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willywilly2020
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# Posted: 21 May 2020 01:29pm
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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. See sketch.
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. (See attached sketches). 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!
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willywilly2020
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# Posted: 21 May 2020 01:30pm
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Here's the sketch!
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Nickels
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# Posted: 21 May 2020 02:29pm - Edited by: Nickels
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This is how my foundation is. 24x24 cabin. You have to set the sono tubes below the frost line. My frost line was 5' so it was a big pain in the ass. I use 12" Sono tubes with rebar and had a bit of a footing. I used pressure treated lumber. Follow my build on Youtube. Good luck.Build
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Brettny
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# Posted: 21 May 2020 07:37pm
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You need something taller than a 6x8 to span 10ft...beam height matters more than the width. Or you could add another sono tube under the cabin.
Why only 12ft wide and 20ft long? Have you used an interior layout program to see if things will actually fit and work with only 12ft wide? 12x20 may feel like your living in a hallway.
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willywilly2020
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# Posted: 22 May 2020 12:30pm
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Quoting: Brettny You need something taller than a 6x8 to span 10ft...beam height matters more than the width. Or you could add another sono tube under the cabin.
Interesting - that was just what I found from UBC. What height would you recommend?
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ICC
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# Posted: 22 May 2020 01:52pm
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UBC? As in Uniform Building Code? Or do you mean IBC which replaced UBC about 20 years ago? Or is that some code unique to the Cascades? Anyhow, whatever it is a 6x8 sounds small for a 10 foot span, without doing the calcs.
Past experience would suggest that 4 - 2x10 might do the job to support the weight of a roof, walls, ceiling and one clear-span floor for a 12 foot wide building and a desired span of 10 feet. Just FYI a built up beam of the same grade lumber as a solid sawn beam has greater strength than a solid timber.
How much snow load is typical for the area, in PSF ground snow? The Cascades can have a lot and can vary widely. Personally I would rethink a shed roof if there is much snow/
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