The International Residential Code calls for 7 16d common nails per rafter. Jack up the ridge, nail in the ties, thru-bolt them or tie them to the rafters with plywood gussets on each side and lots of galvanized nails. Wood is less likely to raise an eyebrow in the future and it's easier to work with. Even a roof vent can be a big enough hole to bring 2X6's in. all you need is a small hole in one of the gable ends. Jacking the ridge with screwjacks would help.Ĭonventional wood rafter ties can be installed. In other words, don't even start if it doesn't give easy. The walls might not want to move and you could splinter a rafter trying. Cut the lengths and rig up the turnbuckles before you go up in the attic.Ĭheck ceiling edges before pulling the walls in. Too hard to work with.Ĭutting cable up in the attic with an angle cutter could start a fire up there. 'Strawline' is heavier but will not dig in. Or use a short loop of cable and clamps to attach the turnbuckle.įor cable strength, 'airline' cable, the type you might use on an electric winch, could be good, but it will cut in to the wood, unless you lined the hole with a piece of pipe. At the other end you could bolt the turnbuckle but it will pull sideways, unless you add a horseshoe-shaped strap like a yoke. If the wood is soft you may need to install brackets instead held with several thru-bolts. The hole should be as close as possible to the outer edge, the sheathed side. The attachment could be simply a hole in the rafter with cable threaded thru it and secured back to itself with at least two cable clamps. I am not an engineer and this is no substitute for an engineered design. 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. I'm not going to attempt to replace these joists myself but before I start asking builders to take a look I would like to know what to expect when I ask them how they intend to replace them so I can better judge which of them knows their stuff.Im planning on installing rafter ties in my 1952 cinder block home. I'm afraid I don't have exact measurements or a photo to hand but hopefully you get the idea. There is also a large timber (from memory, about 180x180mm in profile) running perpendicular to the ceiling joists, in the middle of the span, on top of them, and bolted down in places. Including the thickness of the walls I would say the joists are around the 6-7m mark. The internal span is about 4-5m and the external overhang is about 400mm on one side and 800mm on the other. The roof construction is a simple A-frame with collar ties sitting on brick walls. Most of the timbers look fine apart from two ceiling joists which have gone soft. One of the first and most important jobs I'll have to do is the roof.
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