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Framing nails to excess (C) Daniel Friedman Wood Construction Framing Table FAQs
Q&A on Deck or Porch Joist, Beam, & Floor Framing Spans & Tables

FAQs about using framing tables for decks, porches & other wood construction: joist & beam spans & sizes.

This article series gives recommended or allowable joist & beam spans and 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.

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Deck Joist & Beam Sizing Tables & Rule of Thumb Joist Sizing FAQs

Big deck on a steep hill inspected by D Friedman (C) Daniel FriedmanThese questions & answers about finding & using wood framing span tables for decks, porches, other common building floor structures were posted originally at DECK FRAMING TABLES, SPANS - be sure to consult the tables and rules of thumb given there.

On 2019-03-02 by (mod) - using 3/4" porch floor boards over joists with what spacing?

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 - 12" o.c. joist spacing and 3/4" white oak boards

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

On 2018-09-26 by (mod) - what size lumber should I use for a 10 foot span

Bob

Please check the joist span tables in the article DECK FRAMING TABLES, SPANS.

There you will see that the span distance that you're allowed depends on the wood species, the joist dimensions, and the joist spacing.

On 2018-09-17 by Rob

What size of lumber should I use for decking that has no joists but will span 10 feet?

On 2018-02-28 by (mod) - deck's supporting joists should be no more than 24" o.c. for nominal 2" thick SYP deck boards

Bob,

Bottom line: your deck's supporting joists should be no more than 24" o.c. for nominal 2" thick SYP deck boards and the joist depth needed depends on the joist spans and beam placements.

I would not frame a deck with joists at more than 24" o.c.

So your "floor board span" is never more than 24" joist - to - joist.

ANSWER:

Using

5/4" thick SPF (Spruce Pine Fir) PT (pressure treated lumber) deck flooring, the 2x deck joists should be 16" o.c. and the joist depth required depends on the joist span.

2" thick SPF, Hem-Fir, northern white cedar, redwood, or western red cedar, or southern pine deck flooring, the 2x deck joists may be spaced 24" o.c.

Incidentally, other readers, nominal 2x8 SPF pressure treated lumber is really only 1 1/2" thick

On 2018-02-27 by Bob R - max span for 2x8 PTs when used as decking boards?

What is the max span for 2x8 PTs when used as decking boards?

On 2016-07-26 by (mod) - can I use 32" on center joist spacing

No, I wouldn't

On 2016-07-26 by Tara

If I have 1.25" thick deck boards can I use 32" on center joist spacing

On 2016-06-20 by (mod) -

In the article DECK FRAMING TABLES, SPANS see Table of Maximum Beam Spans for Exterior Decks

On 2016-06-20 by Doyle Terrell

As a deck cover. Considering a snow load of up to two feet, what size beam do l need?
Camino

I need to span 16 ft. With a beam that will carry 2"x6" rafters which will be sheeted with opaque corrugated fiberglass to serve as. a

On 2016-04-25 by Mike csiro

I want to change out rotted 4x4 post with 6x6 post. Deck is 12 20 with triple 2x8 band. How far apart can I place the 6x6 posts.


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