Rough cost of roof bracing/straps?

27col

Come on, Dryrot, you and I both know that putting in a few diagonal braces is not rocket science. Especially with the comprehensive instructions listed in the OP's post.

Dry_Rot

yes 27col - I think I said it was straighforward; we agree on that. I come across surveyors who sem to enjoy the chance of asking awkward questions, especialy when other surveyors have already been involved. either way will do - specialist or DIY, but all these matters should be thought about first.

Have a nice week all

vaio

davido140 wrote: »

........The paragraph above was only a snippet of a very long section about the roof, bit more info, there has been some evidence of movement and the risk the surveyor was concerned about was a "domino" effect of roofs toppling over if one in the terrace went, apparently there are well documented cases of this happening.......

Happy to be corrected but I thought the diagonal braces where used to keep everything in place before (as in until) the battens were nailed on. Once the battens are nailed on they will turn the whole thing into a “sheet” structure which I can’t see any possibility of any sort of domino effect toppling it sideways. (or if the domino forces are strong enough to overcome the 10 or 15 batten fixings then an extra fixing from the diagonal brace is not going to have any significant effect)

I’d be interested to see some of these “well documented” instances, got any links?

mysk_girl

If you just relied on battens nailed to trusses, then everything is at right angles forming lots of little squares. There is no inherent in-plane stiffness to a square, it will lozenge relatively easily. Diagonal braces turn everything into triangles, which are, well, triangulated.... And therefore stiff in-plane.

I was taught at university that when we saw the Scandinavian countries using prefabricated roof trusses, and though "Wow, that's a good idea!", what the British failed to notice for a while was that the Scandinavians traditionally covered these trusses with plywood (aka solid sarking), nicely nailed to everything. This also acts as a diaphragm and prevents the trusses from going sideways, wheras the English (I believe the Scots use solid sarking) usually use a fabric sarking, which unforunately doesn't prevent this sideways movement (racking). We have since learnt the error of our ways and now use diagonal bracing to fulfill this requirement. Therefore, older houses with trussed rafter roofs may often lack the diagonal bracing required for full stability.

vaio

I stand corrected, thanks

Do you have any links to some of these well documented cases of domino effect collapses?

mysk_girl

I don't have any links, the majority of cases are not catastrophic collapses, but the shifting of between 1 and 5 trusses laterally. While this would not cause a roof collapse, obviously the tiles (which are brittle) would be damaged and there would be some impressively large holes in the roof. In these cases, if the trusses have not been structurally damaged, the solution is to jack them back vertical, add the required bracing and then retile the roof. Expensive enough, I would imagine! Anecdotally, I am aware that there have been a couple of situaions where a whole terrace lacking bracing have all gone together. And it is well accepted in Part A of the Building Regulations that diagonal bracing to trussed rafter roofs is a necessity. I will have a look when I go back to work tomorrow to see if I can find any references to major cases.