How much stone under my shop?

[Ned Bulken]

As some of you rmay recall I'm building a new shop, which will essentially be a small barn or a large outbuilding. I'm not making this a permanent structure for tax purposes, but do want it to survive for at leasts a few years w/out too much fuss. The site I have available to use gets an inch or two of standing water in the springtime. Not a Huge deal, but I'd like to put down landscape cloth with crushed stone over that to help with drainage, as well as to help level the site.

On top of that I plan on putting in cast concrete piers, then the 4x6 PT joists. My question is, how much stone should I put down? I'm thinking between 3" to 5" or so deep. Thoughts, suggestions? (other than poured 'crete floor which just isn't in the budget or the skills' set).

[Steve Clardy]

When I did my 16x64 shop addition, permanent, I used 6" stone under a 4" floor.
I'd say 5-6" would be a-ok for drainage

[Jeff Horton]

If you have standing water the stone isn't going to change anything. You will just have less standing water in gravel then. If thats the case and your building an elevated building, framing above grade and you leaving it open around the edges, I wouldn't put any stone.

Of course I may totally not understand what you meant either. But as a Home Inspector, what I see that causes problems is water trapped under homes with little ventilation. So if you sides are open you should not have a problem.

[Julio Navarro]

If you install drain tile or french drain around the perimeter of the foot print and raise the floor a bit in the center while slopping to the drain you should be able to avoid water under the floor.

[Cliff Rohrabacher]

Standing (ponding) water will need to be drained, the best means is to raise the land or slope the land away from the site. A ditch or perf pipe will silt up in no time. The pipe will last longer if you put a filter soxk on it but it won't be adequate. Slope the land or raise the site to effectively slope. Sloping lets you control where the water goes. Raising the land may cause the water to run to your house.

Isn't the water doctrine for surface water in NY the common enemy doctrine?

[Julio Navarro]

Great minds think alike, eh, Cliff?

[Jim Becker]

Ned, I'll also suggest you deal with the water issue...get it to drain away, not just for the obvious, but any standing water can be a health hazard, too...flying/biting creatures like to breed in it, for example.

[Ned Bulken]

for about two weeks once the snow melts, there is a bit of standing water in my yard, but not where i"m putting the shop, so the stone is to help keep the shop above the water if mother nature gets overzealous. I wasn't planning on closing things in, just PT for the joists etc, and then build atop the platform;

shop
--------------platform--------------
block
stone
ground

my neighbor's shed (in the near background) is sitting on 4" 'tall' block at intervals around the edge of his shed, about15 to 20' from my site. and has been there for years. and while it is simply a garden shed, it shows no additional wear and tear. Perhaps I'm going for overkill.
http://www.woodworking.org/photo/albums/userpics/12900/new_site.JPG

just to the south of my build site, where the yellow rectangle is, back to the corner of the lot, does get standing water, but only in the springtime, and at most just an inch or two above ground.

just for fun, here is a google-earth view of my neighborhoodhttp://www.woodworking.org/photo/albums/userpics/12900/lookfamiliar.jpg

here's my yard, the little blue dot is where i want to put the shop.
http://www.woodworking.org/photo/albums/userpics/12900/yard%7E0.JPG

[Jeff Horton]

If I were you (assuming good drainage)I would just raise it up 8" to 12" of the ground and not worry it. Stone is not going to gain you anything that I can see.

[Vaughn McMillan]

I agree with Jeff...I don't think the gravel won't really provide a benefit drainage-wise if the building isn't sitting directly on it. The only advantage I can see is that it'd help keep the landscape cloth in place, but I'm not sure the cloth will help much, since I don't think there will be enough light under the building for weeds to be a problem.

However, depending on your soil type it might be a good idea to put 4" or deeper gravel "pads" underneath your piers. In clay-type soils, crushed gravel can help stabilize things by bridging the clay and spreading the load. In rocky or gravelly soils, the crushed gravel probably isn't worth the effort and expense. If you do put gravel pads underneath the piers, they should be sized larged than the footprint of the piers. Picture an imaginary 45° line from the edge of the pier down to the bottom of the pad. That'd be a good rough guideline for the pad size. The thicker the pad, the bigger the footprint. Here's a very rough sketch:

38321

- Vaughn

[Ned Bulken]

that's good news, so... massive gravel won't help, but I think I will do the pads under the piers. Still, with 20 of them spaced every 4' around perimeter and underneath I'll still have a good truckload of stone.