Gable Roof Framing Outriggers 1

[asixth]

Hi guys

Can someone please explain to me how the outriggers of a gable roof frame are usually designed and detailed so they can support a fascia as illustrated in the diagram attached?

 

[MiketheEngineer]

Typically, the "last" truss (over the the end wall) is built with a "lowered" top chord. Instead of a normal heel - you have a top chord bearing heel. They basically lower the top chord 3.5'' or the width of the top chord. Then "purlins" are butted to the last "normal" truss and run over this "last" truss. Frame out as desired.

 

[asixth]

Thanks for your response Mike. If you see on the diagram which I have attached (oringal post), it appears that the "last" truss is lowered and is top chord bearing like you mentioned. There are no outriggers at the low end of the building so the top chord will need to cantilever to pick up the overhang.

However, the "last" truss does not bear on the end wall. Is this typical detailing?

 

[MiketheEngineer]

Usually the last roof truss needs to be on the wall or at least "inside" the building so it has something to bear on. Overhangs are usually "sistered" to the top chords/bottom chords. This may put them slightly off center or move the truss a bit (1.5'') to make up the difference.

 

[woodman88]

The attached is some standard details (with a gable end) per the wood truss (WTCA) industry.

Garth Dreger PE
AZ Phoenix area

 

[vandede427]

in commercial wood framed structures, the gable truss with a lowered top chord is usually what's done. outriggers cantilever from first interior truss out over gable. blocking in between outriggers on top of gable top chord.

in residential construction, it's typical to see it the way your sketch showed it. gable studs run up to roof deck, rake joist is nailed to inside of studs. personally i hate this connection, but i guess it works. i'd rather see a stud wall have a double top plate and have the outriggers done like the gable truss with a lowered top chord.

 

[asixth]

Thanks guys. So the gable end truss bears on the end wall. How does the ceiling diaphram fix and transfer lateral forces into the wall?

If the last truss is inside the end wall then ceiling battens can be fixed to the underside of the trusses and a blocking piece can be fixed to the side of the truss to transfer into the endwall.

 

[woodman88]

You can place 2x4 blocking on top of the wall, extending 1.5" into the room, to nail the ceiling sheeting to.

Garth Dreger PE
AZ Phoenix area