Deck Construction Guidance

The following document is being provided as guidance and includes excerpts from 2018 North Carolina Residential Code Appendix M(AM). (To view the full code, go to APPENDIX M WOOD DECKS, 2018 North Carolina State Building Code: Residential Code | ICC Digital Codes (iccsafe.org)

AM101.1 What is a deck:

A deck is an exposed exterior wood floor structure that is permitted to be attached to the structure or freestanding. Roofed porches (open or screened-in) are permitted to be constructed using these provisions

Guide to constructing your deck:

Decks can be broken down into 2 main categories: Footings and Framing.

AM102 FOOTINGS:

What is a footing: a concrete pad or column that supports your deck or structure.

AM102.1 Footings:

Tributary area – the square footage area of the deck surface area carried by one post.
Support posts shall be supported by a minimum footing in accordance with Figure AM102.1(1) and Table AM102.1. Minimum footing depth shall be 12 inches (305 mm) below finished grade in accordance with Section R403.1.4. Tributary area is calculated as shown in Figure AM102.1(2).

	Table AM102.1	Footing Table	(a, b, b)
Size (inches)		Tributary Area	Thickness (inches)
A x A	B x 16		Precast	Cast-in-Place
8 x 16	8 x 16	36	4	6
12 x 12	12 x 12	40	4	6
16 x 16	16 x 16	70	8	8
--	16 x 24	100	--	8
--	24 x 24	150	--	8

FIGURE AM102.1(1) SUPPORT POST FOOTING

For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2.

AM102.1(2) TRIBUTARY AREA

4x4 posts must be a minimum of 30” embedment to top of cap block or concrete 4” from bottom of footing, and 6x6 posts must be a minimum of 42” embedment to top of 4” cap block or concrete 4” from bottom of footing.
Cap block or concrete in bottom of footing must be 4” Deep and 16” x 16”
An alternative method would be to pour a 12” Deep 16”x16” footing and bracket your 4x4 / 6x6 posts directly to footing.
Call in for inspection as soon as footing has been excavated and cap block or concrete has been placed in the footing. As soon as inspection has passed framing of the deck can begin.

Note: Tributary area of shaded section on the free standing deck shown is 5' × 6' = 30 square feet (2.79 m2). Code will require a minimum footing of 8" × 16" (203 mm × 406 mm) in accordance with Table AM102.1.

AM104 – AM111 FRAMING:

Lumber needs to be treated or decay resistant.
Determine if deck will be attached to the structure or free standing

Framing member terminology:

Floor Joists - Floor joists are horizontal framing members that make up the skeleton of a floor frame. The joists span across the deck and are supported on their ends (and sometimes in their middles) by load-bearing footings or girders.
Rim Joists - are the perimeter joists of a deck. The two outside parallel joists, plus those that run perpendicular to all the joists, form the rim of the deck or a band that ties the structure together. Hence, they are known collectively as band boards and rim boards.
Girder - A girder, cantilevered or drop beam is a structural member positioned below the joists to support the weight of the frame.

AM104.1 DECK ATTACHMENT:

When a deck is supported at the structure by attaching the deck to the structure, the following attachment schedules shall apply for attaching the deck band to the structure.

TABLE AM104.1(1)

DECK ATTACHMENT FOR ALL STRUCTURES	EXCEPT BRICK	VENEER
FASTENERS	8' MAX JOIST SPAN (a)	16' MAX JOIST SPAN (a)
5/8'' HOT-DIP GALVANIZED BOLTS WITH NUT AND WASHER (b) AND 12D COMMON HOT-DIP GALVANIZED NAILS	1 @ 3'-6'' O.C. AND 2 @ 8'' O.C.	1 @ 1'-8'' O.C. AND 3 @ 6'' O.C.
OR
SELF-DRILLING SCREW FASTENER (d)	12'' O.C. STAGGERED	6" O.C. STAGGERED

For SI: 1 inch = 25.4, 1 foot = 304.8 mm

a) interpolation between 8 foot and 16-foot joists span is allowed.

b) Nails must penetrate Minimum edge distance for bolts is 21/2 inches.

c) the supporting structure band a minimum of 11/2 inches.

d) Self-drilling screw fastener having a minimum shank diameter of 0.195 inches and a length long enough to penetrate through the supporting structure band. The structure band shall have a minimum depth of 11/8 inches. Screw shall be evaluated by an approved testing agency for allowable shear load for Southern Pine to Southern Pine lumber of 250 pounds and shall have a corrosion-resistant finish equivalent to hot dip galvanized. Minimum edge distance for screws is 17/16 inches. A maximum of 1/2 inch thick wood structural panel is permitted to be located between the deck ledger and the structure band.

TABLE AM104.1(2)

DECK ATTACHMENT FOR	BRICK VENEER	STRUCTURES
FASTENERS	8' MAX JOIST SPAN (a)	16' MAX JOIST SPAN (a)
5/8'' HOT-DIP GALVANIZED BOLTS WITH NUT AND WASHER (b)	1 @ 2'-4'' O.C.	1 @ 1'-4'' O.C.

For SI: 1 inch = 25.4, 1 foot = 304.8 mm.

a) Attachment interpolation between 8 ft and 16 ft joist span is allowed.

b) Minimum edge distance for bolts is 21/2 inches.

AM103.1 Deck Attachment Flashing

When attached to a structure, the structure to which it is attached shall have a treated wood band for the length of the deck, or corrosion-resistant flashing shall be used to prevent moisture from coming in contact with the untreated framing of the structure. Aluminum flashing shall not be used in conjunction with deck construction. The deck band and the structure band shall be constructed in contact with each other except on brick veneer structures and where plywood sheathing is required and properly flashed. Siding shall not be installed between the structure and the deck band. If attached to a brick structure, neither the flashing nor a treated band for brick structure is required. In addition, the treated deck band shall be constructed in contact with the brick veneer. Flashing shall be installed in accordance with Figure AM103.1.

AM109.1 Deck Bracing

Attached decks are required to have lateral bracing if deck height above grade is greater than 4ft.

FIGURE AM103.1 FLASHING FOR DECK ATTACHED TO STRUCTURE

For SI: 1 inch = 25.4 mm

AM109.1.1 Free Standing Decks:

Requires lateral bracing if deck height above grade is greater than 30”.
No lateral bracing if deck height above grade is 30” or less or post embedment requirements of table AM109.2 are met.
For free standing decks without knee braces or diagonal bracing, lateral stability is permitted to be provided by embedding the post in accordance with Figure AM109.1(3) (located in deck attachment section of this document) and Table AM109.2.

TABLE AM109.2 POST EMBEDMENT FOR FREE STANDING DECKS

POST SIZE	MAXIMUM TRIBUTARY AREA	MAXIMUM POST HEIGHT	EMBEDMENT DEPTH	CONCRETE DIAMETER
4'' X 4''	48 SF	4'-0''	2'-6''	1'-0''
6'' X 6''	120 SF	6'-0''	3'-6''	1'-8''

AM106 Floor Joists:

Your floor joists must be sized to carry a minimum 40 lb. per sq ft. live load. In some cases, a center girder is used to help meet this design criteria and allow the use of smaller floor joists.
Check the type of lumber your using, size, and use the chart below to ensure you have the correct joist for the span you require. Be careful to use the correct size lumber to avoid over span.

AM106.1 Joist Spans for Uncovered Porches and Decks

Maximum allowable spans for wood deck joists, as shown in Figure AM106.1, shall be in accordance with Table AM106.1. Deck joists shall be permitted to cantilever not greater than one-fourth of the actual, adjacent joist span.

TABLE AM106.1 DECK JOIST SPANS FOR COMMON LUMBER SPECIES^f (feet — inches)
SPECIES^a	SIZE	SPACING OF DECK JOISTS WITH NO CANTILEVER^b (inches)			SPACING OF DECK JOISTS WITH CANTILEVERS^c (inches)
SPECIES^a	SIZE	12	16	24	12	16	24
Southern pine	2 × 6	9-11	9-0	7-7	6-8	6-8	6-8
	2 × 8	13-1	11-10	9-8	10-1	10-1	9-8
	2 × 10	16-2	14-0	11-5	14-6	14-0	11-5
	2 × 12	18-0	16-6	13-6	18-0	16-6	13-6
Douglas fir-larch^d, hem-fir^d, spruce-pine-fir^d	2 × 6	9-6	8-8	7-2	6-3	6-3	6-3
	2 × 8	12-6	11-1	9-1	9-5	9-5	9-1
	2 × 10	15-8	13-7	11-1	13-7	13-7	11-1
	2 × 12	18-0	15-9	12-10	18-0	15-9	12-10
Redwood, western cedars, ponderosa pine^e, red pine^e	2 × 6	8-10	8-0	7-0	5-7	5-7	5-7
	2 × 8	11-8	10-7	8-8	8-6	8-6	8-6
	2 × 10	14-11	13-0	10-7	12-3	12-3	10-7
	2 × 12	17-5	15-1	12-4	16-5	15-1	12-4

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 pound = 0.454 kg.

No. 2 grade with wet service factor.
Ground snow load, live load = 40 psf, dead load = 10 psf, L/Δ = 360.
Ground snow load, live load = 40 psf, dead load = 10 psf, L/Δ = 360 at main span, L/Δ = 180 at cantilever with a 220-pound point load applied to end.
Includes incising factor.
Northern species with no incising factor.
Cantilevered spans not exceeding the nominal depth of the joist are permitted.

AM105 Girders:

Girders are a part of the deck framing used for support, to break up your joist span, to allow the use of smaller lumber to achieve the span you need for your deck.
Types of Girders:
- Top Mount / Flush Girder
- Side Mount Dropped Girder
- Split Girder
- Cantilever Dropped Girder
Examples of different types of girders you can use on your deck:

CANTILIEVERED DROPPED GIRDER FIGURE AM105.1(4)

Table AM105.1 Girder Connection to Side of Post
Maximum Girder Thickness
Any	3" (Double 2X)	1-¹/₂" (Single 2X)
Two ⁵/₈" diameter bolts¹	Four 6" long screws²	Three 4" long screws²

Bolts shall be hot dip galvanized through bolts with nut and washer
Screws shall be hot dipped galvanized self-drilling screw fastener having a minimum diameter of 0.270", staggered so that the screws are not in a line, and having a minimum edge distance of 1-1/2 inches.

AM105.2 Girder Spans:

AM105.2 Girder Span for Uncovered Porches and Decks
Maximum allowable spans for wood deck girders, as shown in Figure AM105.2, shall be in accordance with Table AM105.2. Girder plies shall be fastened with two rows of 10d (3-inch × 0.128-inch) nails minimum at 16 inches (406 mm) on center along each edge. Girders shall be permitted to cantilever at each end up to one-fourth of the actual beam span. Splices of multi-span beams shall be located at interior post locations.

TABLE AM105.2 DECK GIRDER SPAN LENGTHS^{a, b} (feet — inches)
SPECIES^c	SIZE^d	DECK JOIST SPAN LESS THAN OR EQUAL TO: (feet)
SPECIES^c	SIZE^d	6	8	10	12	14	16	18
Southern pine	2 — 2 × 6	6-11	5-11	5-4	4-10	4-6	4-3	4-0
	2 — 2 × 8	8-9	7-7	6-9	6-2	5-9	5-4	5-0
	2 — 2 × 10	10-4	9-0	8-0	7-4	6-9	6-4	6-0
	2 — 2 × 12	12-2	10-7	9-5	8-7	8-0	7-6	7-0
	3 — 2 × 6	8-2	7-5	6-8	6-1	5-8	5-3	5-0
	3 — 2 × 8	10-10	9-6	8-6	7-9	7-2	6-8	6-4
	3 — 2 × 10	13-0	11-3	10-0	9-2	8-6	7-11	7-6
	3 — 2 × 12	15-3	13-3	11-10	10-9	10-0	9-4	8-10
Douglas fir-larch^e, hem-fir^e, spruce-pine-fir^e, redwood, western cedars, ponderosa pine^f, red pine^f	3 × 6 or 2 — 2 × 6	5-5	4-8	4-2	3-10	3-6	3-1	2-9
	3 × 8 or 2 — 2 × 8	6-10	5-11	5-4	4-10	4-6	4-1	3-8
	3 × 10 or 2 — 2 × 10	8-4	7-3	6-6	5-11	5-6	5-1	4-8
	3 × 12 or 2 — 2 × 12	9-8	8-5	7-6	6-10	6-4	5-11	5-7
	4 × 6	6-5	5-6	4-11	4-6	4-2	3-11	3-8
	4 × 8	8-5	7-3	6-6	5-11	5-6	5-2	4-10
	4 × 10	9-11	8-7	7-8	7-0	6-6	6-1	5-8
	4 × 12	11-5	9-11	8-10	8-1	7-6	7-0	6-7
	3 — 2 × 6	7-4	6-8	6-0	5-6	5-1	4-9	4-6
	3 — 2 × 8	9-8	8-6	7-7	6-11	6-5	6-0	5-8
	3 — 2 × 10	12-0	10-5	9-4	8-6	7-10	7-4	6-11
	3 — 2 × 12	13-11	12-1	10-9	9-10	9-1	8-6	8-1

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa, 1 pound = 0.454 kg.

Ground snow load, live load = 40 psf, dead load = 10 psf, L/Δ = 360 at main span, L/Δ = 180 at cantilever with a 220-pound point load applied at the end.
Girders supporting deck joists from one side only.
No. 2 grade, wet service factor.
Girder depth shall be greater than or equal to depth of joists with a flush beam condition.
Includes incising factor.
Northern species. Incising factor not included.

R312.1.2 Deck Height:

If the walking surface of the deck is 30” or more off the ground, within 36” around the perimeter of the deck, you must have guardrails at a minimum of 36” high. The steps for the deck must also have a handrail on at least one side if there are 4 or more individual risers (spaces between steps). If steps have a total rise of 30” or more above grade, guardrails must also be provided on the open sides of the steps.

TABLE AM108.1 DECK SUPPORT POST HEIGHT
POST SIZE^a	MAXIMUM POST HEIGHT^{b, c}
4" × 4"	8'-0"
6" × 6"	20'-0"

a. This table is based on No. 2 Southern Pine posts.

b. From top of footing to bottom of girder.

c. Decks with post heights exceeding these requirements shall be designed by a registered design professional.

R312.1.1 Guard rails:

R312.1.2 Height
Required guards at open-sided walking surfaces, including stairs, porches, balconies or landings, shall be not less than 36 inches (914 mm) in height as measured vertically above the adjacent walking surface or the line connecting the leading edges of the treads. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4-inch diameter (102 mm) sphere.
R312.1.3 Opening Limitations
Required guards shall not have openings from the walking surface to the required guard height that allow passage of a sphere 4 inches (102 mm) in diameter.

AM111 Handrails / AM110 Stairs:

Stair member terminology:

Riser - The stair risers are the vertical pieces on the stairs. The height of each step is called the rise.
Tread - Stair treads refer to the horizontal pieces that form the stairs. Think of them as the part you "tread" or step onto as you climb the stairs. The depth, or the distance from the front of the tread to the back, is part of the run calculation in building steps.
Stringer - The stringer is basically the backbone of any staircase. They are the notched pieces of wood that run for the entire length of the stairs and support the steps (also called treads) of the stair.

AM110 Stairs: per R311.7.5.1 (8 ¼” max riser) & R311.7.5.2 (9” maximum tread depth). Stairways min 36” width per R311.7.1 (rail projections allowed).
1. AM110.1 Stair Construction
  Stringer spans shall be no greater than 7 feet (2134 mm) between supports. Spacing between stringers shall be based upon decking material used in accordance with AM107.1. Each stringer shall have a minimum of 3¹/₂ inches (89 mm) between step cut and back of stringer. If used, suspended headers shall be attached with ³/₈-inch (9.5 mm) galvanized bolts with nuts and washers to securely support stringers at the top. See Figure AM 110.1.

AM111 Handrails shall be provided on not less than one side of each continuous run of treads or flight with four or more risers.
R311.7.8.1 Height
Handrail height, measured vertically from the sloped plane adjoining the tread nosing, or finish surface of ramp slope, shall be not less than 34 inches (864 mm) and not more than 38 inches (965 mm).
R312.1.3 Opening Limitations
Required guards shall not have openings from the walking surface to the required guard height that allow passage of a sphere 4 inches (102 mm) in diameter.
Exceptions:
- The triangular openings at the open side of stair, formed by the riser, tread and bottom rail of a guard, shall not allow passage of a sphere 6 inches (153 mm) in diameter.
- Guards on the open side of stairs shall not have openings that allow passage of a sphere 4³/₈ inches (111 mm) in diameter.
- The opening between adjacent treads is not limited on stairs with a total rise of 30 inches (762 mm) or less.

Reference Diagram

Depending on the height of your deck and if it is attached to the structure or free standing it may require bracing.

AM109 Deck Bracing

Decks shall be braced to provide lateral stability. Lateral stability shall be provided in accordance with one of the methods in Sections AM109.1.1 through AM109.1.4.

FIGURE AM109.1(1)NO LATERAL BRACING

AM109.1.1 Lateral Bracing Not Required

When the deck floor height is less than 4 feet (1219 mm) above finished grade as shown in Figure AM109.1(1) and the deck is attached to the structure in accordance with Section AM104, lateral bracing is not required. Lateral bracing is not required for freestanding decks with a deck floor height 30 inches (762 mm) or less above finished grade.

FIGURE AM109.1(2)KNEE BRACING

For SI: 1 inch = 25.4, 1 foot = 304.8 mm.
AM109.1.2 Knee Bracing
- 4 × 4 wood knee braces are permitted to be provided on each column in both directions for freestanding decks or parallel to the structure at the exterior column line for attached decks per Figure AM109.1(2). The knee braces shall attach to each post at a point not less than ¹/₃ of the post length from the top of the post, and the braces shall be angled between 45 degrees (0.79 rad) and 60 degrees (1.05 rad) from the horizontal. Knee braces shall be fastened to the post and the girder/double band in accordance with one of the methods shown in Table AM109.1.
FIGURE AM109.1(3)POST EMBEDMENT

For SI: 1 inch = 25.4, 1 foot = 304.8 mm.

AM109.1.3 Post Embedment

For free standing decks without knee braces or diagonal bracing, lateral stability is permitted to be provided by embedding the post in accordance with Figure AM109.1(3) and Table AM109.2.

TABLE AM109.2 POST EMBEDMENT FOR FREE STANDING DECKS
POST SIZE	MAXIMUM TRIBUTARY AREA	MAXIMUM POST HEIGHT	EMBEDMENT DEPTH	CONCRETE DIAMETER
4" × 4"	48 SF	4'-0"	2'-6"	1'-0"
6" × 6"	120 SF	6'-0"	3'-6"	1'-8"

FIGURE AM109.1(4)CROSS BRACING

AM109.1.4 Cross Bracing

2x6 diagonal vertical cross bracing is permitted to be provided in two perpendicular directions for free standing decks or parallel to the structure at the exterior column line for attached decks. The 2x6 bracing shall be attached to the posts with one of the methods in Table AM109.1.4 at each end of each bracing member in accordance with Figure AM109.1(4).
If span between posts is greater than 7 feet, center blocking with fasteners per Table AM109.1.4 required. (Referenced in Figure AM109.1(4))

Table AM109.1.4 FASTENING OF BRACE (CHOOSE ONE)
Fastener Type	Diameter (inches)	QTY	Length
Bolt	⁵/₈^a	1	As required
Screws	0.27^b	2	Long enough to achieve a 1 ¹/₂" thread penetration of structural member opposite head of screw

Bolts shall be hot dip galvanized through bolts with nut and washer
Screws shall be hot dip galvanized (ASTM A153, Class C, minimum) self drilling screw fastener having a minimum diameter of 0.27", and installed in the center of the post with a minimum of 1" space between screws.

This document has been created to provide you information to guide and assist with deck construction. All information has been obtained from the North Carolina Residential Building Code (Appendix M). For further guidance and or questions, please contact Morehead City Planning & Inspections Department by phone (252)-726-6848 ext. 125 or email MHCPI@moreheadcitync.org.

TABLE AM107.1 FLOOR DECKING THICKNESS
SPACING	DECKING (nominal)
12" o.c.	1" S4S
16" o.c.	1" T&G
19.2" o.c.	¹/₄" S4S
24"-36" o.c.	2" S4S

Deck Construction Guidance

FIGURE AM102.1(1) SUPPORT POST FOOTING

AM102.1(2) TRIBUTARY AREA

TABLE AM104.1(1)

TABLE AM104.1(2)

AM103.1 Deck Attachment Flashing

AM109.1 Deck Bracing

AM109.1.1 Free Standing Decks:

TABLE AM109.2 POST EMBEDMENT FOR FREE STANDING DECKS

AM106 Floor Joists:

AM106.1 Joist Spans for Uncovered Porches and Decks

Southern pine

AM105 Girders:

TOP MOUNT/FLUSH GIRDER FIGURE AM105.1(1)

SIDE MOUNT DROPPED GIRDER FIGURE AM105.1(2)

SPLIT GIRDER FIGURE AM105.1(3)

CANTILIEVERED DROPPED GIRDER FIGURE AM105.1(4)

AM105.2 Girder Spans:

Southern pine

R312.1.2 Deck Height:

R312.1.1 Guard rails:

AM111 Handrails / AM110 Stairs:

FIGURE AM110.1 STAIR STRINGER

AM109 Deck Bracing

AM109.1.1 Lateral Bracing Not Required

FIGURE AM109.1(2)KNEE BRACING

FIGURE AM109.1(3)POST EMBEDMENT

Length

Bolt

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