LM: Drying out/dehumidifying my workshop aka my leak has a pole barn

My workshop is a pole barn that partially sits on a slab - two thirds of it are enclosed and on a slab, the remaining third is an open stall with a gravel floor. We're on a hillside that's a bit damp to put it mildly and we get standing water on the lawn/gravel area in front of the shop during heavier rains.

The pole barn itself is mostly but not completely watertight by now after I had a large part of the roof repaired, and from what I can tell, the majority of the damp is getting wicked up/pushed up through the concrete floor. This got a lot better since I remove some of the accumulated mulch and soil at the back of the shop and the rear part of the slab isn't below grade anymore, but I can still see areas where the concrete is slightly damp. I don't know if the people who originally built the pole barn put any kind of water/vapour barrier under the concrete, but my guess based on other workmanship would be  a resounding "no". There's also not much in the way of venting - it's got vented soffites all around, but unless I either open the garage doors on the enclosed bays or the side door, no other venting or windows that I could open to get some air moving.

I currently don't have a means to heat the shop which might help. I also have an uninsulated metal roof that I suspect any attempt at heat would quickly escape through We have a fairly large wood-fired furnace in there that's supposed to heat the house (if it were hooked up correctly at the house end, long story) but there's also the bit about how safe it is to run that in a building full of cars with internal combustion engines.

All that said, the damp problem really is a year-round problem, it's just more noticeable in winter than it is in summer.

At this point in time it's not really helping with the preservation of the vehicles in the shop to the extent that the most endangered car (the X1/9) is actually crammed into the garage in the house that I keep my motorcycles in. Right now I'm wondering what the options are that don't involve a new building. Although TBF at some point this might become a sunk cost fallacy and it might be cheaper to tear it down and have a new metal building put up.

Any suggestions/success stories people could share?

oops, seems like somebody didn't put a vapor barrier under the concrete before it was poured.  

I have done two cures.  1.  tear up concrete and do right, with french drains if needed.  2.  Pour another floor on top of original.  (cheaper if there is space available.

Always a chance its not that bad.  Sometimes if the concrete gets colder for a period of time and warm humid air is allowed on top of the floor, it condenses on the floor (think iced tea glass).   In which case one has to keep warm air from entering... hard to do in pole barn.

In reply to Purple Frog (Forum Supporter) :

Thank you.

Re the last paragraph - there is a strong correlation between the damp and rain. IOW, for the concrete to appear having damp spots, it will have to have rained outside. This happens both in summer, when the interior temperature of the building is higher than the outside temp, and in winter, when it often is or feels like it's colder in the building than the outside air.

When you say "pour another floor on top of the original", would one essentially put the vapor barrier on the existing floor and then pour a relatively thin layer of concrete, or would I end up with a another full-thickness layer of concrete? And how would that impact the potential installation of a two post or four post lift?

If you poured another floor it would probably require a thickness of ~3.5 inches.  Would that effect a two post height in your application?  I double up on layers of 6 mil plastic as overkill and another layer of wire.

In residential applications I have used "Schluter - DITR Uncoupling Waterproofing Membrane."   But, in houses we are laying ceramic tile or or vinyl plank flooring on top.   That whole process only adds less than an inch.  Have not tried to drive cars on that application, although from experience it might probably hold up if installed to spec (those Germans are pretty stout engineers).

Do you have any pics?

It sounds like you are built into the side of a hill, and that ground water/ roof runoff contribute a lot. 
 

There's a good chance that you could improve the situation by addressing some drainage

There's a good chance that you could improve the situation by addressing some drainage

This!  Use gutter/downspout and drainage to direct the water away from the building.

Thirded on the drainage.  You probably have a French drain setup in your future.  You have standing water in front of your shop, and the rear -was- below grade.  It sounds like water is coming downslope to your building and it's the lowest point nearby.  

It's a lot of work if you don't have access to a mini-ex, but definitely worth it.  We only put one in along the worst side or our shop, and it has made a huge difference in the softness of the soil around the building.  Now we have gutters, I have somewhere to direct the downspouts to as well.

Here are a couple of photos of the shop I took between rain showers:

When we have British Drizzle (tm) like yesterday and today, the flat area in the front of the shop is a bit squelchy, but with no standing water. If it rains harder, there is usually a thin layer of standing water there.

You can also see that the roof slops into the hillside they cut into to build the shop.

This is what the area behind the shop building looks like. Yeah, I know I need to clean it out again, currently the pile of leaves is essentially filling the trench I dug:

I know I also need to cut back the trees that are touching the roof of the shop in the back.

Based on the comments above, gutters and a downspout would make a lot of sense as all the water currently running of the roof of the shop gets dumped into the area in the second photo.

One of the local builders/handymen around here who's done a fair amount of work for me suggested building a knee high retaining wall back here to stop the soil from eroding further and keeping a bigger gap towards the shop. I guess that might be a decent place to run a french drain as well, although to me it's not quite clear where said french drain would drain towards as it's all relatively flat and damp.

In reply to BoxheadTim :

You can do a French drain essentially above grade (if your foundation is high enough). 
 

Clean out the leaves/ debris. Then fill the area with gravel. Slope the gravel towards the exit side, add a perforated plastic drain pipe, then bury the pipe in more gravel. Finished product will be exposed gravel, but the pipe will carry water to the low side.

The entire area of the roof is also dumping into that ditch. Add a gutter to divert all that water.

This would go a really long way.  I would do those 2 things long before doing anything to the concrete floor inside. 

In reply to BoxheadTim :

What I was trying to say is that you CREATE the pitch with the gravel and how you lay the pipe. 

Agree with above - trench it out, some gravel and drain tiile, pitch it to the far side of the hill.  Maybe add a proper gutter to the back to lessen the burden on a french drain.

Keep the leaves and whatnot out of the back area, get as much washed gravel as you feel happy with back there and you will be in a much better place.  

Thanks, that gives me something to work with.

Is there a specific minimum depth I should dig the trench to? For example, at least the same depth as the slab, or even deeper?

In reply to BoxheadTim :

Do the gutter first. It may solve the problem. 
 

If you end up with a French drain, you will want the pipe lower than the concrete floor. (Assuming it can still drain to daylight)

Does the grade behind the shop (above the ditch) drain away from the ditch, or dump water into it?

If it drains away, you probably won't need the French drain. The water source is the roof, and the gutters should solve it. 
 

If the grade dumps into the ditch, then your water source is both the roof and the grade. You will probably need both the gutter and the French drain, but the gutter is half the water source, so it's possible you won't need the French drain. 

The grade doesn't visibly dump into the ditch, although the whole hillside is very damp and we have a seasonal spring maybe 100' west of the garage.

Sounds like cleaning out the ditch I dug and putting up some gutters would probably be a good first step. That, and figuring out what plants I can grow on that steep grade to prevent further erosion.

Look into rain garden plants, they have a good root system for getting water to hit the rain garden and basically drop into the soil vs rolling into the foundation.

Regular lawn type grass and leaves are about the worst.  

As far as depth, if its set up properly there should be no standing water in your French drain, mine in Wisconsin is about 6" below the surface and follows a natural grade and never has an issue even in the winter.  Probably a bit shallow but it was there when I moved in.  

Figure out what pitch you need and how far you have to move the water and let that guide your digging decisions.  Don't forget to call Diggers Hotline.

Didn't think about rain garden plants, that sounds like a great idea! Grass was out anyway, that slope is always in the shade and even grass that is supposed to be OK for shaded areas won't properly grow on the continuation of the slope.

I've not had any issues with standing water on the rear of the shop building. All the standing water seems to be in areas I expect to be compacted already and that have traces of gravel on it. IOW, basically the areas one would drive on.

In reply to BoxheadTim :

Right. It is standing BECAUSE it's compacted and water can't absorb.

Its not standing in the rear because the soil is recently disturbed and not well compacted, and the water can soak in easily, AND soak through to your slab. 

In reply to SV reX :

That makes sense. Kinda obvious now that you pointed it out, thanks.

In reply to BoxheadTim :

No problem. We've all been there!

Indeed!

Spent a not very enjoyable hour or so outside and cleared out most of the accumulated leaves. I was surprised that my trench still seems to be in good condition.

Finished up just in time for the rain to start. Can't make things any worse as the leaves were soaking wet.

In reply to BoxheadTim :

That's good!

Those wet leaves were not helping your problem.