When you deviate from the drawings and the joist placement plan

I work on a lot of joist placement plans. Normally, I’ll take a design and create a joist placement plan for it, based on the loads indicated by the designer or structural engineer.

Problems when not following the joist placement plan

The placement plan is then sent out with the drawings to the field. How closely the GC and crew follow the joist placement plan varies. Often, the buyer requests changes. Sometimes, these are implemented without being added to the design drawings or joist placement plan.

That said, here are some of the top problems I encounter in the field, that most often come from these deviations.

Notched chords or webbing

Unfortunately, I see this problem on a regular basis. Cutting into chords or webbing is bad under any circumstance and will require a repair detail. The best way to avoid this problem is to indicate the precise location of the floor penetration in the design. This is accounted for in the joist placement plan. If needed, a joist can be moved over an inch or two without affecting overall floor performance. Have a look at my previous post on this subject.

Insufficient or missing reinforcements

I sometimes see insufficient or even missing reinforcements under concentrated loads. On TRIFORCE® joists, there are two basic ways to reinforce. For the OSB end panel or for the webbing. In both cases, it is usually recommended to use ½ inch plywood or OSB panels as the filler. If you are reinforcing for side loads, such as for a stair header, use the following:

  • OSB end panel. Add two or three plies of filler (depending on the size of the joist) to the appropriate side, or to both sides when more reinforcement is needed.
  • Webbing: add one or two plies to the appropriate side or to both sides
  • A reinforcement must be fixed to the top and bottom chords with 3” nails and adhesive, and fixed to the filler using adhesive

For more robust applications, double up the joists. See my previous post on how to connect doubled up TRIFORCE®
for more details.

To reinforce a top load (such as a load bearing wall), reinforcements need to fixed to each side of the top and bottom chord using adhesives and 3-inch nails. Filler isn’t needed, in most load cases.

In all cases make sure to check with a TRIFORCE®
representative or a structural engineer to confirm, as each situation has unique requirements.

Misaligned joists

If joists are out of plumb across a floor system, TRIFORCE® webbing won’t be aligned. Consequently, mechanical installation will be more difficult. You don’t want to negate one of the great advantages of working with TRIFORCE®. The easiest way to align joists is to set the block end on the straightest run. Because the other end of the joist is adjustable, you just need to cut for a snug fit. Even if the structure isn’t perfectly parallel, you’ll be able to compensate for it.

Inappropriate hangers

Sometimes (mostly on sites using non-engineered plans), the framing crew get only a couple of different types of connectors. However, you are begging for trouble if you are not using the exact type of connector needed for your joists. “Standard” hangers can be bent and nailed into place. This can compromise load bearing. Chose connectors according to their role in the structure. Be sure to confirm the types of hangers used in the joist placement plan. At least make sure to check with the designer or with the structural engineer. Naturally, I also recommend you consult our spec guide.

Finally, if you have any questions, please don’t hesitate to contact us! We’ll be happy to help.  

Triforce Analyzer Software


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