Phillip Posted March 6, 2008 Report Share Posted March 6, 2008 Image Insert: 96.82 KB The purling for the attic roof framing is supposes to be the same size of the joist(rafters). There are areas where they are not the same size. R802.5.1 Purlins. Purlins are permitted to be installed to reduce the span of rafters as shown in Figure R802.5.1. Purlins shall be sized no less than the required size of the rafters that they support. Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees from the horizontal. The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet (2438 mm). The builder said that 2 x 4 was all that was needed for the joist for the roof. They used 2 x 6s instead so 2 x 4 purlins is all that needed. I did not measure the length of the joist. Link to comment Share on other sites More sharing options...
ozofprev Posted March 6, 2008 Report Share Posted March 6, 2008 I can't see much from the picture, but... If a span calculation is done correctly, uses the correct live and dead loads and the result of that calculation indeed requires only 2X4 rafters then - the way I read the regulation - the builder is correct. Link to comment Share on other sites More sharing options...
charlieb Posted March 7, 2008 Report Share Posted March 7, 2008 Originally posted by Phillip Image Insert: 96.82 KB The purling for the attic roof framing is supposes to be the same size of the joist. There are areas where they are not the same size. R802.5.1 Purlins. Purlins are permitted to be installed to reduce the span of rafters as shown in Figure R802.5.1. Purlins shall be sized no less than the required size of the rafters that they support. Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees from the horizontal. The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet (2438 mm). The builder said that 2 x 4 was all that was needed for the joist for the roof. They used 2 x 6s instead so 2 x 4 purlins is all that needed. I did not measure the length of the joist. As Gary said. He COULD be right. The key words are "required size" 03 IRC table is 802.5.1 Link to comment Share on other sites More sharing options...
Brandon Whitmore Posted March 7, 2008 Report Share Posted March 7, 2008 The way these codes are written irritate me. So what you guy's are saying, is that the 2x6 rafters are potentially oversized for the span? Since they potentially could have gotten by with 2x4 rafters, they can use a 2x4 purlin (if that is the case)? Am I reading into that correctly? My brain is starting to hurt reading into these dang codes. I don't see many purlins used in these parts on newer construction, is it common in other areas? Link to comment Share on other sites More sharing options...
randynavarro Posted March 7, 2008 Report Share Posted March 7, 2008 I don't see many purlins used in these parts on newer construction, is it common in other areas? Conventional stick frame roofs are obsolete. Trusses are the norm. I can't figure why a builder would think stick framing is more economical than trusses. We don't see purlins around here on anything newer than the 50's, maybe the 1960's. Link to comment Share on other sites More sharing options...
randynavarro Posted March 7, 2008 Report Share Posted March 7, 2008 The black, splotchy stuff caught my eye. I've never anything like that before. Link to comment Share on other sites More sharing options...
hausdok Posted March 7, 2008 Report Share Posted March 7, 2008 Hi Randy, I see that stuff occasionally. I think it's marking dye used to place the markings on the lumber. I've always assumed that every once in a while they get a leak or some kind of failure that spatters that stuff all over. OT - OF!!! M. Link to comment Share on other sites More sharing options...
emalernee Posted March 7, 2008 Report Share Posted March 7, 2008 Phillip, Small correction; Joists are horizontal members that support floors or ceilings, Rafters support roofs. In my area, the biggest mistake that the stick builders use to make on the roof system is to not locate the bottom of the brace on a bearing partition. With open living spaces the norm, most builders just oversize the rafters to eliminate braces and purlins. Ezra Malernee Canton, Ohio Link to comment Share on other sites More sharing options...
Phillip Posted March 7, 2008 Author Report Share Posted March 7, 2008 Ezra, You are right. There is a lot of Conventional stick frame roofs around here. Just about everyone I see has the 2 x 6 purlins even with the span of the rafters that was in this house. The next time I see this set up I will have to check the length of the rafters and the span tables. Link to comment Share on other sites More sharing options...
Steven Hockstein Posted March 7, 2008 Report Share Posted March 7, 2008 Originally posted by randynavarro I don't see many purlins used in these parts on newer construction, is it common in other areas? Conventional stick frame roofs are obsolete. Trusses are the norm. I can't figure why a builder would think stick framing is more economical than trusses. We don't see purlins around here on anything newer than the 50's, maybe the 1960's. Stick framed roofs are the norm around. I only see truss roof on "Cookie Cutter" projects where there is an economy of scale in repeating the design. Link to comment Share on other sites More sharing options...
ozofprev Posted March 7, 2008 Report Share Posted March 7, 2008 Likewise in Buffalo, Steven. Link to comment Share on other sites More sharing options...
randynavarro Posted March 7, 2008 Report Share Posted March 7, 2008 Stick framed roofs are the norm around. I only see truss roof on "Cookie Cutter" projects where there is an economy of scale in repeating the design. Likewise in Buffalo, Steven. Wow. Blows my mind. Trusses are far superior, easier to install and cheaper. Isn't that a builder's life goal? Mike, I was thinking some sort of ink also. Cool. Link to comment Share on other sites More sharing options...
hausdok Posted March 7, 2008 Report Share Posted March 7, 2008 Steven and Gary, That's interesting. My father built houses in Dutchess County, NY for more than 50 years. Though I watched him hand-cut and frame dozens of roofs over the years, the majority of homes he built after about 1965 utilized manufactured trusses custom made at an out-of-state factory. I see trusses with metal press-plate gussets going back to the early 60's here in the Seattle area and wood-gusseted trusses go farther back to the mid 1940's around here. ONE TEAM - ONE FIGHT!!! Mike Link to comment Share on other sites More sharing options...
Richard Stanley Posted March 7, 2008 Report Share Posted March 7, 2008 i find the scenario of the original post about 1/2 the time around here. I'm not about to check the span tables for the appropriate sizing. If there are 2 x 6 rafters, then they should have minimum 2 x 6 purlins and I call it if they don't - another frequent finding is bracing in excess of 4' spacing under the purlins. I also report in the same comment that a structural enginer should prescribe and/or approve any required reparations. I tell the client that if an SE says its ok, get it in writing and hold on to it for when you sell. Link to comment Share on other sites More sharing options...
ozofprev Posted March 7, 2008 Report Share Posted March 7, 2008 Mike, Around here, Ryan homes use trusses but most other local builders frame on site. Cathedral ceilings are popular in newer homes, and of course there are MANY homes over 50 years old around here. Link to comment Share on other sites More sharing options...
hausdok Posted March 7, 2008 Report Share Posted March 7, 2008 Hi Gary, Are they framing those ceilings with engineered I-joists or conventional lumber? OT - OF!!! M. Link to comment Share on other sites More sharing options...
ozofprev Posted March 7, 2008 Report Share Posted March 7, 2008 Generally, they are using nice conventional lumber from Canada. Download Attachment: Pic.jpg 260.48 KB Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now