Why do truss companies insist upon it (and inspectors) if it does nowt? Seems a bit odd to me.
Roof diagonal cross bracing
- Thread starter dazzler9000
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Thanks for your help everyone. Hopefully this thread will help anyone else in my position.
All diagrams I have, show the gable end trusses being omitted (low level fixing) with the emphasis being that the bracing continues to the WP. There is wording in both the TRA (Truss Rafter Association) book and the Alpine Truss Rafter Guide saying that the bracing 'must extend to wall plate'.
On raised tie rafters (as we are building at present) such is the emphasis on reaching the wall plate, that they insist you either run the bracing across the face of what will be the internal ceiling (sloped bit) of your roof and then 25mm batten the remainder accordingly, or omit that part of the bracing and use 9mm ply sheathing over the whole of the sloping ceiling, to mitigate.
We opted for the ply. I'm surprised you have not bothered with this important aspect before Woods.
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Nah that's a crap way which leaves the bottom part of a truss unrestrained and independent of the others.All diagrams I have, show the gable end trusses being omitted (low level fixing) with the emphasis being that the bracing continues to the WP. There is wording in both the TRA (Truss Rafter Association) book and the Alpine Truss Rafter Guide saying that the bracing 'must extend to wall plate'.
On raised tie rafters (as we are building at present) such is the emphasis on reaching the wall plate, that they insist you either run the bracing across the face of what will be the internal ceiling (sloped bit) of your roof and then 25mm batten the remainder accordingly, or omit that part of the bracing and use 9mm ply sheathing over the whole of the sloping ceiling, to mitigate.
We opted for the ply. I'm surprised you have not bothered with this important aspect before Woods.
The trusses should be designed and constructed as a single unit (the roof) placed on the other unit (the building). This way it all acts as one, and you don't want to be leaving one end truss out of the unit. The roof unit is then fixed to the building unit by other means.
Fixing the brace to the plate does nothing to help the bracing, and nothing to help holding the roof down.
On diagonal bracing, there can be a gap of one truss unfixed. The bottom part of any of the truss is the least vulnerable in terms of racking.
If it was crap then why do all manufacturers insist upon it?
It's a recommendation in BS 5268, 2006. It was not in the previous version, and yet I don't recall there being a rush of trusses leaning over in the 90's.
If you actually run a calculation on a braced roof plane, then one with all the members braced together performs better than one with the end member detached.
how does the bracing get fixed to the wall plate. Are they not supposed to just stop at the wall plate
All diagrams I have, show the gable end trusses being omitted (low level fixing) with the emphasis being that the bracing continues to the WP. There is wording in both the TRA (Truss Rafter Association) book and the Alpine Truss Rafter Guide saying that the bracing 'must extend to wall plate'.
On raised tie rafters (as we are building at present) such is the emphasis on reaching the wall plate, that they insist you either run the bracing across the face of what will be the internal ceiling (sloped bit) of your roof and then 25mm batten the remainder accordingly, or omit that part of the bracing and use 9mm ply sheathing over the whole of the sloping ceiling, to mitigate.
We opted for the ply. I'm surprised you have not bothered with this important aspect before Woods.
Have you any pics of the raised tie truss your installing with the ply, bracing etc.. It would nice to see because im thinking of doing my garage roof to raised ties in the summer.
You (obviously) leave it long enough to extend over the WP. You then fix a piece of infill timber to the plate then fix your bracing into that.
We have only just tiled it in and will be screwing the ply sheathing to the slopey bit after the insulation goes in, sometime in the NY. Those trusses are massive each one weighs 91kgs. There are doubles and triples too! Because of the 7.5m span they calculated that we needed a 'stacked' rafter meaning two pieces of 150mm timbers on top of each other.
The crane man was brill.
I would need to see pics of this because i cant get my head around it for now. Would extending it over the wall plate then nailing the bracing to the wall plate be ok?
We have only just tiled it in and will be screwing the ply sheathing to the slopey bit after the insulation goes in, sometime in the NY. Those trusses are massive each one weighs 91kgs. There are doubles and triples too! Because of the 7.5m span they calculated that we needed a 'stacked' rafter meaning two pieces of 150mm timbers on top of each other.
The crane man was brill.
Excellent! You can see they have been installed properly however why is there only bracing on the peak part of these trusses. I cant see non on the bottom of the rafters which will be the room. Will you be installing these at a later date or is this where you will be installing the plywood for bracing.
When your back on site, can you please take more pics of all angles of the bracing and what youll be doing once you go back.
My span is over 8m so ill need the double stacked timber also. We have installed trusses before and did this by hand. My trusses will be 8m span and 3m high. Think they will be 85kg but lifting these ones up might be heavy unless i get another 3 men in for help.
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With raised tie trusses, extending the 25mm x 100mm bracing all the way down to the WP is contentious because it interferes with what will be your internal ceiling (slopey bit). To mitigate this, you have the option to use 9mm ply sheathing over this part of the roof/ceiling and do away with the 25mm x 50mm bracing across the slopey bit.
All the rest of the roof is braced normally.
Yes i see, but would it not be cheaper to fill in with battens instead of the ply where there's no bracing like in attic trusses. . Would 9mm ply have enough strength for bracing. id have thought it would need thicker.
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