Owner Building a Strawbale House
in the Bega Valley,
NSW,
Australia.



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Suspended Ceiling

We have a skillion (single-pitch) roof with simple (constant depth) webbed trusses, but wanted a flat ceiling in the bed/bath/study area. In the lounge/dinning/living room we use the trusses to get a cathedral ceiling. So how do you change a cathedral ceiling into a flat ceiling ? Simple, add more materials to create a "suspended ceiling".

Our trusses are steel ladder-frame style, with two parallel chords (top chord and bottom chord) made of 65x65x4mm square hollow section, and spaced 270mm apart. On the bottom chord I made some brackets from 65x65x5 mm flat bar. The brackets are "U" shaped, and fit over the lower chord to provide a level plate with a one-half inch hole in it (with space for a nut & washer, plus extra space, above the plate. Some of the brackets needed to be offset relative to the truss, so I welded some spare 65x65x4mm SHS sideways out from the lower chord (twisted relative to the truss so that it the spare SHS is level) with a one-half inch hole in the bottom of it.

The "droppers" are made up from some 12mm all-thread rod on the top end and some 12mm solid rod in the middle (lap welded), with a 6mm cleat plate welded on the bottom end. This provides and adjustable hanger onto which bolts the C shaped 100x1mm galvanised steel purlin. The purlins are carefully pre-ordered just the right length with holes in just the right spots (spend extra time sorting this out !). The droppers are different lengths (basically, the solid rod is shorter or longer) depending upon where the dropper is attached to the truss. A bonus of the solid rod lapped onto both the cleat and threaded rod is that the centre of the threaded rod is straight above the purlin-side face of the cleat.

The purlins are C sectioned 100mm on one face, and 1mm thick. They span up to 4 metres, so at the half-way point extra holes were pre-ordered and bridging units (to stop twisting) installed. This makes a very strong ceiling that can take foot traffic above it (at least, I think so). The purlins are spaced at about 1200mm centres, starting as close as possible to each wall and evenly spaced in between. Pay attention to the purlin spacing, think ahead to your insulation (batts) standard sizes, to make insulation installation easy. Also think ahead to things such as a heater flue penetration, leaving adequate space to enable easy installation and to meet the building code on the distance from the flue to structural members.

Below the purlins galvanised steel battens (roughly 20mm deep and 40mm across) are screwed up to the purlins at 600mm centres, or some distance dependant upon the material you are suspending.

The end result is an adjustable platform under which you can screw plasterboard (or any other ceiling material, it will take quite a load) up to.