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Dual Pitch Hip Roof Questions

Dual Pitch Hip Roof Questions

Dual Pitch Hip Roof Questions

(OP)



Homeowner is adding an addition in the courtyard area of the 'U' which is formed by the existing two gables intersecting the long.

The addition will be a hip roof and the backside will receive a new ridge to match the old ridge forming a large cricket.  That will be a manufactured truss and the side crickets will be framed.

The questions are with the new dual pitch Hip roof.
1. South Florida region.  Should the girder truss be in 6 or 8'?
2. I show the top and bottom of the framing of the hip as two alternatives (I think only the top works.  Should the truss be framed similar to the top half of the drawing?  The bottom half is just funky with the returns hitting the ridge at different points.
3.  When you run into a building distance that is not even, say 21', do you just space the last truss at 1' or do you reduce the 2' o.c. distance between each.  Sorry for what i am sure is obvious to you.
4.The determining pitch is 5:12 with the other about 5.75:12.  Can a continuous hip vault be designed for the ceiling?  At about 3:12?  I don't recall seeing hip ceilings, is it odd?  Would a single (gable type) vault be better..easier...more conventional?

Best Regards,
Ryan

RE: Dual Pitch Hip Roof Questions

1.  If you are talking about the set back of the girder... I don't think it matters, as long as the trusses work.  In my region (midwest) we typically design for a 7' set back.  
2.  We typicall design a hip end similar to the one you show on the bottom half of your drawing.  However, we place an end jack (mono truss) at the intersection of the hip ridge and the hip girder (both sides).  We also use hip rafters at the ridge.  I would check to see what is the typical framing style of hip ends in your region.  There are several types and they vary depending on location and truss manufacturer.  
3.  For the case you show.  I would place a truss at the peak and step them down at 2' o.c. in both directions, you shouldn't have an odd space.  For cases where you don't have an even dimension, I would adjust the spacing of the last truss... not all of them.  Try to keep your spacing at 2' o.c. for as many trusses as you can and adjust the odd ones accordingly.  
4.  Hip vaults can be designed into the ceiling.  Shorter spans make this a little bit easier.  You are probably pushing the limit with a 3:12 ceiling pitch and a 5:12 roof pitch.  I'm not saying this can't be done, but I would certainly check with a local truss manufacturer before you decide.  

Good luck.  

RE: Dual Pitch Hip Roof Questions

I agree with CJ, RE: "pushing the limits" with a 3:12 under a 5:12.  On our work, we can hardly even find a manufacturer who will still even build a scissor truss with the bottom chord at 1/2 the slope of the upper chord.  Going beyond that makes the truss much too slim for a span of much distance at all.

-- just wandering.

RE: Dual Pitch Hip Roof Questions

One point of note:

You are increasing the lenght of the roof, therefore the cladding pressures will increase in some areas.

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