InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Framing tables for decks: joist & beam spans & sizes.
Recommended or allowable joist & beam spans: this article explains typical spans for deck joists, deck beams, and deck flooring, giving both standard span tables and a quick "rule of thumb" that works pretty well. Our page top photo shows a hybrid deck structure that encompasses a boat. No fasteners were found securing the boat to the deck however. This article explains deck framing. Basic building framing information is found at FRAMING SIZE & Spacing, Age, Types.
Spans, sizes and spacings for deck joists and deck beams are shown
in Table 4-7 and Table 4-8 (shown below in this article) as well as in most carpentry texts and framing guides. Here we give a rough "rule of thumb" that will provide a reasonable guess at allowable deck joist spans for most lumber species and grades:
A Quick & Easy Rule of Thumb for Estimating Allowable Joist Spans
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.
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"
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:
Visually Graded Lumber
Machine Stress Rated Lumber (MSR)
Machine Evaluated Lumber (MEL)
2400f - 2.0E
1650f - 1.5E
1500f - 1.6E
Recommended Maximum Joist Span
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.
The Southern Forest Products Association's (SFPA) current suggested lumber spans are found at http://www.southernpine.com/span-tables/
Table of Maximum Beam Spans for Exterior Decks
[Click any image or table to see an enlarged, more detailed version.]
Table of Maximum Joist Spans for Exterior Decks
[Click any image or table to see an enlarged, more detailed version.]
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.
Details about the evolution of lumber standards are at FRAMING SIZE & Spacing, Age, Types. The Southern Forest Products Association's (SFPA) current suggested lumber spans are found at http://www.southernpine.com/span-tables/
Continue reading at DECK LAYOUT if you need to know how to lay out and square up the deck plan to set exact pier & post locations, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or if you have not read it see see DECK LEDGER BOARD INSTALL - for the basics of locating & installing the deck ledger in our online deck design-build guide.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Questions & answers or comments about allowable spans for deck, floor, or porch framing. .
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
 Paul DeBaggis is a building inspector and certified building code official with special interest in the history of and standards for wood products. (The American Wood Standards Committee). Mr. DeBaggis has served in the Easton MA. Building Department since 2002 , has worked as a building trades instructor, and also writes about land use regulations, building regulations, and standards. He is a past president of Southeastern Mass. Building Officials and is currently writing a book on the Massachusetts building code. Email: email@example.com
Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: firstname.lastname@example.org
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones