Which product is better… I-Joists or floor trusses?

This is a question that has been kicked around for a long time. Which one is better overall? Each product is unique in its own right and has advantages. The question really lies on what you wish to achieve with the product selected.


In my opinion the manufactured floor trusses are the better choice in the heavily populated regions. In the more remote regions, I-Joists are the way to go. What if construction errors happen, such as the foundation being poured wrong? This would cause floor trusses to not fit properly, whereas I-Joists can be easily modified to fit. Trusses would require a costly repair or another design and delivery. Who pays for this? Such a crucial error would delay the project’s completion date, preventing the homeowner from moving in on time.

Open-web floor trusses have much more capability for loads, based on span and depth. Advantage: Open areas for wiring and ductwork and do not have to be modified in the field. They are designed to fit without any trimming and do not require holes cut for trades to install their products so the installation process is quicker and easier. Disadvantage: They must be supplied by a truss manufacturer, AFTER being reviewed by an engineer. Strongbacks must also be applied to create rigidity.


I-Joists have many standard features that allow the builder flexibility on the job site. Advantage: They can be shipped without waiting for design and production to be completed prior to shipping. Most lumber yards can provide a placement plan (if the spans are simple spans that can be called out from a span chart). Disadvantage: Blocking must be applied at specified intervals between spacing. Holes must be cut to allow wiring and ductwork (only certain locations and sizes allowed).


Open-webbed trusses are a fully engineered and designed product and are more user-friendly for other trades to come behind them and perform their work. I-Joists require additional blocking and squash blocks that floor trusses do not need. Also depending on the hangers used I joist may require additional blocking at these locations. And let’s not forget about R values for insulation. Rimboards around I-Joist perimeter will achieve a much higher value than plywood and ribbon boards.

So the question remains which product is better or is it just a preference of the builder? Cost and time are both factors to be considered into deciding which product to use. With a growing awareness of “green” building, perhaps floor trusses with rimboard are the way to go. Which product do you prefer? Why?

Read part 2 in this series here.

Doug Walter

Gould Design, Inc.