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Floor trusses or I joists?

Posted by jpham76 (My Page) on
Sun, Feb 15, 09 at 15:23

Does anyone have an opinion on Floor trusses vs. I joists? I want the floor to feel solid, which is the best to avoid a bouncy feel?


Follow-Up Postings:

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RE: Floor trusses or I joists?

It's impossible to say without knowing the span and loading but in general a floor truss is needed for heavier loads or very long spans and/or to accommodate duct work.


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RE: Floor trusses or I joists?

My framer said that what's really important is the sub flooring above the
trusses or joists . He insisted that we use Advantech tongue and groove .
It was nailed and glued down and we could'nt believe how solid the floor
was .


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RE: Floor trusses or I joists?

We are in the final stages of completing construction on our house and I decided to specify trusses after speaking with a number of knowledgeable structural engineers. After installing the subfloor with polyurethane adhesive and screws, we have a VERY solid floor. It is generally the cut-outs for plumbing and mechanical that seriously reduce the stiffness of a I-joist. In addition, I ended up with much better bids from the HVAC and plumbing Subs since we built in the required chases for both into the trusses.


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RE: Floor trusses or I joists?

Floor framing similar to roof framing in snow country, should be figured overkill rather than code/engineers minimums. This can be done by going with 16" centers vs. 24" if engineered that way on your project. We went with i joists simply because we have no ducting and ran them on 16's rather than the called out for 24's. Gluing and screwing the 3/4" tongue and groove sturdi-floor plywood helped as well and can be significant as mentioned above.


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RE: Floor trusses or I joists?

The nature of the floor framing should not be a factor in bounce; either system can be designed to prevent it.


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RE: Floor trusses or I joists?

Yep, it's mostly a matter of local/builder familiarity. We had spec'd I-joinsts but the builder has worked mostly with trusses in the past so we had those. At least I didn't have to worry about some tradesman cutting a hole in the web of the I-Joist when it's much easyier to go through the gaps in the trusses.


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RE: Floor trusses or I joists?

Mightanvil is right - trusses, I-joists, even 2x10's can be designed to equal stiffness. Trusses and I-joists advantages (compared to solid sawn lumber) are they are able to span longer lengths with less deflection, and they are engineered to be flatter. Trusses are nice because you can channel mechanicals through them, but they do take up more space in your basement ceiling.

And just because they may be designed to be stiff, if they are not installed correctly you might still end up with a bouncey floor.

The subfloor has little do do with deflection. Strengthening the joists, adding more joists, or reducing the span are much more effective ways of reducing deflection.

One more option is steel floor joists (Dietrich, Cemco, or similar). Haven't seen too many people use this - I guess most carpenters are more comfortable with some sort of wooden product. However, they offer many of the same advantages as I-joists and trusses.


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