The PrefabNZ Deep South Event was held in Queenstown this week. The event provided a hands on chance to visit a prefabricated residential build, as well as listen to a variety of speakers present on the advantages of prefab construction.
Prefabrication, also known as prefab or offsite manufacture, is an innovative approach to construction. Simply put, it means manufacturing and assembling whole buildings or parts of buildings prior to installation at their final location. Many buildings these days are constructed with some form of prefabrication, whether it be pre-nailed trusses & frames, panel construction, or complete buildings. Panel construction includes structurally insulated panels (SIPS), triboard, cross-laminated timber (CLT) and concrete panels.
PrefabNZ is a not-for-profit organisation that is passionate about pre-built construction in NZ. PrefabNZ is an 'industry hub to connect, catalyse, inform, inspire, and promote prefabricated building solutions'.
The Taramea Passive House is being constructed by Climate House for owner Michael Sly and family. Michael kindly opened up his building site for all to view and talked us through the construction method and benefits.
The home is constructed using SIPS - a structural frame made from a sandwich of two layers of structure and one layer of insulation. Michael, director of Climate House, sourced the SIPS from Eco-Panels in the USA. SIPS panels are widely available in NZ, however all panels are constructed differently and the Eco-Panels suited this project best.
The SIPS panels will provide the home with an insulation rating of R8 in the walls and R10 in the ceiling. A Maxraft slab also supplies maximum underfloor insulation. The windows are triple glazed, thermally broken and a combination of aluminium/PVC and timber joinery. Michael imported these from Germany from the company Kneer-Sudfenster. Airtightness products from proclima assist the home in becoming airtight, meaning that the home uses minimal energy for heating and cooling. With a solar system installed from Infinity, the home is expected to have a net zero energy output.
So how much does a house like this cost? Surprisingly Michael estimates that the house will be comparable with what a traditional build would have cost. Although some of the products are more expensive, savings will be made in labour costs. A smaller building footprint was also selected to make the build more economical as well as easier to heat. More important though is the long term savings of virtually no power bills. A smart investment indeed.
Welhaus is a design and build company based in Christchurch. Founder Dan Tremewan presented their vision for constructing sustainable homes that meet the social, environmental and economic needs of their inhabitants. In other words, smart homes that are also affordable. They specialise in panel construction using materials such as SIPS and CLT. Most of their homes rate as a Homestar 6-7, which keeps them affordable not only for construction, but also for the long term energy use. A recent build of theirs, The Beach Barn, boasts of average $60/month power bills.
Nick Hamlin and Glenn Carter from Arrow International presented an overview of the 'remarkable' feat of building the upgraded Remarkables Base Building. Designed by Architect Michael Wyatt, the result is a truly world class building. The project was undertaken in just 8 months and faced many challenges including snow, 120km/h winds and a 14km access road. In addition to efficient project management, the factor that helped the project be delivered on time was prefabrication. Prefabricated methods utilised were concrete panel walls and Kingspan SIPS ceiling and internal walls.
Offsite Design is a design and engineering consultancy specialising in design for prefabrication and structural engineering of timber buildings. Timber Engineer and Prefab Specialist Johann Betz presented about the need for team work and collaboration from day one in planning prefab projects. It is essential that from the start of a project, your designer works closely with the prefab manufacturer, engineer and various other consultants to ensure that the design is maximising efficiency and other benefits prefabrication has to offer. This includes understanding benefits as well as the limitations of prefabrication and how design for manufacture will affect overall project cost and quality.
Johann also commented on a relative comparison of building costs between a prefabricated build and a traditionally built home. Prefabrication is simply a different mode of construction, a different way to deliver a building. Depending on what is being built and how it is prefabricated the cost of a prefabricated project may be less, equal, or more than a traditional project. Prefabrication can be more efficient if on-site savings offset the overheads of the prefabrication process. In mature prefab markets prefabrication is increasingly seen as a way to achieve superior quality impossible to be achieved with a traditional build. In this case superior quality can come at a premium compared to lower quality site based construction.
The main difference to be aware of is a prefab approach requires a frontloading of the design process and earlier expenditure for prefab materials, essentially to solve details and potential problems early. The savings are made at the construction phase, where faster build times help reduce labour and site costs. Higher upfront costs are one reason why prefabrication often struggles to compete with traditional site based construction in the eyes of shortsighted clients. However those considering prefabrication need to be aware of all project costs and lifecycle costs in general - including ongoing running costs of a home too.
Justin Wright from Assembly Architects presented an inspiring overview of some recent projects including a collaborated project at Britomart in Auckland. After the initial concept had be done, this multi storey commercial building was designed and constructed in just 14 weeks, thanks to the utilisation of prefabrication methods. The design took only 3 weeks, followed by a building consent process of 6 weeks. During this time the prefabrication process took place off site. Once consented, a 5 week on site construction period completed the project in time for the Rugby World Cup. Amazing stuff.
Lauren McKay introduced her new company Insiteful. Although not relating directly to prefab, the service they provide is useful for anyone who owns a home. One of Insiteful's products is 'Home Oversite,' which is an online hub for document storage of all things relating to your property, from plans and maintenance schedule to paint colours and materials used. The information can then be passed on to a new owner when sold without having to look for random paperwork. A great idea.
Architype Director Tim Ross presented an overview of recent projects working with prefabricated materials.
- The Peninsula House in Dunedin is being constructed with Magroc SIPS. These SIPS panels don't come precut so the builders have to cut them to size on site. The SIPS panels were also used for the flooring, creating an R8 insulated slab and walls. The ceiling was standard trusses, so Intello building wrap by Pro Clima was used to make the building airtight.
- The Stuart St House is being constructed from Kingspan SIPS. These do come precut to size, so the SIPS panels were craned in fully assembled. The home was made further efficient by the use of triple glazed Enersign windows, imported from Germany.
- High St Co-housing. This is a project under development in collaboration with multiple clients that wanted to create a development of highly efficient homes on a shared site with a maximum budget of $2500/sqm.
These projects go to show that there is a growing demand for smarter built homes that offer long term cost savings.
Simon from proclima discussed the importance of airtightness for low energy homes, as well as ensuring connections remain weathertight. proclima provide a variety of airtight and weathertight products that can assist with this, such as tapes to seal panel joins and window connections, and Intello airtight wrap. These products can be used in not just prefabricated builds but traditionally built homes too.
Thanks to PrefabNZ for facilitating this inspiring event. We learnt so much and I personally am now inspired to build a SIPS panel house sometime in the future. For further information on prefab construction, visit the PrefabNZ website, or talk to your designer about prefabricated options for your new home.
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