Alternatively, you can install roof trusses, which do not exert any outward load on the walls, and do not require rafter ties, since the truss replaces the rafter. You CANNOT REMOVE the rafter ties unless you undertake expensive work to replace the ridge board with a ridge beam, properly size the rafters (probably need to be larger than the existing, and connect the rafters to the ridge beam using appropriate brackets. For pictures and further discussion, see The collar tie is typically too light, and in the wrong location, to resist outward thrust on the walls generated by the rafters. A collar tie is a horizontal structural element usually located approximately 2/3 of the way from the floor to the peak of the roof. A rafter tie is normally located at floor level, and is usually the same as the floor joist. A rafter tie is a horizontal structural element intended to resist outward thrust on the walls. You could use steel rods, but you need to make sure they are designed to handle compressive loads during high wind events, so the rods do not buckle. I do not recommend replacing with cables. If you are required to have collar ties, you may want to consider replacing them with attractive lumber, or just paint them and call it good. There are a few jurisdictions that do not require collar ties at all, check with your local building inspector to see what the rules are in your area. If you want to get rid of the ceiling joists and collar ties completely, two common methods are to either replace the ridge board with a structurally designed ridge beam (expensive, complex operation), or replace the rafters and ceiling joists with roof trusses (expensive). Under certain conditions, the collar ties can go into compression, so use of cables is not recommended, since cables obviously cannot carry compression. Under normal load conditions, you could remove the collar ties and there would be no change to the configuration of your framing.ĭuring high wind events that generate uneven loading on the roof, particularly uneven uplift, the collar ties distribute the load across the roof, and are useful in minimizing the potential for roof failure. If the collar ties were installed after roof and rafter installation, the collar ties would carry no load under normal conditions, since the outward wall thrust would be carried entirely by the ceiling joists. The collar ties are intended to equalize uplift pressure on the roof during high wind events. If you were able to measure the stress in the ceiling joists (which requires special equipment not commonly available), you would find that the ceiling joists (also known as rafter ties) are in tension, because the walls are forced outward by the rafters, and the ceiling joists pick up the load. Collar ties mainly come into play where codes require improved ridge strength, such as in high-wind climates. The ceiling joists are intended to carry the outward thrust on the walls generated by the ceiling rafters. I am not sure you fully understand the function of collar ties.
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