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    Revolution for prefab homes: moving digital fabrication back onsite

    Nathan Johnson

    London-based architecture and construction firm Facit Homes believe their onsite digital fabrication system is a revolutionary change for building design and construction.  

    Their concept is a lot like the computer aided and computer controlled cutter prefabrication methods already used in Australia. Their main point of difference however is that the entire process is purely digital and entirely controlled by them - from design to production - and that all their fabrication is done onsite rather than in an offsite location.

    Facit call their system the ‘D-Process’, and believe they are the world’s first company to digitally fabricate a bespoke home on-site using a compact mobile production facility.

    The seed for the Facit concept was planted at London architecture firm, Foster + Partners where Facit managing director Bruce Bell worked with 3D computing and imaging. Bell then moved on to the Royal College of Art where he studied product design and began plotting the idea for a consolidated engineering, architecture, manufacturing company, much like Facit is today. Bell’s studies and discoveries were preoccupied with what he calls the process disconnect between digital design and fabrication, and he believes this can be overcome through digital manufacturing, on a small scale, on-site.

    The Process

    First, the firm’s architects and engineers design the house using a 3D computer model, which details every aspect of the project from its orientation and material quantities to the positioning of its trade access points in cavities, floors and ceiling voids.

    Their D-Process then transforms the 3D digital designs into the home’s exact physical building components, by use of a computer controlled cutter (CNC Router) and building materials.

    The CNC router is delivered to the building site in a shipping container, where it mills every component of the home into modular elements which snap together like Lego to form the building.

    Central to their concept is the shell of the house, which they call a Facit Chassis. Like the chassis of a car, the shells are designed ready for all services, including electrical, air conditioning, insulation and plumbing to be fitted around it – with no ‘interpretation’ by people on the ground.  

    More on the process in the video below:


    Performance

    A Facit Chassis predominantly comprises  FSC certified spruce plywood sheets which are not particularly cheap building materials. However, the firm believes they save money and contribute to sustainability by manufacturing onsite and removing the need to power a manufacturing warehouse.

    Because of its light weight composition, the entire home can be installed by two people, eradicating the need for concrete footings and heavy machinery for assembly.

    Another confessed contribution to the concept of sustainability is the firm’s use of steel helical micro piles instead of resource intensive concrete beds for their projects. Facit says this system means foundations for large homes can be installed in a single day, which significantly lowers the cost.

    Facit also recruits 100 per cent recycled cellulose fibre insulation for their projects which is blown into the building’s cassettes through prefabricated access points.

    Limitations

    • Amenity: no excavation and no concrete beds mean no basements – a great place for services.
    • Cost: the houses are expensive considering the homes are without a foundational pour.
    • Production: limited to one house per CNC milling machine because it is taken to the site and left there until the home is complete.

    Case study

    Villa Asserbo by Danish architects Eentileen and Facit Homes

    • Cost: $300,000
    • Construction time: six weeks
    • Size: 115sqm
    • Materials:
      800 Nordic plywood sheets made 400 components for beams, sheathing, floors and walls
       

    Facit Homes (in general)

    • Insulation: 100 per cent recycled cellulose insulation from Warmcell (blown). Walls are generally 275mm, floors 100mm and roofs 290mm.
    • Thermal performance:
      0.14 W/m²/K heat-loss co-efficient for floors, walls and roof
      R Value of 2.7 per 100mm (very similar to SIPs)
    • Ventilation: Mechanical Heat Recovery Ventilation
    • Waste: timber off-cuts are sold back to the same timber supplier, who burn it in a CHP plant to make more timber, which Facit then buy
    • Footings: 0.1 Steel Piles required per m2 floor slab

    Images: Facit Homes

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