Less opportunities for error with structural ridge. Areas with higher snow loads I assume can't get away with these errors and may have them less frequently (I hope at least) RE: 2x8 roof rafters, adding collar ties jdgengineer (Structural) 29 Jan 17 20:27īecause these are so common I'm nevervous about contractors properly installing conventional framing. As we don't have snow loads these roof defects tend to perform "OK". Typically, at least one (usually more) is present:ġ) ceiling joists perpendocular to rafters in some area without additional rafter tiesĢ) rafter tie to ceiling joist occurs only every 3rd rafter and connection only has a few nailsģ) one side of the ridge is partially vaulted but no consideration to the fact that the rafter tie no longer runs plate to plateĤ) purlins are overspanned and only have braces at perpendicular partition walls rather than closer spacing required.ĥ) ceiling joists are not properly connected at splice locationĦ) no structural support at hip / ridge intersection.Ĩ) at prulin brace locations no consideration given to impact on floor loading below for concentrated load.īecause these are so common I'm nevervous about contractors properly installing conventional framing. To this day I have never seen one of these roofs without a "flaw". Most homes built earlier than 1980 in our area are conventionally framed. Most other engineers in our area show it the same way so it isn't a fight. Yes, thankfully builders around here are used tonl framing everything around here with structural beams. RE: 2x8 roof rafters, adding collar ties jdgengineer (Structural) 29 Jan 17 15:15 Aside from large wind events, I don't think you will see noticeable roof framing improvement as a result. ![]() I think the requirement based on conventional construction is to have collar ties 48" oc max so adding in additional infill ties will meet that requirement. They will help with some ability to resist unbalanced snow loads and wind uplift. If you are referring to adding additional collar ties at the top, fhey won't really help you too much. If your rafters are over spanned, adding additional rafter ties won't help you increase the capacity of the rafters but it will help reduce the demand on the rafter tie connection. ![]() Rafter ties allow you to form a field built truss and remove the necessity for a structural support at the ridge. See attached for good explanation from fine homebuilding. Collar ties occur at the top 1/3 of the rafter and are in place to resist wind uplift to keep rafter from seperarting from the ridge. I'm assuming you are confusing collar ties with rafter tie. I think you need to analyze the roof system so you can have an understanding of the impact.
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