How to Install Collar Ties to Roof Rafters
Collar ties in conventional rafter framing help prevent the rafters from spreading apart under heavy loads. A collar tie is fastened between two opposing rafters on opposite sides of the ridge beam and the lumber size is specified by the architect or engineer. A collar tie is not a quick fix for sagging rafters. Collar ties will change the load bearing capabilities of the roof and, in some cases, will cause additional problems with the home's structural framing. An architect or building engineer should approve all structural changes to a home, including adding collar ties.
Hold the 1-by-4 lumber between two opposing rafters and place the level on top of it. Adjust the 1-by-4 until it is level and the bubble in the level's vial is centered. Loosen the wing nut on the bevel gauge and adjust the angle to match the angle between the 1-by-4 lumber and the rafters.
Place the bevel gauge against the side of the 2-by-6 lumber for the collar tie at one end. Transfer the angle to the end of the plank with a pencil and extend the line fully across the plank.
Cut the collar tie with the circular saw on the line. Measure from the point of the cut to the other end of the collar tie according to the length required and mark the same, but reversed angle cut at the other end of the plank. Make the second cut with the circular saw.
Hold the collar tie against the bottom edge of two opposing rafters with the level sitting on top of it. Adjust the collar tie until it is level. Drive one nail through each end of the collar tie from the bottom of the angled portion into the rafters to hold it in place.
Place a tie plate across the joint between the collar tie and the rafter on one side. Nail the tie plate to the rafter and to the collar tie using one nail in each tie-plate nail hole. Use all of the nail holes in the tie plate. Each collar tie requires four tie plates, one on each side of both rafters and the collar tie.
- A better fix for sagging rafters is to reinforce the existing rafters with a second rafter nailed alongside the first. If an interior weight-bearing wall is present, adding kickers that support the rafters is an even better option. Install collar ties no lower than the height of the ridge beam divided by 3.
- The 2-by-6 lumber is sized accordingly for 2-by-6 rafters. Increase the size of the collar tie lumber to match the collar ties if necessary.
- Adding collar ties to sagging rafters may increase the forces where the rafters meet the vertical wall framing. This can cause the rafters to push the walls out. Don't add collar ties unless recommended by a building engineer or architect.
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