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I just bought a new property with a large garage and I'm curious about the roof structure. The roof structure is supported entirely on the front/rear walls using rafter and collar ties. The rear wall is block and the front wall is just a few posts between doors with framing on top (the front has an overhang over the aprons, so the walls are different heights). You can see the rafters are notched in front to sit on this framing. However, there are a total of 3 tension cables that are attached toward the rear of the rafters using a clevis and an eye bolt in front (there is a plate and nut on the other side of what looks like stacked 2x6). What I'm curious is why these tension cables are there and what they are doing (if anything at all). The one in the picture is somewhat in the way of where I plan to install a small lift and would like to remove it if possible.

During the home-buying/inspection process we've heard many things about these cables:

  • it was temporary for construction
  • it's a "repair" to keep the front wall stable from spreading because it was shifting
  • it's necessary to counteract the moment on the front wall due to it not really being a wall (but shouldn't the rafter ties be handling this?)

However, the one cable in question here has clearly been stretched and damaged over time, the bolt holding the clevis seems much too small to me to deal with any real force in a heavy load situation (e.g. snow), AND I can easily deflect the cable about 1.5" with a single finger, which leads me to believe even if it was supposed to be there, it's not really doing it's job anymore... the rafter it's bolted to also already has a 20' rafter tie, and the front rafter is sitting on that same 4x4, and the notch should allow the front rafter to counteract forces in the same direction as tension on the cable... unless the cable is just to support because the rafter tie is not large enough..

Has anyone seen anything like this before and can comment on the effectiveness or necessity of these tension cables?

From what I've read tension cables like this, even if used in the past, are pretty much useless over time unless you install them with turnbuckles and adjust them every year or so... makes sense. I can guarantee these things have been there as-is for at least 25 years. Not sure if I need to explore reinforcing properly or just ditch the cable.

Thanks in advance! Pics below:

You can see the cable on the other side of the garage door track, hard to see in the light tension cable Clevis bolted to rear rafter rear clevis Front eyebolt through 4x4 front eye bolt The cable has clearly been stretched beyond capacity or kinked/damaged at some point kink/twist in cable

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I think steel is not used because carpenters are not used to working with it. I would replace the cable that is damaged and the anchor bolt looks skimpy, If nothing else a bigger one would look better. Otherwise, I seen no reason to replace them. I have used cable a couple times for gate diagonals with turn buckles. The only place I have seen steel cable used in home construction was an acquaintance (another metallurgist) had a old garage that was collapsing because the joists were weak in tension. He put steel cables with turn-buckles across the span. He tightened them up to pull the walls to vertical and raise the roof back to normal. You can deflect the wire easily but it puts a large tension force in the cable; the same as hanger wire on the back of a picture frame.

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Yes, the cables were added at a retrofit to hold the front wall in plumb. You can confirm the straightness of the columns through surveying using instruments. The deflection will be quite small, yet leaving it unattended can lead to breaking up the rafter-wall connections. I don't recommend replacing or retightening the cables, it can provide a false impression of safety. I strongly suggest engaging a structural engineer to perform evaluations and make recommendations.

My assessment of the cause of the problem is twofold - the flexibility of the front wall and the rafter ties were set too high. Also, for a high pitch roof, the collar ties seem either missing or inadequate.

By the way, I don't think the strength of the roof, or the front wall, is an immediate concern, nonetheless, the problem can progress and cause significant structural damages down the road.

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One way of safely (with the limited knowledge we have about the case) removing the cable in question is:

  • To check the garage header and if it's not continuous double it by a continuous one. Check for the plumpness of the portal of the doors.

  • Then add 2- 2x4 tie beams to that header and back wall on the sides of space you need clear using Simpson Strong-Tie DTT2Z Deck Tension Tie or the like while holding the cable tight.

  • Then remove the cable.

here is a photo

tie

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