Vertical trusses

[MortarThePoint]

I wondered what people's expectations were for truss verticality. The chippie has got the trusses roughly set and is fine tuning as he fits the trimmers. Being as I am, I can't help but get a level on it. I wanted to check my expectations though. My feeling is as long as the bubble is just touching or inside the lines it is OK. Trusses are made of wood that can be slightly twisted and warped so better than that feels unrealistic to me. You want to be using a 1800mm level for this.

 

If you like numbers: My level is +/-0.5mm/m accuracy which I think means it is +/-2mm between the lines (https://www.leveldevelopments.com/2020/10/sensitivity-accuracy-of-spirit-level-vials/). 2mm/m (0.1degrees) would give a horizontal deviation of 6mm and a vertical deviation of 0.0mm on a 3m truss. To reach 1mm of vertical deviation the horizontal deviation needs to reach 77mm, or ~25mm/m (1.5 degrees).

 

I expect a roof would actually be fine if the trusses were off by 1.5 degrees or more because the trusses are all braced so it's not so much about the trusses toppling. The profile of the roof isn't substantially affected even at 1.5 degrees. The exceptions to these are at hips, valleys and gables as such deviaton would move the positions of these elements that would then affect the profile of the roof. You'd be asking more out of the battens though with 1.5 degree error as the nominal 600mm could become 600+77+77=754mm so about 25% over what it should be.

[Oz07]

Isn't textbook like within 15mm  from plumb?

I set my first by eye, temp brace off scaff, chuck all my others in at 600, nail longitudinal braces, go back to the first and set bang on for plumb, then 're nail temp brace and fit all diagonal bracing. 

[MortarThePoint]

Easy to find Australian guidance suggests up to 50mm out of plumb is acceptable. That's a bit much for my liking, but shows it's not very critical.

http://www.hyne.com.au/documents/Feature Documents/TQ_26_TrussInstallation_final.pdf

[Russell griffiths]

I think you need to find something else to worry about 10-15mm out of plumb would hardly show up on the chippies level

 

if you can still see the bubble it’s fine. 

[MortarThePoint]

1 hour ago, Russell griffiths said:

I think you need to find something else to worry about

 

I'm not worried about it, that's what worried me ?