Pro's Picks: TrimJoist

Open-web floor trusses are great for routing utilities, but having to custom order them can hold up a framing schedule. Enter TrimJoist. 

November 29, 2017

Chris DeBlois

Principal, CFD Structural Engineering

Roswell, Ga.




I frequently use open-web floor trusses when it comes to designing the structure for a big, open space, such as a kitchen and great room with a second story above, as they make it easy for mechanical contractors to route utilities through the floor. And, unlike wood I-joists or 2-by stock, an open-web truss gives the framers a 3 ½-inch-wide nailing surface. 

The problem with using these in a remodel is that I often don’t know the exact length needed until the demolition has been done. At that point, the lead time for a custom-made truss can hold up the framing schedule.

Enter TrimJoist

Available in lengths from 4 to 30 feet, in 2-foot increments, it’s an open-web floor truss that turns into a trimmable I-joist for the last 12 inches at either end, letting the contractor trim it on site for a perfect fit. There can be a bit of a cost premium, but given the advantages, none of my builder clients have ever complained about it.

The only potential drawback is that TrimJoists only work for an open span—if you want a supporting wall in the middle of the span, or if you need to support a load from above out on the span, you can’t use them. But of course, if that was the case, you wouldn’t be using trusses anyway.

About the Author



Couldn't you double or triple these joists to carry a wall or wall/roof load placed on top of them ? ..and couldn't blocking be placed between the trusses' top and bottom chords to stiffen it above a wall placed below ? maybe not conventional but seems a reasonable engineering maneuver .. Fred Galvez

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