Piggyback Truss Connection 5

[TampaSGM]

We were recently in our attic and discovered that the piggyback trusses are not properly installed/attached. We know that since they span over 24' they are required to be connected with 2x4x6 (which they are not).

There are 2 questions I have about the diagonal braces and purling.

There are no diaganol braces installed along the top chord of the main truss as I have seen in the BCSI instruction. So I am assuming they are not to code.

The purlins do not over lap by two trusses, they are butted against each other, they are also not attached to either the main or piggyback truss throughout most of the connections and finally there is a gap of 1-2" between the purlins and the piggyback trusses so no actual support.

Should the piggy back sit directly on the purlins?
Should they be overlapped by 2 trusses like the lateral bracing?

Pictures attached.

Thanks in advance

 

[MiketheEngineer]

I have done truss work off and on for over 35 years and this looks "bizarre" to me. While the top chord of the main truss is laterally braced as required - I have never seen a "raised" piggyback setting on the braces. The piggy needs to be attached to the main truss to insure proper load transfer and piggy stability.

Get a good local truss engineer to go over it. It can probably be made to be "OK" but from these pictures - just not sure from here.

 

[Splitrings]

The builder did not install CLR 2x's as shown on page 52 of the BCSI. There should be 1 1/2" gap between the two, just for the CLR's. The piggy back bottom chord would sit on these CLR's. I am looking at a truss design right now that requires 4 rows of CLR's under the piggy back.

I have rarely seen all planes of a wood truss braced in residential construction as they should be. Both the top and bottom chord planes need CLR's and diagonal bracing. I have never seen where top chord purlins have been shown to lap 2 trusses. I am not sure why this CLR is different than the CLR used on a bottom chord, which is suppose to be lapped.

 

[Ron]

Trusses are "piggy-backed" for shipping purposes. When put together in the field, the stub and the piggy-back should be contiguous.

Get a copy of your truss drawings from the truss supplier. If you have defective condition (which it appears you do), then you need to put the contractor on notice ASAP. Don't worry about the contractor's warranty...this would likely be a latent defect, so (roughly) the clock starts ticking when you find it (assuming from your handle that you are in Florida and the house is less than 10 years old).

 

[peal724]

I was out with the wife and kids looking at houses yesterday and we were in a new construction home. As all curious structural engineers do, I peeked into the attic to see whether it resembled some sort of intellegent design or the typical hodge podge of random toothpick chaos.

They were piggybacked pre-fabricated trusses and immediately I thought of this thread. The top chord permanent bracing of the low truss was similar to the pictures posted by TampaSGM. It was a "raised" piggyback with the flat 2x4's between trusses.

While my first reaction to this is similar to MikeTheEngineer's, I wondered why that was my reaction. The top truss was a queen post truss and they arranged the bracing at panel points of the top/bottom truss as to not imposed any bending in the chords between connections.

I used to believe that the trusses must be in contact, but I now believe that having the bracing between the truss chords is the better detail.

Attahced is the Commentary for Permanent Bracing of Metal Plate Connected Wood Trusses by the Structural Building Components Associate. Figure 7 on page 13 shows permanent bracing for a piggyback condition. It clearly shows that one option is to put the bracing between the trusses.

 

[BAretired]

peal,

I agree with you. Placing the bracing above the main trusses seems like a good idea because they can be nailed directly down to the top chords. The bottom chords of the piggyback trusses could then be nominally toenailed to the bracing members.

BA

 

[woodman88]

TampaSGM,
The top trusses should bear per their design or may bear upon each purlin per the truss engineer details. I have design the top trusses (and the bottom trusses to support them) for continuous bearing/each purlin, bearing only at the ends and bearing at each panel point of the truss below.
The purlins should lap or have an engineered connection such as metal straps for continuity.
Diagonal bracing is typically required for the lateral bracing. In a few conditions, I have design the end connections of the purlins such that the diagonal bracing was not required.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[TampaSGM]

All,

I appreciate and thank you for all the input.

My issue, one of many unfortunately with this construction, is that the piggyback are not "resting" on the purlins. There is a gap of up to an inch between the bottom of the piggyback and the purlin. When I step on them some of them buckle downward in atting to horizontal movement if you push them from the side. Also the piggyback are connected with gussets even though the plans call for them to be installed with 2x4x6 conencted to the main and piggy backs. The span of the piggy backs is aproximately 26-28 feet.

On top of this nearly half the trusses have been "shaved" during installation and are as smal as 2x2.

Again thanks for all the feedback.

 

[ToadJones]

i installed many piggybacks in my nail bending days.
Whoever built this was completely lost.
It is a complete abomination.
What he did to build this actually looks 500 x's more difficult than it would be to build it correctly.
The truss plans that come with the trusses clear show how to erect the trusses properly.
The builder screwed the installation up so bad that he had to shave the top chords to get the roof plane "right"
Im guessing this is a Hip roof.

 

[woodman88]

TampaSGM,
I would contact the builder and request the repair/modification drawings for your building and/or that they (and/or the truss engineer) come out to inspect the trusses. Many of the things you have posted may be questionable and they should have drawings to show that they are okay or they need to be fixed per the code requirements. You should send them the pictures you have posted here.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[ToadJones]

a repair drawing would be the original truss plans and cut sheets