GB2238329A - Building panel - Google Patents

Abstract

A prefabricated building panel has insulation 36, an outer wall 52 comprising moisture-resistant and fire-resistant material, for example plasterboard, and an inner wall 54 of structural boarding, for example plywood, such that the outer wall has a lower vapour resistance than the outer wall. The internal plywood sheathing provides lateral bracing for the panel which, in earlier designs, was previously provided on the outside (Fig. 1). The relatively high vapour resistance of plywood, in comparison with that of the external moisture-resistant plasterboard, means that airborne water vapour will naturally pass through the wall to the exterior. No separate breather membrane or vapour barrier is required. There is also disclosed a building structure using a pair of such panels which abut each other 74 so ensuring that the integrity of the wall insulation is not broken by the intermediate floor 14 or the joists 10, 12. <IMAGE>

Description

BUILDING STRUCTURE The present invention relates to building structures and particularly though not exclusively to timber frame constructions.

The design of timber frame walls for volume housing in the UK has changed very little since its introduction over twenty five years ago. The systems which have been developed have been largely free of major faults, and the finished housing has a good record in terms of quality and long term performance.

However, a number of site studies in the early 1980's identified certain problems relating to construction methods and the associated quality of workmanship, which do have the potential to cause future difficulties. These problems, which have become known as "buildability" problems, are most significant in a number of particular problem areas. These relate, specifically, to the susceptibility of the building to differential movement between different materials (for example the timber structure and the masonry cladding); the fire performance (for example incorrect cavity barrier installation); the condensation risk (for example site damage to vapour barriers); and secondary protection against rain-water penetration (for example damage to breather membranes). These problem areas will be discussed in more detail below.

The "buildability" problems are inherent in the current design and construction methods, and cc-nnot be eliminated simply by refining existing systems.

Accordingly, the present invention arises from a radical re-think of current building methods and the associated structures that are involved.

It is a first object of the present invention at least to alleviate the difficulties and problems associated with conventional building techniques, and the structures involved. It is a particular object to alleviate the "buildability" problems, referred to above and subsequently.

It is a further object to improve performance generally, specifically energy efficiency thorough higher insulation levels and superior air infiltration control.

It is a further object to increase safety margins against condensation risk, for example by the substantial elimination of cold bridging.

It is a further object to make building construction more cost effective.

According to a first aspect of the present invention there is provided a panel for a building structure comprising horizontal and vertical spars defining an internal panel support, an outer wall of fire resistant material secured to one side of the support and an inner wall of structural boarding secured to the other side, the space between the inner and outer walls being filled with an insulating material, and the vapour resistance of the outer wall being less than that of the inner.

The structural boarding could be plywood, orientated strandboard or particleboard.

With such an arrangement, the wind bracing strengths of the panel can derive mainly from the inner plywood wall, so that the outer wall need not be particularly strong. The outer wall is desirably of moisture resistant plaster board, but could instead be of any other suitable fire resistant material such as fibre cement type board or cement bonded chipboard.

Preferably, the inner wall is secured directly to the internal panel support, without any intermediate vapour resistant membrane. Thus, the vapour resistance arises substantially from the plywood wall itself. The outer wall should have less vapour resistance then the inner, so that vapour can pass from the interior of the building to the exterior, through the panel, without building up inside the panel. It has been found that an appropriate vapour resistance ratio between the inner and outer walls is 5:1 or greater.

The outer wall is preferably secured directly to the internal panel support, and is a unitary structure designed so that the panel can be used without an subsidiary separate external breather membrane. To that end, the external wall is preferably moisture resistant; either a naturally moisture resistant material could be used for the wall, or the wall could be impregnated and/or surface treated with a suitable water-resistant material such as a resin.

The panel is preferably provided with horizontal and/or vertical batten or battens secured to the inner wall. Such battens can then be used, on site, either to support a further plaster board wall, with services running between this plaster board wall and the inner plywood wall; or alternatively a batten may be the means by which the panel is to be secured to the structure of the building of which it is to form a part.

Panels that are intended for the ground floor of a two storey building are preferably rather longer than usual so that they can extend through the intermediate floor zone and be secured to the first floor panel immediately above. To that end, a panel for the ground floor desirably has a vertical height of greater than substantially 2.4 metres.

The invention also extends to a building structure including a panel as previously defined or substantially as described in the specific description with reference to figure 2. The invention also extends to a method of building.

According to a second aspect of the invention there is provided a building structure having a structural wall including a first prefabricate panel, and parallel floor joists supporting an intermediate floor, the joists being supported by support means secured to and extending inwardly from an inner wall of the panel.

The support means is preferably a horizontal ledger, desirably of timber, which is secured to the inner wall of the panel. The ledger or other support means may be in the region of or adjacent an upper edge of the panel.

With an arrangement such as this, the first panel can extend upwardly past the joists, so that the joists hang from the inner wall of the panel rather than being supported at the panel's top edge. This means that a second prefabricated panel can be positioned on top of the first panel, so forming a substantially continuous structural wall, without that wall having to be broken by the interpolation of the joists and/or the intermediate floor. If the panel is of the type previously defined, including an insulating material, this means that the integrity of the insulation does not need to be broken by the floor and/or joists. This results in better thermal insulation and a substantial lack of cold bridges to the exterior.

The joists may have notches in their lower edges, these notches being received over the ledger. There may be a blocking member or stretcher, extending generally perpendicular to the length of the joists, and intended to support the edge of the intermediate floor.

Preferably, the first and second panels may abut each other at or adjacent the floor joists and/or the intermediate floor. In this way, there is a single gap at the joining of the two panels which can easily be sealed by a suitable tape from the outside.

A secondary wall may be secured to the inner wall of one or more of the panels, so providing a services zone or cavity between the additional wall and the inner wall of the panel. In this way, where the inner wall is of plywood the additional wall may be q plaster board, which provides a more convenient surface for the user of the resultant building, for example to paper and hang pictures upon. The services zone or cavity may be filled with additional insulating material, should this be so desired.

Where the outer wall of one or more of the panels is of a fire resistant material, such as moisture resistant plaster board, cavity fire barriers may be dispensed with in the cavity between the outer wall of the panel and the surrounding brick cladding.

To reduce the problems likely to arise from differential shrinkage of the timber structural wall and the brick cladding, it is preferable if the first and second prefabricated panels are secured directly to each other. Thus, where the panels have an interior timber support frame, including vertical studs a horizontal base plate and a horizontal top plate, the top plate of the first panel may be secured directly to the base plate of the second. The resultant join may be taped to reduce air flow therebetween.

The invention extends to a building structure substantially as specifically described with reference to Figure 2.

The invention further extends to a prefabricated panel for a building structure, or to a building structure, including any one or more of the features referred to or specifically defined, in any compatible combination.

In the present specification and claims the expression "building structure" is intended to encompass not only buildings as such but also structures comprising parts of buildings and structures intended or suitable for use as an integral part of a building.

The invention may be carried into practice in a number of ways and one specific building structure embodying the invention, along with a method of building, will now be described by way of example, with reference to the drawings, in which: Figure 1 shows a conventional timber frame building construction; and Figure 2 shows a building structure embodying the invention.

Figure 1 shows a conventional timber frame wall construction. Parallel timber floor joists 10, 12 support an intermediate platform floor 14, of plywood or similar, and a plaster board ceiling 16 to the room below. The outer edges of the floor 14 in the ceiling 16 (not visible in the diagram) are supported by a timber structure 18 which extends between the ends of the joists 10, 12.

Secured to the floor 14 is a wall panel, generally indicated at 20, which is generally supplied by the manufacturer as a prefabricated unit. The panel 20 comprises vertical timber supports or studs 22, 24 (each of which are typically 89 by 38 millimetres in section), a timber base plate 26 and a corresponding timber head plate (not shown). These, together, form the support frame for the panel. Secured to the outer side of the frame there is a plywood sheathing 28 which, amongst other things, imparts rigidity to the panel and enables the panel to take the expected wind loadings. On the outer face of the plywood sheathing 28 is a breather membrane 32 the purpose of which is to protect the plywood from rain-water, particularly when the panel 20 is exposed to the elements during construction.Secured to the inside of the frame there is an intermediate polythene vapour barrier 34, a high vapour resistance membrane whose purpose is to minimise condensation risk, and a plaster board lining 30.

The resultant cavity within the panel 20 is filled with mineral wool 36, to provide thermal insulation. A typical panel will have a U value of around 0.35 W/m2K.

A similar panel 38, forming the internal wall of the room below, is similar to the panel 20. The top plate 40 of that panel, however, is not secured directly to the joists 10, 12 and the stretcher 18 but is attached via the intermediary of a timber head binder 42.

Once the wall structure shown in Figure 1 has been built on site, it is protected from the elements and hidden behind an exterior brick built wall (not shown).

Alternatively, the exterior wall could be of timber boarding, cement render or tile hanging. Normally, to assist with insulation and to provide additional protection for the timber structure against seeping rain-water, there is a space or cavity left between the brickwork and the panels 20, 38.

With that basic introduction to conventional timber frame wall construction, we can now turn to a consideration of some of the "buildability" problems which have been referred to above.

The first problem relates to the differential movement between -the supporting timber structure and the external masonry cladding. In the intermediate floor zone (indicated by numeral 44 in Figure 1) there is an abundance of timber in which the grain lies horizontally. Because timber tends to shrink in cross section with age, the intermediate floor zone tends to shrink in the vertical direction while the external brickwork does not. It has, in the past, been difficult to ensure sufficient gaps are left under sills and at eves to allow for this. Thus, one sometimes finds that window frames, for example, tend to part company after a while with the surrounding brick work.

In a timber frame building fire is always a potential hazard, and conventional timber framed buildings incorporate horizontal and vertical fire barriers within the cavity between the plywood cladding and the exterior brick work. Barriers are also required at the eaves, across the intermediate floor zones, and around windows and doors. Cavity barriers, generally made of flexible strips of mineral wool, are time consuming and tricky to fit properly.

Consequently, much time can be wasted on site installing such barriers, and efforts to reduce this time are quite liable to result in imperfect installation, and thus a resultant fire hazard. The reason for the barriers, as will readily be understood, is to prevent flames and hot gases from a fire from spreading within the cavity and feeding on the combustible plywood cladding.

The polythene vapour barrier 34, a high vapour resistance membrane required to minimise internal condensation risk, is both time consuming to install and relatively easy to damage. Where surface ducts or pipes (for example water or gas pipes) have to pass through the barrier, condensation is likely to occur near where the pipe enters unless the puncture has been properly repaired and sealed around the pipe. This operation is likely to become increasingly difficult as the need for air tight construction increases.

Site damage to the breather membrane 32 is always a serious difficulty, as this membrane is exposed and vulnerable as construction proceeds. Breather membranes are difficult to repair, and even the more modern ones are relatively susceptible to damage.

With the recently increased emphasis on energy effciency, the construction at the intermediate floor zone 44 gives rise to some concern. The main insulating material, the mineral wool 36, does not extend across this zone, and accordingly there is effectively a "cold bridge" from the exterior of the building to the interior via the stretcher 18 and the ceiling 16. To plug this cold bridge, there has been a recent tendency to position extra insulation between the joists 10, 12 and while this alleviates the problem to a large extent, it creates another one in that there then becomes a need for an additional vapour barrier to prevent condensation from building up. In practice, the installation of a vapour barrier between the joists is a difficult task.

A related problem at the floor zone 44 is the presence of small gaps or cracks which are likely to exist between for example the floor 14 and the base plate 26; and between the floor and the stretcher 18.

While these gaps can be sealed by taping, this is a fairly lengthy and difficult operation.

Reference should now be made to Figure 2, which shows a timber frame wall construction in accordance with an embodiment of the present invention. Jn this drawing, similar parts are labelled with the same reference numerals as were used in Figure 1.

In the embodiment illustrated, the known panel 20 of Figure 1 is replaced with a novel panel 50. As before, this is a prefabricated unit that comprises studs 22, 24 and a base plate 26, the space between the studs being filled with mineral wool 36 or any other convenient insulating material. The studs in this embodiment have a cross section of 140 by 38 millimetres, this greater depth being introduced not for structural reasons but to allow for thicker insulation. Studs of this size are, however, not fundamental to the novel panel and conventional 89 by 38 millimetre studs will be entirely satisfactory for structural purposes. With the dimensions shown the panel has a U value of 0.23 W/m2K.

The external sheathing of the panel, rather than being plywood as before, is now moisture resistant plaster board 52. No breather membrane is required.

The interior cladding, previously the vapour barrier 34 and the plaster board 30, is replaced simply by plywood sheathing 54.

The internal plywood sheathing 54 now provides the lateral bracing of the panel that was previously provided on the outside. The relatively high vapour resistance of plywood, in comparison with that of the external moisture resistance plaster board 52, means that internal airborne water vapour will naturally pass through the wall to the exterior without any substantial built up of moisture inside the panel.

This results in some material savings, but more importantly in a panel with is easier to fit, and less likely to be damaged on site.

The replacement of the external plywood sheathing 28 with moisture resistant plaster board 52, which is much less susceptible to damage by rain-water, means that the breather membrane 32 can also be dispensed with. Removing the necessity for this membrane again reduces manufacturing costs, but once again more importantly largely removes the possibility oft inadvertent damage to the integrity of the panel on site.

By making use of moisture resistant plaster board (a fire resistant material) on the outside means that cavity fire barriers are no longer needed since there is now no combustible material within the cavity which would enable a fire to spread.

Instead of moisture resistant plaster board, the external wall 52 could be replaced by any non combustable sheet material, for example fibre cement type board, or cement bonded chipboard. The preferred type of moisture resistant plaster board has a resin mixed in with the plaster, along with an additional moisture resistant surface treatment. However, other methods of treating plaster board to make it moisture resistant might also be envisaged. Similarly, the interior plywood 54 could be replaced by any suitable sheet material of sufficient rigidity to deal with the expected wind loads.Of course, if the plywood and/or moisture resistant plaster board were to be replaced by other materials, care would have to be taken to ensure that the material of greater vapour resistance is on the inside, so that the higher vapour pressure within the building does not cause moisture to pass into one side of the panel at a greater rate than it can leave the other. An appropriate ratio for the comparative vapour resistance is 5:1.

Secured to the inner plywood sheathing 54 of the panel are battens 56, 58, 60 (preferably factory fitted) to which are secured on site an internal plaster board wall 62. The cavity 64 thus created acts as a services zone through which electrical cables, pipes 66 and so on may be routed. The services zone enables quicker and easier installation of services, and increases the air and vapour tightness of the building since the services do not need to penetrate the panel 50. By obviating the need to take services through the panel, the previous problems relating the sealing of the barriers around the resultant hates immediately disappear.

If higher levels of insulation are required, mineral wool or some other insulating material (not shown) can be installed in the services zone 64.

In the known arrangement of Figure 1, the base plate 26 of the upper panel and the top plate 40 of the lower panel are separated by a considerably amount of timber within the intermediate floor zone 44. In the novel arrangement of Figure 2, however, this timber is omitted by continuing the lower panel 68 up through the intermediate floor zone so that its top plate 40 directly abuts the base plate 26 of the upper panel 50.

This means that the lower panel 68 is likely to be longer than conventional panels, which are typically 2.3 to 2.4 metres; the new panels, for the ground floor, might be up to around 2.6 metres for a typical domestic house. In other words, rather than being secured respectively above and below the joists 10, 12 the novel panels 50, 68 are now secured to the outer ends of the joists so that a continuous external wall is in effect provided. The exclusion of the platform floor 14 and the floor joists 10, 12 from the wall minimises the cross sectional timber in the wall, and therefore virtually eliminates any problem associated with differential movement. As is well known, timber shrinks much more across the grain than along the grain, so the vertical shrinkage arising from the vertical studs 22, 24, is negligible.

The panels now support the joists 10, 12, by means of a horizontal timber ledger 70, which is factory fitted to the plywood sheathing 54. The ledger is nailed, screwed, or otherwise secured into suitable notches provided in the lower edges of the floor joists 10, 12. Support for the outer edge of the floor 14 is provided by a reduced-depth stretcher 18' which fits between the floor joists.

The integrity of the external wall through the intermediate floor zone substantially eliminates cold bridging, and also improves energy efficiency, minimises condensation and improves air tightness. As will be seen from the figure, there is now just a single possible joint or gap 74, between the panels, which can easily be taped from the outside.

In buildings which are to be exposed to particularly severe climatic conditions it may be desirable for additional protection against penetrating rain-water for a supplementary breather membrane (not shown) to be secured to the outside of the plaster board exterior wall 52. While such a membrane is not likely to be required in most situations, its absence is by no means essential to the overall operation of this proposal.

Claims (23)

CLAIMB:

1. A panel for a building structure comprising horizontal and vertical spars defining an internal panel support, an outer wall of fire resistant material secured to one side of the support and an inner wall of structural boarding secured to the other side, the space between the inner and outer walls being filled with an insulating material, and the vapour resistance of the outer wall being less than that of the inner.

2. A panel as claimed in Claim 1 in which the structural boarding is plywood, orientated strandboard or particleboard.

3. A panel as claimed in Claim 1 in which the fireresistant material comprises plasterboard, fibre cement board or cement bonded chipboard.

4. A panel as claimed in any one of the preceding claims in which the inner wall is secured directly to the internal panel support, without any intermediate vapour resistant membrane.

5. A panel as claimed in any one of the preceding claims in which the external wall is moistureresistant.

6. A panel as claimed in any one of the preceding claims in which the vapour resistance ratio between the inner and outer walls is substantially 5:1.

7. A panel as claimed in any one of the preceding claims in which the vapour resistance ratio between the inner and outer walls is substantially higher than 5:1.

8. A panel as claimed in any one of the preceding claims including horizontal and/or vertical battens secured to the inner wall.

9. A panel as claimed in any one of the preceding claims having a vertical height of substantially 2.4 metres.

10. A panel substantially as specifically herein described with reference to Figure 2.

11. A building structure including a panel as claimed in any one of the preceding claims.

12. A building structure substantially as specifically herein described with reference to Figure 2.

13. A building structure having a structural wall including a first prefabricated panel, and parallel floor joists supporting an intermediate floor, the joists themselves being supported by support means extending inwardly from the inner side of the first panel.

14. A building structure as claimed in Claim 13 in which the support means comprises a horizontal ledger secured to the inner side of the first panel.

15. A building structure as claimed in Claim 14 in which the joists have notches in their lower edges, these notches being received over the ledger.

16. A building structure as claimed in Claim 15 in which the outer edge of the intermediate floor is supported by a stretcher extending between the joists.

17. A building structure as claimed in any one of Claims 13 to 16 including a secondary wall secured to dhd spaced from the inner side of the first panel, so providing a services cavity between the first panel and the secondary wall.

18. A building structure as claimed in Claim 17 in which the secondary wall is of plasterboard.

19. A building structure as claimed in Claim 17 or Claim 18 in which the services cavity contains insulating material.

20. A building structure as claimed in any one of Claims 13 to 19 in which the outer side of the first panel is fire resistant.

21. A building structure as claimed in any one of Claims 13 to 20 including a second prefabricated panel, the second panel being located on top of the first, without the interpolation of the joists or the intermediate floor, so that the first and second panels together form at least part of the structural wall.

22. A building structure as claimed in Claim 21 in which the first and second panels abut one another at or adjacent the joists and/or the intermediate floor.

23. A building structure as claimed in Claim 22 in which each panel includes a horizontal base plate and a horizontal top plate, the top plate of the first panel being secured to the base plate of the second.