IRC R507 · Decks · 2021 / 2024 IRC

How to use IRC R507 deck framing requirements

Joists, beams, ledger fastening, posts, and footings — the order to size a prescriptive deck and where each answer lives. Free links to the IRC and the AWC DCA 6 deck guide.

Need the actual tables? Read IRC R507 free at codes.iccsafe.org → or get the free AWC DCA 6 deck guide →

Size a prescriptive deck in this order

Step	Part	What sets it	Where to look
1	Decking	Decking type and joist spacing (and angle of the boards)	IRC R507 decking section / DCA 6 decking rules
2	Joists and cantilever	Species, size, spacing, and the joist span you want	IRC R507 deck joist table / DCA 6 joist table
3	Beams	Beam size and ply count, plus the joist span it supports	IRC R507 deck beam table / DCA 6 beam table
4	Posts	Post size and height	IRC R507 post table / DCA 6 post table
5	Footings	Tributary area of each post and the soil bearing value	IRC R507 footing table / DCA 6 footing table + local frost depth
6	Ledger to house	Joist span (tributary load on the ledger) and what the ledger attaches to	IRC R507 ledger fastener table / DCA 6 ledger table
7	Lateral connection	Hold-down devices tying the deck to the house floor framing	IRC R507 lateral load connection / DCA 6
8	Guards and stairs	Deck height above grade, stair geometry	IRC R311/R312 / DCA 6

Section and table numbers inside R507 have moved between editions — search by topic in your adopted edition. Our own summary, not the code text. Read IRC R507 free at codes.iccsafe.org or the free AWC DCA 6 guide, and verify against the IRC edition and local amendments adopted by your AHJ. Not engineering advice.

Worked example — ledger-attached deck, 11 ft joists, southern pine

Input / step	Value	Source
Design loads the prescriptive tables assume	40 psf live, 10 psf dead	DCA 6 / IRC R507
Joist span wanted (ledger face to beam face)	11 ft 0 in	Layout
Joist choice	Southern pine No. 2, 2x8 at 16 in o.c.	Lumber on hand
Maximum joist span from the table	11 ft 10 in	AWC DCA 6 (2015), joist table
Result	Works — 11 ft 0 in is less than 11 ft 10 in	Compare
Ledger fasteners	1/2 in lag screws or through-bolts with washers, spaced per the ledger table for an 11 ft joist span	DCA 6 / IRC ledger fastener table
Posts	6x6 minimum	DCA 6 post requirements
Footings	Bottom at least 12 in below undisturbed ground or below the frost line, whichever is deeper	DCA 6 / IRC R403.1.4

Worked example values only. Look up the full tables in the free AWC DCA 6 guide or the IRC at codes.iccsafe.org.

Common field mistakes

Mistake	What to do instead
Nailing the ledger to the band joist	Use the lag screws or bolts in the ledger table — nails alone are not a ledger connection
Lagging into brick veneer, or using lead anchors in masonry	Veneer can’t carry a ledger — go free-standing (non-ledger deck) or attach to the structure behind it
Skipping ledger flashing	Flash the ledger so water stays off the house band joist
Bolting the beam to the side of the post	Notch the post or use a post cap so the beam bears on the post
Setting a deck footing next to the house above the house footing	Deck footings close to the house bear at the house footing elevation (see DCA 6)
Measuring joist span to the end of the cantilever	Span is face of support to face of support; the overhang is checked separately

Our own summary, not the code text. Read IRC R507 free at codes.iccsafe.org or the free AWC DCA 6 guide, and verify against the IRC edition and local amendments adopted by your AHJ. Not engineering advice.

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Building a deck that passes the first inspection

Two free sources: read IRC R507 free at codes.iccsafe.org, and download the American Wood Council’s DCA 6 Prescriptive Residential Wood Deck Construction Guide. This page explains how to use them; it does not reproduce their tables. It covers the 2021 and 2024 IRC — verify against the edition your AHJ adopted.

Work from the top down. Decking sets the joist spacing. Joist span and spacing set the joist size and how far it can cantilever. The joist span sets what each beam carries, which sets the beam size and post spacing. The area each post supports sets the footing size. And the joist span sets how many ledger bolts you need at the house. Change the layout and you rerun the chain.

The ledger is where decks fail. The prescriptive rules only work when the ledger bolts or lags through into a solid band or rim joist, with flashing. Brick veneer, cantilevered floors, and I-joist rims without blocking are outside the tables — go free-standing on its own beam, or get it designed.

Worked example. A ledger-attached deck needs 11 ft joists. Southern pine No. 2 2x8 at 16 in o.c. is listed at 11 ft 10 in in DCA 6 (40 psf live, 10 psf dead), so it works. The ledger gets 1/2 in lag screws or bolts at the spacing the ledger table gives for an 11 ft span, posts are 6x6 minimum, and the footings go below the frost line and at least 12 in below undisturbed ground.

Related: how to read IRC span tables, IRC footing sizes, and frost depth and design criteria (R301.2). Estimate footing concrete with the concrete calculator, and log the footing and final inspections in the inspection request log.

FAQ

What is AWC DCA 6?+

DCA 6 is the American Wood Council’s Prescriptive Residential Wood Deck Construction Guide. It is free to download from awc.org, follows the IRC deck provisions, and adds illustrated details for ledgers, posts, beams, guards, and stairs. Many building departments hand it out as the deck standard.

How far can a 2x8 deck joist span?+

It depends on species, spacing, and cantilever. As one example, DCA 6 (2015) lists 11 ft 10 in for southern pine No. 2 at 16 in on center with 40 psf live and 10 psf dead load. Look up your exact case in DCA 6 or IRC R507.

How do I attach a deck ledger to a house?+

Through the house band or rim joist with 1/2 in lag screws or through-bolts with washers, spaced per the ledger fastener table for your joist span, with flashing to keep water off the band. The prescriptive tables don’t cover attaching to brick veneer or cantilevered floors — use a free-standing deck or a design.

How deep do deck footings need to go?+

At least 12 in below undisturbed ground or below the frost line your jurisdiction lists in Table R301.2, whichever is deeper. Footing size comes from the deck footing table based on the area each post supports and the soil bearing value.

Do decks need a lateral connection to the house?+

The IRC includes a prescriptive lateral load connection — hold-down devices tying the deck joists to the house floor framing — or an approved design. Check the lateral provisions in the R507 edition your AHJ adopted.

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