Which product is better… I-Joists or floor trusses? Part 1

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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.

mind-qs

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.

floorTrussLayout

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).

IJoist_Floor2

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.

18 comments

  1. I have engineered floor trusses. When a previous owner installed a deck,I m sure the assumed the house had traditional framing and put 1/2″ lag bolts through the deck ledger into the house. The lag bolts are in two rows, some of them hit truss verticals, but most hit nothing but sheathing…the top row of bolts hit the bottom 1/3rd of the 2×4 ribbon board.The deck has been there a long time and I see no structural problems. Is this something that needs corrected immediately? I’ve seen advice online to contact the truss manufacturer, but the house has been there almost 30 years…how can I find out who made the trusses?

  2. I am a design manager in the UK and although we do not have floor trusses over here we do have metal web joists and one huge (possibly the biggest) advantage which I think you have overlooked is flexibility of design. Metal web joists provide a whole array of support options and I am yet to come across an unusual detail which cannot be overcome using them. The same cannot be said for I-joists which to all intents and purposes are not much better than solid joists in this respect.

  3. I like to have the advantages of both an I-joist and an open web joist. TriForce Open web joists are open web joists with 2′ of trimable i-joists on 1 end. They are lighter weight than an I-joist or most open web joists, have no metal plates to strip wires as they are pulled, field trimable. Coastal stocks them in 2′ increments ready to be pulled for next day delivery. The best of both worlds!!

  4. I believe it boils down to contractor preference and how educated the contractors and subs are with each product. In some areas, a 2×10 is still preferred over I joist and floor trusses. Each product has its place. In an area where you have stick built roofs, the obvious choice is I joist, because they can take point loads, which can be disastrous for a floor truss if not properly designed into the truss. Trusses make life easier for hvac, electrical, and plumbing. As for which product to use, sometimes it boils down to who is the better salesman, the I joist or truss salesman.

  5. Interesting read as ever Chris. Fundamentally it comes down to knowledge & cost. Knowing your follow-on trades & there capabilities is as much a part of building information as component design is. Communication is the key to this. I do however disagree that foundation error would give prevalence to either system. Surely any sub-structure would be inspected prior to prefabrication of any component. But on an ease of construction principle a trussed floor system is the easy forward.

      1. Yes in certain respects communication is poor within the construction industry, between all parties & not just trades. But as architects, engineers, designers, project managers etc, we should be proactive in bringing that communication to the front. In a company I worked with in the past, part of my role was analysis of non-conformance issues & implementing long-term solutions to these. One idea i had was to take trades/installers/contractors etc to our HQ & brief them in the systems we used, from design to manufacture to installation, especially if we introduced something new. Seeing how we worked & how we designed & how we interpreted installation, but also getting their views helped us reduce NCR’s by 85% in the following 12 months of that year. From it we also generated a list of recommended contractors etc. In my opinion that’s a proactive view instead of reactive, this is what I think as construction personnel we need to aim for. Given the world economy no-one wants to carry the can for costly mistakes anymore.

  6. Weather conditions such as rain and snow during the rough frame process or storage can make it challenging when using materials such as timber strand and engineered wood I joist.
    Steve

  7. My biggest problem with I-joists is the other trades. They have absolutely no knowledge of engineered wood products and are only concerned with putting holes in I joists in the most convienient location to them. They can be the equivilent to termites with power tools. It is much easier to tell them “Do not cut ANYTHING” as is the case with floor trusses.

      1. From most of the comments it seams that you are using shoe makers to build houses. The right sub knows how to cut and repair a floor truss. Knowing the building code in your area as to how big and where to drill a hole for the plumbing, should be known. This is where a good G.C. is on the job.