gas califont, located in the utility bay at the end of the longer container, along with the rainwater tank and electrical equipment. There’s a heat pump for heating, and cooling is provided by a shade canopy over the deck.

The house is ventilated by manually opening windows, and using extractor fans in both the kitchen and bathroom. 

Kitchen

Sitting on the edge of the Waitakere Ranges Regional Park, the house is surrounded by bush so already meets HomeStar’s native planting requirements. Brenda has added her own plantings, including the native grasses in the wastewater treatment beds. In addition, she has a 3m2 vegetable patch and a couple of citrus trees, as well as a bokashi composting system and recycling bins.

A picture of recycling bins

Construction and waste

The containers were imported new and, because the bulk of the fit out was done in controlled conditions off-site, construction waste was minimal. Per square metre, construction created about 10% of the average landfill waste generated in the construction of a typical New Zealand home.

This included about 250kgs to landfill (unrecyclable offcuts and packaging), and around 100kgs of recyclable waste collected separately (including cardboard and plastic containers). Untreated timber offcuts became firewood.

With prefabricated construction, there is less energy used in the construction process. The South Auckland covered yard where the fit out was done was much more accessible for commuting builders and suppliers than traversing out to the Waitakere. The delivery was made with one truck movement, minimising street disruption as well as transport energy.

The consent inspection process for prefabricated construction differs a little from traditional onsite construction. Two of the inspections were done at the yard – one before the linings went up (pre-line), and one before transportation to site. The final inspection was done onsite at Parau.

The project was awarded one HomeStar innovation point for the use of prefabrication with processes that allow waste to be designed out, minimised and recycled more effectively than with on-site builds.

Smart space

Brenda admits that a compact home such as this is a challenging concept for many Kiwis brought up with the dream of a large three or four bedroom home on a quarter acre section. But innovative design and smart furniture options mean that a smaller home doesn’t necessarily have to feel confining.

In a compact house, every piece of furniture has to be dual purpose or it doesn’t make the cut. Space saving furniture, such as desks and couches that convert to beds, built in storage or hidden tables are all great ideas.

“Smaller homes give people more money in their pockets and more leisure time, with less area to clean and maintain” Brenda says.

Recognising smart choices

There are independent schemes and services available to help you to specify and understand the likely performance of your house design. Some of these give a score which can indicate how efficient and environmentally friendly your home will be once it’s built.

Brenda had her plans assessed by the Auckland Council Eco Design Advisor service and was assessed as on track for a seven Homestar rating (out of a possible 10). An additional point for innovation has increased that rating to 8 stars.

Note that this document is published by the Ministry of Business, Innovation and Employment Chief Executive as Guidance under Section 175 of the Building Act 2004. This is a guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case.