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Portals

The overarching roof system for buildings

In 1983 the architectural practice of Emilis Prelgauskas began to trial alternate methods of building construction to achieve outcomes that conventional building methods can not.

The selected system was to develop independent roof structure from the remainder of the building fabric, notably its walls and floors. This is achieved by creating an overarching exoskeleton of roof covering and structure, and posts and bracing, often positioned external to the building walls, floor and ceiling.

The initial goals for this approach were:- to create a covered building site early in the construction process whereby trade work on site would not be hampered by wet weather during the construction to permit building components underneath (open ceiling, wall and floor framing) to be built underneath so that the interior remained open for services installation far later in the building process than is usual in concrete floor and masonry wall methods to accept composite wall infills where diverse materials could be used in the one project

By applying this alternate system in real world projects which were then post-occupancy tested, a number of further advantages were identified:- the building process could be halted at any time without adverse effect on the part construction in place, as would occur in conventional construction open to the weather the resultant staged process suited on-site work with mixed inputs from both trade and owner-builders materials used together could be very diverse, with thermal mass and insulations placed without compromise where best effect is achieved in comfort performance terms

The resultant buildings also displayed operational benefits:- segregating the roof structure and walls achieves higher bushfire resistance capacity than is achievable in conventional structures where the structure depends on load transfer elementally ground:floor:walls:ceiling:roof on clay land with large heave movement summer to winter, the building system creates a stable roof and portal post structure to the ground, while the floor and wall infills ‘float’ on the soils, the unlinked connection at ceiling/eave permits movement without visible cracking in wall surfaces or at junction to other elements

To achieve these benefits by this alternate system does require specific building design and construction detail approach, which differs both from conventional construction practice and that mindset.

In particular:-

  • the roof and its braced portal structure (posts & beams) seat on independent footings, usually piers to stable substrate (not connected to floor)
  • the infill wall layout under that roof achieves stability by their interconnecting wall directions, not by tie to floor or ceiling or roof planes
  • there is a movement gap left vertically between roof and wall top; this seats within the ceiling/eave lining void; ceiling cornices are avoided and shadowline recesses (Gyprok P50 and similar) are used instead
  • lightweight cold rolled steel section is used in preference to hot rolled closed section to control component weight and enable hand erection rather than needing a crane during erection; the open face of C section beams is enclosed in visually exposed situations internally with plasterboard sheet construction adhesive fixed to the C section return face; the visible sheet end at that joint is casing bead encased and is sealant sealed at the bottom, the junction to ceiling lining is paper tape joined; there is no enclosing structure or lining otherwise; the whole (steel, plasterboard and joints) are painted.
Portal

This approach has evolved over the decades in a succession of projects where the design approach and its consistent application has been proven up.
Attempts to re-introduce conventional construction practice in such projects has always been fraught with difficulties; notably cracking in walls where these are tied to floor or roof, and movement of adjacent surfaces including ceilings and eaves.

Projects where this system has been used:-

  • Packer house Lot 3 Curlew Lane, Mundulla (2002 Green Building conference Gold Medal)
  • Easterbrook house Peters Creek Road, Kuitpo Forest (published in Earth Garden Green House Plans book)
  • both projects are regularly open to the public at SolarHouseDay each September
  • additions to houses at 25 Crozier Ave, Daw Park; Loftia Park house refurbishment; and 38 Leicester St., Parkside
  • houses at Monarto, Wistow, Pelican Lagoon, Rose Cottage Road KI, D’Estrees Bay (as published in Warm House – Cool House)
  • current motel development at Willalooka

Skeleton

Skeleton

Skeleton

These projects reap the comfort performance benefits of the building design possible by this building system;- the roof is separated from structure below, avoiding the transfer of solar heat load in and winter warming out via the structure itself (safari roof form) the walls can be aligned away from the posts, both so that the roof eave can shade the walls where needed, and full sun inflow can be achieved to greenhouses and conservatory, where view and cross ventilation is needed the angled wall can contain both open and curtained window elements without obstructing these features above.

(This approach is fully described in the 2003 Green Building conference R&D Award recipient - the ‘free running buildings achieving energy efficiency’ folder which also post-occupancy measures a dozen such buildings).

For all these reasons, Emilis Prelgauskas is not amenable to conventional building practice in detailing or construction being applied to his building designs.

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