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Joist, Beam, & Floor Framing Spans & Tables

Framing tables for buildings, roofs, floors, porches & decks: joist & beam spans & sizes.

Recommended or allowable joist & beam spans: this article explains typical spans for joists, beams, and flooring, giving both standard span tables and a quick "rule of thumb" that works pretty well. We provide framing and span tables for decks, porches, roofs, and timber framing.

Our page top photo shows a small deck addition to a 1920's bungalow in Poughkeepsie NY.

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Joist & Beam Sizing Tables & A Quick Rule of Thumb for Sizing Joists

Find here: Framing span tables for common building structures using both dimension lumber and timber frame construction methods. We include common rules-of-thumb that can help you make a quick guess at whether or not your framing lumber or timber is properly-sized.

A Quick & Easy Rule of Thumb for Estimating Allowable Joist Spans

Below we give a rough "rule of thumb" that will provide a reasonable guess at allowable deck joist spans for most lumber species and grades:

While it is by no means a substitute for a proper table of spans and sizes of framing lumber, home inspectors often use a quick and dirty "rule of thumb" to guess whether or not deck floor framing has been obviously over-spanned when joists are spaced 16" on center.

[(Depth of the Framing Member) - 2 ] x 2 = rough deck joist span limit for Southern Yellow Pine spaced 16" o.c.

Example:

If you see a deck framed with 2x8 pressure treated lumber (typically Southern Yellow Pine or SYP), spaced 16" o.c.,

(8" -2) x 2 = 12' = maximum allowable span for a generic "deck floor joist"

A look at an actual current joist span table will show that depending on the wood species, the allowable spans for a 2x8 floor joists with 40 pound live load with deflection limit of span/360, ranges from 10'5" (Western red cedar) to 12'9" (Doug fir-larch).

A check with the current (2014) Southern Forest Products Association's (SFPA) span tables for southern pine, and assuming loads of 40 pound load (psf or per square foot), 10 pound dead load, and maximum deflection of 360, and choosing again a 2x8 joist spaced 16" on center for the same example, we found the following data:

Size Spacing Visually Graded Lumber Machine Stress Rated Lumber (MSR) Machine Evaluated Lumber (MEL)
DSS No.1 No.2 No.3 2400f - 2.0E 1650f - 1.5E 1500f - 1.6E M-14 M-29 M-12
   
Recommended Maximum Joist Span
2x8 16" O.C. 13-7 12-10 11-10 8-11 13-10 12-7 12-10 13-1 13-1 12-10

You can read that for visually graded southern yellow pine joists, the rule of thumb will get you within the range of the table-given specifications for joist span for 16" on center spacing. Immediately below are current wood span tables from Best Construction Practices.

Framing Span Tables

Common timber framing span tables courtesy of Hyne Timber, hyne.com.au cited & discussed at InspectApedia.com

Floor Joist Tables - Pine

Ceiling Joist Table - Pine

Rafter Tables (Snow Load, Cd = 1.15) - Pine

Headers & Beams: Allowable Load Tables - Pine

Timber Framing Spans & Standards

Changing Wood Framing Span Tables & Modern Framing Lumber Strength

As we comment at DIMENSIONAL LUMBER,

Our opinion is that modern dimensional lumber is not the same product as it was in 1833 or even 1940. Modern 2x lumber is produced from trees that have been developed to grow rapidly to a size at which they can be harvested.

Rapid tree growth means wide-spaced growth rings which may mean softer, weaker wood than dense-grained first-cut timbers or lumber.

That combined with the increasing number of knots (as 2x's are cut from ever smaller trees) means that the building frame must rely on additional materials (such as plywood or OSB sheathing) for a critical part of its strength.


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