The term “purlin” has several different meanings depending on what part of North America you’re in, what part of the roof you’re talking about, and the background of the person you’re discussing it with, so don’t be surprised if someone tries to correct you. It’s a quality issue unless the roof is sagging then, it’s a structural issue and you should recommend stabilization by a qualified contractor. In older homes in some areas, it’s common to find no strongbacks. rafter for a 1 m half span on a 25 roof slope 307SE 10.25 Calculating rafter. I was doing some research today for my main job and came across this video. Also, look for improper installations, such as braces resting on ceiling joists, braces but no strongback, and too few braces. hip and valley roof 298SE 10.3 Pitched roofing in progress on a large. Fall protection tip, rafter tie off and hip anchor. If you know that the home was required to meet this code when it was built, call it a defect otherwise, limit your inspection to looking for signs of failure, such as sagging or broken rafters and broken components. Modern building codes call for strongbacks to be of equal or greater dimension than the rafter dimension, but most purlin strongbacks you’ll see will not meet this requirement. Purlin systems have been built in many ways - some better than others. Rafters which rest on the exterior walls at the bottom and connect to a hip at the top are called “hip jacks,” shown here as purple. Hips rest on an outside corner at the bottom and connect to the ridge at the peak. Hip rafters are simply called “hips,” and are shown here as brown. Hip roofs have “hip rafters” which are oriented diagonally to the ridge and outside walls. Stabilization typically involves installation of a purlin system. If you see sagging rafters, recommend stabilization by a qualified contractor. If you see rafters installed on centers greater than 24 inches, look for signs of failure, such as sagging of the rafters. Rafters are typically installed on 24-inch centers. It’s an indication that you should look carefully for other problems in the roof framing. In newer homes, many rafters which don’t oppose usually indicate poor-quality framing. If you see many rafters that don’t align, you may comment on this, but in existing homes, refrain from calling it a defect unless you see failure. The illustration above shows a rafter moved to accommodate a combustion vent. Rafters sometimes have to be moved a little to accommodate components of other home systems. Rafters on opposite sides of the ridge should be installed directly opposite each other in pairs - although, if you see a few that don’t align, it’s really not a defect. Limit the use of engineering jokes.Rafters which rest on the outside walls at the bottom and connect to the ridge at the top are called “common rafters” (highlighted here in yellow). No low-effort one-liner comments, memes, or off-topic replies. Answers must contain an explanation using engineering logic, and assertions of fact must be supported by links to credible sources.īe substantive. Racism, sexism, or any other form of bigotry will not be tolerated.ĭon't answer if you aren't knowledgeable. All users are expected to behave with courtesy. Note that questions must still be specific to engineering and not a general opinion survey.īe respectful to other users. Mechanical, Electrical, Civil, Chemical, and Computer are reserved for technical questions only.ĭiscussion can be used for general questions that apply to multiple disciplines, including some workplace topics. Review the wiki prior to posting.Īvoid questions that can easily be answered by searching on the internet.Īvoid questions that have already be answered by a post in the FAQ section of the wiki. Most general career related questions should be placed in the Monday Career Megathread. Post titles must be a question about engineering and provide context - be specific. Call for Engineers: Tell us about your job! (2020) New to AskEngineers? Read our subreddit rules and FAQ page before posting! Topic Filters
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