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. Tie downs is a generic term used to describe various methods of securing a structure in position to prevent potential storm damage. 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. Im sure you can, the trick will be getting it approved by the Building Dept. 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. Re: Substituting ceiling joist with steel rod/cable to prevent wall plate spreading. 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. Figure 4: Free Body Diagram of the Rafter.Moments are summed about a point on the ridge of the roof. Consider the following free body diagram (Figure 4). ![]() ![]() ![]() The collar ties are intended to equalize uplift pressure on the roof during high wind events. To establish the relationship discussed in the article, we need to observe that the sum of the angular momentums must be 0. In age old timber frame buildings, like the gothic cathedrals of the middle ages, enormous stone buttresses stabilized the walls allowing for graceful arched beams to create a beautiful timber ceiling. 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. Steel tie rods solve the age old problem of roof construction they hold the walls from bending out as the roof is loaded with wind or snow. The ceiling joists are intended to carry the outward thrust on the walls generated by the ceiling rafters. An additional cleat is inserted in the eaves beam corners (making two cleats in total) whilst this is backed up by a further butterfly cleat (illustrated).I am not sure you fully understand the function of collar ties. A Ridge Compression Plate sits at the end of the aluminium ridge body where it joins the house wall – this distributes compression forces across the host wall and allows installers to assemble and suspend the starter bars prior to attaching the main ridge body. It also ensures that additional reinforcement is offered where the bar intersects the eaves beam. In many church and barn roofs the tie beam is cut off ( fig. Cast aluminium ‘end stop’ on the eaves beam featuring integral slots for two anchor bolts to hold the conservatory to the host wall even more securely.This short piece of reinforcement in each starter bar ensures that three anchor bolts are drilled into the host wall, when the reinforcement prevents the aluminium bar being crushed under excessive torque. ![]() An aluminium bolster beam extends along the entire length of the ridge and acts as one with the existing aluminium ridge body to virtually eliminate deflection.
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