WO2010130000A1

WO2010130000A1 - Floor for a modular building

Info

Publication number: WO2010130000A1
Application number: PCT/AU2010/000554
Authority: WO
Inventors: Bradley John Drummond; Carlo Paneni; Daemon Lachlan Zirbel
Original assignee: Ausco Modular Pty Limited
Priority date: 2009-05-12
Filing date: 2010-05-12
Publication date: 2010-11-18
Also published as: NZ595016A; AU2010246910A1; AU2010246910B2

Abstract

There is disclosed a floor for a base frame for use in a modular building, the floor comprising: an aerated, hardened composition; and a rigid support underlying the composition, to which the composition is fixed. There is also disclosed the base frame with the floor applied thereto. Furthermore, there is disclosed a method of manufacturing a floor for a base frame for use in a modular building, comprising fixing an aerated, hardened composition atop a rigid support. There is also disclosed a method of applying a floor to a base which includes the manufacturing method.

Description

Floor for a modular building

The present invention relates to construction of structural floors for building module base frames. The invention is applicable to modular buildings comprising one or more building modules which are transportable, relocatable and/or prefabricated, including multi-storey modular buildings.

Transportable, relocatable and prefabricated buildings are particularly popular in schools, construction, mining and resources environments, and remote area or rapid-install housing. Construction of such buildings generally involves offsite fabrication of at least one building module having a structural base frame or "chassis" comprising longitudinal members and cross-members attached at certain intervals to the longitudinal members, including floor joists. The structural members of the base frame are commonly steel but may, for example, be timber or concrete. The base frame forms a rigid structure, to which the floors and walls of the building are fixed, and is sufficiently robust to be transportable, relocatable or repositionable, either on its own or with at least part of the remainder of the building assembled on it.

Commonly, the building flooring surface is formed from timber floor panels, which are laid over and fixed, either directly or indirectly, to the joists. A vapour-impermeable interlayer, such as metal sheeting, may be provided between the timber and the frame to prevent or retard moisture ingress through the floor. Plywood or particleboard panelling, in particular, is readily available, has compressive, tensile and flexural strengths, has generally satisfactory surface hardness, and does not significantly contribute to the weight of the building, so that it is conducive to transportation and thus a popular choice of floor or floor substrate. A plywood and steel base frame is lightweight, and is fast and easy to construct, so is conducive to volume-based factory manufacture. However, plywood, like several other timbers, has a number of drawbacks. In particular, it has a tendency to deflect, rattle and/or vibrate when walked over, and may produce a hollow sound or thrum, which detracts from the building occupants' comfort and perception of floor quality. The floor structure may be somewhat dampened using multiple board layers or conventional topping concrete in combination with the timber. Such additional materials, however, greatly increase the weight of the floor structure, thus adding to transportation complexity and expense. They may also render the final floor structure more brittle, or less robust generally, and significantly reduce the attractiveness of volume-based factory manufacture.

A further problem with plywood and timber generally is that it is vulnerable to damage from termites, or moisture ingress, which it cannot resist without an interlayer, particularly in tropical or damp sub-floor applications where there are significant differences in temperature and/or relative humidity between the building interior and exterior. Moisture ingress may lead to moisture-based decay, distortion and/or swelling of the floor. Moreover, timber has relatively poor thermal insulation properties. Whilst insulation may be arranged between joists of the floor to improve thermal performance, the joists can nevertheless function as undesirable thermal bridges through the floor.

Fibre-reinforced cement sheeting may be substituted for plywood to prevent termite damage and moisture-based decay. However the use of such cement slows construction, and gives rise to a structure which is more brittle, is heavier and has lower tensile capacity. Alternatively, metal (or other skin) sandwich panels, having lightweight plastic cores, may be substituted for plywood. Whilst these can also eliminate termite and moisture problems, and may improve thermal performance, particularly where the plastic core is unbridged, the core may develop permanent distortions from temperature cycles under structural loads from occupancy.

Another alternative is to pour concrete into a steel tray chassis or to use a full precast concrete raft chassis. Whilst doing so may eliminate the drawbacks of plywood outlined above, it gives rise to a structure which has relatively poor thermal insulation properties and which is significantly heavier, potentially necessitating specialist handling and transport or rendering the floor unsuitable for volume-based factory manufacture.

According to a first aspect of the present invention, there is provided a floor for a base frame for use in a modular building, the floor comprising: an aerated, hardened composition; and a rigid support underlying the composition, to which the composition is fixed.

According to a second aspect of the present invention, there is provided a base frame for use in a modular building with a floor according to the first aspect applied thereto.

According to a third aspect of the present invention, there is provided a method of manufacturing a floor for a base frame for use in a modular building, the method comprising fixing an aerated, hardened composition atop a rigid support such that it overlies the support.

According to a fourth aspect of the present invention, there is provided a method of applying a floor to a base frame for use in a modular building, wherein the floor is manufactured in accordance with the third aspect and applied to the frame.

In the preferred embodiments of the invention, the support is arranged to engage the composition generally uniformly over the area of an underside of the composition. The support may thus be provided in the manner of a tray which holds the composition. Preferably, the support is arranged to engage the composition over substantially the entirety of the area of the underside.

In the preferred embodiments of the invention, the support is of sheet-like form. Preferably, the sheet-like support is substantially apertureless. The support may thus form a liquid-, vapour- and/or pest-resistant barrier.

In the preferred embodiments of the invention, the support is formed of metal, preferably steel.

Preferably, the floor is manufactured on the frame.

In a preferred embodiment of the invention, the support is secured to the frame before the composition is fixed to the support. Preferably, the composition is applied to the support in preformed, hardened, sections. The preformed, hardened, sections may comprise, for example, panels, blocks or tiles.

Preferably, support elements are secured to the frame, the support elements collectively forming the support. In a preferred embodiment of the invention, the composition is provided in preformed, hardened sections which are fixed to the support elements.

Preferably, sealant is applied to the support elements to prevent fluid or vapour ingress therebetween. In a preferred embodiment of the invention, the sealant comprises silicone rubber.

Preferably, the composition is bonded to a top surface of the support. In the preferred embodiments of the invention, the composition is bonded to the top surface over substantially the entirety of the area of the top surface. Advantageously, the composition can thus be rendered robust and therefore less likely to crack or crumble in service and/or transit.

Preferably, the composition is bonded to the top surface of the support by a bitumen-based adhesive. Such adhesive is often inexpensive and may be relatively easy to apply, particularly via a trowel.

Alternatively, the composition may be bonded to the top surface of the support using a polyurethane adhesive, which may be of the type commonly applied between bathroom/shower tiles and concrete slabs in buildings to provide waterproofing therebetween.

In a preferred embodiment of the invention, the composition is bonded to the top surface of the support using adhesive which forms a waterproofing membrane between the composition and the support. The bitumen-based adhesive or polyurethane adhesive may be used to form such a membrane. Preferably, adjacent ones of said sections are bonded to each other with adhesive, which may, for example, comprise plain or flexible self-levelling cement or mortar. Preferably, the adhesive is liquid- and vapour-impermeable and applied continuously between the adjacent sections to prevent liquid and vapour permeation therebetween.

Preferably, the composition comprises aerated concrete, which preferably contains an aggregate. In a preferred embodiment of the invention, the aerated concrete comprises autoclaved aerated concrete. Preferably, the aerated concrete comprises that sold under the trade mark HEBEL. In an alternative embodiment, the aerated concrete comprises foamed concrete or cellular concrete.

In accordance with a preferred feature of the invention, a top surface of the support comprises a coating which facilitates bonding of the aerated concrete thereto. In a preferred embodiment of the invention, the coating comprises Foam Grey coating material which is the material used to form the backing coat layer in particular grades of COLORBOND steel sheet, which is a proprietary product of Bluescope Steel Limited, and the coating is bonded to the aerated concrete with adhesive, such as said bitumen-based adhesive or said polyurethane adhesive. In a particularly advantageous embodiment of the invention, the support is formed from COLORBOND steel sheeting, and the Foam Grey backing coat layer thereof is bonded to the aerated concrete with said bitumen-based adhesive.

Preferably, the support is formed to be liquid- and vapour-impermeable.

The support may be glued, and screwed or nailed to the frame. Generally speaking, the frame will comprise a plurality of longitudinal members and cross-members, and the sheet(s) will be attached to at least some of the members, at a plurality of positions over an area of the frame.

Preferably, the frame is configured to brace said composition laterally. Preferably, the frame is configured to abut at least one side wall of said composition to brace the composition laterally. Preferably, the frame is configured to abut opposed side walls of said composition to brace said composition laterally. In a preferred embodiment of the invention, the frame comprises a structure arranged to abut the composition around a perimeter thereof to brace it laterally. Preferably, the structure is arranged to confine the composition laterally. The structure may comprise a perimeter beam. Preferably, the structure is arranged to support a wall structure and/or posts of the building. Preferably, adhesive is applied to bond an interior face of the structure to a perimeter face of the composition. The adhesive may comprise self-levelling cement or mortar, which may be plain or flexible.

Preferably, an overlay is applied over the hardened composition. The overlay may comprise Masonite, plywood, and/or fibrous cement board. In a preferred embodiment of the invention, the overlay is attached to the composition. Preferably, attachment of the overlay comprises bonding the overlay to the composition with adhesive. Preferably, the adhesive comprises a bitumen-based composition. Preferably, attachment of the overlay to the composition further comprises fixing the overlay to the composition using fastening elements, which may facilitate bonding and curing. Preferably, the fastening elements comprise twist nails.

Alternatively or additionally, an upper surface of the aerated, hardened, composition is treated. In a preferred embodiment of the invention, the upper surface is subjected to surface hardening. In a preferred embodiment of the invention, the upper surface of aerated, hardened, composition is sanded smooth or has surface grades formed before the surface hardening. The surface hardening may be effected by application of a resin or self- levelling cement coating over the surface. In one embodiment of the invention, the surface hardening is effected by application of a polyurethane resin over the surface. In one preferred embodiment of the invention, the surface treatment is carried out after the aerated, hardened, composition is applied to the support. In another embodiment of the invention, the surface treatment is carried out before the hardened aerated composition is arranged on the support. Preferably, a final floor covering, such as a layer of carpet, vinyl or floor tiles, is arranged over the composition.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a floor for a base frame for use in a modular building, the method comprising providing, in fluid form, an aerated composition overlying a rigid support and curing the composition to a hardened state, such that it bonds to the support. In a preferred embodiment of the invention, the composition fuses to the support when cured, so as to be bonded to the support.

Preferred embodiments of the invention may address at least some of the problems outlined above.

According to a sixth aspect of the present invention, there is provided a base frame for use in a modular building provided with a floor, the floor comprising: an aerated, hardened, composition; and a rigid support underlying the composition, the support being supported by the frame.

According to a seventh aspect of the present invention, there is provided a method of providing a building base frame for use in a modular building with a floor, comprising: applying a rigid support to the frame; and applying the composition to the support.

According to an eighth aspect of the present invention, there is provided a method of providing a building base frame with a floor, comprising: providing the composition in preformed, hardened, sections; attaching the sections to support elements; and arranging the support elements, with said sections thereon, adjacent each other on the frame, the support elements collectively forming the support. According to a ninth aspect of the present invention, there is provided a method of providing a building base frame with a floor, comprising: attaching the composition to the support; and applying the support, with the composition attached thereto, to the frame.

Because the aerated composition is lightweight compared to ordinary concrete, the invention can have advantageous application to multi-storey modular buildings, in which building modules, each module incorporating a base frame with a floor applied thereto in accordance with the invention, are stacked by a lifting apparatus such as a crane.

The present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective schematic view of an exemplary base frame for a transportable, relocatable or prefabricated modular building;

Figure 2 is a view taken through section A-A in Figure 1 ;

Figure 3 is a perspective view showing steel sheeting being fixed to the frame shown in Figure 1, in accordance with a preferred embodiment of the invention;

Figure 4 is a perspective view showing application of adhesive to the sheeting thus fixed to the frame;

Figure 5 is a perspective view showing laying of aerated concrete panels onto the layer of adhesive, in accordance with the preferred embodiment of the invention;

Figure 6 shows smoothing of an/or formation of a grade on the surface of the thus laid aerated concrete panels; Figure 7 shows surface treatment applied to the aerated concrete;

Figure 8 shows a graded floor application in accordance with a preferred embodiment of the present invention; and

Figure 9 shows a graded floor application in accordance with an alternative preferred embodiment of the present invention.

Figures 1 to 7 depict the stages in the installation of a floor in a base frame 1 for a transportable, portable or modular building. With reference to Figures 1 and 2, the base frame 1 comprises longitudinal outer bearers 3 and transverse bearers 4 connecting the ends of the longitudinal bearers 3 whereby the bearers 3 and 4 form a rectangular perimeter structure. A central longitudinal bearer 5 extends between the bearers 4 and is fixed to them at positions halfway along their lengths. Arranged at generally equal intervals along the length of the frame 1 are transverse floor joists 7, which extend parallel to the end bearers 4 and are fixed to top flanges of the longitudinal bearers 3, 5. The frame 1 further comprises a ring beam or perimeter beam 8 which is formed from longitudinal members 9 and transverse members 10 interconnecting the ends of the longitudinal members 9, the members 9 and 10 being fixed to the top flanges of the bearers 3 and top flanges of the bearers 4 respectively. The perimeter beam 8 is arranged to support the. wall structure of the building (not shown) and has a depth exceeding that of the joists 7 so as to define a containment/confinement structure which laterally braces the floor when installed over the joists 7, as will be described in further detail later.

With reference to Figure 3, installation of the floor in the base frame 1 commences with laying longitudinal strips of steel sheet 20. In the present embodiment, full length sheets are used, as will be clear from Figure 3, though in other embodiments shorter lengths may be used and arranged end-to-end. In the present embodiment, each strip 20 is appropriately surface treated to facilitate bonding of aerated concrete floor panels or blocks thereto (as will be described later). The inventors have found that particular grades of COLORBOND steel coil/sheet, a proprietary product of Bluescope Steel Limited, form a suitable sheeting material, in particular due to its Foam Grey backing coat, which can facilitate adhesion to plastics foam, and similarly facilitates bonding to the aerated concrete. In particular, the inventors have identified two types of COLORBOND sheet material which are satisfactory. One is Insulated Panel coil, referred to as COLORBOND Permaguard, details of which are provided in COLORBOND^® PERMAGUARD™ INSULATED PANEL STEEL FOR COOLROOM PANELS, Technical Bulletin TB-31, Rev 2, May 2006, BlueScope Steel Limited, the entire content of which is incorporated herein by reference, which has a zinc (only) substrate and is used to manufacture insulated cold room panel. The other is architectural panel coil, details of which are provided at http://www.bluescopesteel.com.au/go/product/architectural-panels, including as at 12 May 2009, and incorporated herein by reference in their entirety, which instead has a zinc/aluminium alloy substrate. Both have a Foam Grey backing coat to facilitate bonding to a polystyrene or polyurethane core.

The strips 20 are cut from a coil (though may alternatively be supplied as sheets) and arranged such that the backing coat surface 22 is uppermost and adjacent longitudinal edges of the strips 20 overlap. The strips 20 are then fastened to the joists 7, using adhesive/glue, and by screwing or nailing using a pressure/coil gun, to form a tray which defines a support base 24. Downward pressure is applied to the strips 20 to ensure they will bond adequately to the joists 7. It is preferable to apply tension to each strip 20 along its length when fixing it to the joists 7 to minimise dishing caused by residual camber in the sheeting as a result of its having been coiled or from deflection under it's weight, thereby ensuring the sheets 20 will be as flat as possible when adhesive is applied to surface 22.

The adhesive/glue may be important also to eliminate squeaking of the floor under occupancy loads/foot traffic, which may occur if the sheeting is fixed by screws or nails alone, and which may frustrate occupant comfort and/or amenity objectives.

The strips 20 may be provided in any of a number of thicknesses, which may, for example, lie in the range of 0.4 mm to 1.0 mm.

During bonding and fastening of the strips 20 to the joists 7, sealant is progressively applied around the perimeter of the sheets 20 and also along the exposed overlapping edges of the strips 20. The strips 20 and sealant, advantageously, provide an impervious membrane, which prevents liquid and vapour ingress through the area contained within perimeter beam 8.

In the present embodiment, silicone rubber, which offers an appropriate gelation time, may be used as both the sealant and the adhesive for bonding the strips 20 to the joists 7. However, alternatives may be used.

With reference now to Figure 4, adhesive 30 is applied evenly over the base 24. The inventors have discovered that bitumen-based compositions, some of which can be applied relatively easily with a trowel and in the preferred embodiments form a waterproof membrane, are suitable. Such adhesives are relatively inexpensive and can perform satisfactorily at temperatures up to 70°C and thus well beyond normal service temperatures. Alternatively, the adhesive may comprise polyurethane waterproofing agent, of the type applied between bathroom/shower tiles and concrete slabs in buildings to provide waterproofing therebetween, which adequately bonds the aerated concrete to the base 24, that agent being relatively inexpensive, workable and widely available. An adhesive thickness of 2 to 3mm is generally suitable, such a thickness being sufficient to cover the heads of the screws/nails used for fixing the strips 20 to the joists. Advantageously, this agent thus serves a supplementary waterproofing role, in addition to its bonding role.

In the present embodiment, the adhesive, particularly as applied across the entire base area, provides a large area over which the aerated concrete and base 24 are bonded, whereby forces between the aerated concrete and base 24 caused by movement of the base frame 1 , particularly during transportation can be more or less is uniformly distributed, reducing the likelihood of the aerated concrete, a relatively friable material, dislodging, cracking and/or shattering. Such forces may include uplift forces, such as those created when a truck transporting the frame and floor encounters a pothole or speed bump, forces generated by wind friction/drag, and dynamic self weight forces.

The inventors' determination of the appropriate adhesive for bonding the aerated concrete to the support base was based on the following four desired attributes, each of which is offered by the adhesive employed in the present embodiment, the first two of which are productivity-based and the second two of which relate to the mechanical quality of the bond. The first attribute is that of a sufficiently long gelation time (or "skin time") but a sufficiently short set time, whereby there is adequate time to adjust the positioning of the aerated concrete after it is laid against the adhesive without an undue delay in the adhesive setting sufficiently to allow lifting/handling of the base frame and/or completed building. The second attribute is that of workability or suitability generally for application to the support base, in particular an ability to spread the adhesive in the desired thickness, outlined above, sufficiently quickly. The third attribute is that of adequate bonding between the adhesive and the steel sheet, as outlined above. The fourth attribute is that of adequate bonding between the adhesive and the aerated concrete; if the adhesive is too viscous, it is not only too difficult to spread uniformly over the support base but also unable to penetrate sufficiently into the aerated concrete matrix to form an adequate bond, whereas, if it is not viscous enough, it will not be able to form a uniform covering over the entire surface of the base in the desired thickness unless the entirety of that surface is completely level. Further concerns associated with insufficient viscosity are long set times and/or the aerated concrete moving/dislodging during curing of the adhesive, particularly in the case of foaming-type glues (of which polyurethane adhesive, for example, is one) foaming to different thicknesses due to uneven thickness of the adhesive layer applied.

The inventors have experimented with numerous types of adhesives (in excess of 30), including epoxy-type adhesives of varying strength (including high strength epoxy adhesiver), and determined via sampling and strip tests that many types of adhesive are unsuitable but that the aforementioned bitumen and polyurethane adhesives perform favourably.

Advantageously, because of the fluid/vapour impermeability of the floor, the frame/floor can be installed relatively close to ground level. Moreover, owing to the light weight of the floor, the frame and floor will often be able to be handled by a forklift, whereby the need for static builds and special handling and transport is eliminated.

With reference to Figure 5, the aerated concrete is laid against the adhesive 30 in the form of rectangular blocks 40. In the present embodiment, the aerated concrete is autoclaved aerated concrete (AAC). Autoclaving aerated concrete improves stability. Specifically in the present embodiment, the aerated concrete is a product sold under the trade mark HEBEL, which is registered internationally in the name of Xella Deutschland GmbH.

Various block thicknesses may be used. Thicknesses of 75 mm are suitable for many applications, though smaller thicknesses, for example 50 mm, may be suitable in some circumstances. It is preferable that the distance which the perimeter beam 9 protrudes above the top surfaces of the joists 7 be substantially equal to the thickness of the blocks 40 so that the upper surfaces of the blocks 40 and perimeter beam 10 will lie substantially flush.

The blocks 40 are laid in rows extending along the length of the base frame 1, adjacent rows being offset from each other such that the blocks 40 are staggered. Adhesive is progressively applied to the edges/side walls of adjacent blocks such that they are bonded together. The blocks 40 cover the entirety of the base 24, such that the outer edge faces of the outermost blocks 40 abut the inner faces of the perimeter beam 10, adhesive being applied to those faces also to bond the outermost blocks to the perimeter beam. The perimeter beam 10 thus offers lateral bracing and confinement to the aerated concrete. The perimeter beam, owing to its strength and rigidity, also effectively isolates the aerated concrete, in service or transit, from loads exerted by the wall structure/posts that it supports, which loads may otherwise cause cracking, pulverising and dislodgement of the aerated concrete. In the present embodiment, the adhesive applied to the edges/side walls of the blocks and also to the interior faces of the perimeter beam is self-levelling cement or mortar, though bitumen or polyurethane adhesive as previously described could instead be employed, which may be plain or flexible. The adhesive may comprise self-levelling cement with polymeric additives, to increase its elasticity, for example. In the present embodiment, the adhesive is HEBEL adhesive, a proprietary product of Hebel Australia, which is a division of CSR Limited.

The floor joists 7 are arranged to lie directly beneath the transverse edges of the blocks 40 so as to support them.

Whilst downward pressure may be applied to the concrete blocks to enhance bonding, such pressure is generally unnecessary due to the weight of the blocks 40.

Alternative aerated concrete products are possible without departing from the invention, such as foamed concrete or cellular concrete, which may be of the type widely used in the manufacture of single skin lightweight tilt-up concrete wall panels. For example, such concrete as marketed under the trade mark LITEBUILT, which is registered in the name of Pan Pacific Management Resources Pty Ltd, may be used.

Following bonding of the blocks 40 to the base 24, the upper surfaces of the blocks 40 may be treated. Surface treatment may include smoothing, which can, advantageously, be performed using an electric sander 45 (see Figure 6), owing to the relatively friable nature of the aerated concrete. Advantageously, sanding/grinding can also be carried out to apply a slope or grade to the surface for drainage purposes, as will be described in further detail later.

Surface treatment may also involve hardening the surface, such as by fitting an thin surface overlay, such as Masonite, fibrous cement board, plywood or hardboard, or by application of self-levelling cement, which may be applied by trowel, or resin coating, e.g. polyurethane (PlO) coating, such as that marketed under the trade mark GRIPSET (which is registered in Australia), which may be applied by spray, roller or trowel and which the inventors have found binds with the surface and increases its hardness.,.

Surface treatment may also involve application of adhesives or primers to the surface, to enhance bonding of self-levelling cements or surface overlay boards. Also, surface treatment may involve setting particulate matter into a resin or paint coat on the surface as an alternative to traditional floor coverings.

The floor surface may be the upper surface of the aerated concrete, which may or may not be treated, or a surface coating applied over that surface. Alternatively, the floor surface may be an overlay, such as Masonite, fibrous cement board, plywood or hardboard, or a covering, such as a layer of carpet or vinyl, laid over the aerated concrete. In the case of vinyl in particular, the final smoothness of the floor may be improved by smoothing the aerated concrete, as described previously.

With reference to Figure 7, following surface treatment and/or the installation of any covering layer over the aerated concrete, the floor 50 is complete.

The floor 50 offers numerous advantages. Firstly, it greatly improves the feel of the floor under foot and makes a quiet/dead/flat sound when walked over, comparable to a, much heavier, floor comprising conventional concrete, which concrete may be some five times as dense as the aerated concrete.

Moreover, the aerated concrete renders the floor thermally insulative and thus improves energy efficiency, particularly for hot or cold climates. In particular, since the aerated concrete is arranged above the joists in the preferred embodiment, it forms a zone comprises substantially in its entirety of aerated concrete, with negligible thermal bridging, further enhancing insulative properties. Nevertheless, because the hardened composition is laid as a plurality of elements (slabs, tiles or blocks), it is non-monolithic and thus provides a high level of sound attenuation. Results of attenuation tests applied to the floor suggest that the attenuation performance actually exceeds that of a solid concrete floor, notwithstanding that the latter is denser. All other things being equal, sound attenuation is generally proportional to mass. The excellent sound attenuation performance of the floor may be attributable also to the bonding of the composition to the support sheeting.

In addition, whilst the combined frame and floor weigh considerably less than they would if the floor were instead made of conventional concrete, the weight added as the result of using the aerated concrete will, advantageously, reduce the magnitude of tie-down required in windy areas, and may eliminate the need for tie-down provisions in low wind areas.

Furthermore, the floor 50 will not be vulnerable to distortion due to indoor moisture ingress, for example due to air-conditioning in tropical climates or on sites with damp soil or subfloors which are ponded from lack of stormwater drainage. Also, unlike a timber floor, the floor 50 is non-combustible and free of particular chemicals, particularly preservatives such as formaldehyde, and is not vulnerable to termite damage.

A further advantage of the preferred embodiments is that, because the aerated concrete is laid in solid form, such as in the form of panels, blocks or tiles, the complexities and manufacturing durations associated with pouring concrete to make the floor are eliminated.

Yet a further advantage is that the steel sheeting bonded to the aerated concrete, to form a composite panel, increases the flexural bending strength of the floor (to span between joists) to resist floor traffic loads beyond the capacity of the aerated concrete alone. The steel sheeting, having excellent tensile strength, firstly, compensates for the relative lack of tensile strength of the aerated concrete, and, secondly, enhances or optimises the associated structural performance of the floor as a result of its being arranged beneath the aerated concrete, and thus spaced as far as possible from the centroid of the aerated concrete panel arrangement whilst still reinforcing that arrangement, unlike, for example, conventional steel reinforcing embedded within aerated concrete. The steel sheeting, with tensile strength, supplements the aerated concrete's compressive strength, whereby an effective, composite structural floor diaphragm is formed, enabling the floor frame to transfer offset lateral forces received from the building superstructure (walls, roofs etc.), from wind, earthquakes or other sources. Also, the composite panel structure retains a significant post-failure (or overload) strength, whereby in the event of the floor being overloaded, there is limited risk of catastrophic collapse (which in some instances can result in people literally falling through the floor). Advantageously, the base 24 serves not only as a supportive tray, which reinforces the HEBEL vertically, but also, owing to its adhesion to the HEBEL, reinforces it laterally, and does so at an optimum location, i.e. the maximum distance from the centroid of the panel structure on the tensioned side thereof.

An exemplary flooring application embodying the invention is illustrated in Figure 8, in which the same reference numerals are used for features corresponding to those described above. The floor structure comprises a base 24, fixed against joists 7, and aerated concrete 40 bonded to the support 24 by adhesive 30, consistent with the previously described embodiment. The floor 50' is provided with a downwardly convergent grade which is formed by sanding/grinding the top surface of the aerated concrete 40, the laterally outer ends of the graded sections defining floor boundaries between a wet area W, e.g. a kitchen or bathroom, and dry areas D in the building. A drain pipe 42 is incorporated into the floor between the inner ends of the graded sections. In this embodiment, a wet area board lining 44 is bonded to the sloped upper surfaces of the blocks 40 in the wet area W by a layer of adhesive 35, which is applied to the upper surfaces of the aerated concrete 40. The adhesive 35 preferably comprises a bitumen- based compound as previously described, though may comprises a different adhesive, such as the aforementioned polyurethane waterproofing agent. The wet area board lining 44, which may be formed from fibrous cement, is fixed to the aerated concrete 40 also by a plurality of twist nails 46. The floor 50' additionally comprises dry area board lining 47, which may comprise any of the previously described overlay materials, bonded to the level sections of the upper surface of the aerated concrete 40.

The floor 50' further comprises a floor covering 48, which may, for example, be seam- welded vinyl, defining a primary and absolute waterproof membrane, over which surface water flows to drain pipe 42, such that water ingress through the floor surface into the aerated concrete 40 or water leakage into areas beneath the wet area is prevented. Any resulting gaps at the junctions between board linings 44 and 47 may be filled with patching mortar 49.

The arrangement depicted in Figure 8 may be suitable in particular for single-storey buildings, in which, if there is a failure of the primary waterproof membrane, i.e., the outermost, exposed, floor surface, any leaks in the wet area floor, which might otherwise cause loss of amenity or damage to the area beneath the wet area, such failure is of little or no consequence..

An alternative flooring application embodying the invention is illustrated in Figure 9, in which the same reference numerals apply to features in common with the arrangement shown in Figure 8. In the arrangement shown in Figure 9, the floor covering 48 need not be an absolute waterproof membrane - for example, it may comprise conventional tiles and grout, as shown, which have a degree of porosity. In this arrangement, such a membrane is provided in a different manner, as will be described in detail shortly.

The floor 50" according to this embodiment also comprises aerated concrete blocks bonded to the sheeting tray support 24 by adhesive 30. In this arrangement, the floor 50" includes, instead of blocks 40 into which the grades are ground/sanded, respective pairs of blocks 40A, 4OB. The blocks 4OA underlie the board lining 47 in the dry area D, the board lining 47 being bonded to the upper surface of each of blocks 4OA by adhesive 35. The blocks 4OB have a smaller depth (thickness) than the blocks 4OA and have upper surfaces which, in contrast to the graded sections of the upper surfaces of blocks 40, are level. The floor 50" optionally further includes sloped floor sections 43, which define the floor grade in the wet area W and which may be provided in the form of moisture-resistant routed inserts, having a triangular or wedge-shaped configuration, or may instead be formed via a build-up of the tile bedding material.

The absolute waterproof membrane is formed by waterproof adhesive 35 applied to the upper surfaces of the aerated concrete blocks 4OB and the vertical end faces of the floors in the dry sections D, which in the particular arrangement shown is defined by a panel 49 of a wall separating the wet W and dry D areas, thereby forming returns up those faces. In this arrangement, the absolute waterproof membrane, because it is not formed by the outer floor layer, is concealed and thus protected from damage or rupture that may occur in service. Furthermore, any leakage of water through the outermost layer is thus tanked or confined solely within the wet area W and can thus, in its entirety, drain to the floor drain 42, rather than dispersing laterally under the dry area D, as is possible in the arrangement shown in Figure 8. Accordingly, water is precluded from penetrating the wet area floor to reach areas in a building beneath the wet area W. The arrangement shown in Figure 9 may thus be particularly suited to multi-storey buildings.

Bases of the sections 43, if fitted, are bonded to the upper surfaces of blocks 4OB via waterproof adhesive 35.

To increase surface hardness of the substrate, a wet area board lining may be fixed over the blocks 4OB with adhesive and twist nails 46. In this variant, the waterproof membrane 35 is also applied above the board lining and similarly returned up the vertical faces.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims

The claims defining the invention are as follows:

1. A floor for a base frame for use in a modular building, the floor comprising: an aerated, hardened composition; and a rigid support underlying the composition, to which the composition is fixed.

2. A floor according to claim 1, wherein the support engages the composition generally uniformly over the area of an underside of the composition.

3. A floor according to claim 1 or claim 2, wherein the support engages the composition over substantially the entirety of the area of the underside.

4. A floor according to any one of the preceding claims, wherein the support is of sheet-like form.

5. A floor according to any one of the preceding claims, wherein the composition is bonded to a top surface of the support.

6. A floor according to claim 5, wherein the composition is bonded to the top surface over substantially the entirety of the area of the top surface.

7. A floor according to claim 5 or claim 6, wherein the composition is bonded to the top surface of the support by bitumen-based adhesive.

8. A floor according to claim 5 or claim 6, wherein the composition is bonded to the top surface of the support by polyurethane adhesive.

9. A floor according to any one of claims 5 to 8, wherein the adhesive forms a waterproofing membrane between the composition and the support.

10. A floor according to any one of the preceding claims, wherein the composition is provided in sections which are fixed to the support.

11. A floor according to any one of the preceding claims, wherein the composition comprises aerated concrete.

12. A floor according to claim 11, wherein the aerated concrete comprises autoclaved aerated concrete.

13. A floor according to any one of the preceding claims, wherein an overlay is applied over the hardened composition.

14. A floor according to claim 14, wherein the overlay is bonded to the composition with adhesive.

15. A floor according to any one of the preceding claims, wherein surface hardening is applied to an upper surface of the composition.

16. A floor according to any one of the preceding claims, the floor being applied to a base frame for use in a modular building.

17. A base frame for use in a modular building with a floor according to any one of claims 1 to 15 applied thereto.

18. A base frame according to claim 17, the frame being configured to brace said composition laterally.

19. A base frame according to claim 18, comprising a structure arranged to abut the composition around a periphery thereof to brace it laterally.

20. A modular building including a base frame according to any one of claims 17 to 19.

21. A method of manufacturing a floor for a base frame for use in a modular building, the method comprising fixing an aerated, hardened composition atop a rigid support such that it overlies the support.

22. A method according to claim 21 , wherein the composition is fixed to the support in sections.

23. A method according to claim 21 or claim 22, wherein the composition is bonded to the support.

24. A method according to any one of claims 21 to 23, wherein the floor is manufactured on the frame so as to be applied thereto.

25. A method of applying a floor to a base frame for use in a modular building, comprising both fixing an aerated, hardened composition atop a rigid support such that it overlies the support and application of the support to the frame.

26. A method according to claim 24 or claim 25, wherein the support is applied to the frame and the composition is then laid over the support and fixed thereto.

27. A method according to any one of claims 24 to 26, wherein support elements are secured to the frame, the support elements collectively forming the support.

28. A method according to any one claims 21 to 27, including subjecting an upper surface of the composition to surface hardening.

29. A method according to any one of claims 21 to 28, comprising sanding or grinding a grade into an upper surface of the composition.

30. A method of manufacturing a floor for a base frame for use in a modular building, the method comprising providing, in fluid form, an aerated composition overlying a rigid support and curing the composition to a hardened state, such that it bonds to the support.