INSULATION SYSTEM
Field of the Invention
This invention relates generally to the thermal performance of metal-framed structures, and has particular application to such structures in colder climates. The most common metal frame material is steel, and the structure of principal though not sole interest is the steel-framed wall.
Background Art
A problem encountered with some metal-framed wall structures in colder climates is that the thermal resistance of the wall in the vicinity of the frame elements, e.g. the studs, plates, lintels and noggings, may be much lower than for the intervening parts of the wall. Such regions of lower thermal resistance are known to cause thermal bridges. As well as reducing the overall thermal resistance of the wall structure, these localised thermal bridges can lead to the undesirable phenomenon often referred to as ghosting. Ghosting occurs when dust particles and or other materials are preferentially attracted to, or moisture condenses upon, the localised cold areas of the wall around the frame elements.
Summary of the Invention
It is an object of die invention to enable metal-framed structures to be designed to at least reduce the relative contrast in thermal resistance at thermal bridges, and thereby to reduce the incidence of ghosting while preferably also increasing the overall thermal resistance of the structure.
In a first aspect, the invention provides a frame element for an insulated metal framed structure, including :- an elongate metal member; and a complementary strip of thermal insulation material extending along an adjacent a longitudinal edge face of the metal member over which in situ lies cladding component of the metal-frame structure.
In a second aspect, the invention provides an insulated metal-framed structure including a frame of multiple frame elements according to the first aspect, further thermal insulation material at least between the frame elements, and cladding on one or both sides of the frame.
The structure may typically be a wall structure in which those frame elements that are frame elements according to the first aspect of the invention are composite wall studs.
The metal member may be a channel or box section member. The strip of insulating material preferably engages and is retained on said longitudinal edge face of the elongate metal member, and may be arranged to adhere to the member, or to clip or snap onto the member. Preferably, the strip is configured to define a longitudinally extending air gap between said longitudinal edge of the metal member and the strip.
Preferably, the strip is configured so that, in the insulated metal-framed structure, the thermal resistance through the structure via said frame elements according to the first aspect of the invention is of the order of half or more of that through the structure via the further thermal insulation material.
In a third aspect, the invention affords a frame arrangement for an insulated metal- framed structure, including:- a plurality of spaced elongate metal frame members; one or more panels of thermal insulation material overlying said elongate metal frame members; and means in contact with the metal frame members whereby air gaps are disposed between the metal frame members and the panels.
The contacting means may be, e.g., spaced surface formations on the panels, or fastener means which cause the panels to sit proud of the metal frame members.
The surface formations are conveniently spaced integral rib formations.
The frame arrangement may be contained within a structure which further include cladding on one or both sides of the frame arrangement, and further thermal insulatio material at least between the elongate metal members. The panels would typically li between the cladding on one or other side and the elongate metal frame members.
Again, the structure may typically be a wall structure in which at least some of th elongate metal members are wall studs.
Preferably, the panel(s) are configured so that, in the insulated metal-frame structure, the thermal resistance through the structure via said elongate members is of th order of half or more of that through the structure via the further thermal insulatio material.
In all aspects of the invention, the elongate metal members are preferabl protectively coated steel members. These may be roll-formed from steel strip or plate.
In wall structures incorporating any of the aspects of the invention, and serving a external walls of a building, the strip or panel is preferably disposed to the outside of th elongate metal members.
In a fourth aspect of the invention, there is provided an insulated metal-frame structure, including:- a frame having a plurality of spaced elongate metal frame members; cladding on at least one side of the frame; and means defining a longitudinally extending air gap between each fram member and the cladding.
The air gap may actually comprise a separation between the frame member and th cladding, or may be otherwise formed in the region between the frame member and th cladding.
Brief Description of the Drawings
The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:-
Figure 1 is a fragmentary isometric view of a frame element according to an embodiment of the first aspect of the invention;
Figure 2 is a horizontal cross-section of an insulated steel-frame wall structure incorporating frame elements of the form shown in Figure 1 ;
Figure 3 is a cross-section showing an alternative strip;
Figure 4 is a three-dimensional view of a panel suitable for use in an insulated steel- framed wall structure incoφorating a frame arrangement according to the third aspect of the invention; and
Figure 5 is a vertical cross-section of an insulated steel-framed wall structure incoφorating a frame arrangement according to the third aspect of the invention.
Preferred Embodiments
The frame element 10 illustrated in Figure 1 includes an elongated metal member in the form of a steel channel 12, and a complementary strip 14 of thermal insulation material extending along and adjacent the outside face 15 of one of the flanges 16 of channel 12.
Strip 14 is itself in the shape of a shallow channel, with a base web 20 of uniform thickness and respective flanges 22,23 of differing thickness. Thicker flange 23 has an undercut groove 25 at its inner longitudinally extending corner edge to receive the free edge of the flange 16 to which strip 14 is fitted. The thinner flange 22 of strip 14 has a shallow rebate 27 along its outer inner corner edge to seat the outer corner of metal channel 12.
With this arrangement, channel strip 14 co-operates with metal channel 12 to define a longitudinally extending air gap 30 between the two components and within channel strip 14.
Metal channel 12 is typically a steel channel roll-formed from galvanised steel strip, e.g. coated with an alloy of zinc and aluminium. Channel strip 14 may be conveniently
formed from a material which is porous or otherwise contains multiple cavities. A suitable material is a foam material such as polystyrene foam. The strip may be formed by extrusion or by cutting pre-formed bulk material. A suitable grade of polystyrene has k of about 0.035.
Figure 2 depicts a portion of a steel-framed stud wall module 35 incoφorating frame elements 10 of the form shown in Figure 1 as composite wall studs of the frame 11 of the wall. Steel channels 12 are typically of a form normally used as steel wall studs. The wall further includes thermal insulation batts or other bulk thermal insulation 40 between the studs, and inner cladding or lining such as wall boards 42 fastened to one side of the frame. The studs 10 are oriented so that channel strips 14 lie to the outside of the wall : in situ, these would be overlaid by external cladding such as a course of bricks 44.
Throughout this specification, including the claims, the terms "overlaid", "overlies" and "lies over" do not necessarily indicate contact, but merely that one element lies over the other. There may be a gap or space between the two, and there may be one or more intervening elements.
Heat conduction through stud wall module 35, when in situ, has two primary paths to follow, i.e. via wall studs 10 (path A) and via bulk insulation 40 (path B). If there is too great a difference between the thermal resistances of these paths, path A becomes a thermal bridge, which can give rise to "ghosting" on the exposed surface 43 of inner lining 42. It has been proposed that if the thermal resistance via path A is at least about half that via insulation path B, ghosting will not occur except perhaps in conditions of extreme external cold. In the present embodiment, this proposed condition is met by providing channel strips 14 and by configuring them appropriately. Sufficient thickness is one approach, but the present embodiment takes advantage of the low surface emittance of the zinc/aluminium alloy coating on channels 12 to achieve the desired thermal resistance with the combination of relatively low strip thickness and the air gap 30.
A typical thermal resistance of path B is about 2.92, for R2.5 insulation, brick cladding and plasterboard lining, and including allowance for air spaces between these
components. For the configuration of Figures 1 and 2 at the studs, a polystyrene channel strip 14 of the mentioned material and d = 20 mm base web thickness, and an air gap 30 also of 20mm gives a thermal resistance for path A of about 1.57, above the minimum (around 1.45) suggested by the proposed criterion.
If the strip thickness is d = 10mm, the overall path A thermal resistance is about 1.29.
Figure 3 illustrates an alternative configuration of thermal insulation material, i.e. polystyrene strip 14'. In the Figure 1/2 embodiment, the strip 14 is effectively retained by friction. In this case, a simple flat strip 14a is affixed to the flange face 15' of metal channel 12' by adhesive coated longitudinal cleat pieces 14b that set strip 14a off face 15' and define air gap 30' between them.
In both of the illustrated embodiments, the strip 14,14' is wider than the steel channel, allowing the strips to seal with the bulk insulation 40 in order to avoid direct conductance paths via the channel base webs 13.
A further advantage of the illustrated forms of thermal insulation strip 14,14' is that the contact area between the strip and channel is minimised. If the insulation medium was to become moist these systems would minimise corrosion through the reduced areas of contact and the aid to drying provided by the various gaps and spaces.
Figures 4 and 5 relate to an embodiment of the third aspect of the invention, which utilises panels 50 of thermal insulation material, e.g. a foam material such as polystyrene foam, formed integrally with spaced parallel ribs 52 of triangular or inverted -V- cross- section. In a stud wall structure 135, the external cladding 144 is separated from studs 110 by a lining of the panels 50, oriented with the ribs 52 contacting the studs. The wall is completed by internal cladding or lining 142 and bulk thermal insulation (not shown) between studs 110.
Ribs 52 set panels 50 off the flanges 116 of studs 1 10 and so gives rise to an air gap
130 which extends the length of the studs, broken only by ribs 52. Again, advantage is being taken of the low emittance surface of the stud flanges, and actual contact area between panels and studs is minimised (substantially to line contact) by the triangular or inverted -V- shape of the ribs.
With the arrangement illustrated in Figure 5, the additional thermal resistance at the studs provided by an air gap 130 of 20mm is around 0.58. This can be shown to be sufficient relative to the use of 20mm flat styrene board to achieve the object of the invention.
Instead of ribbed panels 50, or panels with other spaced surface formations, flat boards may be employed, and the gap 130 created by utilising fasteners which cause the panels to sit proud of the wall studs.
It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.
It will also be understood that the term "comprises" or its grammatical variants as used herein is equivalent to the term "includes" and is not to be taken as excluding the presence of other elements or features.