Porch Truss Profile/Framing

[T_Bat]

Hey everyone,

I'm working on a wood project with wood roof trusses. Single story - SDC C and normal wind. I have a proch roof with a shallow slope all over the perimeter of the building. I have some plcaes my exterior wall job so my bearing point goes away and I can't make the normal truss profile work. I've modified the normal truss to provide a "porch truss" so I can span to the exterior walls (see attached - the typical "porch truss modification is on the right). In the attached example I have my typical porch truss on the right side and a short beam for truss bearing on the left. The wall jogs out on the left so I also have a longer portion of overframed porch roof.

My questions are:

1) Is the porch roof even resonable? I don't want to pawn my problems off on the truss designer
2) Does it seem economical to provide a porch truss profile on the left as well and then just frame the roof to a ledger on the truss?

Thanks!

 

[jayrod12]

What would support the standard roof joist at the exterior edge?

 

[KootK]

No problem for the truss guys. I used to be one. It’s quite economical. Only portential issue I see is building envelope depending on where exactly you want to separate inside from outside space.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[T_Bat]

jayrod12 - when you say roof joist I assume you are talking about the standard roof truss. At the "standard" location I have a wall to support the exterior edge. If you are talking about the standard 2x framing for the porch I have posts and girders on the outside of the porch. Let me know if that clarifies.

Kootk - You think it's more economical than the overframing appraoch? As far as building envelope goes I think the truss would stop at the exterior wall so it would be sheathed to the underside of the roof. I would attach the outside porch joists (or rafter rather) to a ledger of some kind that's attached to it.

Really appreciate the help!

 

[jayrod12]

I mean the joist extending out as you've drawn to the left side. It appears to be a fairly significant cantilevered portion.

 

[T_Bat]

Jayrod - what you don’t see is a girder line between posts on the exterior of the porch roof. The porch rafters will end up being simple spans between the porch truss/exterior wall to the girder line not shown in my graphic. Sorry for the confusion.

 

[KootK]

I do think that it would be more evonomical.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

I agree with Koot, let the truss guy take care of it.

 

[T_Bat]

That was my gut feeling - thanks for the back up!

 

[T_Bat]

One more twist - what about a scissor truss with the added porch profile on one end? Again just want to make sure I'm not hosing the truss guy. I'm looking at how this affects the "kick-out" force at the top of my wall.