GB2429719A

GB2429719A - Acoustic isolator for a party wall

Info

Publication number: GB2429719A
Application number: GB0615387A
Authority: GB
Inventors: David Bignell; Richard Parrett; R Sean Smith; John B Wood; Paul Flynn
Original assignee: Icopal Ltd
Current assignee: Icopal Ltd
Priority date: 2005-09-01
Filing date: 2006-08-03
Publication date: 2007-03-07
Anticipated expiration: 2026-08-03
Also published as: IE20060618A1; GB2429719B; GB0615387D0; GB0517784D0

Abstract

The invention relates to a party wall 10 and comprises first and second skins 12, 14 and a cavity 16 between the skins; an acoustic isolator 22; and a fixing means that fixes the acoustic isolator 22 to the inner surface of at least one of the first and second skins 12, 14. The acoustic isolator 22 typically comprises acoustic insulating material, and prevents any mortar droppings that fall into the cavity from mechanically bridging the cavity between the first and the second skins 12, 14. A method of building a cavity wall and a wall tie are also described.

Description

"Acoustic Isolator for a Party Walr The invention relates to an acoustic

isolator for a party wall. The invention also relates to a method of building a party wall. The invention also relates to a wall tie.

A party wall is a wall that is built on the boundary line of adjoining properties and is shared by both owners. Typically, at least one side of the wall is used as a dwelling room for residential purposes, for example, a hotel, a block of flats, an apartment adjoining an office or retail outlet.

Party walls that separate one or more rooms for residential purposes are required to perform acoustically to a standard set down by the relevant building regulations in force.

A party wall typically comprises two work skins, made of masonry (e.g. bricks or blocks) and a cavity therebetween. As the wall is being built, the - base of the cavity collects mortar droppings which fall out of the joints as the wall is being constructed. The term umortar droppings" includes mortar trash and any other construction materials that fall into the cavity.

The mortar droppings build up at the base of the cavity and connect/mechanically bridge the two skins of the wall. This impairs the acoustic performance of the wall.

A damp-proof/gas protection membrane 20 (see Fig 1) is commonly used when building on brownfield sites/contaminated land. The damp-proof membrane 20 performs the dual functions of preventing damp from rising through the masonry and stopping methane and radon gas entering the building. The damp-proof membrane 20 is typically located above 6 inches (around 150mm) above ground level where it spans the cavity between the skins. Where a damp-proof membrane is used, this makes the problem of mechanical connection of the skins even more likely to occur, as the damp-proof membrane 20 prevents the mortar droppings from falling into the foundations and causes them to build up from a base that is already above ground level.

A conventional wall tie is made of metal and is used to mechanically connect two wall skins together, to add strength to a wall.

According to a first aspect of the present invention there is provided a party wall comprising: first and second skins and a cavity therebetween; an acoustic isolator; and a fixing means that fixes the acoustic isolator to the inner surface of at least one of the first and the second skins.

According to a second aspect of the present invention there is provided an acoustic isolator for a party wall and a fixing means for fixing the acoustic isolator to the party wall.

The Inner" surface is defined as the surface of the skin facing the cavity.

The acoustic isolator prevents any mortar droppings that fall into the cavity from mechanically bridging the cavity between the first and the second skins.

Preferably, the acoustic isolator comprises a liner that lines the inner surface of the first and/or second skin.

Preferably, the liner is relatively thin compared to the width of the cavity.

Preferably, the acoustic isolator is resilient.

Preferably, the acoustic isolator comprises acoustic insulation material Optionally, the acoustic isolator comprises a foam.

Optionally, the acoustic isolator comprises polyethylene; optionally, a closed cell polyethylene foam.

Alternatively or additionally, the acoustic isolator could comprise one or more of the following: polyurethane, polyester, polyvinyl chloride (PVC), rubber, foam rubber, any type of fibrous material or fibrous mat, polystyrene.

Preferably, the acoustic isolator is fixed to the portion of the wall around the base of the cavity. Optionally, the wall includes a damp-proof membrane that forms the base of the cavity and the acoustic isolator is fixed to a portion of wall adjacent to the damp-proof membrane.

The term "damp-proof membrane" includes all types of damp-proof course.

It is preferable that the acoustic isolator covers substantially all of the damp-proof membrane. In such embodiments, the acoustic isolator prevents mortar droppings from directly collecting on/attaching to the damp-proof membrane.

Preferably, the acoustic isolator extends up the wall beyond the height of any pile of mortar droppings that is likely to build up in the cavity, to prevent the mortar droppings from connecting the first and second skins.

Typically, the height of any pile of mortar droppings does not exceed 100mm, so it is preferred if the acoustic isolator extends up the wall to at least this height above the base of the cavity.

Preferably, the acoustic isolator extends up the wall to a height of around 450mm above the base of the cavity. 450mm may be the height of two blockslbncks.

It should be noted that the pile of mortar droppings could in theory be any height, depending on the height of the wall being built and the skill of the builders, and the acoustic isolator could extend up the wall even further than the height given here, which is given by way of example only. In some embodiments, the acoustic isolator may even extend up the entire height of the cavity.

Optionally, the acoustic isolator comprises two or more portions, one portion being fixed to a higher portion of wall than the other. Typically the portions touch and preferably the portions overlap. Optionally, the same fixing means can fix two overlapping portions of acoustic isolator.

Typically, each portion comprises an elongate strip.

Optionally, a second end of the acoustic isolator at least partially covers the inner surtace of the other of the first and second skins. The second end may or may not be fixed to the other of the first and second skins.

Typically, the fixing means comprises a mechanical fixing. The mechanical fixing may comprise a bolt and nut, a wall tie (e.g. a compression tie), a screw, a clip, etc. Typically, the mechanical fixing compnses a wall tie according to the fourth aspect of the invention.

Optionally, the mechanical fixing comprises a head that protrudes from the outer surface of the skin. The head can be used as a depth gauge for a wall lining (e.g. a parge coat or internal render) applied to the outer surface of the wall. A parge coat is a thin coat of cement mortar that is applied to a wall for refinement or damp-proofing. The mechanical fixing is typically fixed to the wall before the wall lining is applied. By comparing the amount of protrusion of the head from the wall lining, the thickness of the wall lining can be deduced. This is useful to check whether the wall lining is of a required thickness.

Optionally, the mechanical fixing is located in one of the skins of the wall.

Optionally, the mechanical fixing extends between the inner and outer surfaces of the skin. Typically, the wall comprises masonry and the mechanical fixing is located between two layers of masonry.

Alternatively, the fixing means comprises a bonding agent, e.g. an adhesive.

Alternatively, the fixing means comprises an expanding anchor that is located within the cavity, and which provides a force against each opposing skin to hold the acoustic isolator against the surface of the first or second skin.

Typically, the wall comprises masonry, such as stones, bricks or blocks, or a combination of these. Alternatively, the wall may comprise timber. The wall may also comprise floor structure elements or sub-structure elements such as foundations.

According to a third aspect of the present invention there is provided a method of building a party wall comprising first and second skins with a cavity therebetween, the method including the step of fixing an acoustic isolator to the inner surface of at least one of the first and the second skins.

Preferably, the acoustic isolator is fixed to the inner surface of the first or second skin at the time of constructing the wall.

Preferably, the acoustic isolator is fixed to a portion of the wall around the base of the cavity.

Preferably, the method includes the step of arranging the acoustic isolator so that it covers substantially the entire base of the cavity. Optionally, the acoustic isolator is fixed (e.g. bonded or mechanically fixed) to the base of the cavity.

Typically, the base of the cavity comprises a damp-proof membrane, and the acoustic isolator is arranged to cover the damp-proof membrane.

Preferably, the acoustic isolator comprises more than one portion and the method includes the steps of adding successive portions of acoustic isolator to successively higher portions of the wall as the wall is built.

Optionally, the method includes the further step of fixing the same portion of acoustic isolator or a further portion of acoustic isolator to the inner surface of the other of the first and second skins. Alternatively, the acoustic isolator may be arranged to lie against the inner surface of the other of the first and second skins, without being fixed thereto.

The step of fixing may comprise mechanical fixing and/or bonding (e.g. adhesive bonding).

Optionally, the wall comprises layers and the method includes the step of adding a mechanical fixing between two layers of the wall and engaging the mechanical fixing with the acoustic isolator.

Optionally, the method includes the steps of laying a first layer of masonry, adding a mechanical fixing and a layer of bonding agent (e.g. mortar) to the top of the first layer of masonry, and laying a second layer of masonry on top of the mechanical fixing and the bonding agent.

Optionally, the step of engaging the mechanical fixing comprises perforating the acoustic isolator with the mechanical fixing. Alternatively, the step of engaging the mechanical fixing comprises engaging the mechanical fixing with a pre-punched hole in the acoustic isolator.

Optionally, the step of engaging the mechanical fixing includes coupling first and second components of the mechanical fixing by a ratchet mechanism that hinders or prevents any subsequent de-coupling.

Optionally, the method includes the step of using a mechanical fixing to fix the acoustic isolator to the skin such that part of the mechanical fixing projects from an outer surface of the skin, and the method includes the additional steps of applying a coating to the outer surface of the skin and using the projecting part of the mechanical fixing to check the thickness of the applied coating.

Typically, the mechanical fixing comprises a wall tie; optionally, a wall tie according to the fourth aspect of the invention.

According to a fourth aspect of the invention there is provided a wall tie for holding an object against a side of a wall, the wall tie comprising: a first abutment; a second abutment; and a retaining means for preventing or restricting movement of the first and second abutments away from each other.

Hence, an object can be held against a wall between the first and second abutments.

Typically, the wall tie is adapted to hold an acoustic isolator against a wall.

Preferably, the wall tie is acoustically resilient, i.e. it is flexible such that it reduces or eliminates transmission of impact sound. This is advantageous because, in use, if mortar droppings build up in a cavity in which such a wall tie is used, the wall tie itself will not be able to connect with these mortar droppings to form an acoustic bridge to transmit sound across the cavity and through the wall skins.

Preferably, the wall tie comprises a plastics material.

Typically, the first abutment is provided on a first component, and the second abutment is provided on a second, separate component of the wall tie.

Typically, the retaining means is adapted to couple the first and second components together.

Typically, once coupled together, the retaining means is adapted to prevent subsequent de-coupling of the first and second components.

Alternatively, the retaining means may have a release mechanism to allow subsequent de-coupling of the first and second components.

Typically, one of the first and second components is provided with an aperture to receive an elongate member of the other of the first and second components. Typically, at least a part of the retaining means is located within the aperture.

Optionally, the retaining means comprises a ratchet mechanism.

Optionally, the ratchet mechanism is adapted to allow movement of the first and second abutments towards each other but to prevent movement of the first and second abutments away from each other.

Optionally, the ratchet mechanism compnses at least one pawl and cooperating ratchet teeth.

Typically, the pawl is resilient.

Typically the first abutment has an abutting face and the ratchet teeth are aligned along an axis that is perpendicular to the abutting face.

In this way, the wall tie can be used with walls and objects of varying thicknesses.

Preferably, the wall tie compnses a projection that is adapted to project from one side of a wall. Optionally, the projection is provided by one of the first and second abutments. Typically, the projection compnses a depth gauge for a wall lining.

Optionally, the first and second abutments are adapted to project from opposite sides of a wall skin.

An embodiment of the invention will now be described, by way of example only, and with reference to the following drawings, in which:- Fig 1 shows a first embodiment of the invention where an acoustic isolator is fixed to both skins of a party wall; Fig 2 shows a second embodiment, where the acoustic isolator is fixed to only one skin of the party wall; and Fig 3 shows a third embodiment, where the acoustic isolator is fixed to a first skin of the party wall, covers the base of the cavity and extends part way up the second skin of the wall; and Fig 4 shows a perspective view of a wall tie of Figs 1 to 3.

Referring now to Fig 1, this shows a party wall 10 comprising a first skin 12, a second skin 14 and a cavity 16 of width W therebetween. The width W can be any required width. The first and second skins 12, 14 comprise layers of bricks 12a, 12b, 12c, 14a, 14b, 14c with layers of mortar 18 binding each layer of bricks to its neighbouring layers. The layer of bricks 1 2a, 1 4a will be referred to as the "lower layer", referring to the lowermost layer shown in Fig 1. However, it will be understood that this is not the lowest layer in the wall; as explained below, the lower layer 1 2a, 1 4a is typically located above ground level.

The party wall 10 also comprises a damp-proof membrane 20. The damp- proof membrane 20 is continuous and may be horizontal, stepped or angled. The damp-proof membrane 20 links both skins 12, 14 and acts as a collector or retainer for mortar droppings. The damp-proof membrane 20 defines a base of the cavity 16.

Fig 1 also shows a first acoustic isolator 22 in the form of a closed cell polyethylene foam. The first acoustic isolator 22 is an acoustic insulator.

The first acoustic isolator 22 has the form of an elongate stnp that extends along the length of the wall 10; specifically along the inner surfaces of the skins 12, 14 and along the damp-proof membrane 20. Thus, the first acoustic isolator 22 is a liner that lines the skins 12, 14.

The first acoustic isolator 22 is typically between 1mm and 20mm thick; most preferably around 10mm thick. A thickness of approximately 10mm maximizes the containment volume of the cavity 16 whilst minimising the chance of mortar droppings piercing through the first acoustic isolator 22.

The first acoustic isolator 22 is fixed to the inner surfaces of both skins 12, 14 by mechanical fixings in the form of wall ties 24, 26. The "inner surface is the surface of the skin facing the cavity 16. The wall ties 24, 26 are typically resilient and have good acoustic insulating properties. The wall ties 24, 26 are typically acoustically resilient, by which it is meant that they are flexible such that they reduce or eliminate transmission of impact sound. This is advantageous, as the wall ties 24, 26 will therefore not be able to connect with any mortar droppings in the cavity to form an acoustic bridge to transmit sound across the cavity and through the wall skins 12, 14 themselves.

The wall ties 24, 26 typically compnse a plastics material, for example a mixture of polythene and polyvinylchlonde (pvc). However, the invention is not limited to wall ties formed from any particular material.

The first acoustic isolator 22 is fixed at the top of the lower brick 1 2a, extends down the surface of the lower brick 1 2a, along the dampproof membrane 20, and extends up the surface of the lower brick 14a, where it is fixed at the top of the lower brick 1 4a.

The wall ties 24,26 are located in and extend through the mortar 18 between the lower layer of bricks 12a, 14a and the middle layer of bricks 12b, 14b. The wall ties 24, 26 also extend through perforations in the first acoustic isolator 22; however the wall ties 24, 26 do not physically bridge the cavity 16.

The perforations in the first acoustic isolator 22 may be pre-punched.

Alternatively, the perforations may be created by the wall ties 24, 26, when these are pushed through the first acoustic isolator 22. The latter has the advantage that the locations of the perforations need not be predetermined, so one size of first acoustic isolator 22 can be used for many different walls and different sizes of masonry.

The first acoustic isolator 22 may optionally have a reinforced upper edge portion. This may be achieved by hemming the upper edge portion, or by fixing additional material, e.g. fabric, along this region. Alternatively, the upper edge portion may be stiffened by compression. Optionally, a similar reinforcement is also applied to the area around the lower edge. Such reinforcement portions are typically provided around any area of the first acoustic isolator 22 that is/will be perforated.

The wall tie 24 has a head 24h, a shank 24s and a disc 24d. Similarly, the wall tie 26 has a head 26h, a shank 26s and a disc 26d.

The wall ties 24, 26 hold the first acoustic member 22 against the skins 12, 14 by compressing the first acoustic member 22 against the skin 12 between the head 24h and the disc 24d, and by compressing the first acoustic member 22 against the skin 14 between the head 26h and the disc 26d.

The head 24h protrudes slightly from the outer side of the skin 12 and the head 26h protrudes from the outer side of the skin 14 (the outer sides are those that are accessible after the wall has been completed).

The heads 24h, 26h can be used as a depth gauge for a wall lining. For example, the outer surfaces of the skins 12, 14 are often lined by a parge coat or internal render. Once the wall lining has been applied, it is impossible to tell the thickness of the wall lining from a visual inspection, without damaging the wall. However, when a wall lining is applied to a wall of the present invention, which has protruding heads 24h, 26h, the extent of protrusion of the heads 24h, 26h from the wall lining can be used to deduce the thickness of the wall lining.

A more detailed view of the wall tie 24 is shown in Fig 4. The head 24h and the shank 24s are formed as one piece and comprise a first cooperating component of the wall tie 24. The disc 24d comprises a second co-operating component of the wall tie 24.

The head 24h has a thickness t that determines how far an end of the head 24h will protrude from the skin 12. The thickness t may be greater than the desired thickness of the wall lining, so that even after the wall lining has been applied, a portion of the head 24h should still be visible.

Alternatively, the thickness t could be less than the desired thickness of the wall lining, so that, after application of the wall lining, it the head 24h is visible, this would show that insufficient wall lining had been applied. The thickness t is typically around 8mm. However, alternative embodiments can use different thicknesses t.

The shank 24s is elongate and is provided with ratchet teeth 24r on an upper surface thereof. The ratchet teeth 24r extend from substantially the opposite end of the wall tie 24 to the head 24h to a point part way along the shank 24s. It is useful if the ratchet teeth 24r extend along a significant portion of the shank 24s, as this enables the same wall tie 24 to be used wfth walls having a variety of skin thicknesses.

The disc 24d compnses a flange 24f and an extension portion 24e which extends axially from one face of the flange 24t to add extra length to the disc 24d. The disc 24d has an axial aperture that extends through both the flange 24f and the extension portion 24e; the axial aperture is dimensioned to receive the shank 24s in a close fit. Inside the axial aperture is at least one pawl, for example, a co-operating resilient pawl.

The pawl and the ratchet teeth 24r are adapted to allow movement of the disc 24d along the shank 24s in the direction of the head 24h (e.g. by flexing of the resilient tooth), but to hinder or prevent any movement in the opposite direction.

Also shown in Fig 1 is a second acoustic isolator 28. A further wall tie 30 having a head 30h, a shank 30s and a disc 30d extends through a perforation in the second acoustic isolator 28 and through the mortar 18 between the middle layer of bricks 1 2b and the upper layer of bricks 1 2c.

The head 30h lies against the outer surface of the skin 12, and the second acoustic isolator 28 is held between the disc 30d and the skin 12. The wall ties 26, 30 are typically the same as, or similar to, the wall tie 24 described in detail above.

The second acoustic isolator 28 is essentially the same as the first acoustic isolator 22 (except for its height), and typically has reinforced portions around its upper and lower edges.

The second acoustic isolator 28 is fixed at its lower edge by the wall tie 24.

The shank 24s of the wall tie 24 extends through a perforation in an area around the lower edge of the second acoustic isolator 28. The perforation may be pre-punched or created by the wall tie 24. The second acoustic isolator 28 is held between the disc 24d and a further, similar disc 24d'.

Thus, the lower end of the second acoustic isolator 28 overlaps the upper end of the first acoustic isolator 22.

When the wall 10 is built, the acoustic isolators 22, 28 are added in stages, because the cavity 16 will no longer be accessible after the wall 10 has been completed. The wall 10 is built conventionally until the stage where the damp-proof membrane 20 is added.

The lower layer of bricks 12a, 14a is laid on top of the damp-proof membrane 20. Then, the shank 24s of the wall tie 24 and a layer of mortar 18 are laid on top of the lower layer of bricks 1 2a, so that the head 24h engages the outer surface of the brick 1 2a and the end of the shank 24s opposite the head 24h extends into the cavity 16. The middle layer of bricks 1 2b, 1 4b is then added on top of the mortar 18 and the shank 24$.

A pre-punched perforation of the first acoustic isolator 22 is then engaged with the shank 24s, or alternatively an upper part of the first acoustic isolator 22 is pushed into the shank 24s to perforate the first acoustic isolator 22.

The end of the shank 24s opposite the head 24h is then located in the aperture of the disc 24d and the disc 24d is pushed along the shank 24$ until the disc 24d cannot move any further, due to the flange 24f abutting and being compressed against the first acoustic isolator 22. The disc 24d is held in this position by the engagement of one of the ratchet teeth 24r and the paw!. Hence, the first acoustic isolator 22 is now held against the skin 12 by compression of the first acoustic isolator 22 against the skin 12 between the head 24h (that abuts the skin 12) and the disc 24d, (that abuts the first acoustic isolator 22).

The wall tie 26 is built into the skin 14 and is engaged with a second end of the first acoustic isolator 22 in a similar way, ensuring that the first acoustic isolator 22 lies substantially flat against the inner skins 12, 14 and the damp-proof membrane 22, as shown in Fig 1.

Next, a further wall tie 30 and a further layer of mortar 18 are added to the upper surface of the middle layer of bricks 1 2b, in a similar way. The upper layer of bricks 1 2c is then added on top of the mortar 18 and the wall tie 30.

The second acoustic isolator 28 is then fixed to the skin 12 by its upper end using the wall tie 30, by the same process as described above for the fixing of the first acoustic isolator 22. The lower end of the second acoustic isolator 28 is engaged (by a pre-punched perforation or by creating a perforation) with the protruding shank 24s and the disc 24d' is applied over the shank 24s to hold the lower end of the second acoustic isolator 28 between the discs 24d, 24d'.

If deemed necessary, further acoustic Isolator(s) could be added to the upper layer 1 2c and subsequent brick layers, in the same way that the second acoustic isolator 28 has been added to the middle layer 1 2b.

Enough acoustic isolators should be added so that they will reach higher than the predicted total height of the pile of mortar droppings. Optionally, further acoustic isolators could be fixed to the second skin 14.

The rest of the wall 10 is constructed conventionally.

As the wall is built, any mortar droppings that fall into the cavity 16 collect at the base of the cavity 16, on top of the first acoustic isolator 22. Since the upper end of the second acoustic isolator 28 extends higher than the pile of mortar droppings, the pile of mortar droppings cannot form a direct mechanical bridge across the cavity 16 to link the skins 12, 14. Any sound from one side of the wall will be reduced by the acoustic isolators 22, 28 in the lower region of the cavity 16. Furthermore, as the wall ties 24,26, 30 are acoustically insulating, the wall ties prevent the formation of a direct mechanical bridge across the cavity and through the wall skins 12, 14.

Hence, the wall 10 has improved acoustic properties.

Referring now to Fig 2, an alternative embodiment of the invention is shown. This embodiment is very similar to the Fig 1 embodiment, and like parts are designated by like reference numbers. However, in the Fig 2 embodiment, the first acoustic isolator 32 is shorter than the first acoustic isolator 22 of the Fig 1 embodiment, and does not extend up the surtace of the second skin 14. Instead the lower end of the first acoustic isolator 32 lies across the upper surlace of the damp-proof membrane 20 and terminates where it meets the second skin 14. The Fig 2 wall has the advantage that it will be easier to construct, since the wall tie 26 is not necessary. Having acoustic isolators 32, 28 only fixed to the first skin 12 provides adequate acoustic isolationhinsulation in many situations.

Refernng to Fig 3, a further alternative embodiment is shown; like parts are designated by like reference numbers. In this embodiment, the first acoustic isolator 34 has an intermediate length, and extends partly up the inner surface of the first layer ot bricks 14a, but is not fixed to the second skin 14 by a mechanical fixing. Optionally, a bonding agent could hold the first acoustic isolator 34 against the inner surface of the lower layer of bricks 14a, although this is not essential. Hence, in this embodiment, the wall tie 26 is not required.

In any of the embodiments of Figs 1, 2 and 3, a bonding agent/adhesive could be used in addition to the wall ties 24, 26,30. For example, a bonding agent could be used between the acoustic isolators and the dampproof membrane 20 and/or between the acoustic isolators and the skins 12, 14.

Modifications and improvements may be incorporated without departing from the scope of the invention.

For example, the type of fixing means used is not important to the invention. Any suitable fixing means (mechanical and/or adhesive) could be used.

In the embodiments that use an adhesive bonding, the wall ties 24, 26 are not essential. The acoustic isolators can be bonded to the inner surfacesof the wall as necessary as the wall is built. As with the embodiments using mechanical fixings, each acoustic isolator would be typically added as each layer of masonry is added.

In a modification to the Fig 1 embodiment, a further acoustic isolator could also cover the inner surface of the middle layer of bricks 1 4b, in the same way as the second acoustic isolator 28 covers the middle layer of bricks 12b of the first skin 12.

Although an above-ground level wall 10 is shown in the illustrated embodiments, the invention can also be used in floor structure and substructure elements, such as foundations.

The invention may also be used with walls that do not have a damp-proof membrane 20.

Claims

Claims 1. A party wall comprising: first and second skins and a cavity

therebetween; an acoustic isolator; and a fixing means that fixes the acoustic isolator to the inner surface of at least one of the first and the second skins.
2. A party wall as claimed in claim 1, wherein the acoustic isolator comprises acoustic insulation material.
3. A party wall as claimed in claim 1 or claim 2, wherein the acoustic isolator comprises a liner that lines the inner surface of the skin.
4. A party wall as claimed in any preceding claim, wherein the cavity has a base and wherein the acoustic isolator covers the entire base of the cavity.
5. A party wall as claimed in any preceding claim, wherein the cavity has a base and wherein the acoustic isolator extends up the skin to at least 450mm above the base of the cavity.
6. A party wall as claimed in any preceding claim, wherein the acoustic isolator comprises two portions that are fixed to the skin in contact with each other.
7. A party wall as claimed in claim 6, wherein two overlapping portions of acoustic isolator are fixed to the skin by the same fixing element.
8. A party wall as claimed in any preceding claim, wherein the acoustic isolator covers at least parts of the inner surface of both of the first and second skins.
9. A party wall as claimed in any preceding claim, wherein the fixing means is located in one of the skins of the wall.
10. A party wall as claimed in any preceding claim, wherein the fixing means comprises a mechanical fixing that has a portion that protrudes from an outer surface of the skin to provide a depth gauge.
11. A party wall as claimed in any preceding claim, wherein the fixing means comprises a wall tie according to any of claims 21 to 27.
12. A party wall as claimed in any of claims 1 to 10, wherein the fixing means comprises an expanding anchor that is located within the cavity, and which is adapted to urge the acoustic isolator against the first and/or second skin.
13. A method of building a party wall comprising first and second skins with a cavity therebetween, the method including the step of fixing an acoustic isolator to the inner surface of at least one of the first and the second skins.
14. A method as claimed in claim 13, wherein the cavity has a base, and the method includes the step of arranging the acoustic isolator to cover the entire base of the cavity.
15. A method as claimed in claim 13 or claim 14, wherein the acoustic isolator is arranged to lie against the inner surface of both of the first and second skins.
16. A method as claimed in any of claims 13 to 15, wherein the acoustic isolator is fixed to the inner surface of the skin at the time of construction of the wall.
17. A method as claimed in claim 16, wherein the acoustic isolator comprises more than one portion and the method includes the steps of adding successive portions of acoustic isolator to successively higher portions of the wall as the wall is constructed.
18. A method as claimed in any of claims 1310 17, wherein the skins comprise layers and the method includes the step of adding a mechanical fixing between two layers of a skin and engaging the mechanical fixing with the acoustic isolator to fix the acoustic isolator to the skin.
19. A method as claimed in claim 18, wherein the mechanical fixing includes first and second components and wherein the method includes the step of engaging a first component of the mechanical fixing with the skin, arranging the acoustic isolator between the first and second components of the mechanical fixing and coupling the first and second portions of the mechanical fixing together to fix the acoustic isolator to the skin.
20. A method as claimed in claim 18 or 19, wherein the mechanical fixing fixes the acoustic isolator to the skin such that part of the mechanical fixing projects from an outer surface of the skin, and the method includes the steps of applying a coating to the outer surface of the skin and using the projecting part of the mechanical fixing to check the thickness of the applied coating.
21. A wall tie for holding an object against a side of a wall, the wall tie comprising: a first abutment; a second abutment; and a retaining means for preventing or restricting movement of the first and second abutments away from each other.
22. A wall tie as claimed in claim 21, wherein the wall tie is acoustically resilient.
23. A wall tie as claimed in claim 21 or claim 22, wherein the wall tie comprises a plastics material.
24. A wall tie as claimed in any of claims 21 to 23, wherein the first abutment is provided on a first component, and the second abutment is provided on a second, separate component of the wall tie.
25. A wall tie as claimed in claim 24, wherein the retaining means is adapted to couple the first and second components together.
26. A wall tie as claimed in claim 25, wherein once coupled together, the retaining means is adapted to prevent subsequent de-coupling of the first and second components.
27. A wall tie as claimed in any of claims 24 to 26, wherein one of the first and second components is provided with an aperture to receive an elongate member of the other of the first and second components.
28. A wall tie as claimed in any of claims 21 to 27, wherein the retaining means comprises a ratchet mechanism.
29. A wall tie as claimed in claim 28, wherein the ratchet mechanism is adapted to allow movement of the first and second abutments towards each other but to prevent movement of the first and second abutments away from each other.
30. A wall tie as claimed in any of claims 21 to 29, wherein the wall tie comprises a projection that is adapted to project from one side of a wall to provide a depth gauge for a wall lining.