Odd New Construction Foundation Design

 
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Old 07-07-2015, 01:29 AM   #1
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Odd New Construction Foundation Design


Maybe this is common but I'm not used to seeing it. It's basically a heavy joist foundation with no beams. 32" spacing with 1 1/8 OSB subfloor. I'm not worried about the joist span or subfloor span. 1 1/8 is rated for 160 psf at 32" span.

So many posts and footings. Seems like bigger footings, beams and joists would be easier, and if there is 1/2" of settling, it's over the beam span, not the subfloor span, so not as problematic. I started my career in the land of soil problems, so maybe I'm overthinking things for the Pacific Northwest.

Full disclosure, this is for another house I'm looking at purchasing.
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Old 07-07-2015, 06:44 AM   #2
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Re: Odd New Construction Foundation Design


What ever this going to be and for whatever reason it was designed that way, this will definitely going to support some hefty load... so I assume the reason this was designed that way to suit a certain purpose, if not maybe the designer invested into a local concrete company

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Old 07-07-2015, 09:12 AM   #3
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Re: Odd New Construction Foundation Design


It's a cookie cutter house. So yeah, maybe concrete investor.
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Old 07-07-2015, 10:33 AM   #4
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Re: Odd New Construction Foundation Design


Looks like someone was going to do a radiant heat concrete floor, but opted out. Why else would someone build like that?
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Old 07-07-2015, 01:17 PM   #5
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Re: Odd New Construction Foundation Design


I don't think they were going to do concrete. It's just how it was on the plans. Glad I'm not the only one who thinks it's weird. If I buy this house, maybe I'll find something out.
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Old 07-07-2015, 02:19 PM   #6
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Re: Odd New Construction Foundation Design


So.... all of those circles are concrete posts? I don't have a clue about foundations so I don't know a thing. But, from the outside just "looking" at it, I tend to agree with you guys.... it sure looks like a LOT.

The builder may know something about some soil issues or shifting that he wants to avoid maybe?

Another curious thing that comes to my feeble mind.... is 32" spacing between the joists now acceptable? Coming from my HVAC days MANY years ago.... I've never seen them that far apart.
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Old 07-07-2015, 05:46 PM   #7
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Re: Odd New Construction Foundation Design


Apparently this is somewhat common around here. My plumber does a lot of them and just refers to them as post and beam. It's kind of halfway between stick and post and beam (timber frame) in my mind.

The joist spans are equivalent to 2x8s 16OC spanning 8', since they are 4x8s 32 OC. That's plenty adequate.

The subfloor is 1 1/8, which I think is fantastic at 24" OC, but technically it's rated at 160 PSF loading at 32" OC spacing. So that's OK.

Each circle is a small footing, because there are no beams/girders perpendicular to the 4x8 joists. That's the odd part to me. Seems like fewer larger footings is way easier. It's also the slight source of my concern. Spaced just 32" apart N-S, if there is slight settling, it's way more noticeable than settling over more standard 8' spacing.
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Old 07-07-2015, 07:04 PM   #8
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Re: Odd New Construction Foundation Design


At first glance, the layout reminded me of the modulars that are common around here. Short spans, many posts.

We just call them "porcupine basements".

That 1-1/8" - used it on one house as a trial. Incredibly stiffer floor.

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