Patent Description:
The construction industry faces a number of unique challenges in providing affordable housing. The field of building prefabrication attempts to address some of these challenges.

Prefabricated dwellings can be constructed in a factory and then transported to a site. This offers the advantage that weather and travel of construction professionals are not factors in the construction process. One downside is that the design of prefabricated dwellings is limited by the mode of transport and route to the construction site, in New Zealand predominantly by truck and possibly by rail. This introduces limitations of width and height of the load to be transported, with the limitation of length being defined by the vehicle. These limitations are usually addressed in one of two ways: by designing the dwelling to fit onto a single truck, known as a "tiny house" or by designing the building as modules to be fitted together on-site.

An advantage of a prefabricated dwelling design is that if the New Zealand Ministry of Building, Innovation and Employment (MBIE) approves the design, they will grant a multi-proof building consent on the design. This means a building consent application corresponding to the multi-proof consent documents must be approved by the Building Consent Authority without questions within <NUM> days.

Prefabricated dwelling designs made in a factory using conventional components, for example timber framed construction, are offered as factory-made dwellings and also as kit-sets for constructing on-site. nz offer such transportable homes in both formats.

Factory-made dwellings using conventional timber-framed construction use a large number of components and are labour-intensive to assemble, whether on-site or in a factory. Transporting assembled dwellings introduces a number of additional challenges.

A sandwich panel or structural insulated panel (SIP) is a structure comprising three layers; a core of low-density insulating material such as polyurethane (PUR) and an outer skin each side of the core. Sandwich panels can thus provide integrated structural and cladding systems. Their strength and light weight means they can span large distances, making them particularly useful for wall and roof systems in commercial or industrial buildings; their use is less common in domestic buildings. Sandwich panels are usually flat and elongate in form, although curved sandwich panels are also available for installation on curved roofs. In use, a side edge of the elongate form is fixed to the side edge of an adjacent panel. For this reason the side edges of the panels are usually designed with complementary profiles to fix together, often employing screw fixings.

As used herein, the term "sandwich panel" means a structure comprising three layers; a core of low-density insulating material and an outer skin each side of the core.

<CIT> is a conventional building module.

<CIT> is a conventional building structure and method of manufacture.

According to one aspect of the present invention, there is provided a building module as defined in claim <NUM> hereinafter.

According to another aspect of the present invention, there is provided a method for constructing a building module as defined in claim <NUM> hereinafter.

Preferred embodiments of the invention will now be described with reference to the drawings.

<FIG> shows a cross section view of sandwich panels <NUM> and <NUM>. Sandwich panels <NUM>, <NUM> have a width W of <NUM> and <NUM> respectively, although it will be understood by persons skilled in the art that other widths can be chosen. The depth D of sandwich panels <NUM>, <NUM> is shown in <FIG>, and in this example is on the order of <NUM>. While the length L of sandwich panels <NUM>, <NUM> is not shown in the cross section drawings of <FIG>, it will be understood by persons skilled in the art that sandwich panels usually function as a simply supported beam and sometimes as a cantilever beam, and that known principles of beam.

design can be applied to determine the required depth D of the sandwich panel with reference to a given length L, and vice versa.

The sandwich panel has a core <NUM>, <NUM>, and a thermoplastic skin <NUM>, <NUM>. The lightweight core comprises an insulating core comprising a foamed material which provides rigidity to the panel. This can be for example a polyurethane foam, including a polyurethane foam formed utilising carbon-capture technology, or a polyethylene foam, or a foam formed from recycled polyethylene terephthalate (PET). In other embodiments the lightweight core can comprise a material such as a mycelium composite. Mycelium composites are formed by growing mycelium spores on a substrate such as wood chips, agricultural by-products, wool or fleece.

A preferred material for the thermoplastic skin is polyethylene, for example high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE). Thermoplastics have a number of advantages, including that they can easily be moulded into simple or complex shapes, and can be heat welded together. The thickness of the thermoplastic skin <NUM>, <NUM> in this example is about <NUM>. The thermoplastic skin can be formed in a number of ways, including but not limited rotational moulding, extrusion, and vacuum forming, as is known to persons skilled in the art. Advantageously, flame-retardant additives can be added to the thermoplastic skin, as known in the art.

In sandwich panels known in the art, the side edges of the panels are usually designed with complementary profiles to fix together, often employing screw fixings. The sandwich panel of the invention comprises a lip <NUM>/<NUM> which fits over a crest <NUM>/<NUM> of an adjacent sandwich panel.

Sandwich panels <NUM>, <NUM> comprise steel joists <NUM>, <NUM>. In these examples, steel joists <NUM>, <NUM> have a profile known as MS Tophat, generally an inverted V-shape with a flat top and protruding flanges on the bottom which can receive fixings (<FIG>). In the embodiment shown in <FIG>, steel joists <NUM> have a depth of <NUM>. Suitable steel joists are available from commercial suppliers including Metalcraft Roofing and Steel and Tube Holdings Ltd. An advantage of using a commercial steel joist is that span tables are already available.

One side of the thermoplastic skin <NUM>, <NUM> has a ribbed profile <NUM>, <NUM> to accommodate steel joists <NUM>, <NUM>. The other side of the thermoplastic skin has a flat profile <NUM>, <NUM>.

Steel joists in sandwich panels <NUM>, <NUM> have a spacing J of <NUM> centres and <NUM> centres respectively, although the person skilled in the art will appreciate that other spacings are possible. In a preferred embodiment, the steel joists have a cross member rivet-fixed above the joists at <NUM> centres (not shown in <FIG>). This ensures that the steel joists sit hard into the troughs in the positions shown in <FIG>. The cross member can be for example a <NUM> steel tophat joist.

Ribbed profile <NUM>, <NUM> can be described as a deep ribbed profile, where the depth of the ribs is at least half of the depth D of the panel (i.e. D2 ≤ <NUM> D). In the embodiments shown, D2 is <NUM> and D is <NUM>.

While inserts <NUM>, <NUM> are formed from steel, it is contemplated that aluminium joists could also be used. The high strength-to-weight ratio of steel and aluminium makes these materials particularly suitable to form the joists. The person skilled in the art will understand that the joists need not have MS Tophat profiles, but can be any shape which allows them to function as a beam, including for example open web steel joists and rectangular hollow sections. Similarly, there is no need to provide a ribbed profile in the thermoplastic skin in order to accommodate the steel joists. The ribbed profile matching the profile of the joists <NUM>, <NUM> provides advantages in forming the sandwich panel or building module of the invention, as described below.

Once formed, the sandwich panel of the invention is encapsulated by the thermoplastic skin, which provides weathertightness and durability to the panel. In conjunction with the foamed material, the metal/steel joists provide the thermoplastic-skin panel with greater rigidity, enabling the panel to span greater lengths between supports.

With reference to <FIG>, a Building module <NUM> which is a sandwich panel is shown. Building module <NUM> comprises a first region <NUM> which provides part of the roof structure of a building, a second region <NUM> which provides part of the wall structure of the building, and a third region <NUM> which provides part of the floor structure of the building.

It is generally expected that the floor region of the building module will be flat for functional reasons. While the preferred embodiment advantageously has a roof region pitched at <NUM> degrees to allow for rain runoff and a curved wall region, as discussed further herein, other arrangements are contemplated.

In this example, regions <NUM> and <NUM> possess the structure of a sandwich panel <NUM>, comprising steel joists and an insulating core comprising a foamed material as shown in <FIG>, ribbed profile for the outer skin, flat profile for the inner skin, and lip <NUM> (<FIG>) which fits over crest <NUM> of an adjacent building module. Region <NUM> comprises a thermoplastic skin having a cross section corresponding with regions <NUM>/<NUM>, but filled with foamed material only. Curved wall region <NUM> is non-loadbearing and therefore does not have steel joists.

<FIG> shows another building module <NUM>, generally corresponding to building module <NUM> and comprising first region <NUM>, a second region <NUM>, and third region <NUM>. Building module <NUM> further comprises slot <NUM> in region <NUM>, and hole <NUM> at the junction of regions <NUM> and <NUM>. The purpose of slot <NUM> and hole <NUM> is described below with reference to a preferred way of constructing a building. The steel joists inside each module <NUM> run parallel with, and flank the slot and hole in each panel. Where interrupted by slot <NUM>, the cross members inside each module will not cross the entire panel.

In the embodiments shown, building modules <NUM> and <NUM> have a width W of <NUM>, although it will be appreciated that other widths can be used.

A number of building modules can be fitted together to provide the floor, wall and roof structure, cladding and insulation of a building of desired length L, being a multiple of the building module width W. A method for constructing a building from building modules <NUM> is described in detail below.

The thermoplastic skin of sandwich panel <NUM>, <NUM> or building module <NUM> or <NUM> are formed by rotational moulding. This involves forming a skin of the sandwich panel from a thermoplastic in a rotary oven. This results in a completely enclosed hollow skin <NUM>, <NUM>.

Rotational moulding ovens are available to fabricate larger items such as storage containers, water tanks and playground equipment. The building module of the invention can be formed in a single piece in a large rotary oven. In the preferred embodiment, the length of building module <NUM> is on the order of <NUM> metres, and height on the order of <NUM> metres. A suitable oven is available at, for example, New Zealand company Galloway International.

The following described method is not forming part of the claimed invention:
Once the skin is set/cured, it can be demoulded. To insert the steel joists into the sandwich panel, one end of the panel is sliced off, the joists can then be slid into place. In the case of a sandwich panel which is a building module <NUM>, the ends of roof region <NUM> and floor region <NUM> of the building module are sliced off, the joists can then be slid into place in regions <NUM> and <NUM>. As mentioned above, in the preferred embodiment, the steel joists are fixed to one another using a cross member, which can be for example a <NUM> steel tophat joist cross member rivet fixed above the joists at a regular spacing, e.g. at <NUM> centres, ensuring that the steel joists sit hard into the troughs.

Once the steel joists are inserted, the panel is filled with a foamed material, in one preferred embodiment a polyurethane foam, ensuring that the entire cavity of the sandwich panel is filled. For the U-shaped building module of the invention, this may be achieved by orienting the panel with regions <NUM> and <NUM> pointing upwards and then pouring or injecting the foamed material. Once the foamed material has hardened, the excess material is cut flush with the cut panel end. The end of the panel can then be sealed by heat welding, either using the previously removed end of the panel, or using a custom-made capping, that is then heat-sealed using a custom heating plate to melt the cut end and reseal.

In embodiments where a mycelium composite is used, instead of pouring or injecting foamed material into the panel, a substrate can be inoculated with mycelium spores and then inserted within the thermoplastic skin. After a growth period, the mycelium can be dried or heated to form a mycelium composite material. Another way to form the thermoplastic skin is by extrusion. Either the entire skin <NUM>, <NUM> can be extruded through a die to provide the desired profile of the skin, or separate parts of the skin can be formed by extrusion, for example ribbed side <NUM> and flat side <NUM>, which can then be welded together. The joists can then be inserted and the ends sealed as in the rotational moulding process. To form building module <NUM> or <NUM>, the extrusion must be bent or wrapped around a form while in a plastic state.

It will be appreciated by the person skilled in the art that the sandwich panel <NUM>, <NUM> can be used to form a roof, floor or wall. While the ribbed profile forms the exterior of building module <NUM> or <NUM>, a planar sandwich panel having the cross section shown in <FIG> can be used with the ribbed profile facing either the interior or the exterior of a building.

The rotational moulding process can be used to form the sandwich panel and building module with the steel joists already positioned within the thermoplastic skin. This can be achieved by positioning the steel joists within a mould for a skin of the sandwich panel, supported and held in place by a number of suitable supports, such as stand-off plugs or other suitable spacer elements. The skin of the sandwich panel can then be formed in said mould, by adding a thermoplastic material, rotating the mould in a rotary oven and allowing the thermoplastic to set/cure. Once the skin is set/cured, the thermoplastic skin with steel joists within can be demoulded. The sandwich panel can then be filled with an insulating material by forming an aperture in the panel.

In some embodiments, an insulating foam is formed from a powder which is inserted into the thermoplastic skin while the thermoplastic skin is still warm, i.e. just after it has been formed in the rotary oven. The powder can be inserted by forming aperture(s) in the thermoplastic skin, for example by drilling. After the powder is inserted, the aperture formed by drilling is then plugged. The mould containing the thermoplastic skin is then rotated further within the oven at a lower temperature than the melting temperature of the thermoplastic skin. The powder expands to a foam within the mould and adheres to the thermoplastic skin. Once cooled, the sandwich panel is removed from the mould as a single integrated piece with no seams. In a particularly preferred embodiment, the thermoplastic skin is formed from HDPE and the powder is a polyethylene powder.

This method offers the advantage that there is no need to remove the ends of the mould to insert the steel joists and reseal the ends back onto the mould afterwards. Additionally, adhesion between the respective polymers is enhanced in embodiments using HDPE skin and a polyethylene powder. The sandwich panel/building module so formed is seamless and has a neat finish and simple process of production. Due to the rotational moulding process, this method would result in some thermoplastic material adhering to the steel joists inside the mould, and it is expected this would result in use of more thermoplastic material per sandwich panel/building module.

The person skilled in the art will appreciate that the building modules of the invention can be coupled to one another and fixed to the ground in a number of ways to construct a building. One preferred method is described as follows.

In the preferred embodiment, a screw pile system is used. Screw piles formed from steel are available from, for example, Katana Foundations (NZ). Screw piles have advantages in that they are easy to position and quick to install. They also require no concrete placing and are suitable for deep to soft soil conditions found throughout New Zealand. They can be removed, allowing for the proposed building to be relocated or recycled at end of life. In the method of the example, screw piles are installed in the ground in a grid arrangement, and will each support a steel post P. Screw pile extensions can be coupled to the top of a screw pile above ground. As used herein, the term "screw pile" refers to a screw pile either with or without a screw pile extension.

The method of the example uses building modules <NUM>, which slide onto each other as described further below. Slots <NUM> and holes <NUM> are useful in the construction method, but once the building structural system has been erected, all slots <NUM>, and all unused holes <NUM>, are filled in with moulded inserts of the appropriate shape to fit slot <NUM> and hole <NUM>.

<FIG> and <FIG> show the grid arrangement of steel posts P at positions P1, P2 etc. Slots <NUM> and holes <NUM> (not shown in <FIG>; shown in <FIG>) accommodate the steel posts P. Posts P are arranged in two parallel rows R and S (<FIG>). Posts in rows R and S are at a spacing of 2W, and row R is at a distance X from row S (<FIG>). In the embodiment shown, X is <NUM>.

While <FIG> and <FIG> show a plan view of a building formed from seven building modules <NUM>, it will be appreciated that any number of building modules <NUM> can be used to form a building in this way.

As shown in <FIG>, each building module <NUM> comprises a slot <NUM> extending from the end of region <NUM> to the desired position of row R, and a hole <NUM> at the desired position of row S.

The distance X2 between hole <NUM> and the periphery of building module <NUM> should be sufficient to locate hole <NUM> in floor region <NUM> rather than curved wall region <NUM>. In the example shown, distance X2 is about <NUM> and corresponds generally to the radius of curved wall region <NUM>.

<FIG> shows a schematic front elevation of the structural system for a building according to the invention. In this Figure, a nominal position G is shown for the ground line, and break lines Rb indicate that the proportion of screw piles R above the ground is indeterminate. Adjacent screw piles can be coupled above-ground by cross-bracing as required.

Generally, the top of the shaft of each screw pile can be provided welded to a square drive head. This provides for easy installation of the screw pile and also allows the shaft of the screw pile to be coupled to a post or a pile extension above, by means of a collar, shown as Rc in <FIG>. The collar advantageously comprises a plate or square nut welded to its inner walls to seat the collar on the square drive head. As is known in the art, the collar can also comprise holes for fixings such as M12 bolts to pierce the pile shaft and/or post.

To construct the building, two rows R and S of screw piles are installed in any order, at a spacing related to the width W of the building modules. In the embodiment shown, the spacing 2W is twice the width W of the building module, and only every second building module will be fixed to a screw pile (<FIG>). The spacing can also be e.g. equal to the width W of the building module, in which case every building module will be fixed to a screw pile, or another arrangement as will be understood by the person skilled in the art.

The distance between the two rows R, S corresponds to the distance between hole <NUM> and the end of slot <NUM> on the building module <NUM>.

Once each row R and S is installed, posts P can be fixed to screw piles in row R, and bearer beams <NUM> can be fixed to row R and S respectively, at a height to support floor region <NUM> of the building modules. These steps can be done in any order, provided that no posts P are yet fixed to row S. A bearer beam must be fixed to the screw piles of row S, but it is possible for a bearer beam <NUM> to be fixed either to the screw piles of row R (i.e. below collar Rc), or to posts P in row R (i.e. above collar Rc, shown in <FIG>).

Bearer beams <NUM> can be fixed at row R and S respectively using methods known in the art. The bearer beams can be of any suitable material and profile; a preferred material is hot dipped galvanized steel, preferably of a parallel flange channel (PFC) profile, which will be resistant to corrosion and those at row R can for example be fixed to the posts P using a cleat plate and bolts <NUM> (shown in <FIG>).

In this example, each post P is a <NUM> SHS and is coupled via a collar formed from a <NUM> SHS to a screw pile having a circular hollow section (CHS) and a square drive head of comparable width to post P. However, posts P can be any desired shape, including for example CHS posts.

Once posts P are installed along row R, a beam <NUM> is fixed to the top of posts P along row R, using methods known in the art, to support roof region <NUM> (<FIG>). In this example the fixing means is via cleat plates and bolts <NUM>. A corresponding frame is to be constructed along row S, but is not yet constructed. Thus, in this example, the entire frame along row R is installed (both the top beam <NUM> and a bearer beam <NUM>), and a bearer beam <NUM> is installed to row S, before the modules are fixed to the frame.

Next, slot <NUM> of a first building module <NUM> is slid onto a first post P1 in row R, such that hole <NUM> aligns with screw pile P2 on in row S (<FIG>). Slot <NUM> of the first building module can then be plugged with a HDPE moulded insert. Post P2 in row S can then be installed through hole <NUM> to screw pile P2, either at this stage or after all of the building modules <NUM> are in place.

The moulded inserts can be provided in the appropriate shape to fit slot <NUM> and hole <NUM>, and can also be formed by a rotational moulding process. In this example the moulded inserts are also filled with PUR foam for rigidity. They can be heat welded into place once the module is installed on the frame.

A lip of a second module is then aligned with a complementary crest of the first module, and the second building module is then slid onto the first building module. In the embodiment shown, second building module <NUM> is not installed to a screw pile; it is held to the first module by a friction fit. This means that slot <NUM> and hole <NUM> of the second building module <NUM> will not perform a function, and can be plugged with a HDPE moulded insert. Alternatively, every second building module could be provided without slot <NUM> and hole <NUM>.

Providing every building module with slot <NUM> and hole <NUM> has advantages that only one mould is needed to form the building modules, and provides flexibility during installation.

It will be appreciated that in alternative embodiments, every building module will have a complementary pair of screw piles, and every slot <NUM> and hole <NUM> will receive a post P.

In this example, the slot <NUM> is about <NUM> in length. Thus, once installed, the floor region of each module will cantilever <NUM> beyond gridline R (<FIG>). Optionally, instead of cantilevering the floor regions in this way, an additional steel beam could be placed within each slot <NUM> to bear on a steel end beam underneath the end of region <NUM> (not shown). Advantageously, a balustrade could be fixed to such an additional steel end beam.

As stated above, once each building module is installed on the frame along row R, posts P2, P4 etc. can then be installed to screw pile P2, P4 etc. via holes <NUM>. When all posts in row S are in place, a second beam (not shown) can then be fixed to the top of the second row of posts P2, P4 etc. using methods known in the art, to provide a second frame along row S and support the roof region <NUM>.

Dimensions of the posts P and beams can be calculated by methods known in the art, with reference to the required span for beams and the material used, and the load to be borne by beams/posts. The building modules of the invention are strong and lightweight. For an unloaded building module <NUM>, a post of <NUM> width is expected to be sufficient. This does not take account of snow loads; it is also envisaged that the invention will allow for buildings having green roofs, which increase the load on the structural frame. Calculation of the required increase to the dimensions of posts P and roof beams in such situations can be made using known methods. The width of hole <NUM> and slot <NUM> are governed by the width of posts P; for example, hole <NUM> has a diameter of <NUM> to accommodate a steel post of <NUM> width.

Roof region <NUM> and floor region <NUM> can be fixed to the respective beams by fixing screws into the steel joists within the panels.

While <FIG> and <FIG> and the associated text describe a preferred method for fixing the building modules to the ground, it will be appreciated that the general approach of providing holes in the floor region of the building module can be adapted to accommodate any foundation system.

After forming the shell of a building by the method described above, the open sides of the building shell may be provided with aluminium joinery, for example double glazed sliding doors and windows, or with another partition wall system. A perspective view of such a building is shown in <FIG>. Joinery can be fixed to the regions <NUM>, <NUM> using bolting and/or heat welding techniques. Partition walls can be constructed to the interior of the building using similar bolting and/or heat welding techniques. An exemplary single-bedroom floor plan showing partition walls is shown in <FIG>; it will be appreciated by the person skilled in the art that many variations are possible.

The surface of the thermoplastic, HDPE in the embodiment shown, is durable and does not need painting or other finishing, and as discussed above, can accept a green roof system if desired. The inner surface of the thermoplastic provides a floor surface and exterior deck. This can provide the finished floor surface, or alternatively a finished floor surface can be provided on top of the thermoplastic using another floor system.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in New Zealand or any other country.

Claim 1:
A building module which is a sandwich panel comprising:
an inner core comprising a foamed material;
an outer skin comprising a thermoplastic which completely encloses the inner core;
a first region (<NUM>) which provides part of the roof structure of a building,
a second region (<NUM>) which provides part of the wall structure of the building,
a third region (<NUM>) which provides part of the floor structure of the building, and
metal joists within the outer skin of the first (<NUM>) and third regions (<NUM>).