Spacing of Wood I Joists

[spsiegel]

We are considering spacing Wood I Joists at 24" centers for material efficiency and LEEDs points, and will obviously select so that the numbers work. But does anyone have war stories or cautionary tales about their use at this wide spacing? We will glue/nail, and select a 7/8" span-rated subfloor. Other considerations? Thank you in advance!

 

[BAretired]

For roof joists or trusses, 24" spacing works well. For floors, 16" or 19.2" spacing is more common. If the deck is stiff enough, I suppose 24" works okay for floors.

BA

 

[TXStructural]

LEED is a poor reason to select a construction material, but that's just me. USGBC has no concern about whether the building will be efficient, reusable, nor safe. If the choice is made for the properties of engineered wood, go for it. You can find the right combination of span, depth, and spacing using the manufacturer's reference. I have found these to provide good guidance for all kinds of engineered wood.

Whether 7/8" subfloor is adequate is a matter for debate, depending upon what the floor loads and finish will be. Keep in mind that ASCE 7 requires strength for point loads, not just distributed loads. Sound transmission, deflection, and vibration all can be real issues with longer spans, wider spacing, and shallower framing.

Once you establish that they can take the loads and you can have adequate openings for utilities and services, and that the serviceability requirements can be met, you probably have an adequate design.

 

[spsiegel]

Gentlemen,

I know what is common; we have specified wood I joists at 16" centers for a decade or two. Rather I am seeking commentary from someone who has spaced I joists at 24" and has experience to share. I have not selected a material because of LEED, I have chosen the spacing. I can read references and apply normal engineering practices but would love to hear war stories from those who have used this material as I'm describing. In my experience changing a detail of material use often introduces practical issues I haven't thought of. Thanks.

 

[cap4000]

Make sure you select a rigid sub-floor and glue-nail as you indicate with specifications. Floor Squeaks may result if the istallation is done wrong.

 

[Archie264]

>>>I have not selected a material because of LEED, I have chosen the spacing.<<<

LEED dictates joist spacing?

 

[BAretired]

1F24 Subflooring is a recognized standard in the Wood Design Manual 2001 published by the Canadian Wood Council. I would not expect any war stories about its use. The reason it is not used more frequently is perhaps because a thicker, hence more expensive deck is required to span 24" instead of 16" or 19.2".

BA

 

[RFreund]

The only reason I don't like that spacing is because (in my mind) you seem to start to loose the redundancy. Like when the electrician/plumber/ceiling installer starts putting holes/notches/fasteners into the flanges you start to loose some strength/stiffness. I'm sure some or most of this is covered by the allowable stress that we use in design however when I see joist spaced 24" oc and a large emt strap driven into the bottom chord, it just doesn't look right. Another consideration is distribution at large dead loads (interior walls, bathtub, fridge, etc.). However I don't think these things would prevent me from using 24" spacing, just some thought... Its done all the time with trusses.

EIT

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