guide to pryda floor & rafter truss installation

P R Y D A T R U S S S Y S T E M S

GUIDE TO INSTALLATIONPRYDA FLOOR TRUSS & RAFTER TRUSS SYSTEMS

P R Y D A T R U S S S Y S T E M S

September 2003

P R Y D A F L O O R T R U S S S Y S T E M S2

Pryda Floor Truss Systems are a complete structuralsystem for timber floors made up of flooring material,floor trusses, strongbacks, connections and bracing.There are two different types of web systems for these

trusses. Both have timber chords but Pryda Longreachuses all-timber webs, while Pryda Span uses metalwebs for the diagonals and timber webs for theverticals.

PRYDA FLOOR TRUSS SYSTEMS

TRUSS IDENTIFICATION AND ORIENTATIONIt is imperative that Longreach and Pryda Span FloorTrusses are oriented the right way up. The trusses maybe marked with a “This Way Up” sticker or similar.

If the truss is not marked in this way then ensure thatthe trusses match the following diagrams.

Pryda Longreach Truss

Pryda Span Truss

SUPPORTING STRUCTURETo ensure a satisfactorily level floor on completion, thesupporting structure must be square and theloadbearing surfaces level. The structure must be stablein its own right.

BEARINGTrusses must bear directly on their supports and not beheld above them by the flooring. This may sound odd,but where the support top plate is not level, and theflooring is nailed to the truss top chord, the flooring itselfcan lift the lower truss(es) by a few millimetres and thisconsiderably worsens the perception of floor bounce.

It is important that floor trusses bear over the supportwall plate or beam with a minimum of 30mm forresidential floors and 40mm for commercial floors toguard against localised crushing and encourage properload transference.

SET OUTIn no circumstances should the floor truss spacingexceed the design spacing (usually 450mm or 600mm).The manufacturer should supply a floor truss layout thatclearly defines the correct location of any special truss.

ON SITE VARIATIONSBeing fully engineered components, anymodifications made on site to Longreach orPryda Span Floor Trusses may be detrimental.This includes cutting or notching chords orwebs. Any such modifications should be referredimmediately to the floor truss manufacturer toensure that correct rectification details areprovided from Pryda (Aust.) Pty Ltd.

Timber Webs

Metal WebsRight Way Up Wrong Way Up

Right Way Up Wrong Way Up

P R Y D A F L O O R T R U S S S Y S T E M S 3

INTERNAL WALLS

The floor truss system requires no additional stiffeningwhen supporting non-loadbearing walls, howeverspecial consideration is required for non-loadbearingwalls acting as wind bracing walls. Specifiers shouldnotify the Pryda licenced fabricator of wall bracingpositions and capacities.

Bracing walls parallel to the floor trussesIf the wall is positioned between two floor trusses and isa wind bracing element with a capacity of no more than1.5kN/m and does not exceed 2.7m high, fix noggingsat each end of the bracing element to transfer windforces to the adjacent trusses. Use 2/14gx100mmTimberfixx screws to fix the bottom plate of the bracingelement into the nogging, and 12gx65mm Timberfixxscrews to fix the bottom plate to the flooring at 450mmcentres along the length of the bracing element. Forwind bracing wall capacities of up to 3.0kN/m fix a120x45 MGP10 strongback to the vertical web nearestthe end of the bracing element. The strongback willpass through two trusses either side of the wall and fixto the webs with 2/12gx65mmTimberfixx screws. The flooringmaterial shall be nailed andglued to all floor trusses in theflooring system.

If a bracing wall sits directly overa floor truss then fix 14gx100mmTimberfixx screws into the trussat 450mm centres along thelength of the bracing elementalong with 2/14g x 100mmscrews at each end for 1.5kN/mwind bracing capacities. Use 4screws at each end with thestrongback detail as outlinedabove for up to 3.0kN/m windbracing capacities.

Bracing walls perpendicular to thefloor trusses For wind bracing walls of up to 1.5kN/m wind bracingcapacity with the element no higher than 2.7m, use14gx100mm Timberfixx screws to fix the bottom plate ofthe bracing element to each perpendicular floor truss. Ifthe end of the bracing element finishes directly above afloor truss use 2/14gx100mm Timberfixx screws, and ifnot then use the same screws into the nogging aspreviously mentioned. For wind bracing walls of up to3.0kN/m capacity adopt the same details as for bracingwalls parallel to the floor trusses. The flooring materialshall be nailed and glued to all floor trusses in theflooring system.

Platform FlooringWhere a structural platform floor has been constructedover the trusses, any non-loadbearing wall parallel tothe trusses does not require additional support otherthan that of the platform flooring.

INTERNAL NON-LOADBEARING WALLS

Max. Wind Brace Capacity of 1.5kN/m

Internal Bracing Wall

Fix Bracing Wall to Nogging Using 2/14g x 100mm Timberfixx Screws at

Each Floor Truss Crossing Under Bracing Element

3/3.75 x 90mm Nails Fixing Nogging to Upright Member

3/3.75 x 90mm Nails Fixing Upright to Top And Bottom Chords

2/12g x 65mm Timberfixx Screwsto Strongback

120 x 45mm F5 or MGP Upright Member

End of Bracing Element

Fix Bracing Wall to Nogging Using 2/14g x 100mm Timberfixx Screws

120 x 45mm F5 or MGP Nogging

PARALLEL BRACING WALL

PERPENDICULAR BRACING WALL

Max. Wind Brace Capacity of 1.5kN/m

Internal Bracing Wall

Fix Bracing Wall to Nogging Using 2/14g x 100mm Timberfixx Screws

3/3.75 x 90mm Nails Fixing Nogging to Upright Member

3/3.75 x 90mm Nails Fixing Nogging to Top And Bottom Chords

For wind bracing capacities of up to 3.0kN/m extend a 120 x 45mm MGP10 strongback through two trusses either side of bracing wall

at the nearest vertical web. In the 3.0kN/m case adopt an M10 bolt connection through nogging rather than screws and use 12g x

65mm Timberfixx screws elsewhere instead of 3.75 x 90mm nails.

2/12g x 65mm Timberfixx Screws

120 x 45mm F5 or MGP Upright Member

Length of Bracing Element

Max

. 270

0mm

H

igh

Wal

l

75mm Nails @ 150mm Centres

120 x 45mm F5 or MGP10 Nogging


Fitted FlooringWhere a fitted floor is being used,locate a double truss under eachwall to provide support to both thewall and flooring. Alternatively, usesupplementary ledger plates fixedto the side of the floor trusses.

NON-LOADBEARINGWALLS UNDERFloor trusses must be adequately supported on the loadbearing supports nominated in the design. There may be a detrimental effect on the walls and the flooring system if the trusses bear on a non-loadbearing wall. The tops of the internal non-loadbearing walls need lateral stabilizing by fixing to the truss bottom chords. The trusses must be allowedto deflect downwards, so Pryda Partition Hitches havebeen developed for this purpose, which should be nailedto the truss near the top of the slots.

LOADBEARING WALLS UNDERWhere trusses are designed to sit on internal loadbearingwalls it is important that the vertical compression websor blocks are in line with the support.

Fitted Flooring

Non-Loadbearing Wall

Fitted Flooring

Non-Loadbearing Wall

Single Web

Internal Support Wall

SINGLE WEB SUPPORT DOUBLE WEB SUPPORT

Double Web


45mm Thick Block (Solid or Claw Joined)

250or DeeperMax. 600mm


NAILED BLOCK SUPPORT

FITTED FLOOR FIXING – DOUBLE TRUSS

FITTED FLOOR FIXING – SUPPLEMENTARY LEDGER PLATES


Fully Supported End TrussWhere the end floor truss is supported alongits full length by a lower storey wall or bycontinuous base brickwork or footing whilecarrying an upper storey wall above, asimplified floor truss, as shown, may be used.

End Truss Under Gable RoofWhere the end floor truss is located under a gable endroof and is free spanning, it is appropriate to use asingle floor truss as it is carrying a non-loadbearing walland floor only.

Offset Loadbearing WallsIf the walls supported by floor trusses are required tocarry roof or other loads, please refer to a Prydalicensed fabricator to verify that the trusses areappropriately designed for this situation.

EXTERNAL WALLS

Pryda Floor trusses can bedetailed to suit an openingin a floor, e.g. as required toaccommodate stairs. Aheader beam is normallyrequired to support theincoming trusses while adouble lamination standardtruss is often suitable tocarry each end of theheader beam.

FLOOR OPENINGS

Beam Pocket SupportThe header beam should be blocked hard up against the undersideof the carrying floor trusses and nailed to each vertical web with4/3.15x75mm nails. The beam should bear on both laminations ofa double supporting truss if a double truss is specified.

Diagonal Webs at Max. 6000mm Centres

Additional Block Required For Loadbearing Jamb Stud Above

Modified Floor Trusses

Jamb Studs With Lintel Over

Curtailed Truss Span

Double Truss

Header Beam

Opening

Solid Packing Under

Header Beam


Block SupportAlternatively, a solid block (600mm long) fixed tothe side of the trusses may support the headerbeam. The header beam may be notched into thesolid block or fixed to the block using a Pryda JoistHanger as shown.

The open web configuration of PrydaFloor Trusses permits ductwork andmechanical services to pass through thedepth of the truss.

DUCTS FOR MECHANICAL SERVICES

Under concentrated loadings there may bespecifications for two floor trusses to act as one. In thiscase the web profiles of both laminations shall beidentical and connections should be introduced at2400mm centres maximum via vertical webs forLongreach. For Pryda Span supplementary vertical websmay be nailed to the side of the truss (see strongbackinstallation section) to simulate the vertical webrequirement at 2400mm centres maximum.

A 140mm x 35mm block or Pryda Nail On Plate shouldmake the connection between both vertical webs with3/3.15x75mm into each vertical.

MULTIPLE TRUSS FIXING

Header Beam

35mm Solid Block Fixed To Side of Truss With 75 x 3.75mm Dia. Nails at 50mm Centres

Pryda Joist Hanger

PRYDA JOIST HANGER SUPPORT

NOTCHED HEADER SUPPORT

Header Beam

Pryda Triplegrip

35mm Solid Block Fixed to Side of Truss With 75 x 3.75mm Dia. Nails at 50mm Centres

600mm

Max. 500mm

Max. Pipe Dia. Permitted In-Between Web Profiles (Refer Span Tables)

Max. ClearDepth

CENTRE GAP FOR MECHANICAL SERVICES

MULTIPLE TRUSS FIXING

3/ 3.15mm x 75mm Nails Into Each Vertical


Internal CantileversIn this case the first floor trusses are cantilevered only asmall amount as an architectural feature.

External Cantilevered BalconiesThis detail concerns the cantilever which forms abalcony generally outside the room. The cantileverbalcony beam, fitted alongside the floor truss, shouldrun a similar distance back into the floor truss and atleast to the next vertical web past that distance. Thecantilever joists are to be fixed to the truss bottomchord and vertical webs with 3.75 mm dia nails (75mmlong into 35mm joists and 90mm long into 45mm joists)at maximum 200mm centres.

Note: This cantilever detail is not intended forcantilevers carrying loadbearing walls over.

Offset Wall CantileverA common cantilever issue encountered is one in whichthe timber clad second storey frame is offset 150mmoutside the lower storey frame.

CANTILEVERS

Floor Truss Span

Cantilever Length

INTERNAL CANTILEVER DETAIL

Solid Block to Suit Truss Depth (Min. F5) Trimmer Plate

Upper Storey Loadbearing Wall - Max.4000mm RLW - Conc.Tile Roof

600mm

Skew Nail

Pryda Triple Grips

Floor Truss

90 x 35mm F5 Pole PlateFixed to Top Chord And Vertical Webs With 75 x 3.75mm Dia. Nails (200mm Centres Into Chord)

Lower Storey Loadbearing Wall

150mm

Min

. 250

mm

CANTILEVER – PARALLEL OFFSET UPPER LOADBEARING WALL

Upper Storey Loadbearing Wall

Min

. 250

mm

150mm

Solid Blocking(Min. F5)

Min.300mm

CANTILEVER – PERPENDICULAR OFFSETUPPER LOADBEARING WALL

Cantilever Balcony Beam to Suit

75mm x 3.75mm Dia. Nails at Max. 200mm Centres Along Chords and Webs

Floor Trusses

Balcony Joists to Suit

Not Less Than Balcony Cantilever

Balcony Cantilever


Strongback beams run perpendicular to the trusses andare used to spread footfall impact loads to adjacenttrusses. They are required for all residential floors andsome of the lighter commercial floors.

Strongbacks are not required for trusses up to 3.5m inspan. For trusses 3.6m to 7m span, use one row ofstrongbacks located close to midspan. For trussesabove 7m span use 3 rows of strongbacks located onerow at midspan, and two further rows located at each ofthe quarter points.

Strongbacks should be fixed hard up against the verticalweb, but may be fixed up against the top chord or thebottom chord to suit. Fixings may be hand hammered75 x 3.75 nails, or power driven 75 x 2.9 nails, or 12g –11 x 65 Timberfixx screws. While screws are moreexpensive, they provide the best performance as theyare more rigid, they clamp the timber componentstogether, and they prevent squeaks due to various floorcomponents loosening over time.

Where Pryda Span trusses have been used, and there isno vertical web close to the desired location of thestrongback, a supplementary vertical web may be nailedto the side of the truss instead with 2 nails to the topchord and to the bottom chord, to provide a fixing forthe strongback.

Strongback Size Selection

STRONGBACK BEAM SELECTION

Nominal truss Strongback depth and No. of fixings

depth (mm) grade (all 35 mm thick) per connection

200 90 F5/P10 or 70 F17 2/nails or 1/screw

250 120 F5/P10 or 90 F17 3/nails or 2/screws




In locations where the strongback needs to be joined,either of the following methods may be used:

STRONGBACKS

Strongback Sizeas Per Table

LONGREACH STRONGBACK

Strongback Sizeas Per Table

PRYDA SPAN STRONGBACK

Overlap Strongback at Vertical Webs

STRONGBACK SPLICE

Min. 5/3.75mm Nails Each Side of Joint

Splice Strongback Together With Cleat on Side

ALTERNATE STRONGBACK SPLICE


Non-aligned StrongbacksIn cases where different adjacent spans cause thestrongbacks to be out of alignment, the following detailmay be adopted. Vertical blocks of 90 x 35 mm are fixedwith 2/3.75 dia x 75 mm nails to both top and bottomchords. Strongbacks are then fixed into the side of theblock and the preceding vertical web with the number ofnails specified in the table.

Strongbacks Not RequiredStrongbacks may be omitted from floors when:

• The floor has been designed for live load of 3000 Paand 4.5 kN, or greater.

• Either 25 mm F11 plywood, or 2 layers of 19 mm F11plywood (or better) has been used

In these situations, either the truss will be very stiff dueto the high design load, or the flooring itself is capableof dissipating human footfall impacts.

Instead, use 90 x 35 F5 (on flat) lateral ties fixed to thebottom chord, located approximately at the third pointsof the span.

Pryda floor trusses must be braced back to theirsupporting structure for stability in a similar manner to thebracing stipulated by AS1684.2-1999 for solid deep joists.Use diagonally placed Pryda Strapbrace or timber braces(minimum thickness of 25 mm) at 1800 mm centresmaximum at the ends of trusses and at any internal wallsupports. Alternatively, a continuous trimming beam maybe used at the end of each truss – see End Type 3 – withdiagonal bracing at the end bays only.

Pryda floor trusses are braced laterally at the top chordlevel by the flooring material and at the bottom chordlevel by the ceiling lining. If there is no ceiling fixeddirectly (or by battens) then 90 x 35 binders must beprovided on the bottom chord at 3000 mm centresmaximum.

STABILITY BRACING

Fix Trimmer to Ends of Floor Trusses With 2/3.15mm Dia. x 75mm Nails

End Trimmer

Note: End Brace Requires Diagonal Bracing Down to Wall at Each Endof a Bay of Trusses

Additional Block

Max. 600mm

Vertical Web

NON-ALIGNED STRONGBACKS

Length of Pryda Strapbrace to Suit Height of Trusses

Min. 2/3.15mm x 30mm Pryda Nails Into Side of Top Wall Plate and 2 Nails to Underside

Max. 1800mm Centres

90 x 35mm F5

2/75mm Nails Into Vertical

Web

Max. 1800mm Centres

P R Y D A F L O O R T R U S S S Y S T E M S1 0

Each truss shall be held onto its supporting plate/bearerby a minimum of 2/75 x 3.15 mm dia nails. If preferred,a better fixing may be achieved by using one PrydaMinigrip with 3/35 x 3.15 mm dia Pryda nails per tab.

When supporting trusses on steel or timber beams viatop chords it is preferable to restrain the bottom chordusing skew nails while the top chord should be fixed tothe supporting beam using screws or Pryda Triplegrips.This practice improves the stiffness of the floor byminimising movement and vibration at the supports.

FIXINGS AT SUPPORTS

2/75mm x 3.15mm Dia. Skewed Nails

75mm x 3.15mm Dia. Skewed Nails

Preferred

OPTION 2Pryda Minigrip With Min. 3/35 x

3.15mm Dia. Pryda Nails Per Tab

OPTION 12/75 x 3.15mmDia. Skewed Nails

TYPICAL PLATE SUPPORT FIXING

75mm x 3.15mm Dia. Skewed Nails

Preferred

Screw, Bolt or Drive Pin Fixing

TYPICAL BEAM SUPPORT FIXING OPTION 1

TYPICAL BEAM SUPPORT FIXING OPTION 2

P R Y D A R A F T E R T R U S S S Y S T E M S 1 1

PRYDA RAFTER TRUSS SYSTEMSMany of the installation requirements associated withLongreach and Pryda Span floor trusses are alsorelevant to the same products when used as roof purlinsor rafters. The floor truss installation guidelines for truss

orientation, bearing, non-loadbearing and loadbearingwalls under, and ducts for mechanical services alsoapply to the Pryda Roof System.

Bottom chord bracing Strongbacks are not required forLongreach or Pryda Span roof trusses.

For suspended ceilings, or exposedbottom chords, or where ceiling battensdo not provide restraint to bottomchords under wind uplift conditions, it is recommended that bottom chordties are introduced in accordance with AS4440 –1999: Installation ofNailplated Timber Roof Trusses. Inaddition to this, Pryda Speed or StrapBraces shall be fixed to the truss bottom chords to transfer bracing loads back to the supporting structureaccording to AS4440-1999: Installationof Nailplated Timber Roof Trusses.

In circumstances where the ceilingmaterial and battens do provide effectiverestraint then bottom chord ties shall notbe required.

BRACINGBRACING REQUIREMENTS FOR SUSPENDED CEILINGSAND UNRESTRAINED BOTTOM CHORDS

Top chord bracingThe forces generated by resistance to buckling of thetop chord and wind loading perpendicular to the span ofthe trusses must also be transferred back to thesupporting structure by steel braces. It is recommendedthat Pryda Speed Brace or Strap Brace be applied to

the top chord in conjunction with adequately spacedroof battens in accordance with AS4440 –1999:Installation of Nailplated Timber Trusses. The steel braceshall be continuous over the ends of the trusses and beanchored down to the top plate.

Steel Brace to Underside of Bottom Chord to Transfer Bracing Loads to Structure

Longreach or Pryda Span as

Roof TrussesBottom Chord Ties

Suspended Ceiling

Note: Refer AS4440 -1947 Installation of Nailplated Timber Trusses For Further Guidance on Bottom Chord Restraint Requirements

45O

Roof Battens Continuousi Thi A

Roof Battens Continuous in This Area

Bracing Between 30O And 45O to Top Plate

When Viewed in Plan

Steel Brace

Box Gutter

End Type 1

Loadbearing Wall Frame

Brick Parapet Wall

30O-45O

TOP CHORD BRACING REQUIREMENTS

Pryda roof trusses must be fixed downto the supporting structure usingconnections that match or exceed themagnitude of the wind uplift forces oneach truss. Each truss shall be held ontoits supporting plate/bearer by a minimumof 2/75x3.15mm skew nails, or onePryda Minigrip or Multigrip with3/35x3.15mm nails per tab. Refer toAS1684-1999 for further guidance onfixings and tie down requirements.

Pryda roof trusses shall also be bracedlaterally at the ends of the trusses usingPryda Strap Braces at each end of a runof trusses.

TIE DOWN AND FIXING DETAILS

Minimum Tie Down 2/75 x 3.15mm Skew Nails or Minigrip/Multigrip

With 3/35 x 3.15mm Nails in Each Tab. Refer AS1684 For Minimum

Tie Down Requirements.Bend Steel Brace Over And Fix With 3/35 x 3.15mm Nails

to Side And 2 Nails Over

Lateral Bracing at Ends of Trusses Using Pryda Strap Brace or Equivalent. Cross Brace at Each End of a Run of Trusses.

END BRACING AND TIE DOWN

BOX GUTTERSLongreach and Pryda Span may be designed toaccommodate box gutters. Pryda Span can comprise ofa notched solid block end while Longreach also has theoption of trimming the top chord with additional framingattached.

Austrim NylexBuilding Products Division

PRYDA (AUST) PTY LTD 29 Healey Road, Dandenong, Victoria 3175Tel: (03) 9706 5488 Fax: (03) 9706 5499Email: [email protected]: www.pryda.com.auOffices also in: Sydney, Brisbane, Adelaide, Perth, Auckland, Napier,Christchurch, Kuala Lumpur, Penang, Johor Baru, Bundung, Bangkok

Block Insert Option

BOX GUTTER OPTIONS

On Site Construction Option

guide to pryda floor & rafter truss installation

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