Moving Collars

[crawf1982]

My roof follows the design shown here

Firstly, am I right in thinking that the hangers are purely in tension and are there to help suspend the ties?

Secondly, there are 2 collars in my roof that both originally ran between the rafters at a height just below the purlin. One of the collars has been cut and moved so that it is now about two thirds the way up the roof space. My question is has this affected the roof structure in any negative way?

Would it be worth putting in some extra beams as shown in the "OPEN PLAN" truss here?

I can understand why the collar was raised - I certainly don't hit my head on it as much as the other one when I'm up in the loft. If adding the extra beams to make it an open plan truss will maintain the structure I may well think about moving the other collar up to the same level.

Any advice would be greatly appreciated.

Cheers,

Dave

 

[chappers]

The collar should really be at the same point as the purlin and hanger, this stops the rafter sagging inwards at this point allowing the hangers to then do their job and actually help suspend the ceiling ties, if there was any sag at this point then the hangers would be haveing a negative effect and could be pushing down onto the ceiling ties instead.
How wide is your roof from wallplate to wallplate as if it isn't too wide then moving the collar up a bit probably wont have any dramatic effect.
I would be a little bit more wary of adding the extra supports as they will transfer the load from the roof down onto the ceiling ties which probably aren't designed for the job

 

[crawf1982]

The wall plates are 7m/23feet apart.

 

[chappers]

thats quite a wide span, dependant on the size of your rafters, I would be a bit wary of moving the collars too much