Make damp storage area dry?

[chemistk]

Our house was built in in '65, and around 1980, a concrete patio was added to the back of the house. I think this was done with the express intention of converting it to what is now the dining room addition, done around 1984. See the attached photo. Why else would you choose to pour a concrete foundation, cinder block walls, and a very thick concrete patio surface?

You'll notice the big wood door, which is conveniently on a steel rail with wheels - a very clever covered storage area. The house has a one car garage and the property line wouldn't allow for an expanded garage. If a shed were set up in the back yard, it would take up an annoying amount of space. So, the previous owners created a ~250 sqft covered storage area under the eventual dining room. They went way above and beyond and ran electrical to the 'shed' (in steel conduit no less) - there are 4 light fixtures and a 4-outlet outdoor receptacle inside the 'shed'.

The downside? It's been humid/damp in there since we first saw it back at the end of May. We've had an exceptionally wet summer which doesn't help, but at some point in the last ~40 years, the foundation settled as you'd expect hundreds of sqft of concrete to do, causing some mortar cracks between the cinder blocks along the right wall, which is the only wall that completely buts against bare soil. I'll note and emphasize that the walls are square, so there's no risk of the thing collapsing.

The big white door is also the only egress from that area. There are no vents or other access points (other than where the electrical conduit is run) EXCEPT for where the sill plate is attached to the foundation of the original house. If I stick my face against where the floor meets the original wall in the dining room, I can get the faintest whiff of musty smell - original insulation has most likely deteriorated a bit. I wouldn't really care too much about moisture in there (driving rain also brings a small amount of water inside), except for the fact that I don't really want any of the wood framing of the dining room subfloor to be exposed to moisture.

I plan to go in there with vertical crack sealer and button up any exposed cracks in the mortar, and then paint at least the right wall with kilz (it is painted inside now but that paint is wearing off, so it's probably not drylok). I'm also going to get up to where the sill plate is and fill what I can with spray foam.

But that still doesn't change the fact that I am probably getting moisture up through the slab, and when it rains (and I assume snow will do this too), moisture in there is all but unavoidable.

So my question, long term, what's the best moisture solution? I was thinking I could bore a small hole (few inches diameter) and run a vent pipe (with mesh to prevent critters) that's hooked up to a fan with a hygrometer that would kick on at high humidity levels. But I'd really rather not drill through concrete if I don't have to. I'm assuming that moisture is always going to be in there, so if I seal everything that leads to the house and then drylok/kilz the thing, do I even need to care about mechanical solutions?

I'm also looking to avoid doing anything more than necessary in there, since clearance is just under 4ft.

[Paper Chaser]

Based on the pic, it looks like you've got water that runs under the door in rain/snow? That would be the first thing I'd tackle. I'm assuming that you'd rather not remove all of the concrete in front to regrade, but perhaps it's possible to cut a trench into the concrete for a french drain to prevent water from reaching that door?



From that point on, you could focus on reducing moisture in the crawlspace area. Typical crawlspace encapsulation techniques could work well, but might lead to damage of the plastic on the floor if you're using that area for storage.

You could try to "encapsulate" the framing above the crawl, rather than the crawlspace itself by adding lots of insulation and a seamless vapor barrier. That wouldn't keep the moisture out of your storage area, but it would keep the moisture from getting to your framing or entering your living space. The only thing is, with that done you wouldn't be able to easily access any plumbing/electrical/hvac ductwork that might be under your dining room without destroying the vapor barrier and needing to redo it.

[sonofsven]

You could run a dehumidifier on a timer.

You could get a few "Kil-z-air" containers and buy a bulk container of the pellets. These things work pulling small amounts of water out of the air. I use them in old trucks I store in my pole barn, they're commonly used in boats and RVs.

The downside is you have to empty water and add pellets every few weeks. You can get bulk pellets on AMZ.

[chemistk]

@Paper Chaser the backyard actually slopes away from the house very nicely, and that stamped concrete patio slopes away from the house, probably about 1"/6ft. Water that gets in through the door does so when we have driving rains. The back of the house faces mostly North, but probably a few degrees toward Northwest. Other water entry is morning humidity - all the concrete in there is obviously cooler than the rest of the air, so on especially humid mornings there's plenty of condensation with all the stagnant air under there. I don't even think I'd need a french drain, I could probably grind down the concrete at the entry so that it slopes slightly toward the patio.

Ever open an old barn that doesn't get used much? That's what it smells/feels like. 

As for the framing - the ceiling of the storage area is entirely concrete. It's totally overkill. Instead of installing a deck like the average person would do, they poured a 5" thick concrete patio in two sections. If that door were made of lead and I had some tanked air, I could use that room as a fallout shelter. The only exposed structural wood is at the sill plate, and even then, it's such a small amount that half a can of Great Stuff would cover it. Thankfully all the mechanicals to the dining room go through the ceiling. So, no risk of damage to the room above except at the sill, in maybe like 25 years.

@sonofsven I did consider that. I'd have to come up with a different solution for the door first though, otherwise I'm dehumidifying our backyard which would be a pointless use of our wonderful solar.

I'm going to have to get some dehumidifying pellets anyway if I want any paint I do in there to actually adhere. Maybe that would be enough.

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Here's a video I took of the space. The riding mower's not mine (took this when we saw the house). It's an insane space. https://imgur.com/a/rH4SvFV

I'll point out that it was pretty dry in there when we went to look at it, at the end of May, and because of the rain and humidity since then it's bee a lot more wet.

[index]

Cider block is porous. You need a vapor barrier on the walls and floor and stop any  bulk water intrusion due to during driving rain. It looks like you live somewhere with a decent amount of humidity (green). You will need to add a dehumidifier to remove moisture infiltrating through air leaks.

[TrMama]

Cider block is porous. You need a vapor barrier on the walls and floor and stop any  bulk water intrusion due to during driving rain. It looks like you live somewhere with a decent amount of humidity (green). You will need to add a dehumidifier to remove moisture infiltrating through air leaks.

This. I would also add some kind of overhang over the door to reduce the amount of rain that hits it and/or add a storm door.

[chemistk]

Cider block is porous. You need a vapor barrier on the walls and floor and stop any  bulk water intrusion due to during driving rain. It looks like you live somewhere with a decent amount of humidity (green). You will need to add a dehumidifier to remove moisture infiltrating through air leaks.

None of the above grade cinder block is exposed to atmosphere, though. The brick on the outside of the porch isn't veneer, it's real brick/mortar. The only cinder block exposed to any soil is on the right wall, beneath that concrete patio. Like I mentioned, I will be going in there with a couple coats of drylok.

The big white door isn't flush with the opening, and there's really no way to get it flush without converting it to some sort of hinged opening. If I were to put weather stripping around that, it would be torn to shreds once the door is slid open.

I guess I just have a hard time seeing how a dehumidifier isn't a waste of electricity - it would be like putting a dehumidifier inside a freestanding shed. Essentially, without a way to seal that door, I feel like a dehumidifier (with an attached hose) would be running any time the outside air is >60%RH.

This. I would also add some kind of overhang over the door to reduce the amount of rain that hits it and/or add a storm door.

I have considered an overhang, but it would have to extend kind of far and would really intrude on the patio.

Typing this reply, I think I see what the best door solution would be - a custom garage style door. I bet I could build this myself, too - it shouldn't be too difficult to source some used garage door hardware and cut everything down to size. Heck, with some clever engineering I could probably even rig up an opener since there's electricity in there.

A garage door type seal would be airtight enough that I could justify putting our spare dehumidifier in there on a timer. If I set it up on a timed plug so it only came on when the solar panels would be producing, the cost to me would be almost nothing after the initial door investment.

[yachi]

Going back to the beginning.  What's the concern with moisture?  Is it what you're storing in the space, air quality, moisture migration into other parts of the house?

Can you effectively seal off the area where the sill plate is attached to the foundation of the original house?  For example, putting in a backer rod, and covering that with caulk?  That should keep the moisture from migrating into parts of the house where it could destroy things.

Then you're left with an area that is essentially concrete and block.  You aren't going to lose those to moisture.  You have some metal conduit and lights in there, and some of them could get rusty, but they'd likely last many decades more.

If you're worried about air quality, little beats increasing your air exchange with the outside.  Could you put a simple fan and louver to exchange air with the outside?  This would cost far less than dehumidification.

In your video there is a screened frame in the corner of the room, was this sized to cover the door into the place, and provide some fresh air?

[chemistk]

Going back to the beginning.  What's the concern with moisture?  Is it what you're storing in the space, air quality, moisture migration into other parts of the house?

Can you effectively seal off the area where the sill plate is attached to the foundation of the original house?  For example, putting in a backer rod, and covering that with caulk?  That should keep the moisture from migrating into parts of the house where it could destroy things.

Then you're left with an area that is essentially concrete and block.  You aren't going to lose those to moisture.  You have some metal conduit and lights in there, and some of them could get rusty, but they'd likely last many decades more.

If you're worried about air quality, little beats increasing your air exchange with the outside.  Could you put a simple fan and louver to exchange air with the outside?  This would cost far less than dehumidification.

In your video there is a screened frame in the corner of the room, was this sized to cover the door into the place, and provide some fresh air?

Biggest concern is that we want to store kids toys in there over the late fall/winter, and I don't want to see them get mildewy or even moldy if we store them too soon or take them out too late. Garage is one car and there's not enough property to expand to two, so if we want to park the car in the garage over winter a lot of the toys and yard stuff needs to be in there.

I do think I need a fan that can run occasionally to circulate air, that is indeed a mesh screen and I should probably be using that more than I am.

[former player]

You need ventilation in that space.  Even if you seal it up against penetrating damp (ie damp coming in through the walls, floor or door) the air needs to move to prevent a build-up of humidity.  Is putting vents in the door a possibility?  One vent low down and one high up might do the job, although ideally you would have air blowing naturally through from one side to another, and if that doesn't work well enough then add a mechanical way of moving the air such as a fan.

[chemistk]

You need ventilation in that space.  Even if you seal it up against penetrating damp (ie damp coming in through the walls, floor or door) the air needs to move to prevent a build-up of humidity.  Is putting vents in the door a possibility?  One vent low down and one high up might do the job, although ideally you would have air blowing naturally through from one side to another, and if that doesn't work well enough then add a mechanical way of moving the air such as a fan.

Yeah it's not going to be fully dry in there until I can get ventilation. I probably will put two vents on the door first and if not, then a small outdoor fan on a timer.

[CowboyAndIndian]

... that stamped concrete patio slopes away from the house, probably about 1"/6ft. Water that gets in through the door does so when we have driving rains.
...

Check the seals under a garage door. These are made of Vinyl/Rubber and they have a finite life. Mine were about 22 years old and were flat and non-flexible when I replaced them. Easy DIY.

Not only will it not let driving rain under the garage door, but it will improve the garage temperatures.