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I am having a new home built by a national builder. They are framing now I see that ceiling joists in one area are not resting on a beam that divides two open rooms.

See the photo. The beam that runs in from the left side separates two open rooms. The room to the left of the beam has an 18' span. The room on the right side of the beam, has a 16' span. As you can see, the bottom rail (?) of the joists are not resting on the beam. Is this a structural issue I need to worry about?

joists

The top rail of the joist is indirectly supported since it runs longer but I am not sure if this is enough. The same model is being built down the street and the same joists do rest on the beam, but only by about an inch.

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  • I am not a structural engineer, so just leaving this as a comment: That definitely looks wrong, The floor above is essentially being held up by 2 flat 2x4s. I can't tell from the photo angle, but are you sure that's actually a beam? It looks like plywood? If it is truly a beam there might be a easy way to fix this and that'd be to bolt an additional 2x(whatever that beam size is) to the beam to support the bottom of those joists. (BIG CAVEAT: If that's only an attic above (ie, not a load bearing floor) then this is maybe OK.)
    – DA01
    Sep 21, 2015 at 1:13
  • Not an engineer either, but I can say that the diagonal bracing makes a truss which makes me suspicious that the lack of support on the bottom may not be correct. You can ask the manufacturer of the truss to see what they say.
    – Edwin
    Sep 21, 2015 at 1:28
  • It's not a steel beam, it's engineered wood - woodbywy.com/trus-joist/timberstrand-lsl. Looks like they put 3 or 4 together to make the support. This is the first floor and there is a second floor above.
    – AngerClown
    Sep 21, 2015 at 1:57

2 Answers 2

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This is fine. It's a wooden open web truss system.

The weight is transferred to the column at the one top point. The lower bar and diagonal bracing are to prevent the top bar from sagging over a wide span. The lower bar extends all the way to the wall so there is something for the ceiling drywall to screw into, but isn't supposed to rest on the column.

Here's the more familiar open web steel truss system that is used all the time in commercial buildings. Also called Composite Steel Floor Deck and Concrete Slab

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  • That's what I was looking for, just didn't know the words. I can see plenty of pictures using the same basic idea.
    – AngerClown
    Sep 21, 2015 at 2:12
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    Whether the top rail of the beam or the bottom one is supported by the wall, there is the same amount of weight (from the floor above) trying to snap just one of the rails. The purpose of the two rails and the spacers in between them is to stop the beam bending and sagging in the middle of the span, not to stop it snapping (shearing) where it is supported by the wall. Supporting the top rail on the wall means there is less load in the spacers, because the weight doesn't need to be transferred from the top rail through the spacers to the bottom rail, and then to the wall.
    – alephzero
    Sep 21, 2015 at 2:44
  • @ZachMierzejewski I agree with your answer. I was just adding some more information about why it is correct, (and why two other comments seem to be wrong).
    – alephzero
    Sep 21, 2015 at 2:54
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    These joists are an upside-down version of the first two bridges shown on semgonline.com/structures/struct_22.html, and nobody worries about the bridges not being supported at the top as well as the bottom.
    – alephzero
    Sep 21, 2015 at 15:21
  • @alephzero Dang, you're making some really good points. Add your own answer and I'll upvote!
    – Zach Mierzejewski
    Sep 21, 2015 at 15:26
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These appear to be engineered as top chord bearing floor trusses. The installation appears to be consistent with typical installation requirements for such systems.

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  • 4x2 Floor trusses (in the photo) can designed and built to be either bottom chord bearing or top chord bearing. In this case, they are top cord bearing. That is why in another house it is different. They were designed in that house to be bottom cord bearing.
    – Damon
    Dec 17, 2015 at 7:29
  • Your answer is so spot on, I wish I could upvote it more!
    – Damon
    Dec 17, 2015 at 7:32

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