If they are there to stop roof uplift they are normally positioned in the top 1/3 so moving upwards should be better (if that is their function)
Can I change my roof timbers? (Ed.)
- Thread starter MorphDoc
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Wouldn't uplift, only be a potential problem during construction? Roof in place, no windows or doors in, high wind getting inside.
A roof 'diaphragms' under wind loads. ie. it moves up and down slightly.
I'm not sure they're adding anything structurally, anyway it would need an SE to confirm. @George_engineer
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Its the external suction, similar when tiles are sucked off in storms and planes uplift on the wings when flying.
Possibly as an aid to placing purlins during construction as mentioned in #4. a bit OTT but if the chippy was on his own who knows? as you say structurally the purlin is spragged off in the centre so these timbers would not be doing anything in reality
These are collar ties - while I can't see the width of the purlin(s) in the images, generally collars are used [edit - when used between purlins] to enable you to skin the purlin size right down. The collars then support the skinnier purlin.
Restraint forces are quite minimal - the purlin will take the majority of load and collar just carries the restraint force - so I wouldn't be lulled into thinking they don't do anything only because there is a few nails.
So I wouldn't remove without getting an engineer to come check and you will likely need to reinforce to the purlin.
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Purlins are 5cm in thickness. Span entire house (7m)
The purlins are not resting on those collar ties. I can literally glide a piece of paper between the collar tie and the purlin. There is only 1cm of direct contact between the purlin and collar rie. I just need to put a bit of pressure to slide a piece of paper into that position. Sure, 1cm of contact between the purlin and the collar tie isn't providing any support, right? The only support those purlins have is from the middle V shaped support. This feels very sturdy and is resting on the solid wall.
Those ties are put on every 3rd rafter (apart from the last one, which has 5 rafters behind it without the tie).
Not an expert, just employing common sense, but....
In the great scheme of structures, how can any structure expect to be supported, or held together by a couple of rusty nails? If that timber had any serious intent, then it would have been jointed, or at least bolted in place.
Possibly dried and shrunk over the years and waiting for snow load to occur to put load on tiles to rafters to purlin to collar ties although I am not convinced those are correctly termed collar ties, being so low down low down, and are there for support purposes as opposed to the central sprag.
Back in 1955, the chances are, they would not have a craine to lift those timbers into place, it would be done by mostly by hand, plus chain blocks. Much easier to achieve, if at least some of the timbers are pinned together, at the correct angles, on the ground, then drop those in the correct alignment, and infill the rest, by eye?
Thanks for all the replies! very interesting!
My plan was to move a single "tie" upwards at the head tie and then support purlin at that point by attaching structural timber to the floor frame.
I am not convinced these ties serve any purpose other than prevent wind uplift, but even so, they could be moved higher up to serve the same purpose.
But after this discussion, I think I will have a look at how much structural engineer charge for an opinion. If it is too expensive, I would probably just leave things as they are.
My plan was to move a single "tie" upwards at the head tie and then support purlin at that point by attaching structural timber to the floor frame.
I am not convinced these ties serve any purpose other than prevent wind uplift, but even so, they could be moved higher up to serve the same purpose.
But after this discussion, I think I will have a look at how much structural engineer charge for an opinion. If it is too expensive, I would probably just leave things as they are.
They are there because the purlins where under sized, possibly couldn't get the correct size so just added some bracing. You could remove it and cut it to fit just above where it is now but sat on the purlin at a rafter connection, you would need to shape the 4x2" into a blunt point at both ends, If you cut it neat you could knock it out and replace it every time you needed to work up there.
If that were the case, why just pin it in place with such weak nails?
Some of those diagonal timbers, look like fairly recent additions.
It was just from boarding the loft. I am not really sure whey they did that?
Also, my ceiling joists are working as "rafter ties" as they are connected to the bottom of the rafters.
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