GB2041060A - Rafters; roof structures - Google Patents

Abstract

A rafter comprises two parallel beams 23, 24 connected by elements 25, 26, by means of nail plates 27. When the rafter is in use, elements 25, 26 extend stepwise relative to the slope of the roof. Elements 25, 26 may be mutually perpendicular, and nail plates 27 may be of sheet metal with protruding tangs. The rafters may be arranged with greater spacing between adjacent pairs than is usual. The rafters are particularly useful for a roof structure with a "room-in-the-roof". Combined load bearing and insulating components (50) of L-section may extend between adjacent rafters and stepwise up the roof. The components (50) are of expanded polystyrene faced with wood-wool and include timber inserts (75, 76, 77, 78) for the attachment of counter- battens (80) on the outside of the roof and wall boards (87) on the inside of the roof. <IMAGE>

Description

SPECIFICATION Improvements in or relating to roof structures This invention is concerned with improvements in or relating to roof structures and is particularly, but not exclusively concerned with rafters for such structures and with the so-called room-in-the-roof structure which is found extensively in mainland Europe, especially on private dwellings where the room-inthe-roof often provides one or more bedrooms.

To facilitate the provision of rooms-in-the roof the whole dwelling structure is more robust than that of dwellings where no roomin-the roof is to be provided. For example, the decking, between the room-in-the-roof and the rooms on the floor below, must be of load bearing character and is often provided by prestressed concrete; also the roof timbers, are usually of substantial proportions to withstand the loads applied thereto. This is determined by the fact that the only bracing elements used in such structures are so-called collars which extend between mutually aligned rafters of a pair and parallel to the said decking at a height therefrom consistent with providing room space therebetween.

Normally, where the decking between a roof space and a floor below, is not of load bearing character the rafters of a roof must be provided with tie members extending between the free ends of the rafter pairs to prevent transverse loading of the outer walls of the dwelling; however, where the decking is of load bearing character it assists in prestressing the said outer walls and the lower (free) ends of the rafters may readily and safely be located on preshaped upwardly extending portions of said outer walls.

Over the last few years a radical departure in roof structures has come about with the advent of prefabricated roof sections consisting of rafter pairs and ties which are manufactured off site in apparatus which is essentiaily a jig. The component parts of the roof sections are located in such jigs and are thereafter connected together using nail plates, i.e.

thin gauge metal plates in which are formed, by punching, tangs or prongs. Presses are used to position nail plates overlying joint areas between two or more components of roof a section and pressure is applied to the nail plate to cause the tangs thereof to penetrate into the timber to form a single prefabricated component.

The present invention provides a fabricated rafter comprising two parallel spaced apart beams connected one to the other by spacing elements which, when the rafter is in use, extend stepwise relative to the slope of a roof on which the rafter is used, the beams being connected to the spacing elements by nail plates.

The invention also provides a roof structure comprising a plurality of rafters as described above, means supporting the rafters at a lower eaves and, a ridge board interconnecting the rafters at their upper ends and a roof covering overlying and supported by the rafters.

Preferably at least some of the rafters are parallel and spaced apart, said rafters being further interconnected by combined insulating and load bearing components extending between adjacent rafters, each component comprising an elongate L-sectioned member of expanded polystyrene, the outer surface of the member being faced with wood-wool and the component including timber inserts for attaching the component to parts of the roof structure.

The roof structure may further comprise counter-battens fixed to at least some of the timber inserts of said components and in which the roof-covering comprises tiles supported on battens fixed to the rafters and counter-battens.

Preferably the rafters are arranged in pairs and define, with a decking extending between the eaves ends of the rafters, a room.

The roof structure may further comprise lining material underlying the rafters and fixed to others of said timber inserts.

It is one of the advantages of the arrangement described above to reduce considerably the numer of timber rafters used in dwellings of this type while also providing an alternative structure for the rafters used. It is also one of the advantages of the described arrangement to provide novel insulation and load bearing components which locate on and between successive rafters along a roof to provide support for tile battens on outwardly facing portions thereof and ceiling boards on inwardly facing portions thereof.

A preferred embodiment of a roof structure according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a traditional European room-in-the-roof structure; Figure 2 is a plan view of the structure of Fig. 1; Figure 3 is a section through a roof structure showing the rafter elements provided by the present invention; Figure 4 is a plan view of the structure of Fig. 3; Figure 5 is an enlarged view of part of a prefabricated rafter shown in Fig. 3; Figure 6 is an enlarged view of part of the roof structure of Fig. 3 but showing more detail of the eave assembly and support; Figure 7 is also an enlarged view of part of the roof structure of Fig. 3 showing the way in which pairs of rafters are connected together at the apex of the roof structure;; Figure 8 is a section view through a load bearing insulating component of the present invention; Figure 9 is a perspective view from above of the component shown in Fig. 8; Figure 10 shows the location of a hanger element on a rafter for supporting a load bearing insulating component; Figure 11 is a view corresponding to Fig. 5 but showing the load bearing insulating com ponents in operative position in a roof struc ture; and Figure 12 is a view corresponding to Fig. 5 but showing alternative insulation panels and tile supporting elements.

Referring first to Figs. 1 and 2, the tradi tional structure of roof; where a room-in-the roof is to be provided, comprises main rafters 1 and 2 of substantial dimensions, viz.

80 x 1 60 mm in cross-section. Such rafters are located towards their lower end portions 3 and 4 respectively on upwardly extending portions 5 and 6 of associated outer walls 7 and 8 of the dwelling. The rafters 1 and 2 are conjoined, at the apex of the roof by ridge ties 9, and are supported by a ridge batten 10 also of substantial cross-section.

The walls 7 and 8 are joined by a decking 11 which extends therebetween to provide a floor surface 1 2 to the room-in-the-roof and a ceiling 1 3 to the room therebelow.

The rafters 1 and 2 are spaced along the roof at 600 mm centres and are braced by collars 14 extending between the rafters 1 and 2 of a pair of rafters, see especially Fig.

1, the collars 14 being parallel, or substan tially so, with the decking 11.

Where roof windows 1 5 and chimney stacks 1 6 are provided it is necessary to cut through the rafters 1 and 2 as shown in Fig.

2 to accommodate such features. This of course necessitates further use of skilled la bour and increases the time required to build such a structure.

The roof structure provided by the present invention comprises, see Figs. 3 and 4, pre fabricated rafters 21 and 22 each of which rafters comprises beams 23 and 24 spaced apart by elements 25 and 26, the elements 25 being substantially horizontal and the ele ments 26 being substantially vertical when the rafters are located in position in a roof structure, see Figs. 3, 5, 6 and 7.

The beams 23 and 24 and the elements 25 and 26 are interconnected by nail plates 27, see Figs. 6 and 7, the nail plates being provided by thin gauge galvanised steel plate with tangs, not shown, pressed therefrom, which tangs are caused to penetrate into the timber of the beams and elements forming them into a composite rafter unit.

The rafters 21 and 22 are each similarly located towards their lower ends 28 and 29 on upwardly extending portions 30 and 31 of outer walls 32 and 33 respectively of a dwelling; thus, only the support for the rafter 21 will be described in detail. The wall 32, see Fig. 6, ends in the upwards projecting portion 30, which is inverted "V" shape in crosssection and is conjoined to the wall 33 by decking 34 of prestressed concrete; thus the two walls 32 and 33 are braced against lateral loading applied by the rafters 21 and 22 and the rest of the roof structure.

The inverted "V" shaped portion 30 has an upwardly facing surface 35 which extends the length of the dwelling and has fixedly mounted thereon a timber sill 36 which in turn provides support for metal shoe elements 37 arranged to house and support the corner portions of associated lower ends 28 of the rafters 21, see Fig. 6.

At its lower end 28 the rafter 21 comprises a spacing strut 38 extending between and at right angles to the beams 23 and 24, the beam 23 being somewhat longer than the beam 24 and thus extending, when in use, to provide support for fascia and soffit boards 39 and 40 respectively at the eaves of the dwelling.

At the apex of the roof each pair of rafters 21 and 22 is secured as shown in Fig. 7 with a spacer element 41 located therebetween and tie straps 42 being secured to and lying one on either side of mutually aligned uppermost elements 25 of the rafters 21 and 22; thus, a trussed rafter assembly is provided on the dwelling.

A ridgeboard 43 is located in a gap 44 provided between the uppermost ends of the beams 23 of successive rafters, the ridge board 43 being supported by upper surfaces 45 of the spacer elements 41.

To add rigidity to the structure bracing collar elements 46, see Fig. 3, are secured to undersurfaces 24a of the beams 24 of the rafters 21 and 22, the elements 46 being arranged parallel to the roof decking and being sufficiently spaced from the decking to allow for a room-in-the-roof of adequate heightwise dimensions.

Viewing Figs. 2 and 4 it is readily apparent that the spacing apart of the rafters 21 and 22 is twice that of the rafters 1 and 2 and therefore less work has to be carried out when openings for windows 47 and chimney stacks 48 are to be provided in the roof structure because, normally, such windows and chimney stacks will fit between adjacent rafters 21 and 22 without the necessity to cut through the rafters.

Load bearing insulating components 50, see Figs. 8 and 9, are provided between adjacent rafters. The components 50 are generally of inverted "L" shape when in position on a roof of a dwelling, there being a plurality of such components 50 located between each successive pair of rafters along the roof, the components between each pair of rafters being located in stepwise formation up the roof, see Fig. 11, there also being one such component 50 to each pair of elements 25 and 26 of the rafters 21 and 22.

In order to locate the components 50, as aforesaid, hangers 51, see Fig. 10, of top hat configuration, are located on timber wedges 52 at the up-roof side of each element 26.

The hangers 51 each comprise wing portions 53 which extend one on each side of the rafters 21 and 22 to support an end portion 54 of a horizontal arm 55 of the components 50, as shown in Fig. 11, a downwardly extending end portion 56 of a vertical arm 57 of the component 50 locates on an upwardly facing surface 57 of the portion 54.

At the eaves portion of the roof, see Fig. 6, the arm 57 of the lowermost component 50 may be supported in any suitable manner, e.g. a support element 57a, shown in chain dot line in Fig. 6, may extend between soffit support elements 58 secured to beam 23 of the rafter by a nail plate 59 and to the element 38 by a tie element 60 and plates 61 and 62. The arm 57 of the component 50 will of course be foreshortened to fit into the space provided.

At the apex of the roof structure, see Fig. 7, the horizontal arms 55 of the uppermost components 50 locate on laterally extending flanges 63 of the straps 42. Once again the arms 55 may have to be foreshortened to be accommodated in the space available, the arms 55 of the two uppermost components 50, located between mutually corresponding pairs of rafters 21, 21 and 22, 22, will also be in end to end abutting relationhip one with the other as shown in chain dot line in Fig. 7.

The components 50 will now be described in detail with particular reference to Figs. 8 and 9. Each component 50 is a composite moulded structure comprising an inverted "L" shaped moulding 70 of expanded polystyrene provided on its outwardly facing surfaces with a skin 71 of wood-wool. The moulding is more than twice as long as the longest arm 55 thereof and is designed to be long enough to be a comfortable fit between two successive rafters 21, 21 or 22, 22 along a roof.

Inserted in a chamfered heel portion 72 of the moulding 70, midway between opposite ends 73 and 74 thereof, is a chamfered timber insert 75 of the purpose of which will be described hereinafter.

The arm 55 of the component 50 is provided with timber inserts 76 and 77 adjacent the opposite ends 73 and 74 thereof, which inserts 76 and 77 facilitate the fastening of the components 50 to the hangers 51. Also provided along an end edge portion of the arm 55, see Figs. 8 and 9, is a timber batten 78 which is provided with a chamfered face 79 the purpose for which will become apparent hereinafter.

When a roof structure according to the present invention is to be erected builders procure rafters 21 and 22 and assemble them in co-operating pairs along the top of the precast upper walls of the dwelling. The corners formed by the elements 38 and the beam 24 are accommodated in the shoe elements 37, the upper end portions of the rafters being joined at the roof apex by the straps 42 with the spacers 41 located between said upper ends as aforesaid.

A ridge batten 43 is thereafter secured in the aligned gaps 44 on the upper surfaces of aligned spacers 41.

Beginning at the bottom of the roof adjacent the eaves thereof, the builder locates a first component 50 as shown in Fig. 6 and secures it in position by fixedly connecting the arm 55 thereof to the wing portions 53 of the lowermost pair of hangers 51 located as aforesaid.

A next component 50 is thereafter positioned with its arm 57 supported by the arm 55 of the element below and its own arm 55 supported in the next pair of hangers 51. This process is repeated up the roof between each pair of rafters 21, 21 and 22, 22 and along the roof.

At the apex of the roof the arms 55 of the uppermost components 50 conjoin as shown in chain dot line in Fig. 7, to form a closed system.

With all of the components 50 in position, the outside of the roof may be finished by firstly attaching counter battens 80, see Fig.

11, to the components 50, each counter batten 80 being aligned overlying the inserts 75 of the component 50 and being secured thereto by nails, not shown. The counter battens 80 are also secured at the roof apex to the ridge board 43 and at the roof eave to the fascia board 39. When all of the counter battens 80 are in position their upper surfaces 81 are in mutual alignment one with another and also with upper surfaces 82 of the rafters 21 and 22 on each side of the roof.

The builder (or tile) thereafter attaches an eaves batten 83, roofing felt 84, tile battens 85 and roofing tiles 86 in known manner and the outside of the roof is completed. On the inside of the roof a ceiling board 87 of suitable material is secured to the chamfered faces 79 of the timber battens 78 of the components 50 and to the underside of the collars 46 to thus provide a room-in-the-roof.

If window spaces or chinmey spaces are to be provided components 50 can be omitted completely from the desired location in ths roof structure or they may be cut to shape quite readily. Also extra hanger plates, etc.

may be provided, where a component 50 is omitted, whereby other up-the-roof components 50 are adequately supported. From the foregoing it will be appreciated that the novel structure provided by the present invention is easily assembled and provides an insulated room-in-the-roof dwelling. Also the saving on timber costs can be as must as 60% compared with costs for traditional structures.

In a modified structure, see Fig. 12, utilising the prefabricated rafter structure provided by the present invention, the components 50 can be completely omitted. In this case the outside of the roof is finished by applying roof underlying 90 of suitable material and then metal tile battens 91 which are supported by and secured to the rafters 21 and 22 in known manner. The inside of the roof is finished by securing an insulated ceiling panel 92 to the underside of the rafters 21 and 22 and the undersides of the roof collars 46.

Other modifications may be made within the scope of the present invention.

Claims (11)

1. A fabricated rafter comprising two parallel spaced apart beams connected one to the other by spacing elements which, when the rafter is in use, extend stepwise relative to the slope of a roof on which the rafter is used, the beams being connected to the spacing elements by nail plates.

2. A rafter as claimed in claim 1 in which adjacent spacing elements abut each other and are mutually perpendicular.

3. A rafter as claimed in claim 1 or claim 2 in which at least some nail plates overlie and mutually interconnect two spacing elements and one of the said beams.

4. A rafter as claimed in any one of the preceeding claims in which the beams and spacing elements are of timber and the nail plates comprise sheet metal elements with protruding tangs.

5. A fabricated rafter substantially as here it before described with reference to and as shown in Figs. 3 to 1 2 of the accompanying drawings.

6. A roof structure comprising a plurality of rafters as claimed in anyone of the preceeding claims, means supporting the rafters at a lower eaves and, a ridge board interconnecting the rafters at their upper ends and a roof covering overlying and supported by the rafters.

7. A roof structure as claimed in claim 6 in which at least some of the rafters are parallel and spaced apart, said rafters being further interconnected by combined insulating and load bearing components extending between adjacent rafters, each component comprising an elongate L-sectioned member of expanded polystyrene, the outer surface of the member being faced with wood-wool and the component including timber inserts for attaching the component to parts of the roof structure.

8. A roof structure as claimed in claim 7 further comprising counter-battens fixed to at least some of the timber inserts of said components and in which the roof covering comprises tiles supported on battens fixed to the rafters and counter-battens.

9. A roof structure as claimed in any one of claims 6 to 8 in which the rafters are arranged in pairs and define, with a decking extending between the eaves ends of the rafters, a room.

10. A roof structure as claimed in claim 9 when dependant on claim 8 further comprising lining material underlying the rafters and fixed to others of said timber inserts.

11. A roof structure substantially as here it before described with reference to and as shown in Figs. 3-12 of the accompanying drawings.