Roof Truss:
Timber:
Materials:
Standard trusses
Top/ Bottom Chord
- 90×35 MGP10 or as design requires. 70mm only if height is a restriction by design.
Web sizes
- 70×35 F5 or as design requires.
Girder Trusses
Bottom chords
- Min height 120 MGP10 where truss boots or brackets require height. (eg. TBJ35)
- 90×35 MGP10 or as design requires where brackets are nail fixed 90×35 joist hangers.
Top Chords
- 90×35 MGP10 or as design requires
Web Sizes
- 70×35 F5 or as design requires
Valley Trusses
Top/ Bottom chords
- 70×35 MGP10 or as design requires
Web Sizes
- 70×35 F5 or as design requires
Timber cuts
Cuts at warnervale generally as per the database. Double cuts to webs are fine as cutting time on Hundegger Saw is not a delay and the nesting of double cut joints gives smaller nail plate sizes and cheaper trusses.
Panel Lengths:
Concrete Tile/ Heavy Roof
- Max Panel lengths 2700mm – Unless Multiple laminations allow or special design requires.
Sheet Roof
- Max panel points Max 3000mm. – Unless Multiple laminations allow or special design requires.
Valley trusses
- Max Panel lengths 1800mm king profile Unless special design requires otherwise.
Design Criteria
**Please note that the engineering and quote override these defaults. Refer to the engineering documentation for truss spacing details. **
Wind Speed
Trusses are generally designed using N2 as a minimum for tie down design.
Roof Loads
Loads as architectural or engineers plans require. Assumed 52kg/m2 for concrete tile or 5.6kg/m2, 0.48mm for metal sheet when loads are not specified.
Ceiling loads
NSW – Where ceilings are not specified it is assumed 10mm plasterboard direct bottom chord fixed to truss where trusses are 600c’s.
Truss Spacing
All trusses are 600c’s unless requested by builder and quoted otherwise. Check quote even when engineer says 900 NSW still often designs 600c’s
Special Truss Spacing Allowances:
No special additional truss spacing is allowed for unless noted on plan or by builder for:
- Skylights drawn as 600 – assumed to fit 600c’s (565mm clear).
- Flexible A/C ducting – assumed to fit 600c’s (565mm clear).
- Manholes – assumed to fit 600c’s (565mm clear)
- Fireplace Flues, etc.
Builder must specify where truss spacing doesn’t accommodate additional roof penetrations.
Girder Stations:
All girder Stations are 2400 unless design requires otherwise.
Spans =<4800 – TG will be located to suit best design. Apex girders may be used depending on additional creepers or trusses added within the run.
In some cases the length of the truss run may alter the station location to suit better spacing designs.
Garage lintels and other large openings
Truncated girders or girders may be located parallel to beams or in a direction to reduce loads to beams.
For T-Bars a maximum 2400 parallel station is used to keep roof load width to 2400 max.
Stations greater than 2400 are used only where the design requires such as low pitch and long spans or significant cost savings can be made. (Insert height/span general ratio here)
Internal Load Bearing Walls:
Only load walls that have been nominated on engineering unless specific allowances are made in the client specification.
Standard truss Internal supports to have a web to support. Some short span jacks and creepers up to 2400 may be designed to omit the web only in some cases.
Tip: In cases where a loadbearing wall has not been nominated by the engineering, but a loadbearing wall is required, check that the slab has been designed to carry a loadbearing wall in that section. We can then make that wall loadbearing if we run it past the client and the client confirms that they are happy with the change.
Overhangs:
Hip ends:
Structural fascia is applied to hip ends where overhangs are >610 or as the design requires such as cantilevers.
Structural fascia is not setback in NSW from the standard overhang dimension.
Gable ends:
Overhang < 150mm: Standard truss with blocking to form the rest.
Overhang => 150mm: Sprockets/outriggers to be designed & supplied.
Gable end trusses are set-down type ends unless the design requires otherwise. Z-sprockets are not preferred unless specified by builder due to difficult installation.
Box Gutters
Sizing as per plan.
Vertical end webs to form vertical ends and size as per design.
Additional Loads
No additional loads are applied by default – Additional loads are only applied when noted on plan or specified by the builder including loads for solar panels, hot water units, and A/C units.
A/C Units
A/C Units are supported from top chords in NSW. NO loads are applied to bottom chords as per A/C install guidelines to prevent ceiling vibration noise.
Space to hang the unit is left as minimum 1500wide x 1800(3 trusses) x 600high min.
An assumed weight of 30kg per point load to each top chord (60kg per truss) of the 3 trusses is applied to allow unit to be supported by 2 trusses
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