Author Topic: Sonatube foundation design questions  (Read 77 times)

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Offline willywilly2020

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Sonatube foundation design questions
« on: May 21, 2020, 08:45:41 AM »
Hello friends!

I am building a shed roof cabin in the north cascades. Much fun! Am finalizing my foundation plans and wanted to solicit feedback.

I am building a 12x20 cabin with a 4ft deck. So this would be a 12x24 footprint. The shed roof high/low side is on the 20ft sides, and the sonatubes would be supporting beams along the 20ft side.

I am planning a foundation of 8 sonatubes. This would be a sonatube on each corner of the cabin, sonatubes on the deck corners, and a mid-point sonatube under the cabin. 6x8 beams would be used on top of the sonatubes.

Some questions for the squad:
(1). What diameter sonatube would you use? I was thinking 12'', but wondering if I should use 16''?
(2) I am uncertain about the position of the "mid-point" sonatube. Should I have it at the mid-point of the cabin footprint? Or should I have it at the mid-point of the deck-inclusive footprint?
(3) Would you use pressure treated plywood for your subfloor?
(4) How deep would you put your sonatubes into the ground? I was thinking 18'' below ground, with 18'' above ground.

Any other feedback?

Thanks!

Offline paul s

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Re: Sonatube foundation design questions
« Reply #1 on: May 23, 2020, 03:13:11 AM »
I think frost depth may be a concern.

Lateral bracing may be issue  also,

See what others say.

I am considering a similar size.

Paul

Offline MountainDon

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Re: Sonatube foundation design questions
« Reply #2 on: May 23, 2020, 05:36:36 AM »
I think frost depth may be a concern.

Lateral bracing may be issue  also,

See what others say.

I am considering a similar size.

Paul

Yes, check frost depth.

Piers of any kind can have lateral stability issues. The piers are only ties together at the top and may move indeopendently of each other. That is why Pier foundations are not found as a prescribed, approved foundation in the IRC. But if piers must be used the larger the diameter the better one cam resist lateral movement.

A 6x8 beam is likely too small for a 10 foot span, even with a 12 foot width. But calculatikns would need to be done.

I wonder about a shed roof, usually a low oitch roof, in the Cascades. Does not the Cascades get a lot of snow?

I would build the porch as an add on to the shed. I would not extend the main beams from under the cabin out the end for a porch if that is the idea. That exposes the end of the beam under the porch to the weather which eventually will lead to rot. How much rain is there?

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline akwoodchuck

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Re: Sonatube foundation design questions
« Reply #3 on: Yesterday at 08:19:34 AM »
Don't do it...your proposal is what I like to call "designed to fail".....get help from a local contractor for the foundation at least....
"The lyf so short, the craft so long to lerne."

 

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