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A steel and timber composite floor construction

The extension is of dry construction. The floor is supported on a grid of 178 x 102mm universal beams at 2.5m centres onto which spans a 100mm deep PMF trapezoidal profiled deck, of the type normally used for roof construction. Each deck trough was fixed to the beam flanges with self-tapping screws to form a rigid connection between deck and framework. The deck troughs were then filled with extruded polystyrene battens formed to precisely match the trough profile, in-filling each trough to form a level work surface.

To protect the deck and insulation and to provide a working surface during construction, a 2mm corrugated plastic sheet was laid on top; 100 x 50mm timber joists were then placed at right angles to the line of the troughs at 400mm centres and fixed to the deck's top flanges with self-tapping screws at 600mm centres. The space between the joists was used for services distribution, in particular for fan heaters at the base of the glazed sliding doors.

After fixing the services, 100mm of mineral fibre insulation was laid between the joists and a polythene vapour control layer laid over it. The 25 x 70mm t&g oak floor spans between the joists. Fixing the oak floor and joists to the steel deck creates a small composite action between the floor components, the t&g floor effectively becoming a stressed skin.

At the walls the steel beam frame is exposed and the deck is dressed with a steel flashing which slots under the profiled steel cladding.

A series of laser-cut steel L-shape flats are welded to the beams and are fixed to paired steel angles which support the external deck.

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