How to replace roof cable truss?

[melb22]

Crack in ceiling caused apparently by cable truss in roof space snapping. Can metal cables be replaced and how to access such cables (and installers).

[JacobZ]

Hi @melb22,

A warm welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Roof cable truss systems are engineered structures that use tensioned steel cables to support and stabilise the roof, often over wide spans where traditional timber trusses may be impractical. These cables act much like tie beams, resisting the outward thrust from the rafters and preventing the roof from spreading. The system relies entirely on the tension within the cables, so any failure such as a snapped or loosened cable can compromise the structural integrity of the roof and lead to visible issues like cracks in the ceiling or even sagging in the roof structure.

It should be possible to simply replace the damaged component; however, this is not a repair that should be undertaken lightly. The cables must be replaced with materials of equivalent strength and specification, and they must be correctly tensioned to ensure the stability of the entire roof structure. Incorrect tensioning or the use of substandard materials can worsen the problem or lead to more significant structural failures over time.

Accessing these cables typically requires entry into the roof cavity, which may be constrained or obstructed by insulation, ducting, or other structural members. In some cases, ceiling plaster or roofing materials may need to be removed to allow sufficient working space. Depending on the age and design of the home, the original cable configuration may be custom, requiring a fresh engineering assessment to determine the appropriate method for repair or replacement.

It is crucial to engage an experienced and licensed professional for this type of work. A general builder or carpenter could provide an initial assessment, but any repairs to roof tensioning systems, should be carried out under the direction of a structural engineer. This ensures the integrity of the repair and compliance with building codes.

It is extremely important for the structural integrity of your home that this is assessed and rectified in a timely manner by a professional.

Let me know if you have any further questions.

Jacob

[melb22]

Roof cable truss systems

Hi Jacob,
I know nothing about roof cable trusses.    I was hoping to grab a little knowledge, but was amazed at the amount of information you provided.  Thank you very much. I am impressed.

I have paid particular attention to your caution to engage a structural engineer and will do so -

“but any repairs to roof tensioning systems, should be carried out under the direction of a structural engineer. This ensures the integrity of the repair and compliance with building codes”

I see that the actual work might be undertaken by others, perhaps a builder or experienced carpenter, under direct “supervision” by the engineer.

I suppose it’s beyond your remit to provide direct advice about such personnel – but how do I go about getting this started?  I have absolutely no previous knowledge about building or repair matters.

Are there Association listings of Structural Engineers?
Do I just search for Engineers “near me” and engage directly.
I see one very large building supply company close-by that sells cable trusses very like the ones I need – do I have a chat with them for guidance re how to access suitable professionals and/or installers?
Do Bunnings stores sell these and should I visit there for further follow up - now that I have an idea what I am looking for – perhaps to gain further supply and professional operator advice.

Once again, thank you so much for your impressive, detailed information. Splendid.
I am so pleased I joined Bunnings Workshop.
melb22

[JacobZ]

Hi @melb22,

I'm really glad I could help you with a starting point.

Unfortunately, due to the complexity and somewhat niche nature of the issue, it is going to be outside of Bunnings' scope, so I wouldn't advise heading into your local store looking for advice or supplies. 

I would probably just search for "residential structural engineers near me" and give the ones that look reputable a call. If you explain the issue and see what they think, if it is outside of their expertise, they should be able to at least point you in the right direction. Once you find a structural engineer who can assist, they will have contractors that they work with regularly and knowledge of the suppliers in your area.

Out of curiosity, who was it that told you that the issue was due to a snapped cable truss? They could be another person worth speaking to. If you haven't seen the issue yourself, they may be able to give you a bit of a breakdown of what they saw that you could then pass on to a structural engineer.

If you could gain access to your roof cavity and take some photos, we may be able to offer further advice, but the final determination on a repair would still need to be done by a suitably licensed professional.

Let me know what you think. I'm happy to offer further guidance if required.

Jacob

[melb22]

Hi Jacob,
Thanks your advice regarding how to progress with engaging "residential structural engineers near me" re the broken cable truss.  We will commence soonest.

Background re your curiosity question about the cable truss identification issue.

.There was a very large bang in the middle of the night.  House was inspected then and cause not identified. It was several days later we looked up and saw the ceiling to cornice crack.

.Friends said it might be a cracked or otherwise broken slab.

.Engaged a “free quote’ reputable repair company.  They were thorough in their inspection and measurements in every room and outside.  They said the slab and walls were all good and not part of the problem. They said they didn’t do roofs.

.Next door neighbour said his house and ours were built about the same time, and maybe by the same builder.  A few years back he had a 2nd storey added and noted during construction that his old roof area had steel cable trusses – maybe ours was the same.

Engaged a “free quote’ repair company that did general repairs – including roof areas.

They could not find any immediate or emergency work needed in the roof space and could offer no enlightening comment re the cracked ceiling.

They said there were areas of wear and tear in the rafters and they could quote on refurbishing those to protect the roof integrity for the future.

The inspector found a snapped steel cable in the roof space and photographed it.

He showed it to my daughter who surmised it looked like a broken steel cable truss – as had been described to her by her neighbour.  The inspector did not seem overly knowledgeable about cable trusses, and said they did not do that sort of repair anyway. He did not leave the photo.

.My daughter said it was about pencil-thick or thereabouts and looked like woven steel.

So, as you suggest, we really need to get a structural engineer to confirm this, and oversee his suggested rectifications.

Many thanks for your expert and ongoing assistance,

melb22