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SonnyB
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# Posted: 21 Nov 2014 02:14pm
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I have a 20x32 cabin built on pillars. The front is only 24" off the ground and the back is 7' tall and thinking on how or what would be the best way to enclose it. Some people have told me use 1/2" pressure treated plywood and another said use 3/8" 3'x5' cement board. Any ideas??
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Ruggles
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# Posted: 21 Nov 2014 02:26pm
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My deck is 5 feet off the ground (at my house in Colorado) and is enclosed with 1/2 inch treated plywood. I've been there for 10 years, don't know how long the plywood has been there, still looks good.
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MtnDon
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# Posted: 21 Nov 2014 02:41pm
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Frame the spaces between the piers just like you would frame a regular stud wall. Sheath with 3/4" PT plywood, nailing every 6 inches around the perimeter and every 12" in the field of each panel. Use the correct nails for PT wood. Use nails and not screws for all connections. Best would have the sheathing overlapping the piers and nailed to them as well. The above will result in a structural wall, a brace wall or a shear wall by other names.
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Bret
Member
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# Posted: 21 Nov 2014 03:19pm
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MtnDon, nails not screws? Am I missing something. Wouild have thought deck screws would work although more expensive.
Bret
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MtnDon
Member
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# Posted: 21 Nov 2014 04:55pm - Edited by: MtnDon
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Deck screws in particular, are brittle. They are hardened to help prevent or limit tear out from the bits used in a power driver. That makes the shank snap suddenly under a shear (sideways) load. Nails on the other hand are more ductile. A standard nail will deform, bend, under shear load. Screws can provide better extraction resistance but we want shear load strength first. Ring shank or spiral nails help with extraction resistance and can be found in types that are compatible with PT woods.
Note: there are screws that are structurally rated. Those could be used however they are much more costly.
I was going the structural route as soon as I saw there were posts supporting the cabin that had 7 feet exposed between ground level ans the floor.
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bldginsp
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# Posted: 21 Nov 2014 08:28pm - Edited by: bldginsp
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I don't think 3/4" plywood is at all necessary- maybe MtDon did a typo.
Even if you are trying to make a structural wall to support the cabin laterally, 3/8 or 1/2" plywood will do fine.
If you are going to cover the plywood with paper and some type of siding it doesn't need to be PT, unless it is closer than 8 inches to the dirt. I suggest you hold all wood, PT or not, above the dirt and then use metal siding to contact the dirt. Or cement board.
Remember to ventilate the space if it is entirely enclosed to avoid moisture problems.
Use hot dipped galvanized nails into any PT because the preservative formulations are corrosive to ordinary brite nails.
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MtnDon
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# Posted: 21 Nov 2014 08:42pm
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No typo. When I wanted to reinforce the pier foundation under our cabin I talked to a structural engineer. His suggestion was to build shear walls between the piers under our cabin. He specified 3/4" PT plywood over studs 16" OC, with the plywood overlapping the wood piers as described above. We used PT plywood and PT 2x framing as most of it had portions close to the earth. Only the 2x's that were nailed up against the underside of the floor joists were non-PT.
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bldginsp
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# Posted: 22 Nov 2014 12:36pm
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granted that worked in your application Don but I think it's way overkill for a small cabin. Even the largest wood frame buildings rarely if ever have 3/4 specified for shear. the pull strength of the nails is less than the strength of 1/2" ply, probably 3/8. PT is only necessary where exposed to moisture, and shear ply shouldn't. let's not make this guy spend 3 times more than he needs to....IMHO
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Don_P
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# Posted: 22 Nov 2014 12:38pm - Edited by: Don_P
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Structurally, the panel is the web of a deep beam in MtnDon's wall. The perimeter framing is the flange and the interior framing is web stiffening to keep the plywood panel from buckling out of plane when a lateral load is applied. In a permanent wood foundation, which is what this could be viewed as a variant of, has unbalanced fill, the framing and plywood needs to be thicker to resist that out of plane backfill load. A thicker panel does however give a higher lateral strength. Putting a drained gravel trench under this would not be a bad thing.
I don't believe cement board is made for ground contact, freeze/thaw. That doesn't mean it wouldn't work. One method I've seen sort of along those lines is lath wire well nailed to a frame and several coats of stucco parging on that. I don't think you would pick up much lateral strength, but some.
Metal panels on a frame, same thing as plywood on a frame, keep the web from crippling and you will pick up lateral strength.
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hueyjazz
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# Posted: 24 Nov 2014 11:46am
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Not knowing where you are but if you are subject to any frost heaving you might want to be careful how close to the ground any of these panels are.
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