Sheathed pole-barn and rubble foundation.
Ive read what’s been suggested for pole-barn energy efficiency here, and I understand why the entire exterior needs to be sheathed and air tight. Also, the need for a vapor barrier over the ground soil somehow tied to the wall air barrier.. But what I can’t quite visualize, is the wall to ground intersection between the poles..
I plan on using concrete permacolumn’s under every pole, so no wood rot below grade. But what about the 2X12 horizontal skirt boards that always end up rotting and are thicker than my sheathing? Isn’t there a longer lasting material, and a way to prevent frost heave without pouring a thickened edge under the walls here in Iowa?
My idea is to replace these skirt “splash” boards with advantech sheathing sealed on three sides with self adhering bitumen. Ive found reports from people using unpainted advantech rather than treated plywood outside, and claim there is no comparison. But I have yet to do my own tests.
If I dug a trench 4′ deep between the main poles, attached 4×10 advantech sheathing 2′ below grade supported by a girt just above grade , and then back fill with washed gravel, wouldn’t that prevent or control frost heave since there’s little moisture in the rocks like a old school rubble foundation? It would also deter rodents from tunneling under and into my polebarn. You could go even further and install foam board buried around the perimeter like a frost-protected shallow foundation sealed to the bitumen sealed advantech, shedding rain water further away down the hill? Permacolumn’s maybe overkill with this type of water management..
Yeah, I know it sounds like allot of work for a polebarn, but my county really jacks the levy rate if concrete floors are installed, and you still have the frost heave issue..
I need this hilltop building to be tight, efficient and rodent free.. And maybe even the shell for some living quarters if it remains dry and rodent free, with a floor system installed over gravel. https://www.greenbuildingadvisor.com/article/minimizing-concrete-in-a-slab-on-grade-home
Thanks!
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Mike, Advantech is tough stuff but it can still rot. I've had a sheet in my chicken run for six years and the bottom 6" is rotting and the rest is getting soft. Considering that it's OSB I find that nothing short of miraculous, but I would still not put it in direct contact with the ground. Wrapping it in bituminous membrane might be effective but you would still need to cover that against UV exposure.
Pressure treated wood rated for ground contact and with cuts sealed, in a relatively dry situation, should last a long time. Have you considered a petroleum-based product such as Boral TruExterior or Azek? (Boral is "greener".) The don't have much structural integrity but they should last forever in contact with the ground.
My guess is to use 2x sawn lumber then cover it inside & out with a HDPE plastic sheet, like a dimple drainage mat. Add a french drain under the gravel backfill and be ready to replace it in 10 years
Use the foundation grade pressure treated lumber.
Thanks everyone.
Ive received some good suggestions and I liked composite grade skirt boards the most.. But I don't think any of the wall methods would last as long as a permacolumn unfortunately. The only alternative is a thickened edge slab, and I was trying to avoid that.
I'm sort of surprised that permacolumn hasn't released a skirt board product that addresses my concerns.
Mike, why do you think that plastic "lumber" won't last with ground contact? One of its main environmental drawbacks is that it does not decompose. Perma-column looks like it's simply a precast pier; you could form and pour your own concrete skirt boards but they will be heavy and fragile compared to other options. Boral TruExterior is plastic with fly ash, sort of a synthetic version of concrete.
Create a floor void and the critters will move in. Are taxes a driving force for a building design? I put a 2X skirt board around the outside of my barn. Backfilled with gravel and capped with concrete floor. Works great. Use 2X purlins up the outside with siding attached. Gives a place for rigid foam insulation between the purlins.
Mike,
Do a search for recycled plastic lumber (like this: https://american-plasticlumber.com/lumber/structural/). I bought a 4x4 beam years ago and remember it being extremely heavy. The sun will probably turn into a red giant before one of these things starts to break down.