NYcabana

We want to put a cabana with a hot tub in our back yard and the best/ only place for it is in between some trees. What do I do to prevent frost from upheaving the slab and the roots are a big concern too. Is a slab the only option? Maybe drop a bunch of sono-tubes to 48" and build a deck right close to the ground for it to rest on? The area is pretty damp and I'm not sure going down 4" of stone and putting 6" slab with wire mesh on top of the is going to survive the frost and roots..... any ideas ?????
thanks

Scuba_Dave

I'm on my 2nd house & 2nd hot tub
Both on a slab & neither one moved
Something to do with ~3200+ pounds of hot water on top of it

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GBR in WA

1. Pick both trees and no hot tub.
2. Pick one tree and a hot tub.

"One of the biggest killers of urban trees is soil compaction. Soil compaction restricts water and oxygen uptake by roots, and is associated with roads, parking lots, foot traffic, construction machinery, livestock, poor soil preparation, and a host of other factors."
From: http://www.ext.colostate.edu/PUBS/Garden/02926.html
Be safe, Gary

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CustomBuild

You can use the posts for the cabana as your support for a deck. Then sit the hot tub on the deck. I would add additional posts under the deck for additional support at the four corners of where the hot tub will be. The weak point in a wood structure is the fasteners, so be sure to use appropriately sized bolts in critical load bearing areas(not just nails). To figure load, add the dead load of all the wood members, the hot tub, and figure 8lbs per gallon of water in the hot tub, to the live load, which is all the people that will be on the deck at one time, and snow load, plus any furniture. In your area, 48" is plenty deep for your piers, but since you say it is a wet area, be sure to excavate an additional 12" for drainage gravel, and compact the gravel. Bell shape the excavation at the bottom of the hole for additional protection from upheaval. When setting your sonotubes, make a sled that looks like ]O[ with the O being the sonotube, and the ] [ being 2x4's. The sono tubes should not extend into your hole any more than 4" or so. That way, when you place your concrete, it will come into contact with virgin soil. The sonotube is just there to make the concrete pretty above grade. Don't forget to embed your j-bolts for your post bases in the concrete before it sets. The use of a deck has several advantages. You can repair wood more readily than concrete, a deck allows water to penetrate the soil, and the weight of the hot tub will be transferred to 48" underground, alleviating the soil compaction issue with tree roots. You can also configure the deck with two levels, so that the hot tub is recessed. Good luck and post pics if you can!