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. Test your knowledge with 2 full practice exams based on the Residential Plans Examiner Exam & 1 Plan Review Test.Im planning on installing rafter ties in my 1952 cinder block home. Want to become a Residential Plans Examiner? * Reference Source – 2018 International Residential Code – So this sums up the basic code requirements for collar ties.įor more information regarding detailed requirements, be sure to check out Section R802.4.6 of the 2018 International Residential Code (IRC). Rafter ties are a completely separate topic of discussion but as for now this outlines some of the differences between a collar tie from a rafter tie. While collar ties are located in the upper one-third area of the attic, rafter ties are located in the lower one-third area of the attic space.Īlso while a collar ties needs to be no less than a nominal 1 inch x 4 inch member, a rafter tie must not be less than a 2 inch x 4 inch member. While collar ties are used to resist ridge uplift caused by wind loads, rafter ties resist rafter uplift (thrust) caused by wind pressure applied against the wall which moves up under the roof overhangs. Even though they sound like they have similarities, they are very different. Many people confuse collar ties with rather ties. To see how ridge straps must be fastened, we must refer back to Table R602.3(1) above which basically is the same as collar ties. These straps must also be space no more than 4 feet on center and be a minimum 20 gauge with a 1-1/4 inch width. In lieu of collar ties, the code allows you to use metal collar ties also know as ridge straps. What if you did not want to install collar ties in the attic area? Is there another option? By now you know that a collar ties is a wood member with a nominal size no less than 1 inch x 4 inch, spaced no more than 4 feet on center, and located within the upper one-third area of the attic space.
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