Patent Description:
More particularly, the present invention relates to the type of wall structure of a building which comprises, from the inside to the outside of the building, a load bearing wall, a continuous layer of thermal insulation, a drained air cavity and an external cladding. Such structures are arranged so that the drained air cavity allows water or humidity penetrating into the air cavity, for example through the external cladding, to be removed, notably by running down the rear face of the external cladding and out of weep holes placed near cavity trays which are positioned at regular intervals in the cavity. The air cavity is thus configured to allow water drainage behind the external cladding.

These types of drained air cavity wall structures provide a number of advantages including i) winter and summer energy efficiency and ii) the avoidance of condensation and humidity by removal of any water the infiltrates, for example through weep holes. In order to provide enhanced fire performance, particularly for example where such structures are used for external wall constructions over <NUM> in height, it is recommended to install cavity fire propagation barriers at the junctions between the external cladding and the fire-resisting barriers of the building construction (e.g. the compartment floors, the compartment walls or other walls or door assemblies that form a fire-resisting barrier of the building).

<CIT> relates to a non-combustible cavity tray for a cavity wall of a building having a means for delivering internal moisture towards the other leaf of a cavity wall. <CIT> relates to a building facade which is provided with a rear ventilation slot bridging spacer portions between an outer side of a fire bar and an inner cladding. <CIT> relates to a protective element for holding insulating material pressed against a masonry wall.

One aim of the present invention is to provide an improved fire propagation barrier system for a building, particularly as part of a drained air cavity wall structure, notably as part of a drained air cavity wall structure as described above.

In accordance with one of its aspects, the present invention provides a wall structure for a building in accordance with claim <NUM>. Other aspects are defined in other independent claims. The dependent claims define preferred or alternative features.

In one of its aspects, the present invention is based on the realisations i) that of the many different type of claddings used for drained air cavity wall systems, improvements can be made by using a masonry outer leaf as the external cladding and ii) that an improved and simpler and way of providing a fire propagation barrier in a wall structure having a masonry outer leaf and a drained air cavity can be achieved by securing a fire propagation barrier, particularly a mineral wool fire propagation barrier, by using ties and supporting the ties primarily between the discreet masonry units of the leaf, preferably with the ties passing through the mineral wool fire propagation barrier and more preferably also into the layer of thermal insulation of the system.

The present invention is useful, for example, in the type of structure illustrated in <FIG> which comprises:.

The combination of the horizontal <NUM>' and vertical <NUM>" compartmenting fire propagation barriers separates the drained air cavity <NUM> into discrete cavity compartments <NUM> with fire propagation between discrete cavity compartments <NUM> being prevented or restrained by the fire propagation barriers <NUM>.

Fire propagation barriers are also provided in the drained air cavity around the window openings <NUM>, around door openings (not shown) and around other openings in the load bearing wall <NUM>.

The provision of fire propagation barriers in this way restrains the propagation of fire and temperature increase from fire i) from one drained air cavity compartment to another and ii) from a drained air cavity compartment to an opening (e.g. a window or door opening) in the load bearing wall <NUM>.

The time during which fire propagation will be prevented or restrained by the fire propagation barriers, and by other parts of the system, will depend upon the configuration and materials used. As used herein, reference to fire propagation being prevented by the fire propagation barriers should be understood as referring to fire propagation being prevented or restrained for a certain time duration, for example a duration of <NUM> minutes, <NUM> minutes, or <NUM> minutes when tested according to appropriate test standards as required by local building regulations.

The present invention is particularly applicable for use with a drained air cavity wall structure of a building which comprise a plurality of discrete drained air cavity compartments, notably at least three, four or five discrete drained air cavity compartments arranged one above the other in a vertical direction and/or at least three, four or five discrete drained air cavity compartments arranged adjacent to each other in a horizontal direction.

<FIG> illustrates a known arrangement for incorporating fire propagation barriers in a wall structure having a masonry outer leaf and a drained air cavity. In this known arrangement, the system comprises:.

In accordance with one of its aspects, the present invention provides a drained air cavity wall structure of a building comprising.

wherein the fire propagation barrier is secured within the drained air cavity by a tie, the tie having a portion which engages with the fire propagation barrier, a portion which engages with the masonry outer leaf and preferably a portion which engages with the layer of thermal insulation.

Preferably, the wall structure further comprises a draining cavity tray arranged within the structure to collect any water which runs down a cavity facing surface of the masonry outer leaf (i.e. a surface facing towards the drained air cavity) and allow escape of such water from the drained air cavity, notably through one or more weep holes provided through the masonry outer leaf.

In preferred arrangements, a draining cavity tray is provided in each discrete cavity compartment of the wall structure, each draining cavity tray being arranged to collect any water which runs down a cavity facing surface of the masonry outer leaf of its cavity compartment and allow escape of such water from the drained air cavity, notably through one or more weep holes provided through the masonry outer leaf. Each such draining cavity tray i) preferably extends substantially along the entire length of its cavity compartment, for example in a horizontal direction and/or ii) is positioned towards the base of its cavity compartment, for example slightly above a horizontal fire propagation barrier which defines a base of the cavity compartment.

The load bearing wall is preferably provided by a frame, for example a metal frame or a wooden frame, particularly a frame covered with a substantially continuous sheathing layer facing the drained air cavity. For example, one type of appropriate load bearing wall comprises spaced, vertically arranged load bearing struts, for example wooden struts or metal struts, to which inner panels are attached at the side of the structure facing an interior of a building to form a continuous inner facing surface and to which sheathing boards are attached at the side of the structure facing the drained air cavity to form a continuous outer facing surface, with the spaces defined between the inner and outer facing surfaces being provided with thermal insulation, notably mineral wool insulation. Alternatively, the load bearing wall may be provided by a masonry wall, notably a masonry leaf which forms the inner leaf of the drained air cavity wall structure.

The layer of thermal insulation secured to the load bearing wall preferably comprises or consists of mineral wool insulation. The mineral wool insulation is preferably water repellent, for example thanks to inclusion of water repellent additives in the mineral wool insulation and/or provision of a water repellent facing arranged towards the drained air cavity; this helps to prevent water penetration and helps water run off during installation and use. Stone wool insulation is particularly suitable as it provides a desirable combination of thermal insulation and resistance to fire conditions. Preferably, the layer of thermal insulation is provided by a plurality of adjacent pieces or slabs of insulation, notably slabs of mineral wool insulation. The slabs or pieces of thermal insulation may be secured to the load bearing wall by pins or by being held in a frame which is secured to the load bearing wall. The mineral wool insulation is preferably arranged with its major surfaces arranged in a vertical plane and the majority of its fibres orientated parallel to its major surfaces; this provides advantageous thermal insulation properties for the wall structure. Mineral wool insulation, particularly stone wool insulation, which has a density which is: ≥ <NUM>/m<NUM>, preferably ≥ <NUM>/m<NUM>; and/or ≤ <NUM>/m<NUM>, and/or ≤ <NUM>/m<NUM>, preferably ≤ <NUM>/m<NUM>, notably in the range ≥ <NUM>/m<NUM> and ≤ <NUM>/m<NUM>, is preferred as this provides an advantageous combination of thermal insulation, fire resistance and mechanical properties. The layer of mineral wool thermal insulation preferably has its fibre structure in fluid communication with the air in the drained air cavity; this contributes to the performance of the structure.

The layer of thermal insulation is intended to insulate the exterior surface of the load bearing wall; consequently, it preferably overlays at least <NUM>% and preferably at least <NUM>% of the external surface of the load bearing wall.

The drained air cavity preferably has a drained air cavity width which is: ≥ <NUM> preferably ≥ <NUM>; it may be ≤ <NUM> and is preferably ≥ <NUM> and ≤ <NUM>. The drained air cavity width may be selected to be: ≥ <NUM> and ≤ <NUM>; or ≥ <NUM> and ≤ <NUM>. This contributes to the desired performance of the wall structure. As used herein, the term "drained air cavity width" means the average distance across the drained air cavity between the surface of the discrete masonry units (e.g. bricks) of the masonry outer leaf facing the drained air cavity and the layer of thermal insulation facing the drained air cavity when measured perpendicularly from said surface of the masonry outer leaf.

The masonry outer leaf comprises successive layers of discrete masonry units (e.g. bricks) separated from and secured to its adjacent discrete masonry units by mortar. As used herein, the term "brick" is used to denote bricks, blocks and other forms of discrete masonry unit.

The fire propagation barrier is preferably elongate in form having a length L (intended to lie in a plane parallel to the plane of the masonry outer leaf), a width W (intended to lie in the direction of the width of the drained air cavity) and a height H (in a direction perpendicular to its length and width). The width of the fire propagation barrier is selected to correspond to the width of the drained air cavity and preferably to be slightly oversized i.e. slightly greater than the width of the drained air cavity, for example by at least <NUM> at least <NUM>, at least <NUM>, at least <NUM> and preferably not more than <NUM>. An "oversizing" of the width of the fire propagation barrier by about <NUM> compared with the width of the drained air cavity has been found advantageous. Such "oversizing" of the width of the fire propagation barrier compensates for local tolerances in the width of the drained air cavity so that the width of the drained air cavity is fully filled by the width of the fire propagation barrier wherever the fire propagation barrier is arranged; it also allows the fire propagation barrier to be arranged as a compression fit across the drained air cavity. An "oversizing" of the width of the fire propagation barrier by about <NUM> compared with the width of the drained air cavity has likewise been found advantageous for the same reasons with, in addition, increased ease of use and a reduced risk of causing displacement of the masonry outer leaf during construction. The fire propagation barrier may be provided in lengths which are ≥ <NUM>, preferably ≥ <NUM> and/or ≤ <NUM>, preferably ≤ <NUM>, notably lengths which are ≥ <NUM> and ≤ <NUM>; such lengths facilitate handling and assembly. The fire propagation barrier of the wall structure is preferably formed from adjacent individual lengths of individual pieces of fire propagation barrier whose ends cooperate, for example by abutment, to provide an extended length of the fire propagation barrier, for example in a vertical or horizontal direction. Abutment between individual pieces of fire propagation barrier may be provided by simple abutment of respective planar end surfaces of each length of fire propagation barrier. Alternatively, particularly with a view to reducing risk of fire propagation through such abutments, multi-surface abutments may be provided, for example a stepped abutment, a shiplap abutment or a mortise and tenon abutment. The fire propagation barrier preferably comprises or consists of mineral wool insulation. The mineral wool insulation is preferably water repellent, for example thanks to inclusion of water repellent additives; this helps to prevent the fire propagation barrier retaining water in a way which could be detrimental to the desired functioning of the wall structure. Stone wool insulation is particularly suitable as it provides a desirable combination of thermal insulation properties and resistance to fire conditions. The mineral wool of the fire propagation barrier is preferably arranged to have the majority of its fibres orientated parallel to its width direction. This provides desirable compressive strength in the width direction to facilitate installation and maintenance of the fire protection barrier across the width of the drained air cavity, particularly where the fire protection barrier is arranged as a compression fit across the drained air cavity; this effect is further enhanced when the layer of thermal insulation comprises mineral wool having its fibres orientated primarily in a plane perpendicular to the width of the drained air cavity as, in this case, a lower compression strength of the thermal insulation layer in the width direction of the drained air cavity compared with that of the fire propagation barrier in the width direction will tend to provide a local deformation in the thermal insulation layer around an adjacent face of the fire propagation barrier which can contribute to enhancing fire resistance behaviour of the structure. The mineral wool of the fire propagation barrier, particularly of a stone wool fire propagation barrier, may have a density which is: ≥ <NUM>/m<NUM>, preferably ≥ <NUM>/m<NUM>; and/or ≤ <NUM>/m<NUM>, or ≤ <NUM>/m<NUM>, preferably ≤ <NUM>/m<NUM> , notably in the range ≥ <NUM>/m<NUM> and ≤ <NUM>/m<NUM>; this provides an advantageous combination of fire resistance and mechanical properties, particularly when used in combination with the dimensions of the fire propagation barrier disclosed above. The fire propagation barrier and the thermal insulation layer may be provided by mineral wool insulation, notably stone wool insulation, having the same nominal density; this provides desirable properties and facilitates logistics. Particularly where the fire propagation barrier is provided by mineral wool, it may be encapsulated in a film, notably a plastics film, for example a polythene film; this facilitates handling. Alternatively, or additionally, at least one surface of the fire propagation barrier may be provided with a facing, for example a metal foil facing; this may be provided with marking and/or indications notably facilitating use and/or installation of the fire propagation barrier.

The fire propagation barrier is preferably secured within the drained air cavity, notably to the masonry outer leaf, by a plurality of ties spaced along its length. The distance between ties along the length of the fire propagation barrier may be ≥ <NUM> and/or ≤ <NUM>, preferably ≥ <NUM> and ≤ <NUM>; this provides a suitable number of ties to secure the fire propagation barrier in the wall structure whilst providing for simple installation. For example, where the fire propagation barrier is provided in lengths of <NUM>, a length of fire propagation barrier may be secured in the wall structure with three ties, one tie being arranged at the centre along its <NUM> length and each of the other two ties being arranged at <NUM> from a respective end along the length. In this way, a tie is positioned each <NUM> along the length of each adjacent length of fire propagation barrier. The fire propagation barrier may be provided with a marking, visible during its installation, for example at its surface, to indicate recommended positions along its length for the positioning of the ties.

As used herein, the term "tie" means a structural member which restrains movement in at least one direction between the fire propagation barrier and the masonry outer leaf. Preferably the tie restrains movement between the fire propagation barrier and the masonry outer leaf in all directions parallel to the plane in which the masonry outer leaf is arranged; this prevents vertical up, vertical down, horizontal left and horizontal right movement of the fire propagation barrier relative to a vertical masonry outer leaf and thus maintains the position of the fire propagation barrier relative to the masonry outer leaf during completion of the construction of the masonry outer leaf and, more importantly, if, during the lifetime of the wall structure, fire conditions occur in the drained air cavity.

Each tie may comprise a first end, a second end and a body arranged between the first and second ends. The first end may be adapted to engage with the thermal insulation layer, the body may be adapted to engage with the fire propagation barrier and the second end may be adapted to engage with the masonry outer leaf. Preferably, the body is adapted to be positioned within the fire propagation barrier, the first end is adapted to project into the layer of thermal insulation, notably by a distance which is ≥ <NUM>, preferably ≥ <NUM> and which may be ≤ <NUM> or ≤ <NUM>, and the second end is adapted to project into the masonry outer leaf, notably between adjacent bricks where it is retained by the mortar. Preferably, the first end is adapted to project into the layer of thermal insulation all the way to the load bearing wall. The second end preferably projects into the masonry outer leaf by a distance which is ≥ <NUM>, preferably ≥ <NUM> and/or ≤ <NUM> or ≤ <NUM>. Each tie may be provided by a lineally extending element; for example a rod, preferably a rod of circular cross section, notably having a diameter which ≥ <NUM> and ≤ <NUM>. A rod having a circular cross section with a linearly extending portion of the rod forming the body of the tie facilitates rotation of the tie about the lineally extending axis during installation and/or adjustment. The second end of the tie, notably when the tie is provided by a rod, is preferably provided with a handle to facilitate its handling and/or rotation. Where the tie comprises a rod, the handle is preferably formed by a bend in the rod at the second end so that the handle is provided by a continuation of the rod which has been bent out of the linear axis of the rod. This provides a simple and practical configuration. The handle is preferably arranged such that, with respect to the lineally extending axis, the handle projects in a single direction away from the axis and without crossing the axis; this reduces encumbrance of the handle during rotation of the tie. The body and first end of the tie preferably extend continuously along a single axis; this facilitates rotation of the tie when the body is arranged within the fire propagation barrier. The tie may be a metal tie, preferably a steel tie, more preferably a stainless-steel tie; this allows the use of simple mass-produced ties which provide desired levels of performance in the wall structure.

The tie, notably a handle of the tie, is preferably secured to the masonry outer leaf by being embedded between adjacent bricks of the masonry outer leaf, notably by being embedded in and held by mortar between adjacent bricks of the masonry outer leaf; this is both simple and effective. The tie may be secured between two adjacent bricks in the same row of bricks or between bricks in adjacent upper and lower rows. It is particularly advantageous for the tie to be configured so that its handle lies in a single plane and can be rotated, for example by being gripped between an installer's thumb and forefinger of one hand, from a position in which the handle lies in a substantially vertical plane to a position in which the handle lies in a substantially horizontal plane, such rotation notably being easily accomplished by turning the tie by hand when the body of the tie is embedded in the fire propagation barrier. This facilitates installation by allowing the handle of the tie to be manually gripped in a substantially vertical position during insertion of the tie into the fire propagation barrier and for the handle to be subsequently manually rotated, whilst the body of the tie is arranged in the fire propagation barrier, for example to a horizontal position in which it can be arranged to lie substantially horizontally above a brick of a partially completed portion of the masonry leaf and subsequently embedded in the masonry outer leaf when a further brick is layer on top of it.

The fire propagation barrier is preferably provided as a compression fit between the masonry outer leaf and the layer of thermal insulation; this contributes to maintaining the desired position of the fire propagation barrier in the wall structure and particularly to avoiding the creation of gaps i) between the fire propagation barrier and the masonry outer leaf and ii) between the fire propagation barrier and the layer of thermal insulation when the drained air cavity is subjected to fire conditions. Particularly where the fire propagation barrier is provided by mineral wool insulation, the compression fit may be created by arranging for the width of the fire propagation barrier to be greater than the width of the drained air cavity, for example by at least about <NUM>, at least about <NUM>, at least about <NUM> or at least about <NUM>.

The wall structure is preferably arranged such that i) the layer of thermal insulation provides a continuous, planar insulation surface facing the drained air cavity; and ii) the fire propagation barrier is arranged within the drained air cavity so as to abut a portion of the continuous, planar insulation surface facing the drained air cavity. This greatly facilitates installation of the layer of thermal insulation by avoiding the need to either i) cut recesses to receive a fire propagation barrier out of an insulation layer which has been installed covering the entire area of the load bearing wall; or ii) install the layer of insulation in a way in which recesses are provided in the layer of thermal insulation at positions at which it is anticipated that it will be desired to arrange fire propagation barriers. The continuous, planar insulation surface facing the drained air cavity need not, of course, be perfectly planar or perfectly continuous and the term "continuous, planar insulation surface" as used herein indicates that this surface is sufficiently planar and sufficiently continuous to be substantially without gaps and recesses.

According to a further aspect, the present invention provides a method of constructing a drained air cavity wall structure of a building provided with a fire propagation barrier, the method comprising:.

subsequently laying further bricks to continue construction of the masonry outer leaf and to secure the fire propagation barrier tie between adjacent bricks of the masonry outer leaf, notably to secure the fire propagation barrier tie in mortar between adjacent bricks of the masonry outer leaf.

This provides a simple and effective way of installing the fire propagation barrier.

According to another aspect, the present invention provides a method of constructing a drained air cavity wall structure of a building provided with a fire propagation barrier, the method comprising:.

Either of the methods of constructing a drained air cavity wall structure of a building as disclosed above may comprise arranging for the tie to have a handle which lies in a single plane and manually rotating the handle of the tie, for example by gripping the handle of the tie between thumb and forefinger of one hand, from a position in which the handle lies in a substantially vertical plane to a position in which the handle lies in a substantially horizontal plane, such rotation notably being accomplished by turning the tie by hand when the body of the tie is embedded in the fire propagation barrier.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:.

<FIG> illustrate a portion of a wall structure, for example of the type described in relation to <FIG>, comprising:.

The tie <NUM> is illustrated in <FIG> and comprises a first end <NUM>, a second end <NUM>, a body of the tie provided by a straight rod <NUM> connecting the first <NUM> and second <NUM> ends and a handle <NUM> arranged at the second end <NUM>. In the illustrated embodiment, the entire tie is formed from a single length of circular cross-section stainless-steel rod having a diameter of about <NUM> with the handle <NUM> being formed by bending of the rod so that the handle <NUM> lies in a single plane.

One method of constructing the wall structure with masonry outer leaf system and drained air cavity illustrated in <FIG> comprises:.

Another method of constructing the wall structure illustrated in <FIG> comprises:.

Arranging the second end <NUM> of the fire propagation barrier tie <NUM> to overlie a brick at the first height may comprises adjusting the position of the fire propagation barrier tie <NUM> from an initial portion in which the fire propagation barrier tie was arranged when embedding the first end <NUM> of the tie <NUM> into the layer of mineral wool insulation <NUM> at the first height to initially hold the fire propagation barrier at the first height. In this way, the tie may initially be inserted quickly and easily at an approximate position to hold the fire propagation barrier in place during construction of part of the masonry outer leaf; then, when the masonry outer leaf has been built up to a suitable height, the tie may be removed and re-inserted at its final desired position.

As can be seem in <FIG>, the fire propagation barrier <NUM> abuts a continuous planar external surface <NUM>' of the layer of thermal insulation <NUM> and extends, preferably in a compression fit, between this surface <NUM>' and an interior surface <NUM>' of the masonry outer leaf <NUM>.

Thus, the method of installing a wall structure in accordance with the present invention is preferably carried out i) without cutting recesses for receiving the fire propagation barrier out of the layer of thermal insulation secured to the load bearing wall and ii) without creating recesses for receiving the fire propagation barrier in the layer of thermal insulation when securing the layer of thermal insulation to the load bearing wall.

A series of experimental fire tests were conducted to compare the characteristic of fire propagation barrier configurations. The experimental test rig is illustrated in <FIG> and comprised.

A fire inlet <NUM> having a diameter of <NUM> was provided in the masonry wall <NUM> to allow flames from a gravel bed gas burner to be directed into the air cavity <NUM> below the fire propagation barrier <NUM>.

The centre of the fire propagation barrier <NUM> was arranged <NUM> above the top of the fire inlet <NUM>.

The test procedure consisted of sequentially:.

- installing the fire propagation barrier <NUM> to be tested into the air cavity in preparation for the fire propagation test;
- running the fire propagation test by igniting the gas burner to introduce flames into the air cavity <NUM> and running the test for <NUM> minutes with the gas burner set to an estimated 25kW whilst measuring the temperature using thermocouples at the positions set out in Table <NUM> below. The temperature measurement at position TC6 is of most interest as this gives an indication of heat transfer through the fire propagation barrier.

The configurations set out in Table <NUM> were tested:.

In each case, the fire propagation barrier <NUM> was provided having a width <NUM> greater than the width W into which it was being fitted so as to be arranged with a slight compression fit.

<FIG> shows a comparison between Test A0 (prior art configuration) and Test A3a (according to one aspect of the invention). After <NUM>, <NUM> and <NUM> minutes the temperature measured at position TC6 (<NUM> above the centre of the fire propagation barrier) for Test A3a was comparable to that in Test A0 despite: i) the test rig being at a slightly higher temperature at the start of Test A3a; and ii) the cavity width W being larger for Test A3a; each of which would be thought to have had a detrimental effect on controlling passage of heat through the fire propagation barrier.

<FIG>shows a comparison between Tests A1, A3a and A3b which had respective fire propagation barrier heights H of <NUM>, <NUM> and <NUM>. The <NUM> fire propagation barrier height of Test A1 was significantly the least effective at preventing heat transfer through the fire propagation barrier. Tests A3a and A3b with heights H of <NUM> and <NUM> showed similar results for the temperature at TC6.

<FIG>shows a comparison between Tests A1 and A2 in which the respective densities of the fire propagation barriers were <NUM>/m<NUM> and <NUM>/m<NUM>. Test A2 using the higher density was more effective at preventing heat transfer through the fire propagation barrier.

The arrangement of Test A9a performed better.

An additional test B was conducted in a test drained air cavity wall structure of a building comprising.

During the tests, an exposed side of the fire propagation barrier in the test drained air cavity wall structure was exposed to simulated fire condition using a furnace controlled in accordance with BS EN <NUM>-<NUM>: <NUM> Clause <NUM>.

The results of test B are shown in Table <NUM> below:.

The "Integrity test" required the fire propagation barrier to retain its separating function without either causing ignition of a cotton pad or resulting a sustained flaming on its unexposed side as specified in BS EN <NUM>-<NUM>: <NUM> Part <NUM> (using testing conditions according to BS EN <NUM>-<NUM>: <NUM>).

The "Insulation test" measured the time for the temperature rise to exceed <NUM> on the unexposed side of the fire propagation barrier as specified in BS EN <NUM>-<NUM>: <NUM> Part <NUM> (using testing conditions according to BS EN <NUM>-<NUM>: <NUM>).

The arrangement of Test B met the classification requirements for E <NUM> and <NUM>.

A further additional test C was conducted in a test drained air cavity wall structure of a building comprising.

Claim 1:
A drained air cavity wall structure of a building comprising
i) in order:
- a load bearing wall (<NUM>);
- a layer of thermal insulation (<NUM>), notably of mineral wool, secured to the load bearing wall having a major surface facing the drained air cavity (<NUM>);
- the drained air cavity (<NUM>);
- a masonry outer leaf (<NUM>); and
ii) a fire propagation barrier (<NUM>), notably a mineral wool fire propagation barrier, provided across a width of the drained air cavity, the width of the drained air cavity being fully filled by a width of the fire propagation barrier; the fire propagation barrier (<NUM>) is secured within the drained air cavity (<NUM>) by a tie (<NUM>), the tie (<NUM>) having a portion which engages with the fire propagation barrier (<NUM>), a portion which engages with the masonry outer leaf (<NUM>) and preferably a portion which engages with the layer of thermal insulation (<NUM>);
characterised in that
the major surface of the layer of thermal insulation (<NUM>) facing the drained air cavity (<NUM>)
provides a continuous planar insulation surface and the fire propagation barrier (<NUM>)
abuts said continuous planar insulation surface of the layer of thermal insulation (<NUM>).