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Discussion Starter · #1 ·
I'm building a ground level deck with 2 x 4 joists supported by adjustable post bases, (Bison's). I can't use a thicker joist because of door threshold clearance.

The AMC span table table gives me about a 5 - 6 foot span for a 2 x 4, (depending on species/live load numbers). Honestly, that sounds like a trampoline to me. Sure it may not snap, but it will be bouncy as all hell.

What would you span a 2 x 4 to? I can't see getting much more than 2 feet.
 

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Last ground level deck I built (partially over a concrete patio) was 2x4 joists 16" oc. spanning 4' sitting on 4x4 beams (4' oc) spanning 4' sitting on concrete pier blocks buried in grade sitting on 4" packed gravel. (frost line is 12" deep for us here)

Mac
 

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All floor joist tables start with 2X6 lumber. If you use awc calculator 2x4 can span 6'2" with L360 deflection for decks 40lb LL. I personally think it will be a bouncy floor. Shorten the span maybe to 5' and put them 12" OC or like Mac said 4'- 16" OC.
If you have a threshold that you can only fit 2x4 under it and I assume the concrete is pitched away from the house, why not rip wider lumber from 3.5" under the door to what ever you need on the other end to have a level surface.
 

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The Duke
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You are perfectly fine at that distance. You will be surprised how stiff that will be. Irregardless of the size joist, they figure a minimum (usually) of L/360 and a span of 6' gives you a deflection of .2" , a very stiff floor. You do not need 4x4's. That will not be bouncy in the least bit.
 

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topsail's trimcat
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up here in the great white north 2x8 is the minimum. but we can get away with 2x6 for a very small landing sometimes
 

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You are perfectly fine at that distance. You will be surprised how stiff that will be. Irregardless of the size joist, they figure a minimum (usually) of L/360 and a span of 6' gives you a deflection of .2" , a very stiff floor. You do not need 4x4's. That will not be bouncy in the least bit.
Think about a long 2x4 roof truss. Designed correctly a 2x4 is strong as hell.
 

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Discussion Starter · #17 ·
Cool, Thanks guys.

As to why I didn't think of doubling them up, I dunno, I was so fixated on a dimension I never use that I clearly forgot fundamentals, (or mentals).

As far as busting the pad. It's old and the last old pad I busted up was 8 - 10 inches thick with rod in it.

Thanks Framerman. It's hard to believe but I will take your word for it adn give it a go. I can always add more support bases if I need.

These are the pedestals btw, although the application for the one in the picture is for deck tiles. They make them without the tabs to hold 2 x material.
 

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Discussion Starter · #18 ·
All floor joist tables start with 2X6 lumber. If you use awc calculator 2x4 can span 6'2" with L360 deflection for decks 40lb LL. I personally think it will be a bouncy floor. Shorten the span maybe to 5' and put them 12" OC or like Mac said 4'- 16" OC.
If you have a threshold that you can only fit 2x4 under it and I assume the concrete is pitched away from the house, why not rip wider lumber from 3.5" under the door to what ever you need on the other end to have a level surface.
The surface is pitched all over the place, I don't think I could lay sleepers without gathering standing water somewhere.
 

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The Duke
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Cool, Thanks guys.

As to why I didn't think of doubling them up, I dunno, I was so fixated on a dimension I never use that I clearly forgot fundamentals, (or mentals).

As far as busting the pad. It's old and the last old pad I busted up was 8 - 10 inches thick with rod in it.

Thanks Framerman. It's hard to believe but I will take your word for it adn give it a go. I can always add more support bases if I need.

These are the pedestals btw, although the application for the one in the picture is for deck tiles. They make them without the tabs to hold 2 x material.
I did a house a while back. It was a single story with a crawlspace. The builder had 2x6 floor joists, 16" OC, 8' OC for the 4x6 beams on the prints. I told him he was ****ing crazy. He told me to talk to him after the floor was down. I was schooled. Unbelievable how solid it was. Almost too solid.

And to boot, the guy saved a lot of money using 2x6 instead of the usual 2x10.

4x4's will give you minimal improvement in performance. It carries more load, but the deflection is barely touched. It's better, yes, but minimal.
 
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