(MORE than 10' with fiberglass) 2x4 won't do. Google 'warm/ hot roofs in MN' You still need 8-10' of insulation with foam. Even though it is now allowed under the Minnesota code, it is still problematic, especially if the workmanship is not carried out to perfection. Until recently, Minnesota deleted this section (below) because it causes ice dams on the roof, which cause other problems such as rot and mold. I would bet that the other part of the house already exceeds the 500 sq ft / 20% exception. 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. Minnesota requires a R49 in the ceiling WITH a minimum 6' heel.html Or. Vertical rafter supports and then a new roof cover too. The exact size of a 2x4 is irrelevant when you still need 8-10' of insulation or more. 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. 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. In summary, collar ties and rafter ties perform different functions but are both essential roof-framing members.Im planning on installing rafter ties in my 1952 cinder block home. The 2006 IRC requires them to be at least 2-inch by 4-inch. It's not unusual to see rafter ties of either 2-inch by 4-inch or 2-inch by 6-inch.When rafters are installed on 24-inch centers, rafter ties are typically installed every other rafter.Where rafters are oriented perpendicular to the ceiling joists, rafter ties should be installed just above the ceiling joists.In most homes, the ceiling joists also serve as the rafter ties.A lack of rafter ties is a serious structural issue in a conventionally framed roof. Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses.They should be placed as low as possible in the roof framing. Rafter ties form the bottom chord of a simple triangular roof truss. A sagging ridge is one clue that the home may lack adequate rafter ties. When the walls spread, the ridge will sag. This helps keep walls from spreading due to the weight of the roof. Rafter TiesRafter ties are designed to tie together the bottoms of opposing rafters. Collar ties, contrary to popular belief, do not prevent walls from spreading.The 2006 International Residential Code (IRC) requires they have a minimum nominal dimension of 1-inch x 4-inch.Where they are required, they should be installed on every other rafter where rafters are on 24-inch centers.Collar ties are probably not needed if metal connectors were used to fasten the rafters to the ridge.InterNACHI inspectors should not call out lack of collar ties as a defect unless they know that collar ties were required in the jurisdiction in which the home is located at the time the home was built. They may or may not be required, depending on jurisdiction.Collar ties must be placed in the upper third of the roof.
This helps brace the roof framing against uplift caused by wind. Collar Ties Collar ties are designed to tie together the tops of opposing rafters. Collar ties and rafter ties are both horizontal roof-framing members, each with different purposes and requirements.