WO2011135354A2

WO2011135354A2 - Method for forming a building foundation, building foundation, system, spacer, connector and insulating block

Info

Publication number: WO2011135354A2
Application number: PCT/GB2011/050827
Authority: WO
Inventors: Philip Major
Original assignee: Sig Plc
Priority date: 2010-04-29
Filing date: 2011-04-27
Publication date: 2011-11-03
Also published as: WO2011135354A3

Abstract

Various methods and systems for forming insulating building foundations are disclosed. The methods and systems are for use with fibre-reinforced concrete and allow increased speed and ease of construction because conventional reinforcement is not required. In one embodiment, a method of forming a building foundation comprises: preparing an area of the foundation to substantially the same level; providing shuttering around the outer perimeter of the prepared area of the foundation; arranging at least a plurality of first insulating elements and a plurality of second insulating elements abutting each other within the shuttering to form a continuous layer having a flat lower surface over the prepared area of the foundation, wherein the first insulating elements have a first height and the second insulating elements have a second height which is less than the first height; connecting the plurality of first insulating elements and the plurality of second insulating elements to each other using a plurality of connectors; and pouring fibre-reinforced concrete within the shuttering. The insulating elements are connected to each other using connectors and therefore any tendency of the insulating elements to float during pouring of fibre-reinforced concrete is reduced. Other embodiments relate to the features of the insulating elements and connectors for use in forming insulating building foundations using fibre-reinforced concrete.

Description

METHOD FOR FORMING A BUILDING FOUNDATION, BUILDING FOUNDATION, SYSTEM, SPACER, CONNECTOR AND INSULATING BLOCK

The present application relates to methods of forming building foundations, building foundations and a system for use in forming a building foundation. Other aspects of the invention relate to a spacer for use in forming a building foundation and a system comprising the spacer, insulating blocks and optionally insulating strips. Further aspects of the invention relate to connector for use in forming a building foundation and an insulating block. The present invention also relates to foundations and buildings formed using the spacer, system or method of the present invention.

So-called "waffle slab" foundations are proposed in US-4788809 (Koukourou).

Koukourou discusses a method of forming a foundation with intersecting beams and floor portions. This method comprises levelling the ground on which the foundation is to be located and then assembling a system of inverted hollow members positioned in rows separated by spacers. Reinforcing rods are placed in the space between the inverted hollow members and over the top. Concrete can then be poured to form a building foundation. This method can be faster and more cost-effective than previous methods involving digging individual trenches because a single, level excavation is carried out.

The system of Koukourou can be insulated by a screed covering applied on top of finished foundation. However, this is expensive and time-consuming. An alternative is discussed in GB-2385071. This discusses a system comprising insulating blocks that can be assembled in a grid pattern to provide a foundation with insulating properties. Rather than the inverted hollow members of Koukourou, insulating members are used which improves the thermal performance of the foundation. One particularly advantageous embodiment includes flanges extending from the insulating block and the flanges are adapted to interlock with each other. This enables an interlocking system of insulating blocks to be provided, which provides a complete thermal break between the concrete and the ground. However, the flange is load bearing, it is therefore made from an expensive high performance insulation. In order to minimise damage to the flange during transportation, storage and installation, which could easily occur; current manufacturing practice is to cover the entire width of the insulating block with the higher grade material even though it is not structurally required over the entire area.

GB-2385071 does discuss embodiments in which separate blocks are used with insulating spacer strips. These spacer strips engage flanges formed on the side blocks. These flanges increase the cost of manufacturing the insulating blocks.

Recently, Steel fibre reinforced concrete has been used in building foundations. This has the advantage that a network of reinforcing rods is not required but also presents new problems. One problem is that the elements defining the foundation tend to float on the concrete or move laterally because there are no reinforcing rods to hold them down and in position, as taught in Koukourou. It has been found that blocks with interlocking flanges as suggested in GB-2385071 are particularly suitable for use with metal fibre reinforced concrete because the interlocking between the blocks helps prevent them floating while the concrete is poured. However, as discussed above, producing blocks with interlocking flanges is not the most efficient use of materials and increases production costs to manufacture the blocks with flanges.

The foundation may be provided with edge beams to increase strength around the perimeter of the foundation. In order to minimise thermal bridging at the edge beams, edge beam insulation is provided at the edge or perimeter of the foundation. This is generally thinner than the insulating blocks.

Conventionally, the edge beam insulation is at a lower level than the insulating block. The insulating block is typically placed slightly overlapping the edge beam insulation so that the lower surface of the block is resting on the upper surface of the edge beam insulation. This can potential create a weakness when placing Steel Fibre Reinforced Concrete (SFRC) because the concrete can get under the Expandable Polystyrene (EPS) from which the blocks are made and lift them.

Figure 1 depicts an example of a prior art edge beam 70 discussed in GB-2385071. The edge beam is formed by excavating a trench 72 in a layer of coarse aggregate on which the foundation is to be formed. A layer of high performance insulation 74 is then placed in the trench. The insulating blocks 76 to form the foundation are then overlapped with this insulation 74 to avoid formation of a cold bridge. A network of reinforcing rods 78, 80 are provided to reinforce the concrete when it is poured. The reinforcing rods 78,80 also hold the blocks in place while concrete is poured. When this system is used with SFRC, the insulating blocks will tend to float as the concrete is poured because there are no reinforcing rods to hold them down. The concrete will also exert lateral forces on the insulating blocks and may cause movement of the blocks. It would be advantageous to provide a system for forming a building foundation which is suitable for use with fibre reinforced concrete that is more cost-effective than the system of insulating blocks and interlocking flanges suggested in GB-2385071. All the embodiments of GB-2385071 which are suitable for use with fibre reinforced concrete require an insulating block with a flange to provide an interlock and prevent the blocks floating when the concrete is poured.

Accordingly, one aspect of the invention provides a method of forming a building foundation, the method comprising:

preparing an area of the foundation to substantially the same level;

providing shuttering around the outer perimeter of the foundation;

arranging at least a plurality of first insulating elements and a plurality of second insulating elements abutting each other within the shuttering to form a continuous layer having a flat lower surface over the prepared area, wherein the first insulating elements have a first height and the second insulating elements have a second height which is less than the first height;

connecting the plurality of first insulating elements and the plurality of second insulating elements to each other using a plurality of connectors; and

pouring fibre-reinforced concrete within the shuttering. The use of connectors between the first and second insulating elements minimises movement. Rather than the interlocking flanges of GB-2385071, the use of connectors enables insulating elements without complicated surface features, such as flanges, to be used. For example, plain cuboidal blocks may be used. Within the plurality of first insulating elements and within the plurality of second insulating elements, the individual insulating elements do not all need to be the same length and width. However, they share a common height (the first height for the first insulating elements and the second height for the second insulating element). In one embodiment, the first height may be about 400mm and the second height may be about 100mm. Other depths may be used depending on the particular characteristics of insulation used.

The different heights of the insulating elements allows a foundation with good structural characteristics and minimal use of fibre-reinforced concrete to be produced. For example, when a waffle foundation with criss-crossing internal ribs is formed where the first height is about 400mm and the second height (for forming the ribs) is about 100mm, pouring fibre-reinforced concrete to a height of about 100mm above the first insulating elements results in a foundation with a stiffness equivalent of a 260mm thick, conventionally reinforced concrete slab. Therefore, the method allows a smaller volume of concrete to be used.

Although the second insulating elements have a lower height than the first insulating elements, they are formed from a high performance insulating material to give them similar properties as the first insulating elements. Preferably the first and second insulating elements have a minimum thermal resistivity of 28 mKW^_1and compressive strength of 150kPa at 10% compression and compressive strength of 70kPa at 1% nominal strain. This provides good thermal performance in combination with good structural

characteristics.

The first and second insulating elements may have a cuboid shape. This enables easy manufacture and easy tessellation of the insulating elements within each other. In some embodiments, further types of insulating elements may be provided, for example, insulating elements with heights other than the first or second height.

The step of preparing an area of the foundation will depend on the ground characteristics. It may comprise excavation, infill or a combination of techniques, depending on the ground. If the preparation is carried out by excavation, the method may further comprise providing a substantially flat layer of filling material within the prepared area. The filling material can be any suitable material, such as an aggregate. The method of the invention is particularly advantageous when used with fibre reinforced concrete, for example, steel fibre reinforced concrete. Other types of fibre-reinforced concrete may also be used, such as other metal fibres, glass fibres, synthetic fibres and natural fibres. This is because with fibre reinforced concrete no network of reinforcing rods is provided. When used with fibre reinforced concrete the connectors hold the insulating elements together to prevent movement and/or floating during pour of the concrete. This is not a problem when conventional reinforcement the network of reinforcement prepared before the concrete is poured will act to hold the blocks in place during the concrete pour. The resulting foundation is preferably raft foundation in which the raft transfers the load across the whole area of the foundation. In less preferred embodiments, the foundation may be used in combination with a strip footing to take the load down to a suitable ground bearing formation. However, the benefit of the improved ease of construction and high structural performance of the foundation is of particular benefit when used as a raft foundation.

Preferably, in the preparing substantially the whole area of the foundation is prepared to the substantially the same level; and in the arranging the at least a plurality of first insulating elements and a plurality of second insulating elements are arranged abutting each other over substantially the entire area of the foundation

This allows an insulating foundation to be formed without a perimeter trench required for the edge beams. Previous insulating foundation methods where the insulation is provided under the concrete, such as taught in GB-2385071, required excavation of perimeter trenches for the beams. While Koukourou, US-4788809 does discuss a single flat excavation, it provides its insulation on top of the concrete. This is considerably more expensive than forming the insulating layer under the concrete from the same elements that define the thickness of the foundation as in the present invention.

This also allows the connectors to be omitted in some embodiments because the first and insulating elements cover the entire area, resisting floating and relative movement during pouring of the concrete, including fibre-reinforced concrete because they abut each other.

The use of insulating elements of different heights enables structural features such as beams to be defined by placement of second insulating elements and the remainder of the foundation to be defined by placement of first insulating elements.

For example, the plurality of first insulating elements and the plurality of second insulating elements may be arranged such that the second insulating elements are positioned in higher load bearing areas of the foundation than the first insulated elements. Here, "load bearing areas" are used to refer to areas of the foundation which are used to transfer the

superstructure loads through to the substructure below. For example, where there are high load bearing walls. In traditional foundations, these load bearing elements are dealt with by digging through various soil found on site until a relatively high load bearing strata is found.

The plurality of first insulating elements and the plurality of second insulating elements may be arranged such that only second insulating elements are at the perimeter of the foundation, or where load bearing elements, such as walls, are to be formed on the foundation. The lower height of the second insulating element will then allow an edge beam or an internal beam to be defined when the concrete is poured without requiring excavation of a trench.

At least some of the plurality of first insulating elements may be arranged such that they abut another first insulating element. This allows forming a contiguous upper surface of substantially constant height (equal to the first height). Compared to prior art waffle-slab foundation systems, such as Koukourou and GB-2385071, this reduces the number of ribs within the foundation. In order to compensate, the depth to which concrete extends above the insulating element may be increased, for example, it may extend at least 150mm above the upper surface of the first insulating element. Although the depth of the slab can be increased with the method of GB-2385071, the interlocking flanges require a rib to be formed between each block. Depending on the application, a rib may not be required between each block and would only increase the amount of concrete required and therefore the cost and time to create the foundation. The method of this aspect can therefore be used more flexibly to form a greater variety of foundations whilst minimising concrete usage.

The pouring fibre-reinforced concrete within shuttering may comprise:

pouring fibre-reinforced concrete within the shuttering to a depth less than the height of the plurality of first insulating elements;

removing the shuttering and providing further shuttering defining an inner perimeter within the outer perimeter; and

pouring fibre-reinforced concrete within the further shuttering to a depth greater than the height of the plurality of first insulating elements.

This allows formation of a foundation with an edge beam containing a step. The outer course of bricks or building elements may then be located below ground level in the finished foundation, providing an improved cosmetic appearance and a resistance to surface ground water penetrating under the foundation.

The method may further comprise laying a damp proof membrane on the prepared area before arranging the plurality of first and second insulating elements. This is particularly simple in the case where the entire surface of the foundation is level, not requiring additional trenches.

In another aspect of the invention, there is provided a building foundation comprising: an insulating layer with a substantially flat lower surface extending over substantially the entire area of the foundation; and a fibre-reinforced concrete layer above the insulating layer. Unlike the systems of the prior art, the insulating layer is contained under the concrete layer and has a flat lower surface. This is unlike the foundations taught in GB- 2385071 which include a step in the lower surface of the insulating layer to provide for the formation of edge beams.

Preferably, the insulating layer comprises at least a plurality of first insulating elements and a plurality of second insulating elements, wherein the first insulating elements have a first height and the second insulating elements have a second height which is less than the first height.

The plurality of first insulating elements and the plurality of second insulating elements may be arranged such that the second insulating elements are positioned in higher load bearing areas of the foundation than the first insulated elements.

The plurality of first insulating elements and the plurality of second insulating elements may be arranged such that only second insulating elements are adjacent the perimeter of the foundation. The plurality of first insulating elements and the plurality of second insulating elements may also be arranged so that only second insulating elements are located in positions where load-bearing elements, such as walls, will be formed on the foundation. Second insulating elements may also be arranged to provide stiffening ribs in areas of the foundation other than where load-bearing elements will be located.

In one embodiment, at least some of the plurality of first insulating elements are positioned directly adjacent another first insulating element, thereby forming a continuous upper surface of substantially constant height to the insulating layer. The foundation may further comprise a damp proof membrane and/or a gas barrier membrane under the insulating layer. Preferably the damp proof membrane or gas barrier membrane is directly below the insulating layer. If the foundation also comprises filling material below the insulating later, the damp proof membrane or gas barrier membrane is preferably between the filling material and the insulating layer.

Another aspect of the invention provides a system for forming a building foundation, the system comprises: a plurality of first insulating elements having a first height; a plurality of second insulating elements having a second height, which is less than the first height; and a plurality of connectors for connecting the plurality of first insulating elements and the plurality of second insulating elements. The connectors may include connectors comprising a base from which a first barbed portion and a second barbed portion extend in the same direction. Such connectors are particularly suitable for use when the insulating elements are formed from a relatively soft material, such as expanded polystyrene. In that case, the connectors may simply be pressed across the join between abutting insulating elements. The barbs engage the insulating material to prevent the connector being removed and the blocks are held together to minimise movement during pour of concrete.

In another aspect, the present invention provides a spacer which includes a receptacle for receiving part of an insulating block and configured to hold the insulating block in place, such that it is held down and does not tend to float when steel fibre reinforced concrete is used.

According to a first aspect of the present invention, there is provided a spacer for use in forming a building foundation, the spacer comprising at least two receptacles for receiving part of respective insulating blocks and for maintaining the respective insulating blocks at a predetermined separation; wherein each of the at least two receptacles comprises insulating block retaining means for engaging an insulating block and retaining the insulating block within the receptacle. The retaining means prevents the blocks from floating when steel fibre reinforced concrete is poured. The use of spacers with the receptacles means that plain insulating blocks can be used without the need to manufacture features such as flanges into the edge of the blocks. The spacer can be manufactured cheaply from, for example, a plastics material, and is not required to have insulating properties. By using the spacer of the invention to interlock insulating blocks, a foundation can be formed using metal fibre reinforced concrete at cheaper cost than the prior art methods and blocks such as are proposed in GB-2385071. In one advantageous embodiment, the insulating block retaining means comprises a projection within the receptacle for engaging the surface of an insulating block.

Depending on the material of the insulating block, the projection may bear upon the surface of the block and hold it in place by friction, or it may partially "bite" into the surface creating an indentation. Typically, the insulating block will be formed of a relatively soft material that will be compressible so the projection may indent the surface of the insulating block. Preferably, the projection has a shape adapted to provide a greater resistance to the removal of an insulating block from the receptacle than to the insertion of an insulating block into the receptacle. For example, the projection may have an upper surface that defines an acute angle with the surface of an insulating block as it is inserted, reducing resistance to the insertion motion, and a corresponding surface forming an angle 90° or greater to the surface of the insulating block when it tries to move in an upward or removal direction. For example, the projection may have a generally triangular cross-section.

The spacer may further comprise insulating strip retaining means for retaining insulating strips between the insulating blocks. The gap between the insulating blocks can form a thermal path through the foundation. If this thermal path is sufficient to reduce the overall insulation performance of the foundation below acceptable limits, insulating strips can be provided between the blocks. The insulating strips fill in the space and, in combination with the insulating blocks, provide a continuous layer between the foundation and the ground. In order to preserve the overall "waffle slab" foundation, and provide space for the concrete to fill in between the insulating blocks, the insulating strips are thinner than the insulating blocks.

The insulating strips occupy a space at the bottom of the foundation and typically will be covered by the concrete soon after pouring. They will therefore tend not to float up because the concrete pour is directly on top of them. However, in some embodiments the spacer may further comprise insulating strip retaining means for retaining insulating strips between the insulating blocks. In one embodiment this is a ridge for engaging the surface of an insulating strip. The insulating strips can be retained in place by a ridge because their thinner depth than the insulating blocks means that they are likely to be less tall than the receptacle, unlike the insulating blocks. The ridge may extend from a surface of the receptacle which does not engage an insulating block in use. For example, the ridge may be formed on a surface of the receptacle adjacent the space between blocks.

The spacer may comprise four receptacles, each arranged to receive a corner of a respective insulating block such that, in use, the insulating blocks are spaced in a grid layout. This enables a single design of spacer to accommodate many different footprints of foundation by the use of the grid layout.

In another aspect of the invention, there is provided a system for forming a building foundation, the system comprising a plurality of spacers as defined above and a plurality of insulating blocks. The insulating blocks may be formed from any suitable insulating material. For example, they may be formed from expanded polystyrene (EPS) insulation.

Preferably the system also includes a plurality of insulating strips. The insulating strips are thinner than the insulating blocks. Low lambda EPS is suitable for the insulating strips but needs to accommodate significant creep and compression resistance. Such a system makes more efficient use of high performance insulation. It is quicker to assemble prior to pouring the concrete. The system is also cheaper to manufacture because the insulating blocks and optional insulating strips can be manufactured without any special surface features like flanges. In another aspect of the invention, there is provided a method for forming a building foundation comprising: excavating the ground where the foundation is to be formed; providing shuttering around the perimeter of the foundation; providing a spacer; inserting an insulating block into a receptacle on the spacer such that the insulating block is retained in the receptacle; providing further spacers and inserting further insulating blocks to form a rectangular matrix of blocks, separated by the spacers, within the shuttering; and pouring fibre-reinforced concrete into the shuttering. Optionally, if the foundation is required to be more insulating, the method may further comprise inserting insulating strips into the spaces between the insulating blocks before pouring concrete into the shuttering.

According to another aspect of the invention, there is provided a connector for fixing a strip of edge beam insulation to an insulating block when forming a building foundation, wherein the connector comprises:

a base having a generally flat surface;

a connection member extending from the generally flat surface and generally perpendicular to the generally flat surface, wherein the connection member comprises a first surface having means for engaging a strip of edge beam insulation and a second surface having means for engaging an insulating block such that the strip of edge beam insulation is fixed to the insulating block.

The term "edge beam insulation" is used to refer to insulation that is provided at the edge or perimeter of a building foundation. The connector of this aspect of the invention allows the edge beam insulation to be positively connected to the insulating block, reducing the risk of the insulating block floating during the first concrete pour.

The means for engaging an insulating block preferably comprises a projection for engaging the surface of an insulating block, for example the projection may have the properties discussed above for the retaining means of the spacer, such as a triangular shape.

Alternatively, the projection may simply be a sharp edge that engages the insulating block to hold it in place. The means for engaging a strip of edge beam insulation preferably comprises a ridge which is generally parallel to the flat surface of the base. In use, the ridge can engage the upper surface of the edge beam insulation to hold it in place. Alternative embodiments may use other means to engage the strip of edge beam insulation, for example a projection that engages the side of the edge beam insulation.

A plurality of such connectors may form part of a system for forming a building foundation together with a plurality of insulating blocks and a plurality of strips of edge beam insulation. Such a system allows simpler formation of a foundation because the insulating blocks can be connected to the edge beam insulation and are less likely to float when concrete is first poured. According to another aspect of the invention, there is provided a method for forming a building foundation, the method comprising:

excavating the ground where the foundation is to be formed;

providing shuttering around a perimeter of the foundation;

providing edge beam insulation around at least a part of the perimeter of the foundation;

providing a connector as described above;

connecting an insulating block to the edge beam insulation using the connector; providing further insulating blocks to form a rectangular matrix of blocks, within the shuttering; and

pouring fibre-reinforced concrete into the shuttering.

The fibre-reinforced concrete may be steel fibre reinforced concrete, or reinforced with fibres other than steel, for example metal, glass, synthetic or natural fibres. Although it is useful to connect an insulating block to the edge beam insulation using the connector described above, this requires a deeper foundation because the bottom of the insulating block is level with the bottom surface of the edge beam insulation rather than the top surface. This can increase the cost because more excavation is required and the insulating blocks are all required to be thicker.

Accordingly, another aspect of the invention provides an insulating block for use in forming a building foundation, the insulating block having a cross section that reduces in depth across the insulating block, such that one side of the block has a first depth of insulation and an opposite side of the block has a second depth of insulation and wherein the first depth is greater than the second depth. In one embodiment, the insulating block has a stepped cross section but other cross sections, including a slanted or curved lower surface of the block, may also be used. An insulating block of this aspect can be used at the edge or perimeter of the foundation. The greater depth side is positioned adjacent the edge beam insulation and may also be connected to it. The reducing cross section means that the depth of the block then reduces away from the edge beam insulation, so a deeper excavation is only required at the perimeter. A further advantage is that the insulating block with reducing cross section provides increased insulation at the perimeter of a foundation, which is the area of greatest heat loss. A plurality of insulating blocks can form a system for forming a building foundation. Preferably, the system further comprises a second plurality of insulating blocks without a stepped profile and having a depth substantially the same as the second depth of the first plurality of insulating blocks. Thus, the remainder of the foundation can be formed a lesser depth than the perimeter but the upper surface of all the insulating blocks are at the same level.

According to another aspect of the invention, there is provided a method for forming a building foundation, the method comprising:

excavating the ground where the foundation is to be formed;

providing shuttering around a perimeter of the foundation;

providing a first plurality of insulating blocks as described above, within the shuttering, arranged adjacent to the perimeter and aligned such that the first depth of insulation faces the perimeter;

providing a second plurality of insulating blocks inside the area defined by the first plurality of insulating blocks to form a rectangular matrix of blocks; and

pouring fibre-reinforced concrete into the shuttering

Preferably, the second plurality of insulating blocks have a depth substantially the same as the second depth of the first plurality of insulating blocks.

In another aspect of the present invention, a building foundation is provided comprising any of the systems as described above, with or without the optional features also described, and fibre-reinforced concrete. Although the present invention is particularly suited for use with steel fibre reinforced concrete, it can also be used with any other form of fibre- reinforced concrete, such as glass, synthetic or natural fibre-reinforced concrete. In another aspect of the invention, a building comprising such a building foundation is provided. The cost savings provided by the various aspects of the present invention enable high quality foundations, and hence buildings, to be manufactured more quickly and at less expense than existing methods. Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Figure 2 is a diagrammatic representation of a cross-section of a foundation formed according to an embodiment of the present invention;

Figure 3 a is a plan view of a diagrammatic representation of a system of insulating blocks and connectors for forming a building foundation according to an embodiment of the present invention;

Figure 3b is a diagrammatic representation depicting the different heights of insulating elements used in the foundation of Figure 3 a.

Figure 4 is an embodiment of a connector for use with the foundation of Figure 3 a;

Figure 5 is another embodiment of a connector for use with the foundation of Figure 3 a; Figure 6 depicts a diagrammatic representation of a further connector for use with the foundation of Figure 3 a.

Figure 7 is a diagrammatic representation of a top isometric view of a spacer according to an embodiment of the present invention;

Figure 8 is a diagrammatic representation depicting one possible configuration of a projection used in retaining means in an embodiment of the invention;

Figure 9 depicts an isometric view of an insulating block and insulating strips together with spacers according to embodiments of the invention;

Figure 10 is a diagrammatic representation depicting a plan view of a system of insulating blocks, strips and spacers according to the present invention; Figure 11 is a diagrammatic representation of an isometric view of a system of insulating blocks, spacers and strips according to an embodiment of the present invention;

Figure 12 is a diagrammatic representation of a 3D view of a connector according to another embodiment of the present invention;

Figure 13 is a diagrammatic representation of an end view of the connector of Figure 12; Figure 14 is a diagrammatic representation of an end view of the connector Figure 12 connecting a strip of edge beam insulation and an insulating block;

Figure 15 is a diagrammatic representation of a 3D view of an insulating block according to another embodiment of the invention; and

Figure 16 is a diagrammatic representation of a cross section of a foundation according to another embodiment of the present invention.

Figure 2 depicts a diagrammatic representation of a cross-section of a building foundation according to an embodiment of the present invention. In this embodiment, a prepared area is formed by excavating the area of the foundation and filling the excavation with aggregate 100. The aggregate 100 is compacted to provide a level surface for the rest of the foundation and is about 125 mm thick, although other thicknesses may be used in alternative embodiments. On top of the layer of aggregate 100, first insulating elements 102 and second insulating elements 104 are laid. First insulating elements 102 and second insulating elements 104 are both cuboidal in shape. The first insulating elements 102 have a height of

approximately 350mm and the second insulating elements 104 have a height of approximately 100mm. In other embodiments the first insulating elements 102 may have a height of approximately 400mm. Second insulating elements 104 are placed in areas of the foundation in which ribs or beams are required to be formed. For example, edge beam 106 is formed above a second insulating element 104 and interior beam 108 is formed above another second insulating element 104. The dimensions of the first insulating element 102 are generally approximately 1200mm width x 1200mm length x 350mm height. Other dimensions may also be used, depending on the dimensions of the foundation which is to be formed. Second insulating elements 104 tend to be more elongated than first insulating elements 102. For example, they may have a length of about 1200 mm and a width of about 600mm, or smaller if the second insulating element 104 is defining a rib within the foundation rather than a beam. Both first and second insulating elements 102, 104 are both preferably constructed from expanded polystyrene (EPS) with minimum properties as given in table 1 below. In other, embodiments, the insulating elements are formed from a material with one or more of the minimum properties given in table 1 below, where the insulation is load bearing.

Table 1 - minimum properties of insulation

As can be seen in Figure 2, the edge beam 106 comprises a step enabling a first course of bricks 110 to be laid at a level below the ground level in filled after the foundation has been formed. Interior bricks or building elements 114 are contained at a higher level. This stepped construction is formed by initially providing shuttering around the entire area of the foundation, directly adjacent the perimeter insulating elements 104. Concrete is then poured to a first depth, for example 225mm. The first pour of concrete may be to a lower level than the upper surface of the first insulating elements 102. Once the concrete has set, the shuttering can be removed and a second stage of shuttering formed on the concrete within the perimeter of the foundation. This shuttering defines the step in the edge beam 106. Concrete is then poured into the foundation to the final level of the finished foundation. For example a further 225mm depth of concrete may be poured, giving a total concrete depth for the highest point of the edge beam of 450mm. The concrete preferably extends at least 150mm above the upper surface of the first insulating elements 102 in order to ensure that the floor has sufficient strength. As depicted in Figure 2, fibre reinforced concrete, preferably steel fibre reinforced concrete is used. This does not require a network of reinforcing rods. In prior art systems, there will be a tendency for insulating blocks to float during pouring of fibre reinforced concrete. In the present embodiment, this tendency to float is avoided by ensuring that the insulating elements are tightly abutting each other and connecting each insulating element to an adjacent insulating element. This system of connection is depicted in diagrammatic form in Figure 3 a. Figure 3 a shows a plan view of first and second insulating elements 102, 104. Connectors 116 are shown diagrammatically as short lines to illustrate their positions. Thus, as can be seen in Figure 3 a, the entire area of the foundation is covered by abutting insulating elements connected to each other.

The abutting nature of the insulating elements minimises the likelihood of the concrete being able to force its way between insulating elements and underneath them, causing them to float. This is further prevented by the presence of connectors 116 holding the elements together. Furthermore, during initial pouring, the different heights of the insulating elements means that lateral forces will be exerted by the concrete on the higher, first insulating elements. Again, the connection between the insulating elements resists this lateral force. Thus, in a foundation according to this embodiment, the foundation may be formed quickly and simply without requiring a network of reinforcing rods. Furthermore, because the first and second insulating elements 102, 104 are formed from plain cuboid blocks of insulating material, they can be transported and manufactured easily. Should a block not be the right size, it can easily be cut down on site. This is not the case with prior art systems which relied on systems of interlocking flanges. The transport and

manufacture of blocks with interlocking flanges is more expensive than the plain blocks of this embodiment and they cannot be cut down easily to accommodate different forms of foundation. Figure 3b depicts in diagrammatic form the different height regions of the foundation of Figure 3a. Region 118 is made up of second insulating elements and is at a lower level than regions 120 made up of first insulating elements. This demonstrates how the region 118 of lower height corresponding to second insulating elements extends around the entire perimeter of the foundation allowing easy formation of an edge beam without requiring a perimeter trench.

Examples of connectors for use with this embodiment are depicted in Figures 4, 5 and 6. Connector 122 in Figure 4 has a general U shape. The U shape terminates in pointed ends 124 with barbs 126. Pointed tip 124 facilitates insertion of the connector simply by pressing it into a soft material from which the insulating blocks are formed, for example expanded polystyrene. The barbs 126 prevent removal of the connector from the blocks once it has been inserted. The connectors can simply be inserted by pressing them across the interface between blocks. Preferably, the connector is formed from a material such as steel or other metal, although plastics and composites may be used in other embodiments.

Figure 5 depicts an alternative embodiment of connector 128. This has a square or rectangular shape with angled corners rather than the more rounded U shape of the embodiment of Figure 4.

Figure 6 depicts an embodiment of a connector 130 for use between different levels of insulating elements, for example at the interface between a first insulating element 102 and a second insulating element 106. It contains a right-angled portion 132 extending between pointed ends 134. The right-angled portion is positioned at a 45° angle to arms 136 carrying the pointed ends 134. In use, the right-angled portion 132 abuts the right angle formed between the interface of blocks of different heights, as depicted in Figure 6a.

Thus, the system of insulating elements of this embodiment enables an insulating foundation to be formed from fibre reinforced concrete without requiring preparation of trenches. Furthermore, because insulating blocks are plain, there is far more freedom in the design of insulating foundations than prior art waffle slab foundations. Figure 7 is a diagrammatic representation of a top isometric view of a spacer according to the present invention. In this embodiment, the spacer comprises a base 2 and four receptacles 4 extending from the base 2. The base 2 is substantially planar and the receptacles 4 extend substantially perpendicular to the plane defined by the base 2. Each of the receptacles comprises two walls positioned generally perpendicular to each other. The combination of two walls and the portion of base 2 between the two walls define a receptacle for receiving a corner portion of a cuboid or cube insulating block.

Each receptacle includes retaining means 6 for retaining an insulating block within the receptacle. Due to the nature of the top isometric projection depicted in Figure 1, the nature of the retaining means 6 cannot be seen in detail.

Figure 8 depicts a closeup isometric view with a diagrammatic representation of one possible form of retaining means 6. The retaining means 6 comprises a projection 8 that extends from one of the walls from the receptacle 4 to engage an insulating block. The projection 8 has a generally triangular cross section. This defines an upper surface 10 and a lower surface 12. In use, when an insulating block is inserted into the receptacle it will move against the upper surface 10. This forms an acute angle when a block is inserted, minimising the resistance to the insertion. Lower surface 12 forms an angle of 90° in this embodiment with the surface of the insulating block, helping to resist its removal. The insulating block will be further secured within the receptacle by the projection if the insulating block is manufactured from a compressible material. In that case the projection 8 can indent the surface of the block, further improving its retention within the receptacle. In use, the spacer of Figure 7 is combined with a system of insulating blocks 14 and insulating strips 16. A closeup of a single insulating block 14 is depicted in diagrammatic form in Figure 9. This shows how the block is retained in receptacles at its lower corner portions. The gaps between adjacent insulating blocks are filled with insulating strips 16. Figure 10 is a diagrammatic representation of a plan view of a system of spacers and insulating strips according to one embodiment. In this diagrammatic representation, the position of the receptacles 4 has been exaggerated so that they can clearly be seen and the insulating blocks are not shown. Figure 10 illustrates how the gaps between blocks can be filled with insulating strips 16. Typically long insulating strips will be used along adjacent rows and shorter insulating strips will fill in the gaps between these longer strips. In use, the receptacle 4 is preferably as thin as possible so that the insulating strips 16 and insulating blocks 14 are as close together as possible to minimise the chance of providing a thermal path through the insulation to the ground.

Figure 11 depicts an isometric view of a plurality of blocks, spacers and strips assembled into a grid layout. This shows how the strips 16 filled space between the blocks 14.

Typically the insulating blocks will have dimensions of 1050mm length by 1050mm width by 350mm height. The strips will typically have a thickness of 50mm and a width to fill the gap between the insulating blocks of approximately 150mm. Therefore, typically the spacers will define a separation of 150mm between the insulating blocks.

In this embodiment the insulating blocks and insulating strips are formed of EPS insulation with properties as discussed above for the embodiment of Figure 2.

The spacer may be formed of any convenient material, for example a plastics material or a metal or metal alloy. A plastics material is preferred because it has low manufacturing costs.

To use the spacer and system of the present invention the area for the foundation is first excavated with a level bottom. The perimeter is surrounded by shuttering. The spacers and blocks are then inserted in a grid layout filling the area for the foundation, with the blocks being clipped into the retaining means in the receptacles. Insulating strips can then be laid between the blocks to provide a complete insulating layer between the foundation and the ground. Steel fibre reinforced concrete can then be poured directly onto the assembled system and the retention of the blocks in the spacers means that there is no difficulty with blocks floating during the pour. Alternatively, conventional reinforcing rods and concrete can also be used. In alternate embodiments the spacer may be provided with insulating strip retaining means. For example in one embodiment this could be a ridge extending from a side of the receptacle which engages the strip. In less preferred embodiments, the system may be used with insulating blocks without the insulating strips. This reduces the thermal performance but may be suitable for use in countries where building regulations do not require as strict insulating in the floor. It also enables the foundation to be provided more cheaply because the more expensive insulation for use with the insulating strips need not be provided. This embodiment still has the advantage of quick assembly and reduced cost to manufacture a foundation due to its suitability for use with metal fibre reinforced concrete.

In other embodiments the spacer may have different forms, providing that the receptacle is provided. For example, the spacer may not have a base and instead comprise receptacles separated by struts.

Figure 12 depicts a diagrammatic representation of a 3D view of a connector 20 according to another embodiment of the present invention. Figure 13 depicts an end view of the connector 20. The connector 20 comprises a base 22 which is substantially flat. A connector member 24 extends from the base 22 in a perpendicular direction.

Disposed on the connector member 24 are means to engage edge beam insulation on one side and an insulating block on the other. To engage an insulating block, projections 26 extend from one side. In this embodiment the projections have a triangular profile which is positioned resist upward movement of the insulating block, away from the base 22. In other embodiments the projections may have different profiles, such as a sharp spike which indents the insulating block. Although this embodiment includes three projections 26, other embodiments may include a different number of projections or the projection may extend the entire length of the connector member 24.

On the opposite side of the connector member 24 to the projection 26 is a ridge 28 which extends along the length of the connector member 24. This ridge 28 engages the top of a strip of edge beam insulation to hold it in place. In alternate embodiments other means of engaging the edge beam insulation may for be used, for example the ridge need not extend along the entire length, or one or more projections similar to projections 26 may be provided.

Figure 14 is a diagrammatic representation of an end view of the connector 20 of Figure 12 connecting a strip of edge beam insulation 30 and an insulating block 32. A lower surface of the edge beam insulation 30 and the insulating block 32 rest upon the base 22 of the connector 20 at opposite sides of the connector member 24. The edge beam insulation 30 is retained by ridge 28 and the insulating block 32 is retained by the projection 26. Thus, the edge beam insulation 30 and the insulating block 32 are connected and any tendency of the insulating block to float during pouring of the concrete is reduced.

The insulating block 32 is around 350mm high and formed from EPS insulation. The edge beam insulation 30 is around 100mm high and also formed from EPS insulation. The minimum properties for the insulation are as discussed above for the embodiment of Figure 2.

The connector 20 may be formed of any convenient material, for example a plastics material or a metal or metal alloy. A plastics material is preferred because it has low manufacturing costs.

Figure 15 depicts a diagrammatic representation of a 3D view of an insulating block 40 according to another embodiment of the invention. In this embodiment the insulating block 40 has a depth that reduces across its cross section. As can be seen in Figure 15 the depth 42 of insulating block 40 at one side is greater than the depth 44 at an opposite side. In this embodiment depth 42 is around 450mm and depth 44 is around 350mm.

As can be seen clearly in Figure 15, the insulating block 40 has a stepped profile. A first part 46 of a lower surface is a greater distance from the upper surface than a second part 48 of the lower surface, measured in a direction perpendicular to the upper surface. The insulating block 40 is formed from EPS insulation with properties as discussed above for the embodiment of Figure 2.

Figure 16 is a diagrammatic representation of an edge part of a cross section of a foundation according to another embodiment of the present invention. The foundation comprises a lower layer of aggregate 50. At a perimeter of the foundation a strip of edge beam insulation 52 which is 100mm thick is laid on top of aggregate 50. The aggregate extends to a depth of 125mm below the edge beam insulation 52. A connector 54, such as described above with reference to Figure 12, connects the edge beam insulation 52 to an insulating block 56 with a reducing cross section, such as described above with reference to Figure 15. A spacer 58, such as described above with reference to Figure 1, connects the insulating block 56 to anther insulating block 60, which does not have a reducing cross section. An insulating strip 62 is provided between insulating block 56 and insulating block 60. Aggregate extends to a depth of 125mm below insulating block 60. This means that the foundation under insulating block 60, away from the perimeter of the foundation, does not have to excavated to as great a depth.

At the perimeter, first shuttering 64 defines the level of the first concrete pour, after which second shuttering 66 is assembled and a second pour made.

This embodiment allows greater thickness of insulation at the perimeter. It also ensures that the various components are connected to reduce the risk of them floating during the concrete pour.

Claims

1. A method of forming a building foundation, the method comprising:

preparing an area of the foundation to substantially the same level;

providing shuttering around the outer perimeter of the foundation;

pouring fibre-reinforced concrete within the shuttering.

2. A method according to claim 1, wherein:

in the preparing substantially the whole area of the foundation is prepared to the substantially the same level; and

in the arranging the at least a plurality of first insulating elements and a plurality of second insulating elements are arranged abutting each other over substantially the entire area of the foundation.

3. A method according to any one of the preceding claims, wherein the plurality of first insulating elements and the plurality of second insulating elements are arranged such that the second insulating elements are positioned in higher load bearing areas of the foundation.

4. A method according to any one of the preceding claims, wherein the plurality of first insulating elements and the plurality of second insulating elements are arranged such that only second insulating elements are at the perimeter of the foundation or where load bearing elements are to be formed on the foundation.

5. A method according to any one of the preceding claims, wherein at least some of the plurality of first insulating elements are arranged such that they abut another first insulating element.

6. A method according to any one of the preceding claims, wherein the pouring fibre-reinforced concrete within the shuttering comprises:

removing the shuttering and providing further shuttering defining an inner perimeter within the outer perimeter;

7. A method according to any one of the preceding claims, further comprising laying a damp proof membrane on the prepared area before arranging the plurality of first and second insulating elements.

8. A building foundation comprising:

an insulating layer with a substantially flat lower surface extending over substantially the entire area of the foundation; and

a fibre-reinforced concrete layer above the insulating layer.

9. A building foundation according to claim 8, wherein the insulating layer comprises at least a plurality of first insulating elements and a plurality of second insulating elements, wherein the first insulating elements have a first height and the second insulating elements have a second height which is less than the first height.

10. A building foundation according to claim 9, wherein the plurality of first insulating elements and the plurality of second insulating elements are arranged such that the second insulating elements are positioned in higher load bearing areas of the foundation.

11. A building foundation according to claim 8, 9 or 10, wherein the plurality of first insulating elements and the plurality of second insulating elements are arranged such that only second insulating elements are adjacent the perimeter of the foundation.

12. A building foundation according to any one of claims 8 to 11, wherein at least some of the plurality of first insulating elements are positioned directly adjacent another first insulating element, thereby forming a contiguous upper surface of substantially constant height.

13. A building foundation according to any one of claims 8 to 12, further comprising a damp proof membrane and/or gas barrier membrane under the insulating layer.

14. A system for forming a building foundation, the system comprising:

a plurality of first insulating elements having a first height;

a plurality of second insulating elements having a second height, which is less than the first height; and

a plurality of connectors for connecting the plurality of first insulating elements and the plurality of second insulating elements.

15. A system according to claim 14, wherein the plurality of connectors include connectors comprises a base from which a first barbed portion and a second barbed portion extend in the same direction.

16. A spacer for use in forming a building foundation, the spacer comprising:

at least two receptacles for receiving part of respective insulating blocks and for maintaining the respective insulating blocks at a predetermined separation;

wherein each of the at least two receptacles comprises insulating block retaining means for engaging an insulating block and retaining the insulating block within the receptacle.

17. A spacer according to claim 16, wherein the insulating block retaining means comprises a projection within the receptacle for engaging the surface of an insulating block.

18. A spacer according to claim 17, wherein the projection has a shape adapted to provide a greater resistance to the removal of an insulating block from the receptacle than to the insertion of an insulating block into the receptacle.

19. A spacer according to claim 17 or 18, wherein the projection has a generally triangular cross section.

20. A spacer according to any one of claims 16 to 19, further comprising insulating strip retaining means for retaining insulating strips between the insulating blocks.

21. A spacer according to claim 20, wherein the insulating strip retaining means comprises a ridge for engaging a surface of an insulating strip.

22. A spacer according to any one of claims 16 to 21 , wherein the spacer comprises four receptacles, each arranged to receive a corner of a respective insulating block such that, in use, the insulating blocks are spaced in a grid layout.

23. A system for forming a building foundation, the system comprising:

a plurality of spacers according to any one of claims 16 to 22; and

a plurality of insulating blocks.

24. A system according to claim 23, further comprising a plurality of insulating strips.

25. A method for forming a building foundation, the method comprising:

excavating the ground where the foundation is to be formed;

providing shuttering around the perimeter of the foundation;

providing a spacer according to any one of claims 16 to 22; inserting an insulating block into a receptacle on the spacer such that the insulating block is retained in the receptacle;

providing further spacers and inserting further insulating blocks to form a rectangular matrix of blocks, separated by the spacers, within the shuttering; and

pouring fibre-reinforced concrete into the shuttering.

26. A method according to claim 25, further comprising inserting insulating strips into the spaces between the insulating blocks before pouring fibre-reinforced concrete into the shuttering.

27. A connector for fixing a strip of edge beam insulation to an insulating block when forming a building foundation, wherein the connector comprises:

a base having a generally flat surface;

28. A connector according to claim 27, wherein the means for engaging an insulating block comprises a projection for engaging the surface of an insulating block.

29. A connector according to claim 27 or 28, wherein the means for engaging a strip of edge beam insulation comprises a ridge which is generally parallel to the flat surface of the base.

30. A system for forming a building foundation, the system comprising:

a plurality of connectors according to any one of claims 27, 28 or 29;

a plurality of insulating blocks; and

a plurality of strips of edge beam insulation.

31. A method for forming a building foundation, the method comprising: excavating the ground where the foundation is to be formed;

providing shuttering around a perimeter of the foundation;

providing a connector according to any one of claims 27, 28 or 29;

pouring fibre-reinforced concrete into the shuttering.

32. An insulating block for use in forming a building foundation, the insulating block having a cross section that reduces in depth across the insulating block, such that one side of the block has a first depth of insulation and an opposite side of the block has a second depth of insulation and wherein the first depth is greater than the second depth.

33. An insulating block according to claim 32, wherein the insulating block has a stepped cross section.

34. A system for forming a building foundation comprising a first plurality of insulating blocks according to claim 32 or 33.

35. A system according to claim 34, further comprising a second plurality of insulating blocks without a stepped profile and having a depth substantially the same as the second depth of the first plurality of insulating blocks.

36. A method for forming a building foundation, the method comprising:

excavating the ground where the foundation is to be formed;

providing shuttering around a perimeter of the foundation;

providing a first plurality of insulating blocks according to claim 32 or 33, within the shuttering, arranged adjacent to the perimeter and aligned such that the first depth of insulation faces the perimeter; providing a second plurality of insulating blocks inside the area defined by the first plurality of insulating blocks to form a rectangular matrix of blocks; and

pouring fibre-reinforced concrete into the shuttering

37. A method according to claim 36, wherein the second plurality of insulating blocks have a depth substantially the same as the second depth of the first plurality of insulating blocks.

38. A foundation comprising a system according to claim 23, 24, 30, 34 or 35 and fibre-reinforced concrete .

39. A building comprising a foundation according to any one of claims 8 to 13 and 38.