Decks California - builder - contractor - design - construction

Deck beams ans posts

Deck beams and posts

Designing decks for our location

We live in the beautiful wine country of Northern California. When we design decks for our area these are the building practices we follow. Always refer to your local building codes or a structural engineer.

Alter Eagle is a professional licensed and insured deck building contractor

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Serving North Marin & West Sonoma Counties in the San Francisco North Bay area of Northern California

Deck post sizes - 40 psf Live, 10 psf Dead
Height (ft)	Load Area (sq. ft)= beam spacing x post spacing
	48	72	96	120	144
up to 6	4x4	4x4	6x6	6x6	6x6
up to 8	6x6	6x6	6x6	6x6	6x6
Vertical loads figured as concentric along axis. No Lateral loads considered

Decks building codes - Posts - IRC & IBC

IRC R407.3
Columns shall be restrained to prevent lateral displacement at the bottom end.
Wood columns shall not be less in nominal size than 4" x 4"
IBC 2304.9.7
Column and post-end connections shall be fastened to resist lateral and net induced uplift forces.
IRC R319.1 & IBC 2304.11
Wood columns shall be of an approved wood with natural decay resistance or approved preservative-treated wood.
IRC R31S.1.2 Field treatment.
Field-cut ends, notches, and drilled holes of pressure-preservative-treated wood shall be retreated in the field

Post to Pier & Post to Beam Connections

I prefer the adjustable 1" stand-off bases for decks above 30" I also keep my piers a min. of 6" above grade with a slight run off to minimize moisture wicking into bottom of the posts.

These are the simpson strong-tie connections I use there are many other options available

The loading condition is 40 psf live and 10 psf dead

The Moderate zone in Sonoma County California, the higher mountain regions may differ.

Both are adjustable the ABUz post base (left) uses a 5/8 anchor bolt
for heavier loads or hill sides. Typically I'll use the ABAz with a 1/2 anchor bolt.

Typically I use the ACz post caps (right) for most decks, they handle the loads well and are easier to work with placing the heavy beams.

I'll use the PCz post caps (left) if I have a condition on a slope with possible lateral movement or a heavy load with a large joist over a longer span.

Minimum Solid Beam Sizes - 40 psf Live, 10 psf Dead Pressure Treated H/fir #2 or better (group x Douglas Fir & S. Pine)
Joist Span	Space between Posts in Feet
	5 ft	6 ft	7 ft	8 ft	9 ft	10 ft	11 ft	12 ft
5 ft	4x6	4x6	4x6	4x8	4x8	4x10	4x10	4x10
6 ft	4x6	4x6	4x8	4x8	4x8	4x10	4x10	4x12
7 ft	4x6	4x6	4x8	4x8	4x10	4x10	4x12	4x12
8 ft	4x6	4x8	4x8	4x10	4x10	4x12	4x12	4x12
9 ft	4x6	4x8	4x8	4x10	4x10	4x12	4x12	6x10
10 ft	4x6	4x8	4x8	4x10	4x10	4x12	6x10	6x12
11 ft	4x6	4x8	4x10	4x10	4x12	4x12	6x10	6x12
12 ft	4x8	4x8	4x10	4x10	4x12	6x10	6x12	6x12
13 ft	6x10	6x10	6x10	6x12	6x12	6x12	----	----
14 ft	6x12	6x12	6x12	6x12	6x12	6x12	----	----

Minimum Built-up Beam Sizes - 40 psf Live, 10 psf Dead Pressure Treated H/fir #2 or better (group x Douglas Fir & S. Pine)
Joist Span	Space between Posts in Ft
	4 ft	5 ft	6 ft	7 ft	8 ft	9 ft	10 ft
6 ft	2-2x8	2-2x8	2-2x8	2-2x10	2-2x10	2-2x10	2-2x12
7 ft	2-2x10	2-2x10	2-2x10	2-2x10	2-2x10	2-2x12	2-2x12
8 ft	2-2x10	2-2x10	2-2x10	2-2x12	2-2x12	2-2x12	3-2x12
9 ft	2-2x10	2-2x10	2-2x12	2-2x12	2-2x12	3-2x12	----
10 ft	2-2x10	2-2x12	2-2x12	3-2x12	3-2x12	----	----
11 ft	2-2x12	2-2x12	3-2x12	3-2x12	----	----	----
12 ft	2-2x12	3-2x12	3-2x12	3-2x12	----	----	----
---- Denotes Beams Larger than x12

Solid & built-up beam sizes for decks

These are the beam size tables I use from the UBC code I find they still work well, I laid them out so they are easier to read and I found them better than the interior IRC table or the new deck prescriptive.

I put the built-up beam span table below but I would very rarely use a built-up beam in an exterior application where they are exposed to the moisture conditions like a deck. With the min. code for nailing they will still check, may warp and will shrink at the splices which allows moisture to get trapped with dirt promoting the compromise of the beams over time.

If you have to use a built-up I suggest placing a flashing cap or membrane that won't break down and not use the ardox (threaded nail) as prescribed but use sds screws or thru-bolts. Also on triples use 20d like we used to not the 10d.

Solid blocking

Solid blocking over beams should be mandatory for decks.
Most locations have added it to their deck framing code.

Decks building codes - Beams - IRC & IBC

IRC R502.9 & IBC 2304.9.7
Where posts and beam or girder construction is used to support floor framing, positive connections shall be provided to ensure against uplift and lateral displacement.
IRC R502.7 & IBC 2308.8.2
Joists must be supported laterally at the ends by solid blocking or attachment to a full depth header, band or rim joist (IRC & IBC). Lateral restraint must be provided at each support (IRC only).
IRC 502.2.2 & IBC 2006 1604.8.3 Cantilevered Applications
Decks with cantilevered framing members, connections to exterior walls or other framing members shall be designed and constructed to resist uplift resulting from the full live load acting on the cantilevered portion of the deck.
IRC R31S.1.2 Field treatment.
Field-cut ends, notches, and drilled holes of pressure-preservative-treated wood shall be retreated in the field
IRC R502.6 & IBC 2308.8.1 Bearing
The ends of each joist, beam or girder shall have at least 1 ½" of bearing on wood or metal except where supported on a 1"x4" ribbon strip nailed to adjacent studs.

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