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Framing nails to excess (C) Daniel Friedman Deck Construction Framing Tables
Joist, Beam, & Floor Framing Spans & Tables

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 small deck addition to a 1920's bungalow in Poughkeepsie NY.

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

Table 4-7: Maximum Beam Spans in Feet for Exterior Decks (C) J Wiley, S BlissFind here: Framing span tables for decks, porches, other common building floor structures. Deck beam span table. Deck joist span table. Deck joist rule of thumb. Deck framing tables, codes, specifications.

Framing span tables for all types of wood construction, not just decks, are given separately

at FRAMING TABLES, SPANS where in addition to span tables for dimension lumber & timbers, we also give a rough rule of thumb that gives the span for a common 2x joist.

As explained in Best Practices Guide to Residential Construction , Chapter Four, Best Construction Guide for Building Decks and Porches

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.

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.]

Table 4-8: Maximum Beam Spans in Feet for Deck Joists (C) J Wiley, S Bliss

From the joist span table image above we repeat:

Table 4-8 Maximum Spans for Deck Joists in ft-in 1
Joist Sizes: 2x6 Joists 2x8 Joists 2x10 Joists 2x12 Joists
Joist Spacing 12 in. 16 in. 24 in. 12 in. 16 in. 24 in. 12 in. 16 in. 24 in. 12 in. 16 in. 24 in.
Wood Species o.c. o.c. o.c. o.c. o.c. o.c. o.c. o.c. o.c. o.c. o.c. o.c.
Douglas fir - Larch 10-9 9-9 8-3 14-2 12-9 10-5 18-0 15-7 12-9 20-11 18-1 14-9
Hem-fir 10-0 9-1 7-11 13-2 12-0 10-2 16-10 15-2 12-5 20-4 17-7 14-4
Southern Pine "SYP" 10-9 9-9 8-6 14-2 12-10 11-0 18-0 16-1 13-2 21-9 18-10 15-4
Western Red Cedar 2 9-6 8-3 6-9 10-5 10-5 8-6 14-9 12-9 10-5 17-1 14-9 12-1

Notes to the table above

- - Adapted with permission from Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) .

1. 40 lb. live load, 10 lb. dead load. Deflection allowed = span in inches / 360

2. Western red cedar No. 1/No. 2, all other lumber graded as No. 2 or better.

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Details about selecting the proper fasteners for constructing decks and porches and how they are installed can be read at Deck Nails, Screws, Hidden Fasteners.

Also see DECK COLLAPSE Case Study (collapse of a new code-approved deck)

and DECK FLASHING LEAKS, ROT Case Study for an example of an older deck with rot and collapse due to improper construction and missing building flashing.

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.

Details about the evolution of lumber standards are

at FRAMING AGE, SIZE, SPACING, TYPES.

The Southern Forest Products Association's (SFPA) current suggested lumber spans are found at http://www.southernpine.com/span-tables/

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-05-01 by JD

House in question was built in 1949. Builder used 4"x6" df girders spaced 5' apart in width with posts beneath girders spaced 6' apart then toenailed 2"x 8" T&G DF perpendicular to girders. There are no floor joists.

House has been standing for 70+ years. Can 2"x 8" T&G DF really span 56 1/2"(60-3 1/2")?

I can't find anything anywhere that will support this information. That is why I am asking this question here. Thanks

On 2019-09-24 by Wayne

I’m doing a 14ft x 14ft deck double 2x12 beams outside and center 2x8 joist how many 6x6 posts should I use?

On 2019-08-19 - by (mod) -

Anon you need to either meet standard flat roof framing specifications (which is over-building since there's no weight of the roof that's not going to be installed atop the joists) OR have an engineer do the calculations for you since the frame is almost a zero load except for the weight of the framing itself - not something in the framing tables.

Our own little pergola, a bit smaller than yours, that I built using 2x10s around the perimeter of a 20 x 15' pergola is supported on 6x6 posts, 2x10s through bolted to the posts; the joists are simple 2x4s 16" o.c. It's been there without sagging, with added weight of an insane vine growth and occasional snow, for nearly 20 years.

I agree that it makes sense to have a single or doubled center beam so that your 25' span in one direction uses 2x10 cedar joists that are just 12 1/2' long. An engineer needs to calculate your load as it's not a standard deck or roof framing situation.

I'll do some looking to see what I can find.

As a general rule of thumb for beam sizing for a deck (figure that's more load than a pergola roof), if you're supporting joists that span 12 ft (almost your size), then a doubled 2x12 beam itself can span 12' (the number of ft of span = the doubled beam nominal depth in inches).

To go to a longer span for your center beam you'll expect to go to an engineered deck beam rated for outdoor use - such as a glulam beam.

But ticking with that 12' joist span example, there's STILL no engineered beam rated for a 25 ft. beam span. I think you need some mid-span posts for your pergola, else your'e going to be building an ugly huge beamed pergola that looks out of balance.

Where we spanned a 25' cathedral ceiling our glulam beam was a tripled 2x14 engineered wood beam

On 2019-08-14 by Anonymous

I would like to build a Pergola over my flagstone patio. The size of the Pergola would be 25' x 25' and would be attached to my brick house. What size middle support beam would carry the weight of the 2' x 10' cedar joists ? Also, what size vertical cedar post's would be needed ?

On 2019-07-22 - by (mod) -

Thank you for your comment

You make a good point.

Where I have used built-up beams under decks, which is quite common in some parts of the country, I've recommended flashing atop the built-up beam to prevent runoff from going between the members. I agree with you that that's potential rot point

On 2019-05-21 by Suburbangeorge

Why does your beam span table consist of only built up 2" by packages instead of 4" by or 6" by actual beams. I know that in the midwest and east headers in a 2x4 wall consist of two 2" bys with a 1/2" plywood spacer but in the west where the labor to do so costs more it's common to use 4x6 through 4x12 depending on span.

I guess either is OK for interior work but I would never package two or three structural elements because of moisture that is trapped between plies. Even pressure treated lumber can rot. Why take that chance? I'll continue to use 4" by beams under any deck.

On 2019-03-02 - by (mod) -

Mike

Standard deck framing for joists of various depths (you don't give the depth nor span of your porch floor joists) are in the article above.

Just specifying "12" OC joist spacing is not enough to even make a wild guess at spans allowed.

I agree that building codes are probably not going to specify joist spacing for 3/4" thick boards (of unspecified width) directly placed onto the joists.

Common porch flooring is not 3/4" thick but rather is 7/8" in these widths:
Tongue-and-groove profile – 3-1/8" x 7/8" x 10', 12' and 16'
Solid profile – 3-1/8" x 7/8" x 12'

Those are commonly installed on joists that are 16" o.c.

So your 12" o.c. with the thinner flooring may be ok.

Comparing a porch floor with 3/4" boards to a deck with heavier flooring:

Typically actual deck boards are 5/4 thick lumber and requires 16" o.c. joists. If you were building a deck (not a porch) using 2x lumber (like 2x6s) that flooring can be installed over joists that are up to 24" o.c.

Indoors where 3/4" thick flooring is installed in modern construction it's placed over at least a layer of 3/4" subfloor. So when you're going to a non-standard construction plan for an indoor floor you probably need to find suggestions either from your deck board supplier/manufacturer or from a local engineer or architect.

Keep in mind that the joist tables above are for the deck structure and don't address whether or not your flooring will be saggy or bouncy as it spans the joist themselves.

More tables that you might want to check out are at FRAMING AGE, SIZE, SPACING, TYPES inspectapedia.com/structure/Framing_Size_Spacing.php

On 2019-03-01 by Mike

I’m using 3/4”White Oak for a porch deck. I’m planning on 12” OC for the joist spacing but can’t find anything in the code that states that is correct.

Mike


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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 the closely-related articles below, or see the complete ARTICLE INDEX.

Or see DECK FRAMING TABLES, SPANS FAQs - questions & answers about framing tables, spans, sizes, strengths posted originally at the end of this page.

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