Steel cables instead of roof tie beams.

[roughbert]

My 1940s prefab was dismantled and re-erected on its present site in 1963. After a negotiation with the local authority planners, the low pitched roof of asbestos panels was replaced with a roof of more conventional pitch and covered with Marley tiles. Sixty years later, the rafters are sagging and the lap joints in the purlins are threatening to fail. As yet i have not detected any spread, but I am inclined to put in some ties to discourage it anyway.

Any practical experience of using multistranded stainless steel cable (or Dyneema!) fixed to rafters or wall plate to do this job would be of much interest, particularly regarding tensioning and fixings.

 

[a twig]

It’s something I’ve seen done in outbuildings but no practical experience of doing it myself.

Honestly given the other issues it’s something I’d be getting an opinion from a structural engineer about as the cables and mountings will need to be specified properly - you don’t want a steel cable under tension giving way - pretty lethal.

Steel rods might be a better solution.

 

[roughbert]

I should have mentioned that I know steel cables are used in this context.

Steel rods are heavy and expensive... a stranded steel cable of say 6mm or 8mm diameter is unlikely to fail catastrophically, the

You don’t want a steel cable under tension giving way - pretty lethal.

Steel rods might be a better solution.

I should have mentioned that I know steel cables are used in this context.

Steel rods are heavy and expensive... a stranded steel cable of say 6mm or 8mm diameter is unlikely to fail catastrophically, the most likely point of failure will be the bracketry coming away from the timber, and no human targets in range in my roof space! The tension in the cable will only be circa ½ ton.

 

[a twig]

I guess in that case it comes down to your confidence in calculating the loads, sizing the cable and fixings to suit and ensuring that the timber you are mounting them to is in good enough condition to take the fixings.

 

[skierhughes]

and no human targets in range in my roof space! The tension in the cable will only be circa ½ ton.

Unless you just happen to be up there to fetch something, check on something else, do some other repair work etc?