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How important is it to use a weed barrier or some kind of geotextile between gravel and ground? In cases when crushed gravel is poured and tamped 6" deep as a shed foundation, on relatively flat ground with some trenching dug in the soil around it and top soil removed.

Site prep

I plan to dig out the top soil (root zone and a couple inches of soil) as the shed will go on a meadow with lots of herbaceous species and some trees. A few Japanese Honeysuckle are on site and very invasive, but I have uprooted (I think) all of them, or at least cut them down to stump/root.

Materials

I prefer to use minimal plastic or material that cannot be reused or safetly biodegrade (wood, metal and screws). On top of crushed gravel gravel 2" diameter and smaller, the 8'x14' shed will sit on 4"x6" of larch separated 16" on center, with larch joists and then a moisture barrier below hemlock planking. The field in front of it will be mowed and behind it is Japanese Honeysuckle thicket that will probably try to grow into the shed.

Ground barrier

Cardboard seems like a decent barrier for the weeds maybe lasting ~2-3 years, long enough to kill off what roots may try to grow back that are already under the shed. I figure I will tamp the soil that is dug 2" down all around, lay cardboard, then lay 6" of gravel (or I could lay more). How will cardboard rot under a shed? Is it likely to help or hurt its chances of settling, as it protects gravel from sinking into soil but maybe only for a short period?

I also saw this material as a ground barrier but I don't think it would help much with a shed. Maybe better than nothing, but not helping distribute the gravel weight to avoid settling:

http://www.dewittcompany.com/Garden_Weed_Barrier_.aspx?productid=66&categoryid=21

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  • start with recycled material, build the shed floor from discarded shipping pallets supported off the ground on recovered bricks.
    – Jasen
    Aug 30 '20 at 5:06
  • @Jasen that sounds good but I have more money than time for this project, so buying a simply-made prefab is more accessible to me than building one from scratch using recovered materials. That said, much carpentry around and inside this structure will be or is already from scrap wood and pallets.
    – cr0
    Aug 30 '20 at 14:37
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If you don't choose to use geotextile, you may (depending on soil conditions) find that over time your gravel migrates into the ground, and the fine soils of the ground migrate up through your gravel layer - that is one thing geotextile is used specifically to prevent.

Weed barrier or cardboard are not geotextile, even if one roll of black plastic "cloth" looks much like another. And weed barrier is of very limited use against weeds, in my experience - new organic material (leaves, etc) get into the spaces in the gravel along with weed seeds and you have new weeds growing on top of the weed barrier in short order, unless you are going to vacuum all the rocks up, wash them and replace them regularly - I don't consider that to be a viable use of my time anywhere, much less under a shed.

Expect your larch in contact with the ground/gravel to rot. Being totally biodegradable oriented means you'll be replacing parts that biodegrade. If you'd like to do a bit less of that but are (apparently) also avoiding concrete, consider elevating the larch on somewhat larger rocks - done right it's lasted a fairly long time in some old barns I've met. The trick is to keep the wood dry, and water likes to wick...

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  • Thanks for the info. So geotextile under the gravel will make that gravel last much longer, and putting blocks on top of the gravel, to support the skids, will help the skids last longer? I figured the uninterrupted contact between skids and gravel would help distribute the shed's weight and thus reduce settling, as I understand the geotextile does under the gravel (distribute gravel pad's weight so it does not settle into soil). But I could see the trade-off where separating larch from gravel will reduce wicking and better preserve larch.
    – cr0
    Aug 30 '20 at 14:36
  • I am at the stage of laying down geotextile and still looking at options. I see US200 is the standard geotextile to use for separation and stabilization between subsoil and aggregates. Local farmers suggested evenly spread mat of straw will do the same thing. Coconut coir seems like another option. Do you have any feedback about organic materials for separation and stabilization? Wouldn't cardboard of a thick even mat of straw do the same as coir geotextile, separating subsoil and aggregate long enough for the shed to 'settle' evenly?
    – cr0
    Oct 7 '20 at 15:56
  • (As for separating larch from gravel/ground, I'll use cinders, stones, or locust beams for that)
    – cr0
    Oct 7 '20 at 15:56

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