OT- Vapor barrier for gravel barn floor?

Hi,
I'm trying to decide whether to install a vapor barrier under a gravel floor for a 24x32" small polebarn that I am going to build. I'd appreciate an opinions from experience on this. I want to limit moisture coming up from the ground and rusting equipment to be stored there. This is in northeast Pa which can get fairly wet and slow percolation. I'm concerned that plastic sheeting between the ground and gravel will make the moisture levels worse by collecting water that may get above the plastic layer. I'm thinking about putting the barrier on gravel above grade, then add a final gravel layer on top (finishing about 3-4 inches above grade) at least to prevent any seepage from the perimeter from getting over the barrier. The structure will be below a slight slope which is unavoidable. Seems there are mixed opinions on this from the little info I could find. Also, is it really necessary to remove all the topsoil other than to level the site if it is fairly compact? I plan to use geotextile fabric to stabilize the 6-8" gravel layer. No intention to use concrete for this.
Thank you

if it's on a slope put some drainage pipes under the gravel

Can you build up floor several inches above existing grade? Did that on mine, and moisture has not been a problem.

I did put plastic sheeting under gravel in a hay barn for the same
reason. It worked well as long as it didn't rain in the barn lol. Put the
hay on pallets and what little water that got in evaporated quickly. Most
important part was it was not sealed up air tight.

Always. It keeps down the moisture, keeps the water in the concrete as it cures. Always.

I am going to assume your vapor barrier is plastic. I suggest you put material on both sides of it that will not perforate the plastic, making it pass vapor. Sand on each side comes to mind.

Perhaps a sand lift, then plastic, then sand, then washed rock so you don't track fines onto or into your equipment or vehicles. Others here may have even better ideas for materials.

Regarding the slope, you need to deal with the water coming off that slope so it does not go under or in your shed. A ditch of some form comes to mind. Maybe even a ditch with drain tile at the bottom and filled with washed rock to absorb the water.

You are doing the right thing thinking about managing the water, both surface and ground. Don't forget to deal with the water coming off the roof.

By the way, don't forget to make sure your subgrade drains, not just the top grade. What is a subgrade? It is that interface between native clay or poor drainage dirt and any lift you use, e.g. sand or gravel. I have seen a lot of people dig a hole and put sand in it and build on that. Well, they just created a swimming pool under their building if the hole was not properly drained. I hope this is clear what I am talking about.

By the way, my bother ruined a good Chevy Blazer sitting on a dirt floor. Everything underneath rusted out including the brake lines. He dug down a couple inches, added a vapor barrier, sand, and put washed rock on top. Problem solved.

Hope this helps.

Paul

I have 2 poles barns that I built a little
bigger than yours, and only put down 6 mil
reinforced poly on bare ground with gravel
over in sections where I store hay. I live
in north MD, similar weather as you. The
heavy duty 6 mil is good, with fine gravel
on top. I rented a walk behind Ditch Witch
and made trenches around barns with
perforated plastic drain tile connected to
gutter spouts. No problems in any other
areas without poly where I store tractors
and hay equip. Gutters are key.

Thanks to all for the replies. Paul, thanks for the detailed info. Thinking about putting down about 4" of #57 clean stone (1/2"-1.5") over a permeable geotextile on the bare ground, then put down a plastic vapor barrier, then layer 3-4" of an aggregate with mixed small rock and fines on top of that which will pack tight as the top surface. The quarry says they usually do it the opposite way, with the packable aggregate on the bottom and the #57 on top. I would have thought that you'd want better drainage at the level where you would more likely get seepage from the perimeter or down the slope. The aggregate containing fines on top doesn't drain as well, but since there will be a roof over it, I wouldn't think that would be an issue. I'd also lay down some small drainage tile between the gravel and the geotextile fabric to help remove any water, as well as run a trench and put in perforated pipe along the upslope side of the barn. Welcome any further comments. Thanks again.