![]() Heck, I might go with 7k lbs cables, just to be safe. 1600 is the highest suggested, so if I doubled or maybe tripled that, I should be safe. I understand its not exact, which is why I would put a safety margin in the strength. If it is possible to support the ridge somewhere around midspan I'd slide an LVL ridgebeam under the current one, jack it into place and repair it that way. If so enter actual measurements of the ridge height and the proposed tie to ridge height, I suspect you'll be in the 1600 pound range. I'm assuming the cables will run above the current ceiling joists. You probably do have a raised tie situation though. 1281 pounds horizontal thrust, same as before, confirming both calcs are giving the same answer if the inputs are entered correctly. For a tie at plate level enter 34" tie to ridge height. Multiply this by the 102.5 span = ~34" ridge height. Enter that as rafter load in the raised tie calc. Multiply 17.08 square feet of tributary area by 50 pounds per square foot load = 854.16 pounds per rafter load. The rafters are spaced 2' on center so each rafter is carrying 8.54' X 2' of area, or 17.08 square feet. Taking half the 205" building width gives a rafter span of 102.5". ![]() I suspect there is an error in the way the load is being calculated when using the raised tie thrust calc. ![]() at your own riskįrom another forum Paul gives the load as 50psfĮntering that into the rafter thrust calc gives 1281 pounds of horizontal thrust per rafter pair at design load. I'm a builder rather than a computer geek so. is mine, it is where I keep my construction calcs and is free for anyone to use if they wish. Sorry for barging into your forum, I've found this post 2 other places on the net so far, hopefully paulmars will come back and read it somewhere. So, I want to know how strong a cable to buy and if a single attachment point to the rafters is adequate.ġ4 rafters (not including the gable rafters), 24" oc 2圆 This site formula gave me thrust of 1250 I have a bad back and cable is so much lighter too. One would be easy, more requires a special designed fastener.Īnother reason for not using wood rafter ties is that I would need to cut each rafter into three pieces to get them thur the attic access hole. Now, Im not sure how many that i need to connect the cable to the rafters. Using enough fasteners to hold it secure. ![]() Can someone help?Īlso, many sites discuss the number of nails/screws/bolts that are needed to fasten wood rafter ties. I have spent many hours trying to figure this out. Its most likely because I am using the formulas incorrectly. I have found several formulas on the net on figuring side thrust, but each i use gives different results. I have two unresolved questions concerning using cable. I do not plan on trying to take out all the sag (3'), just a little to remove some existing pressure on the side walls. I have a string pulled straight across the ridge inside the attic. Cable is stronger and will allow me to remove some of the pressure on the side walls, using a turn buckle I can pull up the roof slightly. In my research, I have discovered the idea of using cable instead of wood for the rafter ties. So, I decided to add the rafter and collar ties too. Vertical rafter supports and then a new roof cover too. However, Im adding hurricane straps, supports for the gable ends, and extra fasteners to hold the roof planking to the rafters. The roof does not have much sag and the walls have no apparent bow. The ceiling joists run parallel to the roof ridge. Every time Im in the attic and look around, I wonder what holds up my roof. Im planning on installing rafter ties in my 1952 cinder block home.
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