Rafter to truss conversion.

[bagged89s10]

This is not exactly garage building but a construction question. We are starting a remodel to open up the floor plan in our house. The wall is bearing the weight of the ceiling joists. We expected to have to install an lvl beam, but the engineer is speccing us to convert the rafter roof framing to a truss. Has anyone seen or this done before using 1x4s or 1x6s at 60 degrees to convert rafters to a truss type roof? See Attached drawings.



The roof over my garage uses site built trusses. Here is a picture of that.

 

[matt_i]

I am purely guessing here not knowing multiple factors but I would think rafter to truss framing means tearing off the entire roof, shingles, sheathing and all, whereas an LVL beam is all done with the existing roof in place. So its possible the truss conversion could be more expensive for other tangential reasons. But, then the future is wide open so to speak, if they are designed for clear span.

 

[readhead]

Several flags pop up for me. 1x4 with no grade called out, the rafters and joists do not plane so a good flat connection is not possible, screw size and pattern is not called out and screws don't work well in shear. How much experience does the designer have? You have a normal ridge and rafter roof in your garage, not site built trusses.

 

[firebirdparts]

The wimpy look of it all may actually make sense. There's no load on those joists except the weight of the ceiling and insulation, and that is all he is trying to hold up. I would probably use bigger lumber than that no matter what he said.

I think the word "truss" has us confused a little bit.

 

[readhead]

There is also no note about the splice in the ceiling joists. That will be the most critical connection since it will be under tension. It is pretty unlikely that those are 27' joists. I can see the intent but the execution is seriously lacking.

 

[Kaizen]

Why wouldn't he just spec 2x for added strength? Nothing is happening in the outer walls below the ridge right?


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[Beemie]

You mentioned your Engineer. He needs to actually design the trusses for you including specifics on connections, not just listing "screws"....how many, what size, spacing, etc. The truss member layout to the panel points needs to be specified. Member splice details, material specs, etc are needed. Is any lateral bridging required for any diagonal truss members?

In otherwords a precise drawing on how to fabricate your trusses.
Truss designs are not rule of thumb or guestimates so don't wing it.

And to make things legal and formal rquire his Engineer's seal on the drawing making him responsible for the design. The Building Inspector and Code may require that anyways.

Keep in mind that you're liable for altering the structure (re: future buyers) so you want his certification to fall back on.

I would;t personally use 1xs for truss members. They are too weak laterally and are likely to require significant lateral bridging if they work at all. There is nothing to be saved by avoiding common 2x material.

 

[Beemie]

The wimpy look of it all may actually make sense. There's no load on those joists except the weight of the ceiling and insulation, and that is all he is trying to hold up.

Actually the Codes require an attic live load in areas that have potential. I forget the height but it's somewhere around 3' minimum vertical space to bring in that requirement, so anywhere with headroom gets live load.
He may not be using the attic but the next owner might.

In addition, the ceiling weight may not be a small thing if it's an old house with plaster.

 

[yeldogt]

have you ever seen a modern truss ? it's surprising how thin everything can be and still work.

That's why you hire an engineer ... ask him?

You can always ask for a bump up in strength -- just did that with a wall I'm building.

 

[Stuart in MN]

We expected to have to install an lvl beam, but the engineer is speccing us to convert the rafter roof framing to a truss.

Ask the engineer why he's specifying the truss conversion. Besides coming up with a solution that works, part of the design process for an engineer is to also provide a solution that is affordable and (at least relatively) easy to build. That may be why.

 

[The Tool Tyrant]

Forget the word "TRUSS" guys. All he is doing is carrying the C/J by the rafters. If he IS an engineer, then he knows what loads the rafters can carry and in theory what he has designed would work, BUT personally (as others have stated) I would not use 1X4's, I'd use 2X6 and nail rather than screw.
Again, there are missing details (as others have stated) nail call-outs, C/J break connection which is critical as they are in a tension load from the roof.

 

[ssdave]

I see no problem with the concept, and the plans if some detailing is added. I presume these are partially complete or concept drawings. The 1x lumber is fine, if good select material is used. It will be easier to work with than 2x. Screws are fine if high strength is used instead of just drywall screws. I'd pay particular attention to the ceiling joist splice, and use a splice plate glued and screwed to both sides of each joist. If I could get to the outside, I'd make sure that the roof rafters are nailed securely to the joists, so as to complete the truss action.

Good sound concept, just needs detail.

 

[bagged89s10]

Thanks all for the insight. Yes I'm still waiting for some details and these are just preliminary plans.

 

[GMCGarage]

Thanks all for the insight. Yes I'm still waiting for some details and these are just preliminary plans.

Cool. there you go.