Larry_Sweeney Posted September 15, 2014 Share Posted September 15, 2014 Truthfully I don't use trusses very often (stick built "old timer") and just thought I could find a quick answer from someone on the forum. I have a customer that wants me to design a pavilion that will have a 4.5/12 roof pitch with a 33' span. The customer wants a cathedral ceiling. I thought it would be much less expensive to use a scissor truss with a less pitch on the interior. Is there a "rule of thumb" as to how much less of a pitch has to be on the ceiling as compared to the actual roof pitch? I wasn't sure if it would depend on the span or a "rule of thumb" and yes, I do know someone is going to tell me to call an engineer or the truss company. Thanks in advance for your input. Link to comment Share on other sites More sharing options...
Bill_Emery Posted September 15, 2014 Share Posted September 15, 2014 The rule that I use is 2 pitches less than the upper truss. This can vary with the pitch, span, and if you have a raised heel; but it's a starting point. Link to comment Share on other sites More sharing options...
DRAWZILLA Posted September 15, 2014 Share Posted September 15, 2014 I try to keep a 2" difference Outside 5:12 Inside 3"12 But I am no expert either. Link to comment Share on other sites More sharing options...
JLDrafting Posted September 15, 2014 Share Posted September 15, 2014 The rule of thumb I was given is 1/2 of the top chord. Of course the truss manufacturer can engineer other options possibly. Link to comment Share on other sites More sharing options...
Larry_Sweeney Posted September 15, 2014 Author Share Posted September 15, 2014 I was thinking the 2" difference was something I would work with for starters also. I had a call into a truss company from last week and they just got back to me while I was writing this reply. I was told that with a 4.5 pitch on the exterior and a 33' span I could do a max. of 2.75 pitch on the interior using 2x6 chords @ 24" centers. Thanks for everyone's advice. They also told me the 2" "rule of thumb" is a good thing to use. Link to comment Share on other sites More sharing options...
Alaskan_Son Posted September 15, 2014 Share Posted September 15, 2014 We have used a lot of engineered scissor trusses over the years and the interior pitch has always been half of the exterior pitch. We also typically have a lot of snow load to account for though too. Link to comment Share on other sites More sharing options...
rlackore Posted September 15, 2014 Share Posted September 15, 2014 If you have the room to provide a large heel height, you could probably achieve a true cathedral with sloping parallel chord trusses. Link to comment Share on other sites More sharing options...
RodCole Posted September 15, 2014 Share Posted September 15, 2014 Larry Is your pavilion a gable roof, or are you looking to make it a hip roof? I agree that the rule of thumb for top cord pitch to bottom cord pitch has been 1/2. The reason I ask about the roof itself is that you will probably end up with one direction of the hip, if that is in fact what you have, being a girder truss with the other trusses bearing on it. If this is the case then I am not sure that the rule of thumb would apply in this situation. Just what you wanted to hear I bet. There's always something! Link to comment Share on other sites More sharing options...
Larry_Sweeney Posted September 15, 2014 Author Share Posted September 15, 2014 It's gable at both ends and I'm not able to add a raised heel due to other factors. I had gone over all this with the truss manufacturer and they said the 2.75 pitch was workable for the span I noted. Link to comment Share on other sites More sharing options...
LevisL Posted September 15, 2014 Share Posted September 15, 2014 Another factor to consider for the inside slope is the type of attic insulation. Up here in Canada, our Code limits the slope to 4.5/12 for mineral fibre or cellulose fibre loose-fill insulation, and 2.5/12 for other types of loose-fill. You guys must have something similar in your Codes. If you're planning on using batts or spray-foam, then this isn't as issue, but I thought I'd mention it. Link to comment Share on other sites More sharing options...
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