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I'm considering removing some walls in the center of a home with Howe Trusses (see pic). I know trusses are normally designed to transfer all the load to the exterior walls, but what concerns me is that the entire length of the house is supported roughly at the center by a wall capable of being load-bearing through to the foundation below. And while I've owned homes with other styles of trusses, these Howe trusses look ideal for a design where the load is split between the center and the outside walls. So I'm not confident I can remove those center walls

Standard Howe Truss

The exterior walls measure 25' apart on the inside (~25' 4" on center); I'm in coastal Maryland, so my snow load is 25 or 30 psf. The roof is a 4/12 pitch, and the house was built in the 1970s.

Does anyone know for certain that the trusses in question can handle the full snow load with no center support? I realized most people, including me, would say "ask an engineer", but I suspect someone here has experience with this truss design over this very common span distance and therefore knows the answer.

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  • "I know whether it will work or not and you should trust me because I'm licensed to use the internet which makes me skilled in all trades. -Someone's Dog" But really, please hire a structural engineer as you noted you should do.
    – statueuphemism
    Commented Jul 15, 2017 at 13:17
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    Even if the trusses are carrying the vertical load to the ends of the trusses, the perpendicular partition may be important to stabilize the trusses by preventing perpendicular horizontal deflection of the bottom cords. I used to think that the entire bottom cord of these trusses was in tension, but I just read that some sections of the bottom cords may be in compression. In certain live load conditions (e.g., high winds sweeping over the roof, or snow loads) the perpendicular partition might be necessary to prevent lateral buckling of the bottom cord. Just a thought from a non engineer.
    – Jim Stewart
    Commented Jul 15, 2017 at 23:08
  • See this rip94550.wordpress.com/2012/04/16/…. I personally have no idea if this analysis is correct, but if it is then the middle two sections of the Howe truss are in compression.
    – Jim Stewart
    Commented Jul 15, 2017 at 23:16
  • @JimStewart the analysis states "Is the entire bottom chord in tension? Yes." for all 3 truss types. Aside from the top chords, the 2 sections in compression in the howe are the ones making up the V.
    – brhans
    Commented Jul 16, 2017 at 2:29
  • I must have misunderstood the diagram. I will look at it again.
    – Jim Stewart
    Commented Jul 16, 2017 at 2:35

2 Answers 2

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Trusses are designed based on 1) top and bottom chord size, 2) size of web members, 3) size of connectors at each chord, 4) species of wood, 5) pitch of roof.

I'd go to your local truss manufacturer and give him all the info I listed above and have him run it through his "truss calculator". It'll take him about 5 seconds and you'll know for sure. (Or, go to your local truss manufacturer and ask him to run a printout for 4:12 truss spanning 25'-7" out to out and take the printout home and compare.)

You will be able to compare everything fairly easily, except the connector plates pressed into the chord joints. For that, ask to measure one of their standard steel plates and measure distances between deformations and depth of deformations.

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  • +1 I would be surprised if those trusses are not designed to carry the full load without your center wall.
    – ArchonOSX
    Commented Jul 15, 2017 at 19:16
  • The truss company will provide the clear span dimensions , my shop in the last home I had was 40' clear span so 25' is no problem if properly designed.+
    – Ed Beal
    Commented Jul 15, 2017 at 23:59
  • Thank you; great suggestion! Though I've never had the pleasure of working on a house new enough that they used steel plates. It's always been 3/8" plywood on both sides, glued & nailed I would guess but never verified. ArchonOSZ and Ed... yes I would be surprised too, but that's not really the point, right? Need to be sure before ripping out walls. Those Howe trusses aren't nearly as strong as Fink and Double-Fink trusses.
    – pbristow
    Commented Jul 17, 2017 at 14:02
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Trusses are made to float over interior walls. There are special metal clips made to allow that function and still keep an interior wall stable. Here is one by Strong-Tie(r)

enter image description here

When the truss is under load as in snow load the bottom cord flexes and in some cases you will see nail pops at interior walls where the drywall was not nailed they way it is needed for trusses.

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    Not to state the obvious, but the effect of these connectors at the crossing of the bottom cord over a perpendicular partition is to restrict lateral movement of the bottom cord while allowing vertical movement. This would suggest that the partition wall has a function of preventing lateral shifting or deformation and buckling. So removing the "non-load bearing" partition wall might reduce the stability of the trusses.
    – Jim Stewart
    Commented Jul 16, 2017 at 2:57
  • @JimStewart True, the clips would stabilize the bottom of the truss against lateral loads (which is required), but I think often the truss manufacturer will require X-bracing on the bottom chord to keep it vertical (keep the truss from laying over to one side). You're right, it should be checked out. I think ALL manufacturers recommend the bottom chord truss clips, but they're not always used (installed).
    – Lee Sam
    Commented Jul 16, 2017 at 4:13
  • Back in the day, these clips were not around, there were specific instructions to not nail the cord to the wall. The company I worked for back in the same day, nailed them anyway. I know better now.
    – Jack
    Commented Jul 16, 2017 at 5:20
  • In construction, when the truss is set in place is the nail in the clip put in the middle of the slot? Or does the framer put it high or low depending on what movement he thinks the bottom cord will make when loaded?
    – Jim Stewart
    Commented Jul 16, 2017 at 11:00
  • I would presume if the cord is already resting on the plate the nails would go near the bottom of the slots. If the cord is already off, then favoring the center would need to be done so the cord could move either way
    – Jack
    Commented Jul 16, 2017 at 16:03

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