30 • TIMBER FLOOR FRAMES The timber floor frame has developed over many years, and there is currently a major transition happening. The movement from what has been the traditional method of floor construction since the 1950s, towards a modern material efficient system, has been developed and promoted by the tim ber development associations and is called the platform floor.
Traditional This system is part of the traditional method of timber framing that tied the floors, walls and roof of a house together and made them totally interdependent. The floor frame was arranged in such a way that all walls were supported by either a bearer line or a double joist line, which were, in turn, supported by brick piers/stumps that followed the line of the walls and provided a pier/stump at every corner. The procedure, therefore, to build a tradi tionally framed timber floor for a timber wall framed house (whether brick veneer or sheet clad) is to first set out the subfloor piers/stumps so that there is support under all walls and subdivide the area under the floors so that there is a pier or stump on a grid not exceeding 1800 x 1800 mm. This grid can be varied by using none of the standard timber sizes, but this would be a break from the traditional. When the base structure is completed, the ant (termite) caps are put in place, along with the damp-proof course if required. On top of the base go the bear ers, traditionally 100 x 75 mm, generally running parallel to the longest side of the building, but this is not essential. The bear ers should be set to be level in all directions and fixed to the piers/stumps if applicable. On top of the bearers are the floor joists. These are traditionally 100 x 50 mm set at 450 mm centres, under all walls, running in the direction of the joists. There are double joists to allow for the stable seating of the wall bottom plate and to provide a ledge on to which to seat the flooring boards.
Platform The main difference between the tradition al framed floor and the platform type is that the internal walls are not supported on piers/ stumps directly, as it is important to use platform floors in conjunction with tim ber roof trusses, which put no load on internal walls. Piers/stumps are still set out on a 1800 x 1800 mm grid but, as no reference has to be taken of internal wall locations, there is generally a saving in the number of piers/stumps that have to be provided. Bearers are laid parallel to the longest side of the house, and joists are laid at 450 to 600 mm centres, depending on the floor sheeting thickness, with only double joist ing at the ends.
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Isolated piers must be set so that all walls perpendicular to bearers occur over a line of piers or stumps
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DETAIL-BASE WALLS AND PIERS SET OUT FOR TRADITIONAL LOAD-BEARING WALL CONSTRUCTION AND CONCRETE FLOORS TO WET AREAS
Pier spacing to suit the most economic bearer size span (commonly I 800x 1800)
Lines of bearers set out to give the most economic use of timber in conjunction with Australian Standard I G84
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Standard Tongue and Groove
DETAIL-BASE WALLS AND PIERS SET OUT FOR PLATFORM FLOOR CONSTRUCTION WITH A TRUSSED ROOF Secret Nailed T +G
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FLOORING BOARD SECTIONS _,,..,.--Wall stud Bottom plate Extra false bearer to fix external cladding to
DETAIL EXTERNAL CORNER OF BEARERS AND JOIST FOR WEATHER BOARD OR SHEET CLADDING
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Double floor j015t
DETAIL INTERNAL FLOOR TO WALL JOIST, WALL PARALLEL TO JOISTS
TIMBER FLOOR FRAMES• 30 Flooring materials
Traditional flooring ('cut in' flooring) was laid on the joists, strip by strip, room by room. If platform construction is used, then sheet flooring is generally used and laid before the walls are erected, giving a safe working platform for the workers as well as simplifying the construction. Traditional strip flooring boards were joined one to the other with simple tongue and-groove joints moulded from the mate rial of the strip. The tongues are inserted in to the groove and the whole is clamped together to give a draught-free floor. The strips are nailed to the joists, then the nails are punched below the surface of the strips, which are then sanded to give a level surface ready for carpeting or other floor covering. If the floor is to be stained and sealed then a second fine sanding is required and the building should be dust free before any sealing is carried out. If the nail holes would concern you it is possible to get strip flooring with secret nailing. Many timbers are used in strip flooring and these vary significantly from location to location. In New South Wales the most common strip flooring is Cypress pine, in Victoria it is kiln-dried hardwood and in Western Australia Jarrah is the most com mon. Other strip flooring timbers include rainforest species that are becoming scarce and there are environmental rea sons for limiting the use of these timbers. Platform flooring structures can be cov ered with strip flooring boards, but are more commonly covered with weather proofed plywood, or chipboard sheeting. This sheeting has been specifically devel oped as a flooring medium and it is capa ble of withstanding up to three months or so of wet weather, which sometimes occurs during a construction period. The edges of the sheets have tongue-and groove edges, sometimes these are cut into the material, but more often the sheets are grooved and the tongue is made of plastic. Sheet flooring should be used strictly to the manufacturer's instructions, as this is critical in avoiding bulges.
Wet areas
In some states it is a requirement of the build ing regulations that floors to wet areas, partic ularly bathrooms, toilets and laundries, must have an impervious subfloor. In the past this has been interpreted to mean poured-in-place concrete, but in recent times this restriction has been broken down; first by the use of com pressed fibre cement sheets, then more recently by the use of waterproof plywoods and chipboards. The compressed fibre cement floor was the greatest breakthrough in provid ing a sensible floor for wet areas. It avoids the inconvenience of pouring concrete in small lots while providing a material that is rot proof and, if used correctly, virtually indestructible. By using fibre cement sheets, plywood or chip board platform floor construction methods greater versatility can be achieved, something that was nearly impossible if a poured-in-place concrete floor was used. If poured-in-place reinforced concrete floors are used in wet areas then dwarf brick base walls must be built to support the edges of the concrete slab, and the sewer drains must be accurately placed in position before the con crete is poured.
Joists for normal flooring are set directly on top of bearers
Joists for fibrous cement sheet are notched over bearers to give required set down ( I 5-25mm)
DETAIL-SET DOWN FLOOR IN WET AREAS USING FIBRE CEMENT FLOOR SHEETS Bearers Area to be sheete to be set down as bove
Floor jOISts
Space between double J015ts to be exactly width of room to be floored in AC sheet fibrous cement
Double floor jOISts under external walls
GENERAL ILLUSTRATION LOCATING SET DOWN FIBRE CEMENT SHEETS
Double floor J015t set to give support to plate and to floor boara ends Stud Bottom plate
DETAIL-FLOORING TO WALL JUNC ION USING PLATFORM Y FLOOR
Floor J015t5
DETAIL-FLOORING TO WALL JUNCTION USING CUT-IN FLOOR (TRADITIONAL)
Internal non-load bearing wall (partition wall) Bottom plate
A double J015t or indeed any J01st 15 not required under internal walls unless they are load bearing
Platform flooring is commonly water resistant chipboard or plywood with tongue and groove joints, but strip flooring can be used with due care and weather protection.
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