Less expensive (1/3rd less board footage of lumber), fewer pieces to handle, fewer joist hangers to have to attach and only one half as many screws to attach the roof steel. Rather than having 2×4 purlins every 12″ it would make far more sense economically to use 2×6 purlins every 24″. Without even running the calculations, I would say there is a good chance the 2×4 purlins will not make the deflection criteria required for a roof framing member supporting steel. In bending, 2×4 #2 purlins would work at 12″ on center, however I personally would not want to walk on top of them. HemFir has a base Fb of 850 psi multiplied by the size factor of 1.5 = 1275 psi The COS of the purlin spacing is because the load on the purlins is vertical and the purlin spacing is with the run of the roof.įor sake of discussion we will assume a minimal roof snow load of 20 psf (pounds per square foot) and a 4/12 roof slope.ĭead load will be the actual weight of the roof steel and the roof purlins. The COS of the Live Load is due to us only having to check for bending about the strong axis of the member as the purlin is restrained in bending in the weak axis direction by the roof steel. Here is the formula for calculation of a roof purlin: (You can brush up on bending moments here: ) Spacing them on each side of the column causes the trusses to work independent from each other and takes away the advantages of the true double truss system (load sharing and minimization of truss bracing).Ĭould one use 2×4 roof purlins in this system? Roof rafters are typically spaced 12, 16, or 24 O.C. After determining the length of the lean to roof rafters, spend some time thinking about your shed roof rafter spacing. In this fashion they truly act as a two ply member. Areas with high snow loads will likely require larger roof rafters. Some custom-made pole barns may have different pole spacing, and tiny pole barns may. My question is can I use 2” X 4” on edge spaced 16” or 12” apart? I intend to have a metal roof on top.ĭEAR DAVE: My preferred method of post frame construction actually places the two trusses face-to-face nailed together and notched into one side of the column. The standard distance between pole barn posts is either 8 or 12 feet. That is exactly what I have, double trusses on each side of a post on 12’ centers. It does not store any personal data.Reader DAVE in MICHIGAN writes: Hi, I saw on your webpage the Pole Barn Guru stated the trusses could be spaced 12’ apart (I called and was told it is a double truss one on each side of a post that is on 12’ centers). The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. The cookie is used to store the user consent for the cookies in the category "Performance". This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other. The additional lento's have less bounce in them than the existing pole barn roof did that was trusses on 10. Purlins were 2x4 laid flat on 2' centers spanning the 4' between rafters. 2x10 rafters on 4' centers with joist hangers attached to a 2x10 header sitting on 10' pole spacing. This cookie is set by GDPR Cookie Consent plugin. We then did an add'l 12'x 40' open leanto hung off of that. The cookies is used to store the user consent for the cookies in the category "Necessary". The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". Installation The installation of metal roof purlins is critical for the structural integrity of the roof. However, for roofs with heavier snow loads, the spacing should be closer, around 2 inches on-center. The cookie is used to store the user consent for the cookies in the category "Analytics". Typically, the recommended spacing for metal roof purlins is 3 inches to 4 inches on-center. These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly.
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