Question for building designers (Australia)

[Allm]

When preparing working drawings for building approval, what methods do other draftspeople use to determine the location of the truncated girder truss in a trussed hip roof construction?

Cheers
Ken Dyckhoff
CA X1 Build:11.4.1.7 metric

[Mark]

from a carpenters point of view they are normally at 2400 if trusses are at 600 centres and if they are at 900 centres the girder will be at 2700

[lofty]

Depends on the specifications, lately most of the jobs I've done had the truncated truss(es) start from 1900 station and on up to half width of a building.

The width of the roof affects how many truncated trusses you require, particularly with note to roof type, wind load and other items, the spacings of the trusses (450/600 is common for tiled roofs, 900 is common for sheet metal roofing). Some wide roofs have up to 5 girder trusses locked together with hips and jack rafters.

It might be easier to get a truss manufacturer to provide you with a drawing of the truss schedule to quote. Its not a usual practice, from my experience, to provide truss the specifications for approval, usually this may only come up if an on site inspection raises any queries (which is a very rare event) for which the truss manufacturer then needs to supply related justified calculations.

[Allm]

I've got no idea where the info came from or any real technical info to back it up, but I've always setout the TG at 2400 for tiled roofs (truss at 600ctrs) and 2700 for sheet roof (truss at 900ctrs),
Although, last week I found some info by SmartFrame to back up the 2400/2700 rule.
However recent truss layouts by truss manufacturers don't always seem to agree with this - maybe the building width does have some bearing on the TG location?
While it certainly would be better to "get a truss manufacturer to provide you with a drawing of the truss schedule" I don't know of any truss manufacturer who will provide this info without a confirmed order.
In the interim we have to provide this info on the drawings for the building application, and its embarrassing if the info provided is incorrect.
At this point I'll stick to the 2400/2700 rule and hope for the best.

Ken Dyckhoff
CA X1 Build:11.5.4.17 metric

[lofty]

Building width does change these, narrow ones do tend to start as short as 1800, while wider would conform to 2400/2700.

I'm sure there must be a formula around to determine this minimum station. If unsure, perhaps note on the plans *Truss dimensions and stations to be confirmed by Truss Manufacturer* or similar to that.