Joist spacing for 5/4 PT yellow pine decking


Old 08-16-01, 11:46 AM
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I have read through past threads concerning this subject and want to comment on the given advice. I see this statement smeared through threads, "Don't use 20" centers use 16" to prevent bounce". I have designed and constructed many decks for friends and family. Currently, I am completing a home deck project that is 3 levels and totals 1,100 sf. I have used 20" centers for most and have never experienced this phenom, called "bounce". I'll use 16" centers if the decking is to be laid diagonally. Also, 20" spacing works quite well when constructing decks with decking lengths in multiples of 5'.

My experience is that if the beams and joists are sized correctly "bounce" is not an issue.

What is the deal?
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Old 08-16-01, 12:35 PM
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Simply put, the 'deal' is 20 inch joist spacing is not enough for 5/4 (1 inch) deck boards. Besides, your building code may not allow it anyway. What's a couple more joists when it comes to sturdiness and safety.
Old 08-16-01, 02:24 PM
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My Building code requires design for a 40 psf live load:

Not to get into any structural calculations, came accross these tables below:

Tables are based on PT yellow pine with minimum of 1200 psi bearing stress rating and a live load of 40 psf.

Recommended Spans for spaced deck boards

Spans in Inches
Laid Flat
5/4x4 5/4x6
16 16/24**
**Although 24 inches is a safe span, undesirable
deflection or springiness "bounce" may occur.

Please note that safety is not compromised.

Old 08-16-01, 03:06 PM
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Well, safety may not be compromised. But quality comes next.
Table 1. Recommended Joist Spacing and Fastener Configurations
Deck Board
Member Residential Use 60 psf
2x6 24" 16" Direct Screw
5/4, C-Deck G&G *16" 12" Direct Screw, Groove & Groove
*12" spans if installing decking diagonally.
Sort of like a house with 24" center joists, something I would avoid. Like I said, it's only one or two more joists in the total cost.
Old 08-17-01, 05:51 AM
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As you know species and grades of wood vary in strength. PT Southern yellow pine is one of the strongest. Redwood and western cedar do require the shorter spans because these woods are weaker. My original Post was only concerning PT southern yellow pine.

Lengthening joist spacing is not done to reduce cost. It can be done as a matter of convenience. A 10 x 20' (20" joist spacing) deck I constructed 12 years ago is as sturdy (no bounce") as it was when it was originally built.

In every deck publication I've viewed lists max. spacing when utilizing PT southern yellow pine to be 24".

In closing, the key to a sturdy deck is the structurual frame not just the decking. Sizing of posts beams and joists is critical. At 20" joist centers NOTHING is compromised!


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