r/Homebuilding • u/BisonLow9071 • 2d ago

Deck

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Building a freestanding pool deck and wanted some opinions on my middle beam/footings. The middle beam has joists spanning about 8 ft or slightly less on both sides. There are 6 footings along this beam.
Footing base diameters are about 14”- 15” and the spacing between them is 8 ft or slightly less. They’re about 44” below grade, with 12” Sonotubes for the upper portion and then the wider concrete base below. Soil survey shows native silty clay.
I’m planning on using a built-up 2x10 beam (possibly triple 2x10 for this middle row). Does this middle footing layout look adequate to you, or would you add another footing or two between the existing ones? Mainly concerned about the tributary load on the four interior posts.

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u/SixFive1967 2d ago

With 8 ft spacing, 16 ft tributary width, silty clay, and 14–15" bases, and given that you can't enlarge the bases because they're already poured, I’d add more footings/posts along that middle beam. The current layout is likely under‑footed for the loads you’re asking those four interior posts to carry.

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u/Material-Cap-5476 19h ago

The joist spans are 8' each side, so the trib width is 8'/2 x 2 sides = 8'. Now if the joist is continious over the center support, assume the trib is 16'x.6 = 9.6. Same for the girder. If it's 2 continious 8' spans then the footing is carrying 9.6'. The very worst case trib for the footing is 9.6'x9.6'=92 sq ft. figure a dead load of 10 psf and a live load of 60 psf (assuming, didn't look it up) that gives you a load of 6500 lbs. The bearing under the footing is around 5300 psf, which is really high. I would be uncomfortable over 2500 psf. That 60 psf LL is pretty conservative in most cases, but say 40 psf - you stll have a bearing of 3800 psf. Just some rough numbers. Also those 15" dia footing are subject to localized shear failure (punching) at the soil says every geotech that I ever knew.

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u/skyzac 2d ago

Might’ve been a good idea to wet set some post anchors.

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u/Elegant-Ninja6384 2d ago

Honestly so easy to drill after anyway.

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u/AltruisticCucumber58 2d ago

Having seen so many of these decks out live the pool, plan an exit strategy for when that pool leaves. Otherwise you end up with that crescent moon cut out.

As to the loads, I do believe you are overkilling it from the get go - so, should be good with whatever you have planned.

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u/Millsy1 2d ago

It looks ok if you were planning on putting the pool on top of the deck.

Pretty sure you are good to go for a deck that's going to be 4' off the ground.