![]() ![]() There are ways to do it, but they all require some engineering. One way to eliminate the collars strucutrally is to install a load-bearing ridge beam, but again, that introduces other issues, with large concentrated loads coming down in random places with nothing below to carry them. The most common reason for installing collar ties is to prevent rafters from spreading apart under load. Collar ties, also known as collar beams, are horizontal members that connect opposing rafters near the upper third of the roof. If the knee walls are made load-bearing, perhaps you could cheat a bit on the height, but that introduces another structural problem…what would support the weight on the knee walls? The ceiling joists are probably barely adequate to become floor joists, if at all, and probably can’t carry the concentrated load from load-bearing knee walls without deflecting excessively. 40ft x 12 480 ÷ 24 on-center 20 rafters + 1 21 rafters per side x 2 42 rafters. You’ll get the number of rafters needed for your roof. After getting the answer, add 1 for the ‘0’ rafter and multiply it by 2. The rafters may bend and allow the walls to move, and the ridge may in turn sag. 40ft x 12 480 (length in inches) ÷ 24 on-center 20 rafters. Collar ties or ridge straps must be located in the upper one-third of the attic space, be a minimum of 1 inch by 4 inches (25 mm by 102 mm), be spaced not more than 4 feet (1219 mm) on center and connected in accordance with Table R602. Building codes such as the ICCs 2012 International Building Code section 2308. ![]() Any higher and you take the chance that they won’t funtion to keep the outer walls from spreading. Rafter tie or Collar Tie Spacing Intervals & Connection Specifications. If you are framing a cathedral ceiling, there are a couple ways to deal with the need for rafter ties. ![]() The rule of thumb I was taught is that the collar ties should be no higher than the upper third of the height between attic floor and ridge. Rafter ties (or ceiling joists acting as rafter ties) are required by code unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof. ![]()
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