2x4 joists ok for deck construction?


Old 09-20-10, 01:30 PM
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2x4 joists ok for deck construction?

Building a 16' x 18' free standing deck (not attached to house) at ~12 inches abouve ground. Nine concrete footers to 24", supporting three twin 2x6 beams (equal to 4x6 beams), set five feet apart running along the 18' deminsion. (three fottings per beam)

QUESTION: is 2x4 lumber suitable as joists across the two 5' beam spans with extending 2' overhang beyond beams? 2x4 (or 2x6 if deamed needed here in forums) will be spaced 12" on center due to diagonal 5/4" decking material.

Looking at 2x4 vs 2x6 for cost savings and overal elevation desires (we want a low deck).

Thoughts? Thanks !
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Old 09-20-10, 02:02 PM
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2x4s are never ok for floor joists! 2x6 is iffy and may not meet minimum code.
Old 09-20-10, 05:24 PM
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I agree with Marksr, that 2x6 would be minimal. Use a 4x6 rather than 2-2x6's for your beam.
Old 09-20-10, 08:36 PM
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What do your plans with the permit say?

The beam footings closest to the house need to be as deep as the house footings: http://www.lancova.com/deckinfo.pdf

2x4's may work, depends on your local Inspector: Maximum Span Calculator for Joists & Rafters

Old 09-21-10, 12:12 PM
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Doug fir 2X4's, spaced 12" with a 40 psf load have a max span of 6' 4". The 3" bearing you are providing is the minimum bearing length allowed.

I suggest that you take your plans to your building inspector and see if he will buy it. As Mark said, some locales may not allow 2X4 in any joist application.
Old 09-26-10, 09:34 AM
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IF you are allowed to use 2X4's for the joists, it'll cost you more money than using 2X6's would. The 2X4's won't span as far, so you would need more beams (and more footings) to support them.

And your math on the beam spacing isn't adding up. 3 beams spaced 5' apart total 10'. Add 2' of overhang on each side and that makes the deck 14', not the 16' you are talking about. Your beams would have to be spaced at 6' to achieve the 16' projection.

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